Drag Racing Bodies - Thinking About Plastics
Note: A majority of this article originally appeared as a series of periodic posts on the DRS Drag Board, and portions have been reprinted in the SDRA Quarterly Bulletin. I've reprinted it for the benefit of those who may not have access to those venues.
Standard Unc Disclaimer: what follows is opinion based on personal experience and memory. Take it for what it’s worth. Remember John Belushi offering Tom Hulce a beer in "Animal House?" "Take one. Don’t cost nuthin’."
Sooner or later in your approach to slot car drag racing, you're going to be confronted with the problem/opportunity of having to make a model car kit or vacuformed styrene body work as a slot drag car. How well it works, and perhaps why, is the province of other sections of this site. In this section, however, we'll take a look at the nature of the material(s) we normally work with when building "hardshell" cars, as well as some solvents, bonders, fillers, and tools useful in dealing with them.
Make no mistake here: I never have been, am not, and will never be God’s gift to hardshell slotcar drag racing (at least not at the rate I'm going), nor am I a chemist or mechanical engineer. I have, however, been messing with plastics and resins for a while now. I built my first plastic car model, a Gowland Highway Pioneer Ford Model T a few weeks after Eisenhower was inaugurated as President for the first time (you figure it out). I started scratchbuilding model railroad rolling stock and structures from sheet and bulk styrene circa ‘68-’69, and started epoxy casting a few years later, transferring these materials and their techniques between the trains, planes, and cars I’ve built over the years Someone suggested that I share what I learned, what little that may be, so I am.
A Bit About The Nature of Styrene Plastics – Polystyrene and its cousins, ABS, acrylics, polycarbonate, PVC, and some other acetal resins, are wonderfully workable materials, provided you understand a little of their nature, composition, and limitations. The basis for most of our hardshell work, plastic model car kits, have been and continue to be manufactured from an evolving selection of thermoform styrenes. With the application of heat below that necessary to fully melt a given part, most compounds of a thermoform material respond by sagging, as you would expect it to do; some, however, go through a stress-relieving phase before further structural failures. Remember those bizarre, twisted shapes models exposed to sunlight (e.g. heat and UV) in a hobby shop window would form. Ever wonder why some sagged and others got really weird? Different materials.
With a few notable exceptions, most of the styrene you’re likely to encounter in a model kit is considered "high impact," and contains a degree of elastomeric compounding – the actual "plasticizers" or rubber modifiers – that give it a greater or lesser degree of flexibility, as well as antioxidants and (anti) UV agents. When you remove these agents, because of color contamination, for example, you get lower cost and impact resistance, accompanied by greater and greater transparency along with greater and greater fragility, until almost all of them have been removed. Poof! Crystal (clear) styrene, which, as you no doubt have learned by now, is unbelievably brittle, has the structural strength and ductility of a fresh potato chip without the reinforcing corrugations, and mars when you wave a closed bottle of solvent in its general direction.
Also present in your new (or old, for that matter) kit are trace elements of anti-biologic agents. Say what? As the description implies, molders are forced to add this stuff to the batches of plastic pellets about to be heated, squeezed, and squished in their gazillion-dollar injection machines to (mostly) eliminate the bacteria and fungi that thinks molten styrene is a great place to grow, not to mention some strains that also think of it as a home-cooked dinner. Not always successfully, I might add. Ever open a rather old kit for the first time and discover strange-colored dark blotches here and there? What, you thought kits got freckles with age?
Last but not least is the presence of injection molding release agents on all the surfaces of your kit, both body and other parts that aren’t metallized. Molders use them, along with blindingly expensive multi-part molds and close-calculated draft angles, to make sure the part they just shot actually comes out of the mold, hopefully in one piece and unwarped. Traces of those release agents are still there when you eagerly rip open the bag to see what the kit body looks like, and are probably happy to see the oils from your fingers join them on the surface. Solvents don’t mind them, but paints…
Additional polystyrene note – Not that you don’t have enough to make you nuts when building hardshell cars, but here’s something else to think about. Certain detergents can cause stress cracking in certain styrene resins, so take it easy with that Simple Green and use plenty of water when you’re washing the release agents off a kit body.
For our purposes, polystyrene’s closest commonly-available relative is ABS (acrylonitrile-butadiene-styrene resin, which, should the question ever come up in Trivial Pursuit, is technically a "terpolymer’), usually found in the Plastruct section at your hobby shop. As provided by Plastruct, the formula they use is slightly weaker in tensile strength than that of the average polystyrene formula (on the order of 5-7%), but roughly equal in ductility (flexural modulus) in their highest impact compounds.
When you get further afield from the polystyrene family, you encounter materials that have a lot of possibilities for modeling but lack either the small-form strength and ductility (e.g. acrylics) or the simple ability to be successfully and permanently joined to styrene (Delrin, other engineering plastics, and our good polycarbonate buddy, Lexan). I’ve built models with a combination of styrene, ABS, acrylic, PVC, acetate, and Lexan in them, and trust me on this, staying exclusively in the styrene family for everything except clear/glazing items would have made life lots simpler. Other than the ease of finding some structural shapes in ABS (of limited to no value in model cars unless you absolute have to have an I-beam somewhere), there really isn’t any reason to work with anything other than polystyrene these days.
Styrene Kits as Slot Car Bodies
I’m aware, as are most of you, that styrene was the first material used for slot car bodies. The English Tri-Ang and American Strombecker sets had fairly well detailed styrene bodies, and the Golden Age of scale slot cars featured the great work of the Cox, Revell, and Aurora companies. I’m also aware that if styrene was the perfect material for slot car bodies, you wouldn’t be able to see through all those that are hanging on the wall at your local track. Injection-molded styrene offers a level of detail that vacuformed Lexan (and vacuformed styrene, for that matter) can’t begin to approach, but it has downsides, as well.
For our application, given that styrene is neither as strong nor as ductile as the two primary materials we use it to supplement or replace (steel and Lexan), we need to think about some things before we start drilling pin holes in bodies.
First, the kit we commonly start with was designed by people as a static display piece with an exterior level of detail and an inner surface adapted to fit some to no level of additional detail. The mold designers don’t sit around over a cup of coffee worrying about what happens when the shell and its parts run into a piece of foam at 60 mph, or whether or not the body structure is really happy supporting 110 grams of chassis supported by four cantilevered pins through its side.
That’s our job, and luckily, it’s not all that hard. While nothing can usually save that Pro Mod from Bent Styrene Heaven when it gets airborne and heads for the floor, a few other considerations can make its (and your) life a little easier before that point. For example:
Good Joint Design and/or Reinforcement – Design styrene joints in much the same way you would design solder joints. Butt- soldering one wire to another (the classic "T" joint) looks nice but has zero mechanical strength beyond the tidy filet of solder, which ain’t all that much. A proper joint has either a mechanical locator (the tab and slot idea) or sufficient area to give the joint a fighting chance to survive (think of a relatively long "L" joint, and the additional solder contact area). Styrene needs the same consideration. The kit manufacturer may think that simply butting the nose piece of a late-model car to the body is sufficient, but for anything other than static display, it isn’t going to be for long. Don’t underestimate the wear and tear the stresses of simply handling one of these cars for an extended length of time can impart. And I don’t know about you, but I wouldn’t want to ride to and from the track in most peoples slot car boxes.
Joint Overlap – Overlap joints whenever possible (a little is good and a little more is better), and where it isn’t possible – that nose piece, for example – use a reinforcement on the inner seam for some additional strength. .010" thick by .100" to .250" width strip does a decent job for me. Note: Like most everything else in life, there is a Law of Diminishing Returns at work here. I firmly believe that lighter hardshell cars work better than heavier ones of exactly the same configuration (we’ll get into the physics of that some other time), so I balance the additions and modifications I make to a body against what, if anything, I can legally remove from it. Like a lot of other people who mess with these things, I spend a lot of time comparing kits and their design, structure, assembly and weight , trying to achieve a compromise that works as well as possible.
Proper Material Selection – When you modify or add, select the material for what it has to do (or what will get done to it by the time you’re through). Say you’re absolutely rabid for a killer Pro Mod style wing on the back of some car. While there’s no reason to build it all out of .040" sheet (strong enough, but probably lots heavier than what you replaced or added to), there’s also no reason to think it will have a long, happy life if you build it all out of .005", either. You don’t have to design it to be as strong as a Hubley cast-metal car, but you should probably remember how these cars get handled and stored. Like the level of detail you attach, it’s part of the appearance/weight/strength relationship you get to make decisions on, so plan ahead.
Deplating "Chrome" Parts – You’ve spent your entire life ignoring those kit instructions about scraping off the plating on parts before you glue them to each other or to something else. Time to follow that advice. The "chrome" (metallized) parts in a kit are usually (but not always) molded from the same material batch as the rest of a kit (if there isn’t a non-plated area on the parts tree caused by the clamp in the metallizing oven, scrape some off the sprue somewhere to reassure yourself). None of the bonders you probably have access to really like those metallic coatings, and all of them do a much better job joining styrene to styrene than styrene to the bright (but thin) zinc and nickel that, mostly for cost reasons, make up a majority of the plastic plating medium.
Styrene Sources & Other Considerations
Sources – This is a no-brainer under most circumstances: Evergreen. If you can’t find it in the Evergreen rack at your local hobby store (with some incredibly limited exceptions), you need to redesign what you’re building until you can find it there. Back in the Dark Ages of Styrene, countless people wasted endless hours turning sheets and blocks of plastic into a) strips that varied in width every couple of inches, depending on one’s cutting/scribing method (or: one of the reasons I own three paper cutters and one Northwest Short Lines Strip Cutter) or smaller blocks of shapeless styrene. Not everyone was born to be a sculptor.
The incredibly limited exceptions are 1) the Plastruct ABS shapes mentioned in an earlier segment, 2) Cliff Grandt’s masterful molding job on model railroad components and carefully-extruded styrene rod, and 3) the German Kibri line of styrene bar, strip, and rod done to metric dimensions. The Plastruct stuff is almost self-explanatory; since your neighborhood hobby shop usually has enough common sense to locate the Plastruct line next to the Evergreen line, as they say in the grocery ads, shop and compare. Given the choice, pick the styrene sheet over the ABS sheet – your long-term mental health will thank you for it.
The Grandt Line products may be hidden over in the model train area; if they’re not, find a store that carries a decent assortment, ignore the scads of narrow-gauge railroad parts, and look for the nut/bolt/washer castings (remembering that our train buddies use a lot of square, rather than hex, nuts. Tough to make out when the whole thing is only .032" wide and molded in black plastic, so read the card header and pay attention. Not something that usually lives on the outside of a slot car drag body, I’ll grant you, but you never know, right? Even if you’ve never even spelled "train," I’d bet even money you buy a few packs of some Grandt Line stuff, some of it’s that neat. Not to mention lots cheaper than the "detailing parts" offered by some of our pals in the static model car biz.
Grandt was the second company to offer relatively consistent styrene rod shapes some years ago (the first being Kibri, to my knowledge), when they (not knowing if Cliff Grandt is still alive or not) brought out a line of .010" to .060" rod in low impact styrene. Very good for straight runs, but unhappy in tight radius bends, a situation Evergreen has relatively recently rectified. For some irrational reason, but to my personal relief at the time, Kibri introduced a line of really small/thin styrene strip, e.g., .1 mm (.004") by 2 mm (.079"), in 1971-72 or so. The line is out there if you look hard enough.
So, you’re asking, why should I care about all those shapes and sizes? Give me a sheet of the stuff and Scotty Cannon’s old Willys is just around the corner! In a word? Utility.
In more words? Practicality, convenience, and weight. There are more than a few times when the appropriate structure you want to add to a hardshell body should be, for want of a better description, real strong and real hollow. If, in addition to these two "reals," it also has to be "real curved," then the best way to make it strong and light, in the absence of access to the dreaded vacuform machine, is to laminate thinner pieces to each other while achieving whatever compound curves the structure dictates. The worst way is to take a big chunk of something and carve away everything that doesn’t look like what you want to end up with. A monumental waste of plastic and time, not to mention a method that ends up with a part that probably weighs a great deal more than it should.
A last bit of advice you can take or leave as you choose: Try to design and build your projects to tolerances that maximize fit and minimize gaps. Yea, I know that fitting two compound curves to one another is a major pain, and that the temptation to get things mostly even and just glue the sucker together is strong. Just remember: given the same two bits being bonded together, the more contact area you have (and the more contiguous contact area you have), the better and stronger the joint.
Bonders/Solvents, Glues, & Adhesives
Solvents – OK, you want to use "glue," or "cement," fine, except that there’s a difference. Honest. The best way to work with styrene parts is to chemically and physically bond them together, and the best and strongest way to do that is to use a solvent that melts them together. At the risk of horrifying all the chemists out there, a few "just like" examples:
Imagine two flat pieces of steel that you need to join together. If your ultimate goal is simply decorative, you can stick one on the other, or overlap them, and use bolts, screws, contact cement, epoxy (single or plural-component), super glue/ACC, double-sided tape, or even a wad of chewing gum, for that matter, to fix one to the other. All have different ductility, expected life-spans, and strengths under various directions of force. But if it really has to stay there, survive abuse, and offer the maximum strength the materials involved possess without the need for attention and continuous maintenance, you only have one option: you weld them together.
It sort of works that way with styrene, as well. There are a boatload of substances out there that will join styrene, one way or another, permanently (as far as the word "permanent" applies to stuff that won’t biodegrade until maybe the sun cools) or otherwise. Given the option and the circumstances, start with the strongest and work your way down the chain. What follows is my personal order of preference.
Bonders/Solvents – The list of stuff (mostly aromatic hydrocarbons, if I recall correctly) that will work as a styrene bonding agent in the desired manner is probably a gajillion screens long, and contains enough known carcinogens to scare the living crap out of you. Good. Stay that way. None of these substances are something you a) want to breathe for a living, or b) pour liberal doses of on your skin. Make certain you use them in areas with proper ventilation and air exchange rates. Pay reasonable attention to not spilling bottles or cans, and, whenever possible, use smaller containers or bottles rather than larger ones. The small-bottle business is also a good idea regarding vapor dispersion, not to mention inhibiting some evaporation rates you can almost watch happen.
My personal bonder of choice is MEK (methyl ethyl ketone, sometimes also referred to as butanone), because a) it’s the most aggressive solvent that doesn’t scare me (much), b) it has an extremely low viscosity, and flows very well, c) its dispersal/evaporation rate is quite high, and d) it’s available from a number of everyday sources in quart (and sometimes pint) cans for a very reasonable amount of money. Translation: It works well and it’s cheap. Acetone is my next choice, for approximately the same reasons, but in my experience (only), not quite as aggressive. I use it when I’m too lazy to make a trip to the hardware store to replace my MEK supply.
The other bulk possibilities are toluene and xylene. Both are a little (or a lot, depending on your point of view) more aggressive that I choose to deal with, but are, nonetheless, some agents we’ll run into again later in this section. I own both but very rarely ever use either. I think you can live without them, as well. Our old pal lacquer thinner will also work pretty well, and is usually the only decent bonding agent you might be able to find in your wife’s/significant other’s purse, masquerading as "nail polish remover" at way too much a bottle to be hobby-significant.
MEK, I suspect, is probably the primary component of most commercial styrene bonding agents. Not surprisingly, all hobby bonders are not the same when it comes to chemical composition and/or bond strength (which is probably a combination of material costs and supply). All of them will work for our purposes, it’s just that some work better than others. My favorite commercial bonder is Tenax 7R, which your local hobby shop should carry if they haven’t been hypnotized by the Testors sales guy. Like most of these bonders, it goes for about $3.
Our friends at Plastruct have also come out with some bonders under the trade name "Bondrene" (and doesn’t that name just cry out "50s" to you?). Note that I said "bonders." They have one for styrene-to-styrene bonding as well as one for ABS-to-styrene (or ABS) work. If the guys who make the stuff see a need for a different bonding agent (in addition to seeing a need for additional profits), maybe you should, too. Check the labels before you stroll out of the store. A little over the $3 range at most places.
A few words about tube cements: why bother? I grew up with Revell Type "S" cement, not to mention Gluco and Duro and a ton of other junk that worked about the same way. I still like it. Why? Because it seems to age so poorly and have so little ultimate bond strength that taking apart any kit that was built with is usually quite simple (unless, of course, the kid who built it ladled it on with a trowel). It may still have a limited number of functional uses, e.g. attaching large chunks of styrene to other large chunks, but given other bonding choices, design considerations, and lack of reasonable application control, I don’t think I can recall actually using it for anything in the last 10 years. Not to mention the newer, bio-based "non-toxic" brands now on the market. With one, lone exception, I feel a little strange using anything derived from stuff I eat as a solvent, bonder, or glue.
Super Glues – I first started working with this stuff (cyanoacrylate ester, which originally was called either aminocyanoacrylate or anocyanoacrylate – I forget – but which has caused me to refer to it by the original abbreviation, ACC, ever since) in the late ‘60s, when Eastman 910 was introduced to the high-end consumer market from the industrial market. It cost 10 whole '60s-early-'70s bucks for a microscopic tube, and was aimed at the film-splicing/editing market (Eastman Kodak, right?). Zowie! I spent hours gluing my fingertips together, and used it on everything. Hot tip: it really doesn’t work that well on everything.
(Incredible oversimplification warning! More really crappy chemistry ahead!) While real bonding agents basically melt stuff together, confusing the parts and their joints about what’s a part and what’s a joint when stresses are involved, glues and cements don’t. Mostly. They can and do interact with the materials all the way down to the molecular level, but the ultimate strength of the joining agent may easily be exceeded by the strength of the materials one uses it on.
Example(s): Super glues are the agents of choice for the (flying) model airplane hobby. Their primary structural materials, balsa and foam, have a tensile strength low enough to make ACC a good, if not the best, choice. Note that these materials have a porosity similarity, e.g. fibrous, grained, and "open-pored" enough to give the glue a purchase or hold, and that while their strength-to-weight ratio is outstanding, both will commonly fail in structure well before proper-designed joint failure. Yes, I know that this country is defended by aircraft that employ adhesives to hold dissimilar structures and materials together, and they hardly ever fall out of the sky because the glue failed. I also know, however, how to spell "exotic," "toxic," "autoclave," and how to say "Holy crap! It costs how much!?" We’re talking model car kits here, not F-117 and B-2s.
Some bad engineering to accompany my pervasive bad chemistry: ruin plastic with me for a moment. Take some pieces of .062" styrene about ½" wide. Bond two pieces together, overlapping their ends about an inch. Since it’s surface to surface, create a ¼" wet dab of solvent (not evaporated) and firmly press the two parts together. Now do the same thing with an similarly sized amount of super glue. Let them both dry for an hour or so (less will probably do, but wait anyhow).
Then a) attempt to pull them both apart by pulling on the ends, and b) take their respective edges where they overlap and twist them in opposite directions until the joint fails or you get bored. If the joint doesn’t fail via twisting, take a hobby knife blade and carefully try to split the joint, applying a small twisting force with the blade until it breaks. This being the '90s, I caution you to avoid slashing, cutting, or otherwise mutilating your extremities while trying this.
Congratulations. You have just conducted "destructive testing," wherein, in the absence of any easy way to pull the true surfaces apart perpendicular to the joint (true tensile joint strength), you have nonetheless performed comparative tensile strength, shear, and peel testing of the joint and material. Examination of the manner in which the way the joints failed should tell you what you need to know about the way the two different agents work with styrene.
Having said that, I use five different kinds, depending on what I want them to do and how long I’m willing to wait for them to do it. They vary primarily in viscosity and curing time. I use the thinnest, fastest setting variation to tack things into place for bonding, and the others primarily as fillers for very small gaps or as glues in those rare circumstances where one large surface has to be joined to another, and where edge bonding alone may not be sufficient.
Some last notes about super glues. Remember that these glues don’t so much "dry" as they do "cure;" the chemical difference is meaningful. These glues actually generate some discernable heat while curing (what looks like smoke occasionally is smoke), as well as detectable outgassing. Those things are what sometimes messes up very thin styrene sheet (almost as much as too much solvent does) and frequently fogs the edges of crystal styrene – windshields and such – when they’re attached with super glue. You can prevent the heat distortion by being judicious in your application of the glue, and prevent the styrene fogging by using a masker or frisket film to cover visible portions of (usually) the inside of the clear parts when you attach them. Test any liquid masking agent on some flat part of the same tree the part came from to determine a) if it fogs it (usually not, but test anyhow), and b) what it takes to remove it after it’s dry (sometimes a real pain). I usually use Testors Masking film (frisket), which is relatively expensive for a repackaged lab product, but worth it anyhow.
I avoid super glue "accelerators" and "kickers" wherever possible, mostly because the words "aromatic amine" occasionally appears on the labels (and having had some experience with amines as core curing agents in industrial foundry and casting practice). I figure if they’re worried enough about it to put it on the label, then maybe I should pay attention. I also avoid it for another reason. "Forces immediate cure of all cyanoacrylates." on the label tells me it’s probably an exothermic catalyst agent, and this one, like many such agents, produces heat during application. Like I need more heat here. Some super glue formulations are advertised as "bonding" Lexan. It may attach it, however strongly (not very, in my experience), and for however long, but by my definition, it sure as hell doesn’t bond it.
A last super glue point: one of the useful, albeit long-term, solvents for the commercial cyanoacrylates we commonly buy is... water. Uh-huh. As in humidity. Now doesn’t that thought make you feel all warm and fuzzy?
Epoxy Resins – Plural and single-component epoxies have been around a bit longer than super glues, which they preceded as the "new, miracle glue." No free lunch here either, but, occasionally, sometimes a cheap snack. While many (if not most) single-component epoxies require an elevated-temperature cure and have a rather short shelf life compared to other glues, the plural-component varieties are substantially easier to work with for our purposes. Available from countless sources in virtually unlimited formulations, their common time-at-room-temperature curing is styrene-compatible, and, as an added bonus, their chief drawback and/or problem when used in other applications can actually be used to our advantage in slot car drag racing with styrene kits.
No matter what far-fetched wording appears on the tubes, the two components are a resin and the catalyzing agent that cures it. Most commercial or hobby plural-component epoxies are formulated to offer maximum strength at a 50/50 mix ratio. Additionally, the best way to achieve this mix is by weight (remember that while you’re trying to squeeze out two equal puddles of slightly different viscosity goop). While reasonably strong, this ratio leans to the hard or brittle side of the curing scale. At the sacrifice of a roughly proportional decrease in joint strength, you might want to occasionally experiment with gradually decreasing amounts of catalyst agent (sometimes, but not always, labeled as "hardener") to a standard amount of resin. The presence of some uncured resin leans the resulting cured epoxy towards the elastomeric or almost flexible end of the scale. Note: the presence of too much uncured resin leans it towards the "sticky crap that doesn’t really stick anything together very well" end, so experiment a bit before trying it on the prized Pacer station wagon body.
You may run into some other forms of "epoxies" or adhesive resins in your travels (or, if you’re into building full-sized boats or homebuilt aircraft, you may already have them). There are a ton of adhesives, like urea-formaldehyde resins (mostly wood) and polyester resins (foams and other composites, not bad, disco-era stuff), out there. Unless you plan on dealing with wood bodies (send me a picture), fiberglass (already been done, even in 1/32nd scale), or some composite (carbon-fiber slot car drag racing bodies – there’s a cost-effective idea), take a pass.
Other (Occasionally) Useful Stuff – Remember that "bio-based" remark a while ago? Here’s that exception: Elmer’s Glue-All. No *shit. It, and similar casein glues are basically derived from – milk (in the event you ever wondered why Borden had a glue division). Yes, I know it works best on porous surfaces, and styrene ain’t all that porous. It does, however, occasionally have its uses in its unthinned form for reinforcing other joints without a major weight penalty, e.g. the backs of chromed bumpers-to-body joints where I was too lazy to remove enough plating to add a thin styrene doubler.
In somewhat thinner form, it can be used as a clear-drying, non-marring adhesive for crystal styrene windows that fit in recesses (in my experience, it’s basically useless for any windows that lack some form of perimeter support, but you may have better luck – and patience). In a very-slightly thinner form, I apply it with a small brush to the edge of a Lexan/styrene "window" joint that has already been super glued in place, overlapping both materials. It adds a little more strength to what is essentially a somewhat tenuous joint. Microscale makes a slightly different formulation under the trade name Micro Kristal Klear that you might want to experiment with. It’s also pretty decent for making headlight and turn signal lenses to replace those that suddenly disappear from the box.
Not that I could recommend it to anyone else, but when I’m reallazy, weight isn’t a problem, and the material is thick enough, I occasionally whip out the hot melt glue gun and glorp some on joints that might need some help. "Crude but effective" is the phrase that comes to mind here.
"Occasionally useful" might also include contact cement. Honest. Contact cement is basically thinned, solvent-suspended RTV – room temperature vulcanizing – rubber (or whichever cheap and sleazy similarly-configured elastomeric they use these days). It’s the glue of choice for attaching rubber/foam tires to metal rims, but a poor choice for gluing styrene together. Too many elastomeric molecules displacing solvent molecules for sufficient small-joint strength, and too much "bulk" for the most efficient large-area joints. Although I have no personal experience with it, it might, however, be just the ticket for attaching the (chrome-removed) bottom of a styrene blower to a non-painted styrene mounting tray slightly below an opening in a hood. Might just be strong and flexible enough to take the wear and tear that protruding components like that constantly suffer in handling and racing.
Commercial Styrene Fillers – I don’t quite recall how old I was when I first tried "Plastic Wood" as a model car filler. I taught me most everything I subsequently needed to know about layering, drying, strength, differential expansion and contraction rates, surface finishing, and paint adhesion when using a filler on styrene. Which is to say, not enough. I don’t recall what some of the early, original model car filler formulations were (AMT, Testors, and some private-branded stuff from Oscar Kovaleski’s legendary Auto World), but I suspect that most were simply repackaged (full-sized) car spot fillers.
Surprise. They still are. Squadron Products "Green Putty" is still a big seller, and has been joined by a "White Putty," the color option being (evidently) the only difference. After 30 years, I presume they finally figured out that some people (primarily military miniature and plastic aircraft builders) were having a paint coverage problem with a dark green filler and the extremely thin, fine-pigmented paints they were using. Both Squadron fillers are toluene-based, and use who-knows-what for their solids content. Curious about these components, I actually called both hobby and automotive filler manufacturers once in an effort to find out, and you can imagine how that conversation went in the era of the class action lawsuit. One wouldn’t discuss it on the phone, but offered to send me an MSDS (Material Safety Data Sheet) on the product. Swell. Based on density, surface finish, and abrasion resistance, however, I suspect they use much the same stuff their automotive cousins do, which is probably a cellulose or polyester solid component.
A good substitute for hobby fillers is Bondo "Instant Scratch Repair" putty, usually available at your local auto parts store. It’s a xylene-based filler, a tad more aggressive than the Squadron/hobby formulations (understandably so, since it’s sold as a formulation that will adhere to paint, primer, and prepped bare metal). Drying a dark golden brown, it applies and works much like a hobby filler. It may, however, actually have a lower specific density than common hobby fillers, because a tube of the Bondo filler weighs about an ounce less than a similarly-sized tube of Squadron White or Green, and I suspect neither company has hung around this long by wasting metal on tube material thickness. Using conventional priming and painting steps, I really can’t detect a practical difference between these fillers.
Neither should be used as a substitute for decent design or the proper bonding agent. For one thing, they simply weigh too much for too little (if any) added strength. Filling in the junction, for example, between an almost-vertical front pan and a styrene diaplane with a ¼" radius fillet may look good, but is inherently poor practice. A few stops in the foam/rags/parachute/whatever will tell you about the strength of large areas of filler being asked to perform structural jobs. Design for a minimum of filler; take some time and use formed styrene to establish flowing shapes that are inherently stronger and need less filler. Given the same material, remember that hollow is always lighter than solid, and fewer pieces almost always stronger than more pieces.
Super Glues – Some of my serious car-model friends swear by super glue as a filler, both by itself and when used in conjunction with fine-grained "fillers." Borrowing a trick from the flying model airplane people, where less weight in fillers can mean a great deal in performance, they started by using the "microball" filler components the airplane guys used (unbelievably small, actually hollow, extremely thin-skinned resin balls used to take up space and reduce resin/filler weight. I wouldn’t be surprised if the model airplane people, in turn, didn’t get the idea from full-sized aircraft construction and/or the composite race car body guys). A few super glue manufacturers and/or distributors introduced their own lines of "fillers." When that got a little expensive, the modelers turned to baking soda as a filler component. Gee, more model car/slot car drag racing stuff you might find in your refrigerator.
I first tried super glue (alone) as a filler quite some time ago on airplane kits, and discovered that I really didn’t like the different way the two materials, styrene and ACC, reacted to shaping and finishing. Careless surface sanding seemed to reduce the styrene at a significantly greater rate than the glue, and when something like raised or lowered panel detail had to remain on a kit’s surface while one attempted to fill seams, this was not such a hot deal. I later tried ACC as a filler on model cars, both with Zap (powdered) Filler and baking soda. "Unsatisfactory" doesn’t begin to describe my luck, the unbelievable mess ("How much powder? Oops, not that much."), or, for me, at least, the claimed speed of filling and curing.
My experience, however, doesn’t mean that it’s a bad idea for small-gap filling. What it means is that you probably need to experiment a bit if it strikes you as a decent filling system. Talk to someone who swears by it, and perhaps observe them at work. It may be the best thing since sliced bread, for all I know, but right now, I have to go clean all this powder off my work bench. Pass that Bondo tube, please.
Unca Frank’s Home-Brew Filler – (Unc would actually give credit to whomever he stole this idea from, but he can’t remember who it was. Sorry, offended person/publication). How about a relatively strong filler that works, sands, and finishes just like styrene, has considerably higher strength, both bond and structural, than commercial fillers, is extremely aggressive, basically dirt cheap, and doesn’t even weigh more than the styrene you use it on? Sound good? The magic styrene filler is... ta dah!... styrene.
Sort of. In my personal blend, it’s styrene partially to fully dissolved in a small jar of MEK. The dissolved styrene stock consists either of the plastic tree from the kit I’m using, along with cut and ground bits from the body (engine compartment, firewall, etc.), or strip/sheet styrene leftovers. Or both, if color isn’t important.
Downsides? A ton. It takes a while to prepare a batch – the smaller the pieces, the more easily they’re dissolved, but none of them dissolve quickly enough to make this an instant deal. Overnight is about as fast as you’ll get. The solvent consumption/evap rate is awe-inspiring, not to mention frustrating as you add solvent to decrease viscosity, then are forced to add more styrene to increase it if you guess wrong. Pot life sucks - what you prepare today will be virtually unusable four hours from now and solid by this time next week (but reintroduction of solvent and a lot of patience will restore it to a usable form). Application is a pain, as it dries extremely rapidly in small sections, and "trails" worse than thick contact cement. When used in quantities other than incredibly thin, it takes forever to dry. Due to the lengthy solvent evaporation rate in quantities, it will destroy thin sections if applied improperly. It is blindingly and rapidly aggressive – apply it to the wrong place and you’ll have to wait a while until that place is hard enough to refinish.
So what’s the point of using it? It is, by far, the strongest, lightest, and best-finishing plastic filler I’ve ever used. Given the right situation and no big hurry, I use it exclusively to fill and reinforce transitions and joints that conventional fillers don’t handle well enough to suit my building tastes. For example, a few weeks ago I decided to see if I remembered how to properly chop a kit top. Having one of Vince Ito’s Hardshell Classes vaguely in mind, I figured a ’40 Ford coupe would be a fair test. To keep a reasonably accurate but radically chopped roof profile, the roof itself ended up in six pieces, plus styrene spacing fillers. I used the styrene putty on the inside as a reinforcing "glue" at the junction of the roof-to-rear-body pieces, at the outside of the same juncture as a surface filler, and at the very rear of the rear window openings (lots easier that cutting and inserting a styrene piece to be reprofiled, and a bunch stronger than building up the outline in conventional filler putty.
When it was dry, externally, I ground and sanded away everything beyond what it needed to look like a chopped ’40 Ford, and, internally, removed the excess joint overlap to the level needed to hold it together as a slot drag car body. The resultant body component now weighs significantly less than when I started, something not always possible with standard fillers, whose bulk and density tend to weigh more than the styrene one removes in a radical reprofiling.
It isn’t the filler of choice for everybody, or for every application, for that matter, but it just might work for you, and it certainly doesn’t cost much to try, does it? See what you think, but don’t throw away your Bondo or Green putty tubes just yet.
(Additional glue note: The Monday, December 28, 1998 issue of the Wall Street Journal had an article about a new medical "wonder glue" that was being used to replace stitches on open skin wounds. This new glue was based on... cyanoacrylate, our old pal super glue, with (paraphrasing here) some of the toxins that might cause inflammation and/or infection removed. Uh-huh. Not like some hobbyists weren’t using the stuff (and Elmers GluAll as a degradable topical treatment) in a similar fashion more than two decades ago. Seems the glue dissolves after prolonged exposure to body fluids, which, primarily, are water-based. Not a recommendation, mind you, simply an observation.
Tools for Styrene
Some Basic Considerations – From the outset, try to remember one simple idea: in the long run, you’ll be lots happier if you dedicate the use of a new or fresh tool (with a few, limited exceptions) exclusively to styrene shaping and working. As a general rule, any tool used to shape metal, e.g., brass, stainless, or carbon steel, will retain sufficient contamination of and by those materials to eventually deposit some of it on that nice, clean kit and/or modification you’re working on. Which will, of course, resist all attempts at removal after you notice, say, the primer coat really looks like crap at that hood/fender junction. Some contaminants resist even aggressive cleaning in soap and water (you arecleaning those parts and bodies after each handling, aren’t you?), leaving you with both a refinishing problem and a not-real-positive attitude.
If you’re serious about this styrene business, having a separate collection of segregated styrene-only tools is a good idea, as is making a habit of not having the metal-working and styrene tools on the bench at the same time. Some times the temptation of simplicity and time-saving doesn’t pay off in the end, and this is probably one of those circumstances. Your call.
The "Basic" Stuff – Those who have read some of my articles about tools elsewhere already understand that I look at tools primarily as devices that have to demonstrate their value. Put another way: If I can’t clearly see how it will save me money, save me time, or accomplish something that nothing else I own will do as well, why do I need it (this from a guy who has a gajillion dollars worth of shiny, chromed automotive tools and isn’t even a mechanic, right?)?
To that end, then, there are some things I think you must have to approach kit building and bashing, mostly because nothing else does what they do as well. In no particular order, they’d include an 8" #2 cut mill file, a selection of #2 cut Jewelers’ files, a small X-acto (or equivalent) blade holder with a collection of #11 blades, and at least 220, 400, and 600 grit, wet-dry sandpaper. Given the option, skip the useful but expensive Flex-I-Grit film to start with, and buy the wet-dry variety at a discount or auto parts store. As you can see, most of these things, with the exception of the finer grades of sandpaper, are designed for basic shaping and forming, not finishing.
The "Yes, You Have To Spend A Bit More" Stuff – My personal recommendation would be to start out with two or three "Flex-I-Files" of the foam-cored, "Flex-Pad" variety. Available in coarse (part #1500), medium (part #2800), fine (part #3200), and extra-fine (who knows what number – I’ve never found a use for one), they’re moderately flexible tools that are invaluable for more detailed shaping, particularly in their coarse and medium grades.
While some more advanced automotive modelers swear by the very flexible variety (which resembles a looped strip strung between two legs of a "C"), I’ve never been satisfied with the degree of control I get over the sides of the band. I find they tend to load one side or another, causing uneven material removal and occasionally some unwanted grooves if one doesn’t pay enough attention to what the strips are really doing to the surface. Should you be having problems getting the right contour to a curved structure or surface, however, you might want to seek out someone who uses them extensively for better tips on their use. Since I learned to shape curved surfaces back in the bad old days of solid balsa wood models (kit instructions: "Congratulations on your new kit! Glue the balsa chunks together and simply cut away everything that doesn’t look like an authentic Boeing B-17. Good luck!"), I frequently make and use templates to finish such surfaces, and hack away at them with a succession of finer and finer flat tools. See what works best for you.
For rapid material removal in non-precision situations, e.g., removing engine compartment sides and firewalls to reduce some of that nifty track-hugging weight so many car kits are prone to, I fire up the Dremel (at low) and throw a sanding drum in the chuck (Dremel part #432 for medium/120 grit and 408 for course/60 grit, both of which require a mandrel with expanding rubber element, and no, I don’t remember the part number for that).
Zowie! Plastic everywhere, melted, powdered, strung, you name it. Perfect for destroying the hood opening edges, windshield base, and most anything else near where you want to remove material. The rules here are simple: a) wear eye protection, b) treat the situation like you’re a dentist and the car/part is your patient’s mouth, c) work carefully and deliberately, d) leave some room to trim and finish what will be a molten mass of styrene around the edges, and e) unless you want to track bits of styrene everywhere, forever, have a vacuum handy. "Crude but effective" is the operative term here.
The Best $3 You Can Spend – The next time you’re in a drug store, supermarket, or larger discount chain, stroll over to the cosmetics area and look for, lacking a better description, the "accessories" area or racks. Look for the Revlon stuff. Hanging on a peg should be something called an "Emeryl File." Buy one. Better yet, buy two, they’re reasonably inexpensive. Why? Because the little hummers are one of the best plastic-working tools I’ve ever seen at any price, that’s why.
If your sleazy store doesn’t carry Revlon "accessories," try one of any 4" nail file clearly labeled "permanent," "diamond," or "diamond-coated." Are they really diamond-coated? Who knows. Bulk industrial diamond and garnet dust/powder is a great deal cheaper than you’d suspect, particularly when you’re making 50 million nail files a year.
Like their conventional emery board cousins, they have two working surfaces, generally labeled as "shaping" (about a medium grit) and "finishing (a fine grit). Unlike emery boards, they remove material without sacrificing particles of their surface abrasive. Used with care, they form, edge, and trim styrene at least as well as a Flexi-File, with less deflection and more precision. They are also thin (approximately .025" to .030" thick), which permits them to get into recesses and slots no thicker than a few sheets of fine sandpaper. Special bonus to Revlon buyers! An "Emeryl" file may be the cheapest tool you ever bought that was made in Germany.
The Free Stuff – OK, so you had to wade through piles of ideas and interminable Unc verbiage to get to the part you were really looking for, right? Free tools! Woo-woo! So where, you are wondering, does one get the free stuff? Cutting to the chase:
Hey, stop moaning and kvetching and hear me out here. Your dentist, thoughtful healthcare practitioner that he/she is, has a bundle tied up in really spiffy tools for doing various things to teeth and soft tissue inside your mouth. A vast majority of those tools are really expensive stainless steel bits (all the better to autoclave, sterilize, etc.). Occasionally, those tools break (and let’s not dwell on how or where they may break, shall we?) and are discarded. Hmm.
They frequently include probes, scrapers, and fiendish devices otherwise known only to Dent School grads. They universally feature knurled, non-slip grips – for obvious reasons. For our purposes, however, they are configured pretty well to do a lot of the things we need to do with styrene, like shaping, moving, scraping, and scribing. Additionally, they can be reshaped to do even more.
Take scribing, for example. There is a difference between the tip shape of a scriber designed to make a break line in a sheet, for example (usually a "V" shape) and one designed to make panel or door lines ("a rounded "U" shape). With some care and a Dremelgrinding wheel, it takes about 20 seconds to convert the broken end of a dental tool to just about any scribing shape one might desire. Narrow scribes use the outer end, and wider ones any desired thickness down the "neck" of the tool.
I’ve spent some time and money investing in commercial tools designed to do the same job(s), and universally prefer home-made ones. For example, a few seconds worth of grinding turns one of those awful-looking, "L"-shaped scrapers into a precise tool for smoothing, routing, and generally refinishing right-angled recesses like windshield and window mounting channels. With a little bit of thought, you can come up with literally hundreds of different shapes and uses for these things.
Just make sure your dentist knows what you want them for when you inquire about their availability, and doesn’t think you’re going into practice yourself.
More Free Stuff (sort of) – In addition to the tools you can buy or modify, there are a few simple things you can make that occasionally solve particular problems. When the thought is along the lines of "Gee, I wish I had something that would fit in there and do that," don’t overlook the possibility of taking a piece of styrene stock, shaping it to size, and attaching the appropriate grit of sandpaper to it via a small dab of instant adhesive. Not a lifetime investment, to be sure, but sometimes a life-saver nonetheless.
Also, don’t overlook the utility of the dumb, old sanding block. For example, you can make a useful dumb, new one from a relatively flat, smooth piece of particle board and some adhesive-backed sandpaper of roughly medium grit. It’ll work wonders flattening and evening the rocker panels and nose of that slammer Pro Mod you’re working on.
Conclusion – To make the most of what you can afford and what’s out there, a recommendation about tools (and a great many other things, for that matter): when you’re looking for a solution to a problem, try not to think "What is the plastic car modeling tool I need to do this job?" Instead, try approaching it from the functional point of view: "What task, exactly, am I trying to accomplish here, and who else out there occasionally has to do basically the same thing?" You might be surprised with what you can come up with.