58 replies to this topic

[JimF]

I just received this from Rick at R-Geo to build the justly famous "GVP" chassis. In a case like this, with a proven winning design, I'm not going to reinvent the wheel (or the chassis). This won't be an exact copy; it will be an attempt to remain faithful to the race winning design of the original. Any deviations will be in the interest of strengthening.

 

Because of my work schedule, I couldn't finish this tonight. I'm going to break this into two segments for the complete job. I promise that I won't drag this out over the next few weeks showing one solder joint a day or somesuch. Off we go...

 

Here's what you get to start with. All brass is .032", bracket is .050". This is a nice builder's kit as opposed to some of the "Lego" kits out there.

 

 

First step is to square and prep the bracket. This is basic stuff. The bracket face is filed until flat then the legs are bent square to the bracket face. The bracket is cut out slightly to accommodate the tuning fork rails which will run along the inside of the bracket. To the side are two bits of 3/32" square tubing about 3/4" long. These are soldered together and then dressed flush and square. These will be the fork hinge tubes.

 

 

Here is the nosepiece with the hinge tubes. Lines on the ears of the nosepiece show they need to be sanded square or at 90* to the chassis centerline.

 

 

Nosepiece squared up and the guide tongue reinforcer is notched to clear the hinge tubes.

 

 

Here's the nosepiece with all parts tacked in place but not yet fully soldered.

 

 

The nosepiece is dropped into your jig along with the motor bracket. The paper template underneath will be your guide for bending, placing, and adjusting the forks. The first bend in the fork will be 1" forward of the bracket face. Both bends in the forks will be 45*. Neither the distance forward from the bracket nor the angles are critical.

 

 

Take two pieces of .062 piano wire about 5" long, and place a sharp mark at about the 2.100" point. Then measure .495" forward of the first mark and make a second. These will be your two bend points.

 

 

Make your first 45* bend. A little hand drawn template is handy here to check your angle.

 

 

Make your second 45* at the forward mark you made on the wire. Again, the template comes in handy to check that the fore and aft legs are as close as possible to parallel. You'll be surprised how accurately you can judge this by eye. After your bends are complete, your angles matched as close as possible, and the legs are parallel, slap this piece on a block and bend the legs until the piece lays flat. Then go back to the template and check the angles and the parallel again Repeat this process for the second fork rail.

 

 

When both fork rails are bent, tweaked, flattened, and aligned, slip the forward ends into the hinge tubes and the aft legs inside the bracket legs and see how you did. The template paper will show you how well you hit the angles necessary and how well matched they are.

 

In this case, my right rail was almost perfect, but my left was off a little at the two points indicated.

 

 

A little corrective bending got the left rail a lot closer as seen here. At this point, I could have just kept on bending and tweaking that rail but I decided to just bend another. The next one was spot on so I called it good and moved on.

 

 

That's the end of the first segment. Next up are the main frame rails, pans, some reinforcement, and finishing up.

[SlotStox#53]

Very nice kit and a very good start to another informative and comprehensive build *how to* thread.

 

Good work, Jim. 

[kvanpelt]

What would those "Lego kits" be?

[James Grandi]

One question; is it a necessity to use square tubing for the fork rails to fit into, or would round tubing be fine?

[Ramcatlarry]

You have a stronger solder joint with the square tubing and less corrosion/sticking on the inside of the tubing as well.

[Greg VanPeenen]

James,

 

Not my thread but I will answer I have built many, many tuning fork chassis with the front hinge Some of the early ones with round tubing but most with square . Square gives the tuning fork rails a little extra wiggle room and that seems to work better for me. 

[Danny Zona]

I'm watching this build like a hawk. My kits should be in next week then I'll give it a try.

 

Thanks for the how-to thread. I need it. LOLs.

[Dennis David]

Silly question, is the fork just slipped into the rear bracket or is it soldered?

[JimF]

Just checking in at lunch (from work). Thanks to all for the comments and esp. to Greg (it IS his design after all.

 

For Dennis... yes, the rear legs of the forks are soldered solid to the bracket.

 

For James, I've done a lot of "forkers" too and while I don't think it matters tremendously, I like the square for this application because it's easier to work with. The rest should wrap up tonight. I've done a few things differently as an experiment but those can be reversed later after testing.

 

I may be a little tardy in finishing this up because I've got this to deal with the parking lot at my apartment. Good for business when you run a ski shop for your daily bread and butter.

 

[bbr]

Ski! I need some good ski.

[James Grandi]

Thanks for the answers, guys. I have one of these R-Geo kits waiting for me to build it, and I'll be watching this thread closely.

At the same time I'm actually about halfway through hacking the hell out of an original JK kit and building one that way. With all the cutting/filing it's taken to do, it makes one appreciate a well-made chassis kit even more.

[JimF]

James:
 
The original JK kit is a great starting point for a lot of projects. It is just a basically good design that one can convert into almost anything. I use the JK kit a LOT as the starting point for experimental stuff that I do. This new kit from Rick just simplifies this particular design to a point that, if this is what you want to build, it's kinda silly to go elsewhere for your starting point.

In the second segment (tonight, I hope) I'll point out some slight differences and choices that the individual builder can make with this kit as the starting point.

[MantaRay]

Why did the nosepiece ears need to be "trimmed"... 1/16" removed?

[Half Fast]

How was the guide reinforcer notched? It looks like that would be a difficult cut in steel.
 
Cheers.

[JimF]

OK... Just got home from work. Have more pics to take and bit more work but should finish tonight.
 

How was the guide reinforcer notched? It looks like that would be a difficult cut in steel.

 

why did the nose piece ears need to be "trimmed"... 1/16" removed?

 
Bill: The GTR was notched with a Dremel disc and finished out with a file. Pretty easy actually as the steel is not super hard. I held 'er in a vise grip and buzzed away at it... didn't even shatter a disc.
 
Ray: Didn't actually need to be trimmed but this bit of brass with all the cuts and shapes is pretty flexible and in the stamping/shearing process there was a bit of flat plane crescent shape to it. You can see in the top view that the front surfaces of the ears still have a bit of forward arc to them. Squaring the rear face up on the disc sander enabled me to use that face as a reference for squaring up the centerline of the tubes.
 
Not necessary... looks better.

[Dennis David]

One more question. What's the dimension between the front uprights?

[JimF]

2.150".

[JimF]

OK... wrapping it up.
 
Paper template out of the way and main rails tacked in place. These are .062" wire about 4.750" in length to start. They'll run wild at the back of the bracket and get trimmed later. Everything is checked for jig wheels flat on the deck, main rails flat... etc. Then we slide the bracket brace in, douse each joint in flux, turn on the fan, and get serious about all the solder joints.
 

 
Out of the jig and wash off the flux residue. Then onto the granite "flat block" to check for flat and examine each joint.
 

 
An additional bit of .055" wire goes on top of the main rail to increase the solder grip of the main rails to the bracket.
 

 
Tubing bits in place for hinges and stops. Hinge tubes are 3/32" round about 3/4" long, up/down stop is 3/32" square about 1/4" long. Front face of the stop tubes will be beveled at about 45° to clear the front tires.
 

 
Setting up the hinges and stops. The hinge rods are .062" and the front stops are .055". All have a dogleg bent into the rod as indicated by the red arrows. There is also a small relief cut (blue arrows) into the pans to help in the hinge rod laying flat on the pan.
 
I'm going off the reservation a little bit here by running the pan windows to the rear. Two reasons for this: (1) the placement of the front pin is farther aft than my normal as is. If I reverse the pans, it'll be 3/8" further back yet. (2) As light as this nosepiece is, I'm considering the fore/aft weight balance. At the end, I checked it and I guessed right.
 

 
Here is a brace for the nosepiece/front axle carrier. One piece of .055" wire per side
 

 
Last things here. Two bits of .047" to reinforce the ears (blue arrows) and body pins. Front is a "floater" back tubes are fixed.
 

 
She's done! Details...
 
Wheelbase = 4.0".
Guide lead = .850".
Weight as shown here = 107.4 grams with body.
Fore/aft balance point is 2.010" forward of the rear axle (.050" to .070" more rear bias than usual for me).
 

 
This was an easy build as all the parts were cut correctly and there was very little straightening or other prep work to do. I know the design is a proven one so I'm excited to spin some laps. There are few things that may get experimented with over the course of time. One might be reversing the pans for even more rear weight bias. Another might be using .047" wire for the pan stops (gaining more pan movement) This is a pretty short guide lead for me so that'll be on the stove as well. For sure, it'll get tuned as is without changes to the build.
 
Edit to add... Forgot to mention... other versions of this frame have used a "limiter" in this area to limit twist flex. I may do this too but it will be very easy to add/remove on the first track day.
 

[Danny Zona]

Sweet build. I love how you explained and showed your step-by-step process in building the car.

[JimF]

Danny:
 
Thanks, I'm glad that you may have gleaned something even though this was not really directed at someone at your level. Rick has mentioned that things that just come without thought to some of us are a complete mystery to others. Thus, something that's a simple and intuitive kit to me may look like one of those 1,000 piece jigsaws of the Eiffel Tower to someone else. Hence these kit tutorials that again, are not really aimed at the accomplished builders out there.
 
Another important reason for my reply is to point out where some credit is due. I'd personally like to thank you for this tool which is nearly indispensable to me in my building efforts.
 

[Rick]

You summed it up well, there are those that this will help a lot for building their kit, and even varying on to their own ideas, but the basics are laid out there in easy steps to follow. Jim did this as a special favor for me, it is snowing and he makes his living in a ski shop and is slammed with his own work now.

Indebted to your amazing building skills. Thank you very much!!!...

[Tex]

I enjoyed the "how-to" also. While I'm no stranger to scratchbuilding, I really struggle to see the different movements built into a chassis just by looking at a picture; holding one in my hands is worth a thousand words. But Jim's write-up and pics make it easy to understand.
 
OK, I do have one question. Would getting the "limiter" installed be as simple as unsoldering just those two mainrail joints on the nosepiece, slipping the limiter over the wishbone, and then soldering those mainrails to the nosepiece again? Of course, to do so I realize that one would have to get the pan hinges, downstops, and wishbone inserted into the proper pieces of tubing first.

[raisin27]

Interesting that you reversed the pans. I am in the process of building my second R-Geo GVP kit and I too am reversing the pans for the same reason as you did. I like my front body pin a bit further forward. If rear weight is needed I was thinking I could fill in the holes with a brass piece.
 
Very nice clean build.

Raisin

[raisin27]

I enjoyed the "how-to" also. While I'm no stranger to scratchbuilding, I really struggle to see the different movements built into a chassis just by looking at a picture; holding one in my hands is worth a thousand words. But Jim's write-up and pics make it easy to understand.

OK, I do have one question. Would getting the "limiter" installed be as simple as unsoldering just those two mainrail joints on the nosepiece, slipping the limiter over the wishbone, and then soldering those mainrails to the nosepiece again? Of course, to do so I realize that one would have to get the pan hinges, downstops, and wishbone inserted into the proper pieces of tubing first.

 
Not sure if this is quite what your thinking, but I installed a "limiter" on my fork rails simply by soldering two pieces of tubing together and slightly crushing them so they fit tight over the rails. By sliding it for or aft it will change the "flex".
 
Raisin
 

[JimF]

Tex:
 
Mike nailed it very well but I will probably not use that device myself. I will probably just use a bit of ~ .039" wire and solder it at the crux point. Not sure if that is necessary or even advisable but it's a quick and easy test that can be done and then reversed while in the midst of a test session.