167 replies to this topic

[don.siegel]

Excellent work Alan, thanks for showing us all the choices, blind alleys, etc. 

 

Don 

[Alan Draht]

Very nice work! I assume you are using Graupner rubber so tire don't "Explode" upon start up?

 

Jess Gonzales

 

Thanks, Jess!

 

The Graupner model airplane tires pictured above are exactly the same "donuts" that 1960's Pro drag racers on both the East and West coasts used to make drag racing wheel/ tire sets.  In fact, "German formula" rubber Graupners were all most Pro racers had to work with for slot car racing in the mid-1960's, period.

 

Graupner tires were not, however, immune to blowing apart under acceleration from the drag strip starting line.

 

Manuel Maldonado himself tells the story of how that happened at a big West coast drag meet and thrilled the spectator crowd.

 

Gene Husting talks about how disappointing it is to see your finest set of Graupner dragster tires unpredictably break apart under full acceleration.

[Alan Draht]

Excellent work Alan, thanks for showing us all the choices, blind alleys, etc. 

 

Don 

 

Thanks, Don!

 

In describing what's involved with scratch-building racing slot cars in general, not just dragsters, one has to strike a balance between reporting too little or too much detail.  Sometimes it's hard to know or predict what the audience will find interesting and useful.

[Jesse Gonzales]

yes the german rubber was the most used non sbr tire in the old days, they really liked a dose of oil of wintergreen and maybe a little glycerin. In the old days I don't think there was a track in the Phoenix area that had a dragstrip so I was speculating that modern usage was to try and keep the rubber from chunking off.

 

Very good work, makes me wonder about drag racing these days. are there rules or some sanctioning bodies where an old pre wing guy can do some reading?

 

Jess 

[Bill from NH]

Jesse, do a Google search on "Slot Car Drag Racing" & see what you find. There used to be several online drag sites with info & BBSs, but I haven't looked for them in months.

[Phloidboy1]

roof flashing aluminum works for bodies.

[Horsepower]

THIS IS THE MOST DETAILED AND INCREDIBLE BUILD i HAVE EVER SEEN! I DOUBT FULL SCALE FUELIES GET THIS MUCH DETAIL. THANK YOU ALAN, FOR POSTING THIS AMAZING PIECE OF MACHINING. YOU MUST HAVE BEEN DOING MACHINING FOR A LONG TIME. 

[Alan Draht]

roof flashing aluminum works for bodies.

 

Thanks, Floyd!  I will keep that in mind for my next vintage-style dragster build.  

[Alan Draht]

THIS IS THE MOST DETAILED AND INCREDIBLE BUILD i HAVE EVER SEEN! I DOUBT FULL SCALE FUELIES GET THIS MUCH DETAIL. THANK YOU ALAN, FOR POSTING THIS AMAZING PIECE OF MACHINING. YOU MUST HAVE BEEN DOING MACHINING FOR A LONG TIME. 

 

Thank you, Gary!  Thanks very much!  

 

Actually, I'm an amateur machinist.  I've owned a Sherline miniature mill and lathe since the late 90's, but didn't use the machine tools much other than occasionally for hobbies, like machining lightened parts for on-road R/C gas cars.

 

I started using the tools more intensively when I was building the slot car inspired by Howie Ursaner's 1965-66 "Rocketship".

 

There are a fair number of professional machinists on Slotblog and in the hobby, I gather from comments and posts I've seen.

[Alan Draht]

Now, if you'll excuse me, I have a bunch of vintage dragster wheels, tires, and Graupner donuts to prep, glue, mount, cure, cut, trim and true before I can take these dragsters to the track.

 

And, I need to finish the Maldonado dragster by disassembling it, polish the outside face of the main rails and other exposed magnesium frame components, clear coat them, and finally, re-assemble the car.  The driver needs to be painted/ detailed...

 

The initial steps involved in mounting Graupner model airplane tires onto Russkit dragster wheels can't be performed on a Hudy slot car tire truing machine.

 

The first step involves cutting the center "core" out of the Graupner tire sized to create a concentric hole matching the Russkit wheel's diameter.

 

Gene Husting had a purpose-built "Graupner-tire-hole-cutting-machine" that shows up in his Rod & Custom magazine dragster-building articles.

 

Normally, I never use my Sherline miniature machine tools to cut anything that's soft rubber, and certainly not tires.  The rubber dust particles gum up the tool's surfaces and moving parts unless they're vacuumed/ wiped off very thoroughly.

 

However, in this case, I didn't want to build a special machine that I'd probably never use again, so I broke down and used the lathe to "core" a dozen pairs of Graupner tires, using a 0.6050" diameter diamond-coated hole saw mounted in the Sherline lathe's tailstock.

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[Alan Draht]

In Post #124 I had a photo of a pile of Graupner tire donuts, Russkit dragster wheels, and a tube of 3M Weatherstrip and Gasket Adhesive, the same adhesive used to mount rubber donuts onto Retro and other slot car wheels.

 

I used 3M Weatherstrip adhesive to mount 5-6 pairs of Graupner donuts about six months ago soon after I finished building the Husting dragster replica.

 

It was a waste of time and Graupner tire donuts.

 

There simply isn't enough time to mount the donut, center and align it on the wheel so that the tire doesn't "wobble" as the wheel turns slowly on the lathe. 

 

The modern slot car tire-mounting process using 3M Weatherstrip adhesive only allows 5-10 seconds, if that much, to position and orient a tire donut on the rim.  After that the 3M adhesive sets up and adjustment time is over.

 

So, except for one pair, my initial set of Graupner dragster tires mounted on Russkit wheels "wobbled" badly and were unusable.  They had to be soaked off the rims.

 

You can't correct this problem with the Graupner tires during the tire truing process either.  There isn't enough Graupner donut material to correct a donut that's been mounted/ aligned incorrectly.

[Alan Draht]

The next batch of Graupner tires were mounted with long-cure (overnight) clear epoxy.

 

Husting used the same method.

 

Epoxy allows plenty of time to study a freshly-mounted Graupner donut as it rotates on its wheel chucked into a slow-turning lathe, and to adjust how the donut sits on the wheel to eliminate wobble and misalignment.

 

The epoxied tires were left to cure for a week or more before the next step in the process:  Trimming the outer "band" of the Graupner tire's tread pattern off.

[Alan Draht]

The lathe was used once more to trim off each tire's outer band of rubber using an Xacto knife mounted in the tailstock.

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[dc-65x]

Epoxy allows plenty of time to study a freshly-mounted Graupner donut as it rotates on its wheel chucked into a slow-turning lathe, and to adjust how the donut sits on the wheel to eliminate wobble and misalignment.

That's exactly the way I've found works best for me too Alan.

 

Using the Sherline lathe is the a great way to do the initial trimming too. I cringe when I see the old magazine articles with the author holding an Exacto knife in his hand while spinning the tire in a drill motor with the other. 

 

I have a Sherline too but I also have this neat old tire trimmer I got from Rodney that I use just for the nostalgia of it. You can even swing the cutter assembly around 90 degrees to trim the sides of the tires if needed:

 

 

The best thing is the wood wedge with an inner tube wrapped around it and stuffed under the motor to cut down on vibrations.  

 

Onward Alan 

[Alan Draht]

This is the finished product:  Seven pairs of Graupner tires mounted on vintage Russkit dragster wheels, trued on a Hudy machine to 1-3/8" diameter.

 

I have a total of eight pairs when I add in the one pair from the first tire-mounting effort using 3M adhesive that didn't wobble.  That pair of Graupner's is mounted on my Husting dragster.

 

There were two pair of bare Russkit dragster wheels that wobbled on their axles and couldn't be used.  It's such a shame to see that many NOS Russkit wheels go to waste.

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[Alan Draht]

The final step in this process is tire-matching.

 

Back in 1966 Gene Husting used a very elaborate process to match his Graupner dragster tires.  He describes it in detail in one of his R & C magazine dragster-building articles.

 

In Post #138 there's a photo of a freshly-cut outer "band" of Graupner tire rubber lying on the lathe bed below the trimmed tire itself.

 

Husting used to save each band along with the tire/ wheel it was trimmed from.  He did this with every tire/ wheel and kept each tire and its associated band separate from every other tire/ wheel assembly.

 

Then, to kick off his tire-matching process, Husting would take each band and associated tire, hook one end of the band on a wooden ruler and stretch the band as far was as it would go until it snapped.

 

Husting would record the number of inches the band stretched out to on the ruler before it snapped.  Then he'd move on to the next band and its associated tire.  The more the band stretched before it broke, the more "elastic" the tire it was trimmed from.

 

That was just one factor Husting used in matching his dragster tires.

 

He also used each tire's porosity and its gray color (dark vs. light) as factors in the process of matching his Graupner tires.

 

Gene was a pure professional who took no shortcuts.

[Alan Draht]

My method of tire matching relies heavily on a tool I borrowed from my on-road R/C gas car racing days, a scale tire durometer.

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[Bill from NH]

I never saw Gene Husting drag race, but I him & his son Curtis racing 1/8 gas RC cars at a ROAR Nationals held at Attleboro, MA during the late '70s or early '80s. I believe they ran Associated cars then. Their preparation was immaculate.

[don.siegel]

Thanks for sharing your "tired" story Alan, very interesting! 

 

I must admit that I did a few like in the old magazines before getting a tire truing machine. Chuck it in the Dremel, hold an X-acto in the other hand... and pray! Not really that hard if you can keep the revs down, but don't know how precision it all is... 

 

I assume the guys in the photos were just mostly showing the tools and not actually doing it like that, since they had to use their third hand to hold the cameras. A few, like Husting, did show the wheel and tire chucked in a drill press.

 

I haven't done too many Graupners, but I often trim the sides on big urethane tires to get them to fit on slightly narrower wheels. 

 

Don 

[Alan Draht]

Here's a photo of the tire durometer from a different angle showing the small movable plunger tip protruding from the bottom of the tool.

 

This should clarify how the tool works.  

 

I had a hard time one-handing the durometer against the tire to get a realistic reading of 60 while hitting the camera's shutter button with the other hand.  

 

I found that this group of recently-purchased Graupner model airplane tires consistently measured between 60 to 70 "units" on this durometer.

 

To this day I don't know how the durometer's units of measurement are defined.

 

I do know that in on-road R/C gas car racing about 10 - 15 years ago the typical car manufacturer's racing tires were rated anywhere between 25 to 35 "units" of hardness right on the box.  And sure enough when you measured your brand new racing tires, the readings on this durometer and the manufacturer's numbers matched.

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[Alan Draht]

Oh, now I remember, the unit of measurement on a durometer is called "shore".  The manufacturer tire boxes had the word "shore" on them next to the shore number.  

 

With a durometer, "...hardness is a measure of the resistance a material has to indentation".  So sayeth Wiki.

[Alan Draht]

In Post #124, my photo of Graupner tire donuts and Russkit dragster wheels also showed a group of five pairs of vintage K&B Modelrama aluminum 4-hole dragster wheels made for use with 0.1250" diameter axles with 5-40 threaded ends.  There are five pairs of 55+ year old K&B "German Formula" dragster  tires which came in sealed packages.  Two pair are mounted without adhesive to K&B wheels; three pairs of tires are not.

 

What's special about the K&B dragster tire compared with a Graupner tire donut is that the K&B tire comes with a 1/16" high x 1/4" wide ridge molded into the tire's inner core opening which fits snugly in between the K&B wheel's rim flanges.  In other words, the K&B dragster tires are made to be mounted onto these K&B dragster wheels.  The K&B tire is wider than the rim and centered on it so the tire overhangs the rim evenly on both sides.

 

Mounting these K&B tires using 3M Weatherstrip adhesive is straightforward.  There is enough time after the adhesive has been re-wetted with solvent to slide the tire over the rim and quickly verify that the tire is on straight.

 

In the R&C magazine article's "Car of the Meet" photos of Manuel Maldonado's dragster, it appears that Graupner tires are epoxied onto K&B 4-hole aluminum dragster wheels.

[Alan Draht]

After letting the mounted K&B tires cure for a couple of weeks it was time to trim/ grind them to to final size on the Hudy tire truer.

 

However, I needed to first make a new spindle to fit into the Hudy machine with a 5-40 threaded end so that the K&B wheels could be mounted for truing.

 

The Hudy tire truing machine is manufactured in Europe (probably Slovakia) to metric standards, so it's natural that the machine's spindles are  made to fit into 3mm ball bearings and a 3mm pulley-drive wheel hole.

 

A 1/8" or 01250" diameter axle is equivalent to a 3.16 mm diameter metrically, so a 1/8" axle with a 5-40 threaded end can be converted to a 3 mm axle with a 5-40 threaded end by simply removing 0.16 mm of material on a lathe.

[Alan Draht]

I took a 1/8" diameter x 5-40 threaded axle, chucked one end of it into the lathe and cut off approximately 0.15 mm of steel using a solid carbide indexed cutting tool.

 

 

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[Alan Draht]

I pushed the 3mm end of this new spindle through the 3mm ball bearings in the truing machine's spindle carrier, slipped the pulley drive-wheel over the spindle's machined end, set-screwed it into position on the spindle shaft, and the Hudy was ready to go to work truing K&B tires mounted onto vintage threaded K&B aluminum dragster wheels.

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