Derby Talk

See "2011 12 08 Wheel Inspection Gage" in Stan's Projects.

The brief video shows operation of a simple Wheel Sidewall Thickness Inspection Gage.

I like it! Simple and straightforward.

gpraceman wrote:I like it! Simple and straightforward.

Me too! Can the gauge work (or be adapted to work) on an installed wheel?

FatSebastian wrote:Me too! Can the gauge work (or be adapted to work) on an installed wheel?

I think it could. Just need to add a cradle for the car and then use the go/no-go gauge on the portion of the wheel exposed on the underbody.

Also, could make some type of assembly that has a base plate that is held against the wheel sidewall. That would make for a smaller unit.

FatSebastian wrote:Can the gauge work (or be adapted to work) on an installed wheel?

The gage, as is, is intended to be used on installed wheels. The text at 0:47 in the vid says that (but it does go by rather quickly.) I'd have used an actual car, but I needed to capture the video quickly and had no cars with 2009 wheels and DerbyWorx wheels installed. Sam was picking up the gage to take to a PW planning meeting! Her steady fingers were operating the gage in the vid!

Scout holds car wheel against base plate. Not shown are (1) a hole in the plate to allow axle head clearance and (2) a guide marking on the plate to locate bottom of the wheel.

In use, I will add a rubber band to attach to inspector's wrist so that sudden movement by Cub Scout doesn't throw the rocker arm onto the floor! I suspect that the machined screws might be too delicate to survive a fall to the floor!

The gage needs greater freedom of movement to allow rocking on two different axes. Side-to-side rocking is "GO", but end-to-end rocking is "No-Go". It could, however, be redesigned as an alligator jaw pivoted at the outboard pin, and use a thickness gage on a center pin to prove that the sensing pin is contacting the inner wheel sidewall. I didn't do it that way because I'm not up to machining precision hinges yet!

I asked Terry if he could think of a clever easy way to hold the screws while the threads were machined off. No response yet. I'll ask the same here.

What I did was construct a "screw holder" as follows: turn a 5/8" dia X 1" mild steel cylinder, drill a 0.35" dia X 3/4" deep hole in one end. Then drilled the remainder of the hole with a #29 drill and threaded the hole with 8-32 tap.

In use, the screw is run into the tapped hole from the inside, exposing about 3/4" of thread. The 5/8" dia screw holder can now be chucked in a lathe. Since the screw threads are right handed, I had to run the lathe in reverse and flip the cutter over. Otherwise, the cutting force would unscrew the screw from the holder.

Even operating the way, the screw needed to be run in tighter than I could do with just finger pressure against the holder... had to grab it with vicegrips to get enough torque to hold the screw against vibration from machining.

There has to be a simpler way to do it, but I couldn't think of one.

gpraceman wrote:

FatSebastian wrote:Me too! Can the gauge work (or be adapted to work) on an installed wheel?

I think it could. Just need to add a cradle for the car and then use the go/no-go gauge on the portion of the wheel exposed on the underbody.

Also, could make some type of assembly that has a base plate that is held against the wheel sidewall. That would make for a smaller unit.

The table top base plate is a result of my design concerns. Since the Cub Scout will be holding the car (our rules, and a cradle that adapts to various car geometry seemed difficult), the design had to assure that whatever portion of the gage that is held by the inspector has little capability of dislodging the car from the Cub Scout's grasp.

In addition, those parts of the gage that contact the car must be "gentle". The end of the baseplate is rounded and polished, allowing contact only with the wheel sidewall. Similarly, the face of the base plate is polished and its edges are rounded and polished. The ends of the rocker arm pins are rounded and polished to avoid scratching the wheel and to assure ability to reach into the bottom of the wheel sidewall interior.

Stan Pope wrote:Since the Cub Scout will be holding the car (our rules, and a cradle that adapts to various car geometry seemed difficult), the design had to assure that whatever portion of the gage that is held by the inspector has little capability of dislodging the car from the Cub Scout's grasp.

(thinking out loud here...) I am wondering if some kind of hand-held pincer arrangement that doesn't require a table could work (think long scissors, except with the very tips curving in like an old-fashioned ice clamp). Paint the overlapping parts when compressed in the "no-go" position; Clip it up to the wheel like a spring-loaded clothespin when testing and it is still a "go" if any of the unpainted section is visible. Would this be too insensitive?

FatSebastian wrote: (thinking out loud here...) I am wondering if some kind of hand-held pincer arrangement that doesn't require a table could work (think long scissors, except with the very tips curving in like an old-fashioned ice clamp). Paint the overlapping parts when compressed in the "no-go" position; Clip it up to the wheel like a spring-loaded clothespin when testing and it is still a "go" if any of the unpainted section is visible. Would this be too insensitive?

The wall thickness difference between an unworked wheel and the 1.8g "speed wheel" is on the order of 0.060". If the goal were to detect variance of 5% from unworked toward 1.8g, then it would have to react to 0.003" change. That seems pretty fine for the mechanism you described.

Another concern is that the gage can not be allowed to "grip" the wheel with leverage. There must be no possibility that the gage can twist the wheel sufficient to damage it. Because of that I didn't delve far into any "alligator" type gage designs.

But don't stop thinking up solutions.

Stan Pope wrote:I asked Terry if he could think of a clever easy way to hold the screws while the threads were machined off. No response yet. I'll ask the same here.

This is a job for a "clamp nut": take an ordinary hex nut that mates to the screw, and cut a slot through one side (by dremel or hacksaw). Thread screw through the nut, and secure the nut in the headstock chuck. The slot in the nut allows the nut to compress slightly on the bolt under the pressure supplied by the chuck.

See e.g. http://homemetalshopclub.org/projects/m ... t_jack.htm.

/JEP

A precision bowl caliper would do the job. I have a cheaper version, might try it this year...

Jeff Piazza wrote:

Stan Pope wrote:I asked Terry if he could think of a clever easy way to hold the screws while the threads were machined off. No response yet. I'll ask the same here.

This is a job for a "clamp nut": take an ordinary hex nut that mates to the screw, and cut a slot through one side (by dremel or hacksaw). Thread screw through the nut, and secure the nut in the headstock chuck. The slot in the nut allows the nut to compress slightly on the bolt under the pressure supplied by the chuck.

See e.g. http://homemetalshopclub.org/projects/m ... t_jack.htm.

/JEP

Thanks for that link! Good stuff there.

Since I'm working with a #8 screw and wanted to leave only about 1/4" of thread, I went a slightly different direction. The mating nut for a #8 screw is typically about 0.1" thick so the length of chuck wouldn't be long enough to keep the screw centered properly ... at least I think that would be the case.

What I did was cut a 3/4" long X 5/8"dia from stock. I drilled from one end with a drill about 0.350" dia (large enough to clear the head of the screw), leaving about 3/16". Then drilled the remainder with a tap drill for #8. Tapped it (just the way they described in the article you showed me.)

To use, I run the screw into the holder from the depth hole side, allowing the bolt to extend out in the clear. Tighten the bolt down firmly. Chuck the holder. Run everything in reverse so that the cutting force holds the bolt tight in the holder rather than unscrewing it.

Maybe I try making my own, longer, "clamp nut" by cutting as above, then slicing along the radius with a hack saw. That should work and I wouldn't have to run everything in reverse!

rpcarpe wrote:A precision bowl caliper would do the job. I have a cheaper version, might try it this year...

Couldn't think of a way to make one with sufficient precision. Precision hinges aren't my strong suit!