Obtaining matching wheel diameters after sanding/polishing?

[Derby Dad]

In prior years, we used a mandrel in my corded drill (secured in my tabletop vise) to hold 1 wheel for sanding/smoothing/polishing.

But, I just broke down and bought an 8" drill press (not too expensive one, though) from Harbor Freight. It was on sale.

So, we're wondering if there's a way to use the drill press to sand/smooth/polish multiple wheels at one time. The mandrel holds only a single wheel at a time. If we could spin all wheels at once, then it seems that we could more effectively ensure that all the wheels have the same diameter after we've completed the polishing.

I've heard about the Pro-Wheel tool for shaping the wheel, but our rules specify only sanding/polishing is allowed. And, I've probably reached the $$ limit as far as PWD tools go. (My wife doesn't know about the drill press yet. )

Any ideas?

Thanks.

[Da Graphite Kid]

Derby Dad,
Although I have not done so, but wanted to, sand and polish a set of 4 wheels at once; there is a Pack web site in the lastest edition of the Pinewood Derby Times (Volume 3, Issue 8 ) from Maximum Velocity. If you have not signed up for this free newletter yet, do so! You could also get a freebie car plan when you do. The web site http://www.pack1421.org/derby/ has a link to a page that shows using a nail and pencil erasers to mount 4 wheels in a drill press at once.

By the way, the Pinewood Derby Times has a good article on car painting/finishing as well.

Da Graphite Kid

[Darin McGrew]

The web site http://www.pack1421.org/derby/ has a link to a page that shows using a nail and pencil erasers to mount 4 wheels in a drill press at once.

Specifically, this is shown at http://www.pack1421.org/derby/help/#Wheels

[DuckBoy]

I would recommend making a jig/setup that would allow you to duplicate your sanding from tire to tire, doing one at a time.

I use a Shopsmith and made a simple setup to for a razor blade to shave the tire down. This allows me to shave all the tires down to the same size even though I'm doing them individually.

I've tried to do all fours wheels at once but found one of the four would stop spinning I would have three wheels spinning and one just sitting there.

I would like to know why you can't use a tool to shave the wheel and must sand? If you take two tires, one sanded and one shaved with a blade, assuming they are done properly could you tell the difference between the two? I wouldn't think so IMO. They are two ways to achieve the same result in the end. I just don't understand this rule...

[Derby Dad]

Thanks for the info. I just received our rules regarding the wheels:

Wheels and axles must be as furnished in the official kit. NO washers, bushings, bearings or springs are allowed. Wheels may be sanded to remove the flashing only. NO reductions in width or diameter, or changes in shape are allowed.

So, I'm now planning on only removing the flashing via sanding. There's typically a few small spots on the tread and at either side of the hub. So, that's all we're planning to do. Hopefully, in the process the wheel will become more rounded, probably not much though.

The limitation about changing shape seems to imply that you're stuck with out-of-round wheels if your kit happens to contain them. So, I'm going to get as many extra BSA kit wheels as I can so we can select the best performing wheels. This seems a little unreasonable to me.

[Darin McGrew]

The limitation about changing shape seems to imply that you're stuck with out-of-round wheels if your kit happens to contain them. So, I'm going to get as many extra BSA kit wheels as I can so we can select the best performing wheels. This seems a little unreasonable to me.

Yep. I agree. I started a Raising the bar by requiring "stock" parts thread about this topic in the Planning, Preps & Running the Race category.

[Stan Pope]

This picture (posted in another thread) shows how you can set up a guide and stop to make depth identical.

[Da Graphite Kid]

Derby Dad,
Sounds like we are the same boat with the "light sanding only" rule. I e-mailed questions about this to our District PWD Chairperson to claify this. I specifically stated that if a light sanding only meant that you could only sand off the molding gate, that this would require the boys to use wheels that are known to be out of round. I even offered to drive the 50 miles to demonstrate that they were out or round if needed. No reply so far so I guess I'll take Stan's advice from another post and call him tonight! If needed, we too will sort through the 18 different pwd kits that we have to get four of the best.

Stan, could you get another picture of you jig as I don't see how this controls the depth sanded to. I was thinking if you had another piece of wood (call it an arm) secured via a hinge to the back piece that you have clamped and had a flat board on the table, that you could make graduated marks on the table board and control the depth sanded to by only sanding down to a certain table mark. Just a thought.

Da Graphite Kid

[terryep]

I use a brass bushing with a ¼” inside diameter mounted in my drill press. I place the wheel upside down on the table and press fit it’s inside hub into the bushing. I use a combination square resting on the table to give me a true 90-degree surface. Using a low speed I gently slide the square to the wheel with a 220 grit sandpaper. Let the paper get the high spots off first. Then sand until flat. Then use wetted 320 grit sandpaper and then polish with pumas on a cloth. Slow and gentle so as not to over heat the plastic! Take your time... 5 minutes per wheel should be about right. (EDIT: see more below)





This pic shows how the bushing holds the wheel. Leave the bushing mounted in the chuck so you can get the wheel off easier.

[Stan Pope]

Stan, could you get another picture of you jig as I don't see how this controls the depth sanded to.

The clamp on the right side of the pic (and one that you can't see on teh other side of the table hold a reference fence to the table. One side of a rectangular block slides against that fence to approach the wheel.

Another clamp holds a smaller piece of wood to the fence. This is the "stop." The stop is used to limit how closely the rectangular block can approach the wheel.

Ideally, the fence surface, stop surface, and rectangular block surfaces don't compress significantly!

I was thinking if you had another piece of wood (call it an arm) secured via a hinge to the back piece that you have clamped and had a flat board on the table, that you could make graduated marks on the table board and control the depth sanded to by only sanding down to a certain table mark. Just a thought.

You are talking about trying to achieve tolerances of 0.005" with a measure that can't measure to much less than 1/32".

[Stan Pope]

... then polish with pumas on a cloth. Slow and gentle so as not to over heat the plastic! Take your time... 5 minutes per wheel should be about right.

Nice pics!

I'd seriously consider stopping after the sandpaper steps. At most, only light buffing with pumice using cloth on the square backing. Too slick is a problem!

[terryep]

Stan, I didn't explain that I only use a finger behind a cloth for the polishing step. It's only a quick touch of a couple seconds then a plain clots to wipe off the polish, another second. You need a light touch or you can heat the surface very quickly.

Too slick? hmmmm Would save some time if I eliminated those steps! New thread! How to save time building cub kars! Wheels get pretty dull anyway after a few runs.

If you did a set of 8 wheels you could try and match them in pairs. Sand some more if needed.

You can take the inside mold mark off the wheel rim while it's mounted on the drill press too. The hub I sand with a tiny piece of sandpaper pressing it into my thumb and rotating back and forth. It only rounds off the corners. No tapering. I usually don't touch the axel hole.

Terry

[Stan Pope]

Stan, I didn't explain that I only use a finger behind a cloth for the polishing step. It's only a quick touch of a couple seconds then a plain clots to wipe off the polish, another second. You need a light touch or you can heat the surface very quickly.

Shorter than I understood. Probably okay. Finger pressure (yes, I understood that) would tend to follow indentations, if any. Goal (to me) would be to knock off the few peaks remaining, leaving a wheel that will roll smoothly but have slightly increased resistance to sliding sideways.

You can take the inside mold mark off the wheel rim while it's mounted on the drill press too. The hub I sand with a tiny piece of sandpaper pressing it into my thumb and rotating back and forth. It only rounds off the corners. No tapering. I usually don't touch the axel hole.

Good plan!

[Whistler]

Wheels and axles must be as furnished in the official kit. NO washers, bushings, bearings or springs are allowed. Wheels may be sanded to remove the flashing only. NO reductions in width or diameter, or changes in shape are allowed.

This seems a little unreasonable to me.[/quote]

I've thought that this type of ruleset was very unreasonable also, so got onto the PWD committee in our pack to lobby, successfully, for a more reasonable plan: wheel profile (flat tread) must be maintained, and no appreciable modification to width or diameter is allowed. Flashing and sprue marks may be removed, by any means as long as the beading (also called tire tread by some) around the outside diameter of the wheel is still visible.

[Stan Pope]

I've thought that this type of ruleset was very unreasonable also, so got onto the PWD committee in our pack to lobby, successfully, for a more reasonable plan: wheel profile (flat tread) must be maintained, and no appreciable modification to width or diameter is allowed. Flashing and sprue marks may be removed, by any means as long as the beading (also called tire tread by some) around the outside diameter of the wheel is still visible.

Congratulations! That is how the process works! When the district rules are too restrictive, it takes more work to accomplish the goal, but I think that it is worth the effort.

What you achieved is much more "inspectable."

You might further improve by specifying "no reduction in tread width" and inspect by comparing with an unmodified wheel. My district's "inspection kit" includes samples of unmodified wheels and axles. This is safe because as the wheel is reduced in diameter, the tread gets slightly wider. Reduction of tread width takes a specific attempt to narrow it!