[OC-Alan]

Hi. I'm looking to use a lathe to help improve the roundness/runout of a plastic model wheel. The wheel is for a specific type of pinewood derby car. The wheel size is about 1" in diameter and has a 1/8" hole in the center

The plastic wheel is made from a mold. There is a burr on the outside of the wheel where the gate from the mold is, and the outside tends to not be perfectly round. Also the center hole in the wheel may not be well centered compared to the outside (non concentric).

Today, I use a drill press and a mandrel to hold the wheel. I use sandpaper to knock down the outside of the wheel to make it smooth.

So I'm looking to improve my wheel quality using a lathe. My feeling is that I need 2 distinct operations:
(1) Hold the wheel by the center hole using a mandrel and then attempt to cut out the outer most defects of the wheel to attempt to make it round(er).
(2) Hold the wheel by the outside and cut a slightly larger but closer-to-center hole in the middle

It may be that by performing operation (1), I don't need (2) because I was using the center hole as my reference point.

That said, here are my n00b questions:

(a) Does the lathe seem like a good solution for this wheel? I ask because the wheel isn't flat at the outside (a flat profile would make the lathe operation pretty straightforward). If not, what would you suggest -- a drill press with a minimal runout chuck?

(b) What is a good lathe to purchase for this effort? I would like to keep the lathe cost to under $500 (before accessories). I am mostly looking for a benchtop lathe since I don't want it to take up a lot of room. So far, I like the Grizzly 4x6 Micro Lathe (Link: Grizzly.com® --) or the HF 7x10 (Link: Mini Lathe - 7" x 10" Precision Mini Lathe)

(c) What additional accessories would I need to order?

(d) Since the outside of the wheel is a curved profile (and not flat), do I need to make a special bit to cut down the wheel? A specialty bit would match the profile of the outside of the wheel and then would shave the entire width of the wheel at once (may not be good for a lathe due to the multiple contact points -- but I don't know).


Here's a picture of the wheel for reference.
Attachment 268510

Thanks in advance,
-Alan

[bladehunter]

I'd stick with the drill press option. If you want to get fancy a jig to help you keep the wheel concentric to the axle could be the go.

Unless of course you really really want a lathe, then it becomes a need. Be aware that tooling, accessories can end up costing a fortune.......and then you'll want a mill, then a bigger lathe, a bigger mill, then a shaper (cos they are really cool) and a surface grinder. And somewhere in between you'll want a metal bandsaw or power hacksaw or both.


Then there's the CNC journey.

[OC-Alan]

Ok, that makes sense. Yes, I had considered a lathe as something nice to have but perhaps it is overkill.

Question is then, where can I get help to make a fancy jig?

[Fastest1]

I would cut the wheels evenly from both sides to create more of a V (if that is legal). I figure the least amount of contact area creates the least drag.

[OC-Alan]

Yes, making a V would help, but sadly it's not legal. The wheel basically needs to keep the same profile with minimal amount of cutting. The inspection process looks for anyone that is changing the shape (e.g. making the wheel flatter or thinner). Any jig would need to basically match the existing shape of the wheel and simply focus on getting the outside edge concentric with the inside hole. That's where I'm at a loss.

Also, is a drill press really a good option since the bearing are typically not designed for a side force?

[bladehunter]

Nothing much more than a length of square section timber with some sand paper fixed to it, drill a hole at one end bolt it to the table of the drill press, at the other end use a clamp to fix it to the table.

If you are able you could even carve\route\cut a profile into the timber and glue the paper to the profile. Just make sure you have a stop on the table.......another block of timber so that you are able to keep the same diameter for each wheel. Maybe even some method of having the wheel at the same height.

Or you could do it freehand and keep an eye on your diameters.

What ever you do don't use anything from the LHC at CERN or have anything to do with intergalatic bank robbers or space cash.