pic: 4in Wheel CAD

This is a 4in wheel I designed after championships. I was trying to make it easier to assemble and cheaper than our wheels this year (and still look pretty good). The outside plates are cut out of .09in aluminum. The inside is 1" thick delrin. Threaded inserts will be pressed into the plastic to bolt the outside plates and sprockets on. The wheel, with two sprockets (but without tread) weights .25lbs.

Looks really nice! I may have to make a sheet metal wheel now…

Anybody know how well this thing would hold up in use?

Do you have a picture without the sprocket on there?

Press in threaded inserts wouldn’t be easy to assemble IMO, and it seems to me that they would spin in the delrin as the bolts are tightened up. It also looks like you have a lot of fasteners not in the model, which will add on a bit of weight.

Maybe think about how you can make the sprocket integral to the structure of the wheel. I would skip on delrin as a wheel material entirely.

What sort of fabrication capabilities are available to you? Perhaps there is a way to take advantage of something unconventional.

This design is similar in many ways to one of our wheel design revisions. Take a look here to see what I mean:

We have been happy with our .190" thick side plates that we pocket for a press fit to align everything. You may want to consider this.

Why do you shy away from delrin? This year, we found it easy to machine. We made our wheels out of it this year. As for the threaded inserts, how would you recommend attaching the side plates instead? I was looking for a way to avoid bolting all the way through, adding much unnecessary weight. This year we used standoffs, but that was expensive. Aluminum bolts would make it even lighter, if we could find a good option. I do like the idea of making the sprocket have more of a structural use.

Here is a picture without the sprocket attached:

Peter, could you elaborate on how this press fit worked? It sounds like a great idea and a way to avoid welding with aluminum. The tube you mentioned, did you just buy an aluminum tube from mcmaster? How were the tolerances? How did you keep the inside part from slipping?

Why not tap the delrin and put short screws on each side? Would that make any sense?

I would guess its because it would be too easy to strip the treads?

delrin doesn’t handle threads well, if i were doing that i would just get a nice bolt and run it through the whole thing, another way to do it would be rivets, but that would be a pain.

Are there spacers between the sprockets and outer plates? I can’t tell and didn’t want to assume. You’ll definitely need these if they’re not already there.

While the design looks great, it’s going to be difficult to get those sharp corners in the plate. Are these being cut out with a water jet? If not, you may need to add blends to the design for your cutter.

Also, since total price is a design factor, with a 4" dia. x 1" thick disc of Delrin costing between $15-$20, are you really saving money?

A waterjet isn’t needed, a laser would work as well. Where did you get $15-20 bucks pricing for delrin that size? I checked McMaster which is usually more expensive than local places.

www.mcmaster.com -> 8497K533

Pretty sure that is what he wanted and it comes out to $66 a foot and about $5.50 per inch. Excluding tax and shipping.


Yes, you’re right, a laser cutter could work, but since they’re not very common, lasers didn’t even cross my mind. Also, I tend to avoid sharp points in cutouts as they concentrate stress (thought they probably won’t be an issue here).

I checked McMaster as well for my prices (p/n 99866K22 - $18.84 for a 1" thick piece). I assumed nothing with what he wanted to do, hence I pointed out the material cost and my question. Of course, you’ll need more than 1" of material if you’re going to slice it from a larger rod (loosing the blade thickness) then making sure both faces are properly squared off. You are correct that it will be cheaper than $15-$20 per wheel if he gets a foot or more, but the question is still valid.

4" diameter 6061 is a little over $5/inch on McMaster. Making a 1-piece wheel will be the lightest, simplest option. No threaded inserts, no delrin, no multi-piece wheels, no big bolts.

If you were to keep within the budget of $15-$20/wheel you could just about use 2024 or 7075 aluminum for your wheel.

We bought 4" outer diameter 1/8" wall tubing from McMaster, then when it arrived we measured the actual OD. We then made our machine program that put the relief cut in the plates .002" over that OD, and the tube essentially presses into the plates giving good concentric alignment of all pieces. We actually weld the plates to the tube in our case, but the alignment is the important part.

Yes, we would use a plasma cutter to cut the outside plates and a mill to cut the inside plastic. We dont have the machining capabilities to make a wheel from a block of aluminum, would take over 4 hours per wheel probably. For this design, we can make each wheel for about $25-30. This is significantly less than our wheels from this year. If we had the ability to weld, we would probably do something more like what Peter mentioned above. We would actually make these out of a rectangular block of delrin. We do not have access to a lathe currently, or else I would like to at least try a 1 piece wheel. And yes, the spacer is considered in the weight. It is made of 1/4" aluminum.

what RMS means is he spent $1000 on wheel material last season HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA::ouch:: ::ouch:: ::ouch:: ::ouch:: ::ouch::

so he is finding ways to make custom wheels cheaper. $30 sounds great to me at this point. Also, there are some cheaper off the shelf wheels out there but we have had bad luck with them. Hopefully we can get a few different wheels designed this summer and try em out!

I’m a grumpy guy when it comes to wheels. I simply do not understand why teams insist on adding machining complexity to wheels.

Our wheels are solid 6061, the CNC op is all from one side (the spokes are on one face), simple tread groove, sick spokes, nothing fancy. I’d wager our 4" wheel is still lighter than most, and we could even make it lighter, we just don’t see a huge need as they are currently .22 lbs.

If you make it simpler, it’s faster to make (large advantage) and easier to analyze the strength of it.

The reason we dont machine ours from solid is because are mill is not capable of producing those parts at a reasonable time. a FR of 3in/min for aluminum on average. Much faster to cut the sides on plasma in a minute. and machine the plastic at 7-8 in/min.

In short Adam, different spokes for different folks. What may seem complex for you is simple for some teams. Some teams don’t have a CNC mill but have great resources to knocking out sheet. It all comes down to resources.

(Plus, these may never be made, just a design exercise)