How do i make this part??

[DonRotolo]

In looking closely at the drawings for the hub, quite frankly it is not all that hard to make. Time consuming, perhaps, but not a technical challenge. It is important that you find someone with machining epxerience, since selection of tools and turning speeds are important.

You do need to get the material first, and you will need material that is at least 2 inches longer than the workpiece - maybe 5 inches for each hub. You first cut the outside profile and then the deep bore on the one side. Mark the rim every 20 degrees for the small holes now, too.

Flip the piece and grip it inside the deep bore, and make the shallow bore. Drill the 4 holes, and then the 18 holes (make a jig to do that, as they suggest, using the 4 holes to locate the jig. That way, you only have to be careful with one piece (the jig) and all four edges (2 hubs) will turn out identical with little extra effort.

I would allow for 3 hours for each one, but I'm experienced, so allow twice that for the first one. Also remember that tolerances are not that critical, so long as both are the same. +/- 0.010 is more than enough.

Don

[Doug G]

I have to agree with Cory and others here. Perhaps we are missing the point - is it that you want to learn how to machine stuff like this?

Otherwise go get a bike hub and fab something similar to match your drive shaft. I remember we used to get those skyway wheelchair wheels and either used the spoke couplers that FIRST supplied or one year we made our own so we could use a keyed shaft. Much simpler than the route you're taking.

[Richard Wallace]

I like your hub design. It transfers the wheel load to the gearhead with minimum cantilever, and that will be important in your application.

Quite a few years back, I was part of a rookie college-level solar racing team. We built custom wheels for our car using 20" rims, and our hubs had a similar aspect ratio to yours -- about 3.5" spoke-hole circle and 3" axial width. Local bike shop guys assembled them for us using a three-cross pattern to help with the side loads. Our car weighed about 700 pounds (plus driver) and had about 5 ft. track width. Those wheels held up nicely during the transcontinental race, with no problems apart from the expected few flats. We never damaged a rim.

Our hubs were machined from billets using a process similar to the one Don Rotolo described above.

What diameter rims will you use?

[dfukuba]

Cory,

the reason why were making out own is because as richard pointed out, it will take a lot more load off of the wheel, and i don't want to cantilever the motor shaft too much by having a 3" long hub, mounted on the end of the shaft.

Rhichard,

I am going to be using a 20" x 1.5" wheel with 36 spokes. The design did go very well (I can't take any credit, it was first made by Trevor Blackwell). He had made three pairs on current projects that i checked out, those things are as solid as a rock, they take lateral load fairly well.

doug,

I actually used 20 skyway wheels on my first prototype of the scooter, but they started cracking due to (what i believe) was the lateral load on it.

Don & eveyone else

what i was told when trevor made his, is that he made a mandrel that bolted on to the four holes. So when he flipped it over he could chuck the mandrel on the lathe. Would this work better then doing it the other way??

I had some 3" diameter Aluminum stock that we got for this years robot (something like 6' of it, tooo bad it wasn't just a little bigger) I tried makeing a smaller version of something that looked just like it. It started turning out pretty nice, the part i was having trouble with was boring out the insides. It was probably because of the tooling that we have at the school...I'm thinking about buying a set of my own cutters. anyone have any good places online to order lathe cutters??

Also, facing off that angle in the cavity seems to be the one thing i'm not sure how to do, any advice?

thanks!!
--daniel

[Cory]

Originally Posted by dfukuba

anyone have any good places online to order lathe cutters??

I order almost all our tooling from KBC Tools. They have a local branch in Hayward you can go to and pick it up. They ship to us for free too, but that may be because we order through the government.

[RogerR]

one more thing you might want to consider:

the width (and diameter) of bicycle hubs isn't determined arbitrarily; the smaller the hub width and/or diameter, the less the wheel will be able to handle side loads (such as those created by sharp or high speed turns). if the hub width/diameter is to small, the spokes will fail, and the wheel will collapse.

[EricH]

Originally Posted by dfukuba

It was probably because of the tooling that we have at the school...I'm thinking about buying a set of my own cutters. anyone have any good places online to order lathe cutters??

Also, facing off that angle in the cavity seems to be the one thing i'm not sure how to do, any advice?

You can make your own lathe cutter with a grinding wheel and a whetstone. You just need some tool steel (3/8" square by 6" is a decent size).

Now, facing the angle is pretty simple IF you have a compound tool holder (I forget the exact name, but it rotates and extends the block that holds the tool). Here's how: Set the rest's lowest rotation to the required angle. There should be a ring showing the degrees. Line up the cutter so that it will cut the whole depth. (You'll also need the right cutter... Right handed and left handed are different and cut differently.) Mark what you want to cut between. Then, you position the slide so that the tool is where it needs to be. Once you start, you only use the long travel to go a little bit at a time. You use the travel on the rest to move the tool across the part.

The tricky part is that this is on the inside, so access and depth determination will be harder. You'll need to stop more often to check depth.

[=Martin=Taylor=]

I'm surprised nobody else has mentioned this yet, but you can purchase those motors and wheels (at least I think they're the same wheels) here already attached together. And if you're worried about the wheels being cantileverd.... don't worry. I've seen some heavy weight combat robots using the same exposed cantileverd wheel system with great success.

[sanddrag]

Have you considered a plastic wheel?. You'd still have to make a hub, but it may (or may not) be easier.

[DonRotolo]

Google ENCO for tools, they sell everything from cheap Chinese to excellent USA/Japanese tools.

You don't need special tooling for the bores, but knowing how to grind a special tool for something is a handy skill; in this case a tool with the cutting tip towards the left side would be fine for the bores.

As EricH wrote, your lathe has three wheels to move the cutting tool: The carriage (towards and away from the headstock), the crossfeed (perpendicular from the axis of the lathe, in other words front to back) and the compound. What EricH means is the compound, which can be adjusted to any angle you need. There are setscrews or screws that hold it in place, and a scale marked in degrees around it. Loosen the screws, move it to the angle you need, and tighten them up again (not TOO tight), then by turning the compound the tool will move at the exact angle you want.

Making a mandrel to hold the workpiece is a good idea, since chucking that hub with those flanges will be a royal pain otherwise. I suggested chucking it internally (inside the bore, pressure pushing outwards) but a mandrel sounds a lot easier.

By the way, that 3" material can probably be used; just modify the hub so the flange is 3" OD and the rest of the dimensions get smaller by a little. The 1/2" shouldn't make much difference.

Don