Machining axles/sleeves and some questions.

i have designed a coasting unicycles hub and need to know these things…

on the kris holm axle, are the splines welded on then the weld beed machined off, or is it all done on a CNC mill?

is aluminum too soft for a unicycle axle?

what are the demensions of a standerd high flange axle?

what is the standerd spoke length of a 20 wheel?

what is the thred size of the bolt that holds the cranks in place?

does anybody know what the the tool is called to be able to thred the inside of a tube with a standard lathe?

can teflon be run at a higher speed than steel on a lathe before it melts?

where can ruber and the stuff to melt it be bought/used?

6in by 2 1/378459 in by 8

at the ruber store… duh!

steel-> metal
teflon-> plastic… lets think here

or you could just buy one…

where can you buy a coasting unicycle that can be riden backward and forwards?

the reason for the teflon question was beacuse i didnt know if it would build up friction and melt

A good rule of thumb is that the softer it is the faster it can be cut. You will be able to run a rod of teflon at speeds that are well abouve the range of the average metal lathe. If you get worried about melting, use coolant.

You are correct, aluminum is too soft to be a unicycle axle, unless you dramatically increase the axle’s diameter.

KH splines are machined directly from a sloid bar, no welds involved. Unless you get a blem hub, there shouldn’t be any welding anywhere on the hub. It is done on a cnc mill (don’t bother trying to buy one to do this job custom on. The average cnc mill capable of this will cost around $10 grand), but you can do it on a precise bridgeport with a good rotary base. It will be extremely difficult. Not something to be attempted for a beginner machinist. The hardest part of the KH axle will be getting the chromoly heat treated. You will have to send it off, and you could have troubles finding a place that will 1-off it.

A standard lathe isn’t equipped to thread long sections on the inside of a metal tube. You would need controlled powerfeed on the tailstock, and that is rare on a normal lathe. If you are thinkiung of something different, you would just use the tool rest and a self-ground bit to do the cutting, but that wouldn’t be very good for long tubes, due to chatter. I reccomend just getting a good, long hand tap of the right size. These can be fo\und up to a diameter of around 2".

Having seen your drawings for the coasting hub, I think you should think about how you will get those keys to line up while riding quickly. You will seriously risk mashing the edges of the keys when they interlock while riding. Maybe you should taper them or use a friction clutch like on a drum brake instead. What if you had a ring with a slightly tapered cone? The cone would be very easy to cut on the lathe.

Teflon won’t be ideal for instide the hub, unless it’s just for sliding lateral forces. It will not be good as a surface for high-rpm rotations.

The average spoke length for a 3-cross 20" wheel is between 180 and 240mm.

thanks so much for the info, the reason for the teflon is i wanted to make a scale model before i start sending money toward expencive metal. you are right the squared off keys would not ingague smoothly, i have designed it so that they are rounded and i dont think i willl be doing high speeds on it anyway.

i am working on an anamation of the hub design.

we have 3 friends with CNC’s and tons with standard mills.

gerble check PM’s in a couple min.

Good idea to use teflon, but I think that if you go to a metal supply place and put on a nice face they’ll give it to you cheap. I got about $400-500 worth of aluminum for $45 when I had a conversation with a guy outside the place about my project. It turned out he was the owner.

Rounded keys could work, but I still theink a friction clutch would be simpler and easier to ride.

I have friends with cnc’s too, but it’s not easy to program them, and you still have to find a place with enough insurance on the mill that you can try it. It’d suck to end up breaking someone’s $100,000 cnc mill by having a typo in the code.

My daddy always told me keep it simple “stupid”, maybe I should have listened more.

Has anyone played with a centrifical clutch like on my lawnmower? dont pedal -freewheel- pedal at a set rate, and the clutch would engage = forward motion. Might have to start off doing a running mount or something, but I will leave all of that for you smart guys.

Just another late night brainfart…

They also have those in old seatbelts and certain types of curtains. I think it’d work, but it would be good to have it engage at a rather high speed.

also with those clutches, they ingauge slowly, you want something that pops right in.

I disagree. A slow engagement allows you to ease into pedalling, which will be easier.

how would that work? a series of slowed teeth?

A series of sprung teeth would have to be rounded in one direction to allow pedalling to engage the wheel and not pedaling the wheel would just roll over the sprung teeth.

but i was hoping that i could try backward coasting:D

Wouldn’t it be much easier to just work hard and learn the skill progressions to do a backwards coast. It could take quite a while, even years. But at least you wouldn’t be cheating…

how the hell would you make sprung teeth.

I think he’s referring to pawls. Thats how a racheting mechanism allow forward rotation but prevents backward rotation.

Basically a bicycle freewheel.

Apologies if I’ve misunderstood.


i think catbot totaly miss understands me, i am building a unicycle hub that in a push of a button is free wheel. not like SWATS coaster

That’s how the rear hub of a good trials bike is built, although the teeth are jagged like on a jigsaw blade rather than rounded. An easier version is to have a steel wire forceed into a small ring, with teeth. The wire springs outwards engaging one of the teeth. They use that setup for the “dive timers” on cheap watches.

While riding?

I can see how it would turn into a freewheel if you got off messed around for a sec, then got back on with a running start and freewheeled, but doing it while riding is quite a bit more complicated if you wanted to be able to turn it on and off…

Yes, I was reffering to pawls, but couldn’t remember the ord. It is basicaaly an easy Idea if you want almost instantaneous engage when you pedal.

Oooh I have been struck with an idea. If you did want to be able to switch directions on the uni, couldn’t you setup a system like a socket wrench??? where it can only turn one way, or the other???

Eh… who know I would say that SWAT’s coaster uni is dope, and i plan to make one some day…