Heat shrinking a hub onto a shaft.

[Allthegearnoidea]

This is what I’m trying to do.

Regards Chris

 

[Screwdriver]

The flange is a much better solution even though it is vastly stronger than anything else on the frame! I guess you'll be taking most of the bulk out of it, there's no point making it any stronger than the spokes in the wheel. I'd still go for a simple cush drive however it gets fitted.

You need about 3-4 thou interference fit prior to heat shrink but you will still need to press it on. You need to press it, not bang it on and I don't see how that's going to be easy to do with the hub attached to the wheel. I assume the "shaft" is the driven part of the freewheel because a freewheel pawl will not last a minute being driven directly from the engine.

However you fix it, there is a lot of power being delivered from the engine all in one bang. You really need to soften the delivery from the engine or it will tear itself apart no matter how strong you make the sprocket mount. Funny thing is, I have a box of super strong springs that would be ideal for building a makeshift cush drive. Similar sort of design you often see on clutch plates or clutch baskets. There's a reason why they put them on there...

 

[Allthegearnoidea]

Hi there will be a rubber belt between the engine and chain drive to back wheel. We are going to use the belt like the clutch on a Myford lathe. As you say I don’t think I will be able to press fit. I was hoping if I heated up the metal hot enough it would just drop on the hub. Just so I understand are you say the hole should be 3tho smaller than the shaft ?

 

[Screwdriver]

I would have thought you'd need at least that to have any chance of a secure connection but only if you insist. Personally I'd go for a good tight fit where a bit of heat will help (maybe 1-2 thou interference) and then rely on whatever mechanical fixing you come up with. Even a belt drive won't have sufficient "give" to absorb the constant pounding. If you rely on the belt to absorb the shock, eventually it will simply snap and if it doesn't snap it will eventually merely spin. I guess if it's a V belt, you might get away with it but you'll need a seriously strong tensioning idler to force it into engagement. If you go that way, make it adjustable!

 

[Screwdriver]

It's a really interesting project by the way. I love the look of the thing!

 

[Allthegearnoidea]

Ok looks like it’s going to be a tight fit and grub screws perhaps

 

[Allthegearnoidea]

So much for a tight fit. Ended up over cooking the bore. I was aiming for perhaps just over size for size and I have gone 4 thou over dammit. A bad work man blames his tools but I’m using a very cheap set of telescope gauges. I was consistently measuring the same and then bang 4thou over. Still it could be me. Unfortunately I don’t have any more steel so going to try and get it in with a shim and maybe have another go. I’m going to carry on making the part as I may as well get some practice with the other machine operation.

If your not from a machining background it takes time to get a feel for the measuring equipment and also just shaft hole tolerance. I guess it’s a learning curve and more practice required.

I am going to drill the circumference of my disk and get the grub screws in. So I have learned today that 4 thou over on a 1.5 inch shaft is a p155 fit rather than a press fit. I’m still smiling.

 

[zzr1200]

So much for a tight fit. Ended up over cooking the bore. I was aiming for perhaps just over size for size and I have gone 4 thou over dammit. A bad work man blames his tools but I’m using a very cheap set of telescope gauges. I was consistently measuring the same and then bang 4thou over. Still it could be me. Unfortunately I don’t have any more steel so going to try and get it in with a shim and maybe have another go. I’m going to carry on making the part as I may as well get some practice with the other machine operation.
.

You could always get someone to weld the bore hole up and then remachine the bore to size.

 

[Allthegearnoidea]

I decided to use it as a practice session and it may be ok think I will give it a try. I just have To drill 4 new holes in the gear sprocket and the new flange. I think I will slightly cross drill into the wheel hub for the cap head screw to get some purchase on. There is also a left handed threaded collar that can be brought into play for something. If it doesn’t work out I will just Machine a new one. Think I have learned from my mistakes a case of better luck next time.

 

[jordan1]

You haven't a hope in hell of the 6mm sprocket holding by 'shrink fit' alone.

 

[Allthegearnoidea]

The sprocket will be bolted to the flange. The flange clamps to the hub using the cap head screw in the photo above.

Chris

 

[Screwdriver]

I think you might just get away with that, depends if the allen bolts can create a little divot on the hub. Hub does look as if it might be hardened though. Could be worth making some little divots for the ends of the allen bolts to engage. You're lucky its a rigid rear end, if it had suspension any deflection would rip the drive off in no time. As the (non existing) suspension deflects, there is a tiny amount of additional stress delivered to the drive system and without a cush drive that would be enough stress to tear out any solid mounting. At some stage, something's got to give...

 

[Allthegearnoidea]

Fingers crossed. It’s only a bit of fun so if it tears itself apart we will have to think again. I have a feeling that the hub is hardened but not tried a file across it yet. I would like to cross drill into the hub slightly, going to try anyway.

 

[Screwdriver]

Carbide drill bit or a lathe centre drill. You only need a little divot but you also need to taper the allen bolts to a point.

 

[Allthegearnoidea]

Yes that’s the way I had planned to do. I have sum left hand carbide drill and was going to sharpen the b9lt.

 

[Allthegearnoidea]

 

[Allthegearnoidea]

A bit more machining mayhem. Enjoying my new milling machine and using carbide hard plate drills for the first time,

 

[eLuSiVeMiTe]

If your not from a machining background it takes time to get a feel for the measuring equipment and also just shaft hole tolerance. I guess it’s a learning curve and more practice required.

Yup tell me about it.
I am improving though. My digital mitoyo are certainly helping.

 

[Allthegearnoidea]

I find I get real close with my machining and then I try and add that little bit more and over cook it. I guess it’s just practice.