Question about height of key for a 1008 taper bush from Challenge

[Jai134]

I don't get it because I got a 8mm wide and 7mm high key from my retailer, keyway in motor shaft is 8 wide, that is correct but 3,5mm deep and keyway of the taper bush is 1,3mm. There is no way of mounting that 1008 bush then - or is it? I have a HPM-10kW with a 25,4 mm shaft. Which sprocket fits my setup for a 520 chain. (That is if I have to buy a new sprocket, otherwise it's a 420). I have found a sprocket.

[Bikemad]

Hi Jai andto the forum.

I would expect keyways in sprockets designed to fit a 25.4mm shaft to be deep enough to accommodate the standard 7mm x 8mm key:



However, if you wish to use the "taper bush from Challenge" you will probably have to grind/file down the height of the key (and re-chamfer the top edges) so that it fits within the combined 4.8mm depth.

Apart from the shaft diameter (25.4mm or 1"), chain pitch (520 = 15.88mm or 5/8", 420 = 17.2mm or 1/2"), width (520 = 6.35mm, 420 = 6.35mm) and roller diameter (520 = 10.16mm or 0.4", 420 = 7.75mm or 0.305"), you will also have to determine the number of teeth required on the motor sprocket to give the optimal gear reduction for your particular application.

Alan
 

[Bikemad]

The Challenge catalogue states the actual depth of the keyway slot for a 25mm bore is 3.3mm or 1.3mm for starred items:



However on the diagram I looked at, it appeared to be ~3.5mm when I scaled it so the internal diameter was ~25mm:



This taper bush hub appears to have the expected depth keyway slot:



Perhaps the taper hub that you have was not fully broached to the correct depth during the manufacturing process. 

Alan
 
EDIT: Information on slot depths corrected.

[Jai134]

I'm not shure but perhaps the seller thought it would be enough without key. I found this on Challenge website "A keyway groove is also machined into the bush allowing a keyway to be used for anything above a low torque application."
It says 1108-25 on the taper bush in your post and I have 1008-25. Could that be the problem? I can tell you that a keyway that deep would not be possible in my bushing.

[Jai134]

Here is a link to the bush i've got
https://en.challengept.com/catalog/product/view/id/9201/
I also found this: Keyways are in accordance with BS 4235 Part 1 1972, DIN 6885 and conform to ISO recommendations except for those which are marked * below which are shallower.
Mine is markt..

[Bikemad]

Thanks for the update, I have just edited my previous reply with the correct details.

To use your 1008 taper bush you can purchase the correct 8mm x 5mm key.
Alternatively, you will have to reduce the height of the existing 8mm x 7mm key by 2mm. 

Alan
 

[Jai134]

Thank You! Good to hear that it wasn't me that did something wrong with the key!