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dsc
19-11-2012, 01:21 PM
Gents,

can someone suggest a way of fixing an off-the-shelf conical shaped grinding part on the end of a shaft without using a key or cutting / machining the part? The part has a hole running through it, has no keyway, or any other holes to attach it to the shaft. The shaft will be machined from scratch, so anything can be done with it to make it accept the part and hold it in place. Forces acting on the part / shaft will be minimal as it will grind soft, crunchy material. Here's a sketch:

http://i1120.photobucket.com/albums/l496/dsc_MT/random/shaft_mount.png

The internal hole in the off the shelf part is 13mm at the top and 13.3mm at the bottom, I think normally it's mounted on a short 13.3mm dia shaft, with the shaft coming through the bottom and a bolt pushing the part all the way from the top. This means the part gets locked in the upper via press fit. My design has the shaft coming in from the other side, so that way of locking it is out the window.

Any suggestions are more than welcome.

Cheers,
dsc.

Jonathan
19-11-2012, 05:18 PM
Could you just put a thread in the end of the shaft, machine a washer to fit on the end and clamp it on with a countersunk machine screw for neatness? If the shaft needs to rotate in both directions that may not work since it could unscrew.

njhussey
19-11-2012, 06:18 PM
If you've got your shaft coming from the 13mm end then the bottom will not be supported on the shaft so the tool will in theory only be in contact with a very small area of the shaft, assuming it's a taper from 13 to 13.3mm?

To me the only way to do it is as they have done it, i.e. push the shaft in from the bottom and a nut on the top to seat the tool.

Unless you have some sort of reverse collet where the bottom of the shaft is slotted and a tapered hole bored and tapped at the end so when you tighten it in it splayes the bottom to grip the tool? Hard to explain properly without a sketch...

7421

Jonathan
19-11-2012, 06:25 PM
Unless you have some sort of reverse collet where the bottom of the shaft is slotted and a tapered hole bored and tapped at the end so when you tighten it in it splayes the bottom to grip the tool? Hard to explain properly without a sketch...


You could do that by just having a thread which expands the parallel portion when the screw is tightened, by specially machining the screw or shaft so that one is oversize.

dsc
20-11-2012, 09:21 AM
Gents,

thank you for your suggestions. I'd rather move away from the press method, as I'm a bit worried it might not be sufficient enough. I was actually thinking of something Jonathan mentioned with the parallel expansion, here's a quick sketch:

http://i1120.photobucket.com/albums/l496/dsc_MT/random/shaft_expansion.png

Is it hard to machine such a thing? it should slide inside the shaft and then lock when the bolt is put it. The dia at the bottom could be 13.5-13.6mm with the 'D' shaped elements bent slightly to the inside so that it fits on the part. Putting a bolt in would push the sides out and press against the part. Main question is how strong will it hold it.

Would it be easier to do it like this or simple cut a 'D' shaped keyway in the off-the-shelf part ?

Regards,
dsc.

njhussey
20-11-2012, 10:05 AM
7427

This was what I was thinking...ish :) only a quick rough sketch...

dsc
20-11-2012, 12:51 PM
Even nicer that way:) I reckon machining the shaft to be thicker on the bottom, threading and putting two cuts to form the cross should be easy enough. Or am I missing something?

Regards,
dsc.

njhussey
20-11-2012, 03:07 PM
The way I saw it was to machine the shaft parallel and then the piece you thread into the shaft has a slight taper and forces out the sides to grip the piece. The shaft will need a shoulder for the piece to sit against so it doesnt just slide up the shaft. If that makes sense?

Peter Griffin
20-11-2012, 10:32 PM
Make the hole parallel and glue it with a bearing fit loctite.

dsc
21-11-2012, 08:31 AM
Gents,

thanks again for your ideas. I managed to get a similar new off-the-shelf grinding part, which has a key way in it, so shaft attachment should be easier now.

Regards,
dsc.