More On Crankshaft Grinding

[Alan Worland 1Participant @alanworland1]

[Alan Worland 1Participant @alanworland1]

I am now up to the stage where I have centred and rough turned my cranks main bearings (Stuart No 4) and I am making a couple of blocks to enable the big end to be rough turned (well, hopfully not too rough!)

I have ‘in stock’ a small air motor which I propose to mount on the saddle, mounted with a grinding wheel to enable me to finish size the crank journals.

The motor runs off 80 psi is ball raced and quite powerfull. I need to make an arbor to fit a slim grinding wheel which will have to be able to rotate at 5500 rpm. This would be trued up with a diamond dresser prior to use.

What sort of grade wheel would I need to look out for, or would I need? one for roughing then a finishing wheel?

Apart fom the need to have the compressor running and the noise of the motor I think it ‘should’ work ok!

[DustyParticipant @dusty]

I take it that your air motor rotates at 5500 rpm. I know that some of these small air motors rotate at speeds in excess of 25000 rpm if yours is one of these forget it. I do not know of a grinding wheel of about 4″ dia, as I suspect that is what you would need standing that sort of speed. I would speak with one of the specialist grinding wheel suppliers if you are rotating at 5500. Try ABCO, just a satisfied customer. Providing you only leave a few thou to remove by grinding then you should be able to grind it in one go.

[Ian S CParticipant @iansc]

How about a wheel for an angle grinder, that should cope with the rpm even at a slightly larger dia if need be. Just thinking of what I would try. Ian S C

[mgjParticipant @mgj]

Well the Quorn wheels which give a mirror fnish when properly dresses are WA 100JV – made by Universal

 

Thats 100grit ali oxide fairly soft. you can get wheels in all sorts of configurations in that grade.

 

If you go to any of the big distributors websites they will have wheels for tool and cutter grinders which will do the job very well

 

[DustyParticipant @dusty]

I am sorry but I am the conveyer of duff info. It is not ABCO but ABTEC who supply grinding wheels.

[mgjParticipant @mgj]

As a matter of interest why grind? What I did for my TE was to make a little shell lap, fill it with coarse and then fine valve griding paste. I left the crank pin .001 oversize and reduced that by lapping, sanding the face of the clamp type lap to reduce dia. Came out to dead size with a good finish, and then polished with oil and fine emery.

 

I know its not a ground finish, but the whole operation took an evening, and its a lot more accomodating than grinding, and there isn’t a bit of major tooling to organise. Cheap too!

 

The lap just looked like a split big end shell bored to size and fitted with a long lever for holding safely while the crank rotated at a steady speed in the lathe chuck.

[Alan Worland 1Participant @alanworland1]

Thanks for your replies!

My proposed air motor is geared and the final spindle speed is 5500.

I have been looking at angle grinder wheels as they are about the right diameter and about 6mm thick and able to run ok at that speed (in fact they are rated a lot higher)

I haven’t looked yet, but the wheels I have don’t seem to have the ‘grit number’ on them? so I was going to do a test gring to see if it was feasable.

I realise mgj that I could turn close and yhen lap to size – it’s just something I want to do and the grinding attachment may well be usefull in the future!

[mgjParticipant @mgj]

No, good idea and why not if you want to.

 

Angle grinder wheels- do you think they will be fine enough.I think they will be way too coarse for this, at least any that I have seen would be.They are metal removing tools, not metal finishers.

 

As I said, the finishing wheels for the Quorn are 100 grit, so thats a good place to start.

 

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