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Reprofiling revolving centre

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mick H29/10/2015 09:00:54
723 forum posts
21 photos

Can anyone please tell me the best way to reprofile the tip of a revolving centre which has had a hard life?

Mick

Involute Curve29/10/2015 09:18:53
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337 forum posts
107 photos

I have done this with a tool post Grinder in the past, I bet it could be done with a dremel or similar also held in the tool post.

Shaun

David Clark 129/10/2015 09:19:25
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3357 forum posts
112 photos
10 articles

Lock the centre and regrind it in the headstock.

KWIL29/10/2015 11:08:05
3286 forum posts
63 photos

How do you lock a revolving centre?

Ian P29/10/2015 11:24:20
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2409 forum posts
101 photos
Posted by KWIL on 29/10/2015 11:08:05:

How do you lock a revolving centre?

For grinding, the forces should be quite low so an optimally sized lump of weld will do it easily, more practical though might be masking tape.

Piling up thin thread soaked in something sticky where the revolving part meets the stationary bit should do the job too (and keep grinding dust out)

Ian P

ega29/10/2015 11:28:27
1780 forum posts
152 photos

I can suggest two possibilities:

My GMT brand revolving centre point has a major diameter the same as the body and it might be possible to lock the two elements together with some form of clamp or perhaps a winding of tape.

My "best" RC is a Gepy which has an oil hole closed by a small screw and I wondered whether temporarily substituting a setscrew would do the trick; this was the method adopted by Lawrence Sparey in the design for a shop-made item in "The Amateur's Lathe".

Does anyone know how the makers do this?

John McNamara29/10/2015 11:30:05
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1313 forum posts
113 photos

Hi Mick H

If you have some sort of slow speed geared or variable speed motor, a tool post grinder and a pulley and belt of some sort, First mount the revolving centre in the tailstock.

Then run belt around the flat on the revolving centre to the geared or variable speed motor and turn it at around 50 to 100 rpm. you will need to do some sort of lash up to hold the motor in position and put tension on the belt. the motor does not have to be very powerful if you grind lightly.

You can then grind the centre running in its own bearings with the tool post grinder. The centre should turn in the opposite direction to the tool post grinder wheel.

Once I had to do this with a centre that did not have a flat. I used a rubber wheel directly mounted on the motor to turn the live centre.

Regards
John

wheeltapper29/10/2015 15:30:30
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420 forum posts
98 photos
Posted by John McNamara on 29/10/2015 11:30:05:

Hi Mick H

If you have some sort of slow speed geared or variable speed motor, a tool post grinder and a pulley and belt of some sort, First mount the revolving centre in the tailstock.

Then run belt around the flat on the revolving centre to the geared or variable speed motor and turn it at around 50 to 100 rpm. you will need to do some sort of lash up to hold the motor in position and put tension on the belt. the motor does not have to be very powerful if you grind lightly.

You can then grind the centre running in its own bearings with the tool post grinder. The centre should turn in the opposite direction to the tool post grinder wheel.

Once I had to do this with a centre that did not have a flat. I used a rubber wheel directly mounted on the motor to turn the live centre.

Regards
John

surely the centre and grinding wheel should revolve in the same direction. if they revolve in opposite directions they will behave like two gears and have hardly any opposing surface speed where as in the same direction they will have maximum opposing surface speed.

Roy.

Involute Curve29/10/2015 15:40:33
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337 forum posts
107 photos

All I did was use the tool post grinder, the friction of the grinding wheel span the revolving part of the centre quite slowly leaving a very good finish.

Shaun

Mike Poole29/10/2015 17:45:07
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Moderator
2688 forum posts
64 photos

I have never tried it, but would araldite hold for a light grind? Maybe a small section O ring to keep the bearing joint clear.

Mike

mick H29/10/2015 20:10:44
723 forum posts
21 photos

Thanks for the ideas gents. I will have a go at it and post the outcome.

Mick

paul rayner29/10/2015 20:39:17
160 forum posts
44 photos

have a look on you tube, john who goes under the name of twastard engineering has done a video of one which includes stripping it down. if you do a search it may be on one of his Sunday night night caps

regards

Paul

Chris Richards 329/10/2015 20:49:52
68 forum posts
13 photos

I managed to clamp a drill upside down against the tool post on a lathe it actually worked fine as a tool post grinder

John McNamara29/10/2015 22:31:55
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1313 forum posts
113 photos

Yes Wheeltapper

I should have said same direction. The relative rotations should oppose each other where they touch.

Regards
John

mick H31/10/2015 14:44:37
723 forum posts
21 photos

I had a go at it yesterday and achieved (by my standards) a half reasonable result using a carbide tool and the set up in the picture. Unfortunately I lost about 1/4" of the tip which crumbled away....probably due to inaccurate centreing of the tool. I any event, it is in better shape than it was!revolving centre.jpg

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