Reprofiling revolving centre

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Reprofiling revolving centre

This topic has 15 replies, 11 voices, and was last updated 31 October 2015 at 14:44 by michael howarth 1.

Viewing 16 posts - 1 through 16 (of 16 total)

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29 October 2015 at 09:00 #32588
michael howarth 1
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@michaelhowarth1
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29 October 2015 at 09:00 #209678
michael howarth 1
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@michaelhowarth1
Can anyone please tell me the best way to reprofile the tip of a revolving centre which has had a hard life?

Mick
29 October 2015 at 09:18 #209684
Involute Curve
Participant
@involutecurve
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
29 October 2015 at 09:19 #209685
David Clark 13
Participant
@davidclark13
Lock the centre and regrind it in the headstock.
29 October 2015 at 11:08 #209699
KWIL
Participant
@kwil
How do you lock a revolving centre?
29 October 2015 at 11:24 #209701
Ian P
Participant
@ianp
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
29 October 2015 at 11:28 #209702
ega
Participant
@ega
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?
29 October 2015 at 11:30 #209703
John McNamara
Participant
@johnmcnamara74883
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
29 October 2015 at 15:30 #209737
wheeltapper
Participant
@wheeltapper
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.
29 October 2015 at 15:40 #209738
Involute Curve
Participant
@involutecurve
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
29 October 2015 at 17:45 #209745
Mike Poole
Participant
@mikepoole82104
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
29 October 2015 at 20:10 #209772
michael howarth 1
Participant
@michaelhowarth1
Thanks for the ideas gents. I will have a go at it and post the outcome.

Mick
29 October 2015 at 20:39 #209780
paul rayner
Participant
@paulrayner36054
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
29 October 2015 at 20:49 #209783
Chris Richards 3
Participant
@chrisrichards3
I managed to clamp a drill upside down against the tool post on a lathe it actually worked fine as a tool post grinder
29 October 2015 at 22:31 #209802
John McNamara
Participant
@johnmcnamara74883
Yes Wheeltapper

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

Regards
John
31 October 2015 at 14:44 #210050
michael howarth 1
Participant
@michaelhowarth1
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!
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