Reprofiling revolving centre

[michael howarth 1Participant @michaelhowarth1]

[michael howarth 1Participant @michaelhowarth1]

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

Mick

[Involute CurveParticipant @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

[David Clark 13Participant @davidclark13]

Lock the centre and regrind it in the headstock.

[KWILParticipant @kwil]

How do you lock a revolving centre?

[Ian PParticipant @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

[egaParticipant @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?

[John McNamaraParticipant @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

[wheeltapperParticipant @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.

[Involute CurveParticipant @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

[Mike PooleParticipant @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

[michael howarth 1Participant @michaelhowarth1]

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

Mick

[paul raynerParticipant @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

[Chris Richards 3Participant @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

[John McNamaraParticipant @johnmcnamara74883]

Yes Wheeltapper

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

Regards
John

[michael howarth 1Participant @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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