Author Topic: Making a Sub Miniature Live Centre  (Read 1002 times)

Offline simplyloco

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Making a Sub Miniature Live Centre
« on: October 29, 2022, 10:33:08 PM »
I've never been happy with the oversize/overscale 'stuff' that the ME trade offers us mere mortals, so here is an attempt to produce a live centre more suited to the task!

This 0MT 'lump' came with the  lathe, I have no idea how one is supposed to get near to the work.  £99.00 from Cowells!


My version made from 1/2" 303 stainless.


The components.Two 9.5mm ball races, centre rod with thrust pad, and a 3 part thrust bearing. Velly Cheep!


Made for the job. It really does run sweetly!


« Last Edit: October 29, 2022, 10:38:27 PM by simplyloco »

Offline crueby

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Re: Making a Sub Miniature Live Centre
« Reply #1 on: October 29, 2022, 11:20:10 PM »
Nice!!  How did you retain the pieces in the shell?


Offline simplyloco

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Re: Making a Sub Miniature Live Centre
« Reply #2 on: October 29, 2022, 11:22:33 PM »
Nice!!  How did you retain the pieces in the shell?

A gentle press fit. After all, I am a retired precision engineer... :LittleAngel: :praise2:
« Last Edit: October 29, 2022, 11:41:05 PM by simplyloco »

Offline Jasonb

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Re: Making a Sub Miniature Live Centre
« Reply #3 on: October 30, 2022, 07:24:01 AM »
I've not found similar live ctrs to be a problem. Quite easy to get neat to work with the right tool, This is my large Skoda live ctr working on a 3mm valve stem. Same setup would be fine on my Unimat3 too with its live ctr. Similar shape HSS tool would also fit without a problem.

If you need to turn smaller dia than that then a half ctr is a good option as you can't easily drill a ctr hole small enough so will catch the revolving ctr.




Offline Jo

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Re: Making a Sub Miniature Live Centre
« Reply #4 on: October 30, 2022, 07:40:46 AM »
Nice  :)

It is easy to see the improvement achieved by using a revolving centre than without.

Jo
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Offline Jasonb

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Re: Making a Sub Miniature Live Centre
« Reply #5 on: October 30, 2022, 07:43:42 AM »
Was the problem being without? I thought it was because the one shown in the first photo had a larger diameter body than the newly made one?

Offline Jo

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Re: Making a Sub Miniature Live Centre
« Reply #6 on: October 30, 2022, 08:01:12 AM »
I was looking at the finish that has been achieved in the last photo on the taper turned using the centre and the finish on the taper on the rotating Centre which would have by necessity been done without it  :).

Jo
« Last Edit: October 30, 2022, 10:46:44 AM by Jo »
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Offline Charles Lamont

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Re: Making a Sub Miniature Live Centre
« Reply #7 on: October 30, 2022, 08:28:56 AM »
Jasonb, the main problem is the amount of tool overhang needed to clear between the toolpost and the body of the centre. I have often found this a problem, even with an extended toolholder. Wanting a hollow centre for some valve stems, I came up with this. It is a revolving centre with a bearing ball rather than a ball bearing.
The unhardened silver steel centres run in a bronze bush bored in situ. The little radial hole is needed to be able to get the ball out, if necessary.
« Last Edit: October 30, 2022, 08:34:59 AM by Charles Lamont »

Offline Jasonb

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Re: Making a Sub Miniature Live Centre
« Reply #8 on: October 30, 2022, 08:37:53 AM »
Fair point on larger machines but this is the Cowells so work is likely to be small and tooling not of a large cross section, 6 x 6 or 1/4" square would be in keeping for the machine so maybe only 12mm / 1/2" tool overhang at the most and not taking any heavy cuts. length of that DCGT insert is more than that projection and you would not want your toolpost clamp screw on the insert

Jo Why by necessity, a cowels live ctr is shown in the first photo and can be seen in the images of what came with the lathe so that could have been used. I think the MT shown in the chuck is a bought in taper and the one with the rougher finish what was on the home made mini one where a live ctr was available.

Offline BillTodd

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Re: Making a Sub Miniature Live Centre
« Reply #9 on: October 30, 2022, 09:14:45 AM »
FYI (at least in England)

Live centre: goes in the spindle end, revolves with the spindle and is soft so can be trued before use.
Dead centre: goes in tail stock end, usually hardened so it doesn't wear.
Revolving or low friction centre : goes in tailstock end revolves with work piece.


Offline Jo

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Re: Making a Sub Miniature Live Centre
« Reply #10 on: October 30, 2022, 10:53:18 AM »
Jo Why by necessity, a cowels live ctr is shown in the first photo and can be seen in the images of what came with the lathe so that could have been used. I think the MT shown in the chuck is a bought in taper and the one with the rougher finish what was on the home made mini one where a live ctr was available.

John's problem is that the toolpost will hit the rotating centre before the lathe tool gets to the metal. One trick to over come this is to put the tool in the right hand side of the tool post - if the work is long enough. With the Cowells the small hole up the spout means you often have to hang things out further than you may otherwise wish.

Charles idea for a rotating centre is very clever  :) I have been known to use my "precision hardened" spring loaded pointer as my rotating centre as its O/D is only 6mm. That has a close fitting hardened pointed pin sprung by the hydraulic pressure of its lubricating oil against the work  :-X .

Jo
« Last Edit: October 30, 2022, 11:00:29 AM by Jo »
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Offline Admiral_dk

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Re: Making a Sub Miniature Live Centre
« Reply #11 on: October 30, 2022, 11:25:35 AM »
I love both SimplyLoco and Charles solutions as I have had similar problems from time to time ....

Per

Offline simplyloco

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Re: Making a Sub Miniature Live Centre
« Reply #12 on: October 30, 2022, 07:33:55 PM »
After using the thing I soon realised that the 'contact patch' wasn't big enough to drive the centre without a bit of end pressure, so I made a top hat for it. Works a treat now!