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Centre finder?

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Matt Harrington01/12/2015 11:23:11
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102 forum posts
6 photos

Hi,

I was given this tool the other day:

img_2442.jpg

It is more than likely a centre finder (?) but does anyone have a similar tool and able to tell me what bits are missing? (It is made by J Whitworth & Co)

(There are a few more photos in an album I have just created)

Matt

jason udall01/12/2015 16:03:06
2005 forum posts
41 photos
It is indeed a centering aid...
A finger fits through the gimbled bit...a point on either end..one short ( near the gimble)..wjich is engaged with the center mark of the stock..the other end wobbles around describing a much larger circle ..the stock is adjusted in the (four jaw) chuck until this wobble is minimised. ..with a typically five to one ratio a very small error can be detected...
Tim Stevens01/12/2015 19:02:58
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1010 forum posts

That is, a steel finger, and not a small child's. Just to be certain ...

Tim

jason udall01/12/2015 20:17:04
2005 forum posts
41 photos
Indeed
Matt Harrington01/12/2015 23:20:11
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102 forum posts
6 photos

Thanks. Do you think the finger/needle is within some sort of collet? Interestingly the gimble is spring loaded in one direction.

Matt

Gary Wooding02/12/2015 13:31:05
526 forum posts
109 photos

Here's a photo of a similar item in use.

centrefinder.jpgSorry for the typo, for sring read spring

Ignatz04/12/2015 02:42:36
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90 forum posts
44 photos

Does a centering finger like this have to run off of a center-bored hole (as in previously-turned item) or would it also work pressed into a center-punched witness mark on new, not-yet-turned work?

Gary Wooding04/12/2015 08:11:00
526 forum posts
109 photos
Posted by Ignatz on 04/12/2015 02:42:36:

Does a centering finger like this have to run off of a center-bored hole (as in previously-turned item) or would it also work pressed into a center-punched witness mark on new, not-yet-turned work?

Yes, that's what it designed to do.

I'm afraid that my photo was created in a hurry and, to save time I just stuffed something in the 3-jaw. In practise, the workpiece would be in the 4-jaw independent with a centre-punched mark that needs to be centred. The pointed end of the finger follows the centrepop as the chuck is rotated, and if its not truly centred the other end wiggles even more because of the difference in the lengths either side of the support.

Matt Harrington04/12/2015 08:57:16
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102 forum posts
6 photos

Thanks Gary,

In your centre finder is the pin fixed or does it slide along and the knurled part used to fix the pin in situ? I'm obviously missing parts here and I still cant see how the small attachments (stored in the body) are used on it.

Matt

Gary Wooding04/12/2015 10:24:48
526 forum posts
109 photos

The needle can be moved back and forth when the knurled nut shown in the photo is loosened.

centrefinder2.jpg

Matt Harrington04/12/2015 17:24:38
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102 forum posts
6 photos

I think I will make a collet and knurled closer similar to yours and see how we go.

Matt

Bernard Greatrix08/03/2019 21:20:22
22 forum posts
4 photos

Hi

If this post isn't dead - does anyone have any simple plans for this device. The links to a similar thread appear to have expired

It has been suggested to me to help centre work in a 4 jaw chuck.

Snag is the old guy who described it to me said the hardest part was drilling a ball bearing.

I think he was having me on, but I can't be sure

 

Any comments welcomed

 

regards

Bernard

 

Edited By Bernard Greatrix on 08/03/2019 21:24:51

Martin Connelly08/03/2019 21:50:29
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839 forum posts
93 photos

Easier to use a dti and spare centre as shown on this page.

**LINK**

Martin C

Nicholas Wheeler 109/03/2019 00:00:37
228 forum posts
13 photos
Posted by Bernard Greatrix on 08/03/2019 21:20:22:

Hi

If this post isn't dead - does anyone have any simple plans for this device. The links to a similar thread appear to have expired

It has been suggested to me to help centre work in a 4 jaw chuck.

Snag is the old guy who described it to me said the hardest part was drilling a ball bearing.

I think he was having me on, but I can't be sure

It's easier to make one using a spherical bearing(rose joint). I'll sort a photo of mine in the morning, but it's not something I've used very much as I rarely use the four jaw chuck

Jeff Dayman09/03/2019 00:31:56
1470 forum posts
37 photos

Kozo Hiraoka described a nice simple version of this type of tool in his "building the Shay" book. Found a link in a different place to it, here:

https://thehobbyistmachineshop.com/cms/workshop/kozo-s-wliggler

The ball in his version is brass, I believe.

roy entwistle09/03/2019 10:59:00
947 forum posts

If you heat the ball to red for a few minutes it should be soft enough to drill

Roy

Ian Hewson09/03/2019 12:31:55
256 forum posts
19 photos

Stainless steel balls are available on the net, use them for governor balls, drill ok without heating.

Maurice09/03/2019 14:28:08
431 forum posts
50 photos

I have one of these, similar to the photos. The collet that holds the pointer is spring loaded to allow the pointer to move endwise if the centre hole is wildly out of adjustment. I can't tell it the photographed one does this, but it would seem to be desirable.

Maurice

Fowlers Fury09/03/2019 18:30:44
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313 forum posts
71 photos

Many years ago in one of the ME mags, it was suggested that you could dispense with gimbals etc and just cut a thin slice of india rubber (= pencil eraser) and fix in a frame. The pointed rod was simply pushed through to provide the magnified "wobble". I remember trying the idea and after cutting a slice from an eraser about 1/16th thick (?) it worked well enough for setting up in a 4 jaw.

Much later, the gimbal below was removed from a broken lab item. The gimbal looks easy enough to make, probably more so than drilling steel balls..

gimbal.jpg

JC5409/03/2019 19:25:10
79 forum posts
1 photos

Another simple method is to cut a short piece of box section (10mm) that will fit in the toolpost fill with silicon sealer then push a long "needle" through it. Same idea as FF. This makes a very quick cheap wobbler..

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