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Chuck locking ring.

A clamping ring that will stop chucks unscrewing in reverse

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Clive Hartland08/12/2011 17:46:23
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2630 forum posts
40 photos
I have placed a photo in my collection of a chuck with a locking ring.
This is the method used by Schaublin to stop screwed chucks from unscrewing in reverse.
The back plate is machined to accept the ring and I do believe the rings are obtainable commercially but have not found a source.
 
Clive
Ian P08/12/2011 18:41:51
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2452 forum posts
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Clive
 
How does it work?
 
I have looked at the picture (in your Myford album?) and I can see it gripping the backplate collar tightly, but what does it connect to on the spindle?
 
The main point is though, will it work on a Boxford?
 
Ian Phillips
Clive Hartland08/12/2011 21:19:48
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2630 forum posts
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Ian, its purely compression on the machined seat of the back plate, all the time I have used one I have never had a chuck shift.
It will clamp on the parallel portion at the end of the thread.
The ring is76mm dia, is 12.95 wide, the bore is 49.99 dia.
It has a step on one face to clear the fillet on the back plate.
Slots are 10mm deep at 90deg and the 4th one cut thro. The clamp screw is M6 Skt hd.
 
Hopefuly you would have enough meat on the backplate to fit such a ring?
 
Clive
Ian P08/12/2011 21:43:21
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2452 forum posts
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Sorry for being thick, I can see thet the ring closes down to grip on an OD but Is the bore stepped so that it clamps on the OD of both the backplate -and- the exposed part of the spindle?
 
Ian
Clive Hartland09/12/2011 08:45:19
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2630 forum posts
40 photos
Ian, the bore of the ring is plain and the small step is just 1.5 x 1.5mm to clear the machining fillet in the corner of the back plate where the round nose tool has machined it. It could be a large chamfer if that is easier.
The ring is the full width of the seat on the chuck back plate and does not touch the mandrel.
The concept is that it clamps the back plate down onto the mandrel plain portion which seems adequte to lock the ring tight.
I will take another photo dismantled shortly, and post it for you.
Am suffering the after effects of a bout of Norwalk Virus, both wife and self, so its a double whammy.
 
Clive
Dusty09/12/2011 09:24:29
484 forum posts
8 photos
I'm with Ian on this one. I cannot see how it works. If I read you correctly you are compressing the back plate register onto the spindle! mm! Am I missing something.
blowlamp09/12/2011 09:54:46
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1473 forum posts
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Yes, it must rely on the clearance between the mating parts being very, very small and the compliance of the backplate register to allow it to be crushed sufficiently to grip the spindle.
 
 
Martin.
Clive Hartland09/12/2011 10:32:58
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2630 forum posts
40 photos
It's a standard fitting on all Schaublin chucks and has worked fine on all four of the Schaublin lathes I used.
When I ordered a new chuck for a Schaublin lathe it came with ring and backplate complete. I did not have to machine or develop it at all.
It is a viable means of locking the backplate to the mandrel, unless someone comes up with a better one for a screwed chuck.
I have used the bolt on type chucks and I prefer the locking ring type much better.
Chucks can be quite heavy and awkward to lift away.
 
Clive
Versaboss09/12/2011 10:45:17
461 forum posts
51 photos

An old story, going back almost to the time when Noah built the ark. I mentioned this system on other places, more than once I think, and almost everytime I saw the same reaction. No one seems to believe that it only works by compressing the neck of the backplate. There is no place where the ring touches the spindle!

I dug out a pic I took a couple of years ago:


I took several attempts to insert the pic directly (without creating an album) but no success!!!

Inserting an URL in the line on the insertion form results only in a empty line here..

mode off, Hansrudolf

Ian S C09/12/2011 11:31:08
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7468 forum posts
230 photos
The idea that I saw a while ago clamped on the chuck and the flange on the mandrel, that was the one I thought of making when some metal comes along. Ian S C
Ian P09/12/2011 13:18:51
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2452 forum posts
101 photos
I can fully understand the concept of the clamp reducing the ID of the backplate collar so that it grips the mandrel better. What I cannot get my head round is how an M6 bolt can provide enough force to close down such a thick annulus of cast iron.
 
Metal is certainly compressible, I once saw a test rig that compressed a 1.5m length of 3" diameter steel (big diesel engine con rod) repetitively, at a guess it shortened by 5mm then sprung back every time). With this chuck clamp, any clearance on the register would certainly nullify any reduction in diameter.
 
Unfortunately I don't have a Schaublin to look at but wonder if there is anything else involved that we don't know about, like slits in the collar to allow it to move?
 
Ian Phillips
blowlamp09/12/2011 14:17:42
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1473 forum posts
97 photos
Ian.
 
Remember that the ring will exert a magnified clamping force across the diameter of the flange by virtue of the fact that a reduction of the circumference will be multiplied by the function of pi.
 
So a change of 1 unit of the circumference (by tightening the clamp) divided by 3.142 equates to a theoretical change of 0.3182 units of diameter.
 
A kind of gearing or leverage effect is in action here and very little movement is required which is why - counterintuitively, it works.
 
 
Martin.
Ian P09/12/2011 17:34:19
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2452 forum posts
101 photos
Posted by blowlamp on 09/12/2011 14:17:42:
Ian.
 
Remember that the ring will exert a magnified clamping force across the diameter of the flange by virtue of the fact that a reduction of the circumference will be multiplied by the function of pi.
 
So a change of 1 unit of the circumference (by tightening the clamp) divided by 3.142 equates to a theoretical change of 0.3182 units of diameter.
 
A kind of gearing or leverage effect is in action here and very little movement is required which is why - counterintuitively, it works.
 
 
Martin.
 
 
Yes, I agree that pi works to our advantage here but its the engineering aspect I dont understand.
 
tightening the bolt will close the gap in the ring, once the bolt and ring are snugged up increasing the torque in the bolt will try and reduce the ID of the ring which I imagine relies on some slip between the (cylindrical) joint faces, so friction must come into play here?
 
Actually its probably not relevant because once the two items are in solid contact they can probably be regarded as one, so if the collar was (radially) thick enough then the chordal clamping bolt could be installed directly in that. Even if there were no slot the principle would still work but would rely on the bolt compressing a segment of the collar reducing its ID. For the locking device that Clive showed to work it has to compress solid metal anyway.
 
Ian
 
 
 
 
 

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