Chuck backplate error

[Martin ConnellyParticipant @martinconnelly55370]

The whole point of the chuck mounting register and thread is to attach the chuck to the spindle in a way that does not allow it to move relative to the spindle under the forces caused by using it. It is normally assumed that unless you have an adjustable 3 jaw chuck you should not expect work to go in concentrically at every diameter. If you want concentricity then use an adjustable 3 jaw chuck, an independent 4 jaw chuck, work between centres, use soft jaws or collets. I am sure you can imagine the effects of a chuck moving on the spindle during machining of a part (reversed spindle work comes to mind as the most obvious example).

Based on this it does not matter how good or bad the register and thread is as long as they allow mounting with no further movement when being used. With some small threads a good register may be important for this. For the Smart and Brown lathes with a 1.75" x 8tpi thread the thread alone may be sufficient.

Martin C

[old martParticipant @oldmart]

Lathejack, you have had good results with close fitting radial registers, but you do not mention any experiance of using loose radial registers. So you are an expert on the subject?

[david bennett 8Participant @davidbennett8]

This argument reminds me of arguments on religion – no-one will be convinced until they try it. For what its worth I intuitively believed that the radial (horizontal) register was important. What made me rethink this was not so was when I realised I was using an ML7 chuck on an ML4 with no collar. It repeated perfectly. Since then I have made many backplates for different lathes, so I could experiment. Experience has shown me that the close fitting spindle (horizontal )

register does nothing to aid repeatability, but can in fact interfere with a free running thread cut into a backplate with the shoulder (vertical register) cut at the same setting. I have made backplates for many Myford sized lathes (Wolf Jahn, Cataract, etc) but my interest is in smaller precision lathes such as Pultras, Unimat 3 and SL's and watchmakers lathes..On none of them do I bother to closely size thespindle (horizontal ) register. I will take expermental resuls over intuition ever time.

Dave

[LathejackParticipant @lathejack]

Posted by old mart on 09/01/2021 17:34:47:

Lathejack, you have had good results with close fitting radial registers, but you do not mention any experiance of using loose radial registers. So you are an expert on the subject?

Unfortunately there are times when I feel that you are coming across as rather unpleasant. Surely the rest of us should be able to comment on our experiences and opinions, just as you do, without receiving remarks such as in your last sentence?

Edited By Lathejack on 10/01/2021 01:16:50

Edited By Lathejack on 10/01/2021 01:33:52

[Howard LewisParticipant @howardlewis46836]

If has any bearing, when I fabricated and machine backplates for ER collet chucks on my lathe, I turned a chamfer on the inner end, to mate against the flange behind the 2.250 inch thread. That improved repeatability, as well as or despite, the register.

Howard

[old martParticipant @oldmart]

Posted by Lathejack on 10/01/2021 01:13:44:

Posted by old mart on 09/01/2021 17:34:47:

Lathejack, you have had good results with close fitting radial registers, but you do not mention any experiance of using loose radial registers. So you are an expert on the subject?

Unfortunately there are times when I feel that you are coming across as rather unpleasant. Surely the rest of us should be able to comment on our experiences and opinions, just as you do, without receiving remarks such as in your last sentence?

Edited By Lathejack on 10/01/2021 01:16:50

Edited By Lathejack on 10/01/2021 01:33:52

Perhaps you could make a comment on the recent post by David Bennet 8.

[david bennett 8Participant @davidbennett8]

Posted by old mart on 10/01/2021 21:25:05:

Posted by Lathejack on 10/01/2021 01:13:44:

Posted by old mart on 09/01/2021 17:34:47:

Lathejack, you have had good results with close fitting radial registers, but you do not mention any experiance of using loose radial registers. So you are an expert on the subject?

Unfortunately there are times when I feel that you are coming across as rather unpleasant. Surely the rest of us should be able to comment on our experiences and opinions, just as you do, without receiving remarks such as in your last sentence?

Edited By Lathejack on 10/01/2021 01:16:50

Edited By Lathejack on 10/01/2021 01:33:52

Perhaps you could make a comment on the recent post by David Bennet 8.

Since I seem to have been dragged into this chat about good manners, I do not regard myself as an expert, just experienced. I hope I would never throw an insult at someone who may have less (or more – how would I know?) experience. This is, after all, for beginners questions. All my answers are for anyone to ignore or not.

Dave

[clogsParticipant @clogs]

If I need to use a small chuck I just put in the large chuck…easy….

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, well how about Clogs idea.

Personally I can't see why the point is having as much argument. If one wants to have a positive register in both planes or not, then I can't see any problem, but as far as getting swarf trapped, surely you should make sure that both the spindle nose and the chuck should clear of debris and be lightly oiled before fitting. As the saying goes; there is more than one way of skinning a cat. (no cruelty to animals intended)

Regards Nick.

[Martin ConnellyParticipant @martinconnelly55370]

Nick, it's only cruel if the cat is not dead at the time The original question is relevant if people are replacing a worn out chuck and need to fabricate a new backplate to suit (for example) or need a new chuck to complement their old chuck for additional features such as soft jaws. The chance of buying a new backplate for an old lathe is pretty low, the Smart and Brown spindle nose for example is not catered for as far as I can tell requiring owners to machine their own. So the original question regarding what is or isn't important when making one is relevant to a lot of people.

Martin C

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by Martin Connelly on 11/01/2021 09:05:11:

Nick, it's only cruel if the cat is not dead at the time The original

cut….

Martin C

Hi Martin, but I didn't want to imply you had to kill a cat.

Regards Nick.

[Howard LewisParticipant @howardlewis46836]

Oh dear!

One way and another, the fur is flying!

[david bennett 8Participant @davidbennett8]

Back to the topic, I wonder how many people actually measure the bore of a backplate after making it a close fit to the radial register? I would not be surprised if it is considerably greater than those last few tenths achieved by cut-and-fit due to tolerances in manufacturing the spindle. Could some people actually measure bore/register figures from well fitting chucks and let us know?

Dave.

[Anders BeParticipant @andersbe]

I push this subject with a similar question: I will (or rather dreams of) make a new backplate for my lathe. The diameter of the spindle nose at the register is 37,97 mm with a tolerance of +0 and -0,005 mm (a schaublin 102 spindle nose for w20 collets). What diameter should I aim at accordingvto you?
Best regards
Anders B

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Anders Be on 12/01/2021 19:55:47:

I push this subject with a similar question: I will (or rather dreams of) make a new backplate for my lathe. The diameter of the spindle nose at the register is 37,97 mm with a tolerance of +0 and -0,005 mm (a schaublin 102 spindle nose for w20 collets). What diameter should I aim at accordingvto you?
Best regards
Anders B

.

If you want it to fit every 102 then the bore must be more than the maximum

If you only want it to fit your spindle, then measure the spindle

…I would aim for 0.005 to 0.010mm more than whichever dimension you select.

I am sure that other opinions will be available.

MichaelG.

[david bennett 8Participant @davidbennett8]

Anders Be, is that the tolerance on the diameter? what is the tolerance on run-out? what is the tolerance on thread/register runout? was the thread and register machined at the same setting in the machines own bearings? On a Schaublin it may well be so, but not on all hobby lathes. On myfords for example the register may well not be concentric to the thread. All the tolerances can combine to conspire against the user. If you have a recommended diameter to cut, how will you measure it? or will you cut-it and-try-it? If you are successful please carefully measure it and educate us all.

 

Dave.

Edited By david bennett 8 on 12/01/2021 22:34:14

Edited By david bennett 8 on 12/01/2021 22:42:03

[Michael GilliganParticipant @michaelgilligan61133]

Post #65 here might be of interest : **LINK**

https://www.practicalmachinist.com/vb/general/comparable-machine-schaublin-102n-vm-cf-291816/index4.html

MichaelG.

[david bennett 8Participant @davidbennett8]

Michael G, sorry to be so long responding. Those Schaublin nose specifications look interesting. Since the thread diameters are about 0.5mm larger than the register size, it looks like Schaublin doesn't belleve in close fitting backplate registers either.

Dave.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by david bennett 8 on 26/01/2021 04:19:43:

[…]

the thread diameters are about 0.5mm larger than the register size […]

.

Are you sure about that, Dave ?

It’s not how I read the drawings

MichaelG.

.

Sorry about the image size … I grabbed it from the referenced discussion.

Edited By Michael Gilligan on 26/01/2021 08:17:11

[Michael GilliganParticipant @michaelgilligan61133]

PostScript :

For a much better image … See here: **LINK**

https://www.roesli-maschinen.ch/schaublin/masszeichnungen.pdf

[ isn’t the internet wonderful ! ]

MichaelG.

[old martParticipant @oldmart]

It's that dimension at the far right hand side that is causing the confusion with both drawings. The thread sizes are definitely smaller than the registers.

Edited By old mart on 26/01/2021 15:53:09

[david bennett 8Participant @davidbennett8]

Hmm, what do you read the 38.453mm dimension as (on the w20 nose) ?

Dave.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by david bennett 8 on 26/01/2021 15:57:02:

Hmm, what do you read the 38.453mm dimension as (on the w20 nose) ?

Dave.

.

The dimension over the 1.8mm wires

… What do you read it as ?

MichaelG.

.

.

Edited By Michael Gilligan on 26/01/2021 16:07:50

[old martParticipant @oldmart]

I don't know what it is there for, but the thread size is M37.6 X 3, which is smaller than the register diameter, 37.97mm.

 Now I see, with the larger picture, it is the diameter over wires. All is crystal clear to me now, I hope it is also clear to everyone else.

Edited By old mart on 26/01/2021 16:07:33

[david bennett 8Participant @davidbennett8]

Ah, thanks for clarifying – I couldn't read that before . I was maybe hoping it was the elusive clearance!

Dave.

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