New backplate and collect plate won't register

Triggerscan

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I recently started using my new LMS 3595 HiTorque lathe. It came with a 4" 3-jaw mounted and a 5" 4-jaw with 5" back plate as an accessory. I also just purchased a 4" ER32 collet plate. I had to tap the 3-jaw with a wooden dowel in the spindle hole to remove it. For those that don't know, the spindle on this lathe (basically a SC4) has a 4" plate with registration ring as part of the shaft, so everything has to fit that plate. When I tried to mount the 5" backplate for the the 4-jaw and the 4" ER32 collet holder, it seems that the recesses on the back are too small by about a thou or two so them won't sit flush with the plate. Has anyone run into this problem before? If so, how did you solve it?

I guess one option is to have the registration recesses on both the 5" backplate and ER32 collet enlarged, but I'm not sure if that is wise. The other option is to turn down the registration ring on the spindle plate about 0.001" to get them to fit, but that might give me some movement on my 3-jaw chuck.
 

cjtoombs

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Movement on the 3 and 4 jaw is less important than the collet chuck. Even a good 3 jaw chuck will have a few thou of runnout, with more typical being around .005, and the only real reason to worry about runnout on a 4 jaw independent chuck is balance. I probably wouldn't turn the spindle plate, to reduce it, just hit it with a file a bit while running (make sure you use a file with a handle, if it catches you don't want it to drive the file tang into your hand or wrist). That gives you much more control over the metal removal, and if you only have to go a thou you will need lots of control. You should do some careful measurements to make sure of the amount you need to remove and shoot for a good fit on the collet chuck and let the others fall where they may, even if that means turning a bit out of the 4 jaw back plate to get it to fit.
 

mikey

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I looked at a video by Frank Hoose that shows the spindle nose, which really helped to clarify the issue. What you're saying is that the spindle register, the ring in the center of the chuck mount, is a fixed diameter. This spindle register is supposed to fit accurately inside a corresponding recess in the back of any chuck that should fit this spindle. That spindle register is an important feature that should be accurately ground from the factory and determines the accuracy of any accessory that you bolt to it; I would not modify it unless the factory screwed up and ground it too large, which is not likely.

If a chuck or back plate does not fit properly onto the register then you have to modify the recess of the accessory. How you do that is the real issue.

The first thing I would do is contact the seller of the 4 jaw and ER chuck and tell them what the problem is. If these accessories are intended to fit the spindle of your lathe and do not then it is on them to correct that. It is possible that the accessories were made to fit another generation of machine with a smaller register. Check with them first.

On the off chance that they cannot offer another solution then the only option is to bore out the recess behind the accessory. That requires the accessory to be accurately mounted and bored on a larger lathe than you currently have. If you know someone that has a larger lathe and who you can trust to indicate the chuck or plate accurately then boring the recess is not a major deal.

Sorry but I can't think of a way for you to solve this yourself. A 3 jaw is not accurate enough for this job unless it is a set-tru chuck, which I assume you do not have. You don't have a 4 jaw independent because it won't fit. I suppose one other option is to use a boring head on a mill if you have the machine and skills to do it. Otherwise, you are going to need some help.
 

higgite

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A couple of questions…

First, have you checked all of the registers and mating surfaces for burrs, gouges, etc.?

Next, have you tried tightening the mounting bolts to see if they would draw the backplate flush with the spindle flange? I would try it with the backplate mounted to the chuck, not by itself, so you have some leverage to remove it from the spindle because, from what you have indicated, it IS going to be tight.

If there is no obvious solution, I agree with Mikey, call the vendor(s) and see what advice or remedies they might offer. I know from experience that LMS customer service is top notch.

Tom
 

Triggerscan

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Thanks for all the insight. What I did was take cjtoombs advise and touched a file to the outside edge of the spindle register. I noticed that it was back cut (got smaller in diameter as you got closer to the spindle plate. Ran at 100 rpm and used a fine touch until I got the collet holder plate to just fit snugly. I then tried the 3-jaw chuck and found no play. Chucking a 0.5" gauge pin showed about 0.7 thou TIR after tapping the chuck at the high spot. The 5" backplate for the 4-jaw now fits snugly and needs a tad persuasion to remove. So I think the problem can be considered solved. Thanks to all who helped.
 

mikey

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Just for future reference if you ever buy another lathe, that register determines the accuracy of anything you put on the spindle. Many/most lathes have a specific geometry at the register. For example, the popular camlock spindle has a DIN standard 7 degree, 7 minute, 30 second taper at the register. This allows any camlock chuck to fit that spindle accurately. If you alter the taper in any way then the expected accuracy of the spindle will be adversely affected. So, unless the register is damaged somehow, try not to mess with it; fix the thing to be fitted to it instead.
 

cjtoombs

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Just for future reference if you ever buy another lathe, that register determines the accuracy of anything you put on the spindle. Many/most lathes have a specific geometry at the register. For example, the popular camlock spindle has a DIN standard 7 degree, 7 minute, 30 second taper at the register. This allows any camlock chuck to fit that spindle accurately. If you alter the taper in any way then the expected accuracy of the spindle will be adversely affected. So, unless the register is damaged somehow, try not to mess with it; fix the thing to be fitted to it instead.
Quite important on other lathes. Probably not as important on a Chinese mini lathe. I expect the lathe spindle itself is probably made to a fairly high standard, but the chucks to go on it are not, as can be seen from the variation experienced by the OP. And again, accuracy matters a lot on a collet chuck, but not so much on a 3 or 4 jaw chuck (within reason). I certainly would be reluctant to modify the spindle nose on a Hardinge HLV or Monarch EE, but not so much on Chinese mini.
 

Triggerscan

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Point taken. For clarification, the registration boss has a reverse taper, so chucks see the maximum diameter first with what appears to be a relief cut closer to the plate. Reading what mikey said, I would have thought it would taper the other way.
 

mikey

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Yeah, it sounds like the spindle was inaccurate, which I've not personally seen before. You should let LMS know because that is unacceptable.
 
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