truing L00 backplate to spindle nose

jmm03 · May 25, 2020

Hello all, I posted this on the southbend forum in search of advice and am trying here also.

I bought a 5C collet chuck and L00 backplate from ebay. I don't expect perfection obviously, but surprisingly, the quality of both pieces appears pretty good. I machined down the backplate to fit the chuck and got under a thousandth TIR. After taking it off and reinstalling it I have .004. I had already checked the spindle nose and it has a half thou runout, I cleaned everything pretty religiously to make sure nothing was lurking on the surfaces, I took the backplate off and then lightly tapped it onto the spindle with a deadblow but that actually made it worse by a couple of thousandth's. Put it back on and still get .004 runout. Suggestions would be appreciated. Thanks, Jim

Richard King · May 25, 2020

Show us some photo please. Your tool bit you used do the facing, the face plate and the ways near the chuck. The way could be worn on bed and saddle - cross-slide. That lets us see what your doing.

johnoder · May 25, 2020

Related thread

truing a collet chuck on an L00 spindle

jmm03 · May 25, 2020

Hi John, your suggestion to seek a method of checking the fit of the back plate to spindle nose brought me here... as to the tool i used for facing, I used a small triangular carbide of indeterminate origin (actually,a Kendex TPG221 if that means anything,I used it because I have them...) cut very well and left a nice surface finish.The backplate I cut on the spindle. The ways on my lathe are worn but should not matter as I locked down the saddle before cutting. I will try and get some pictures when I can, but what I probably need is a method of checking the fit between the backplate and the spindle nose. Thanks, Jim

Richard King · May 25, 2020

It will matter and tightening the saddle down on a worn bed can give you a bad reference. I have seen this before, I am not guessing with this advice. A simple test you can make on the squareness of cut of face-plate to cross-slide is to mount a mag base on your compound and dial indicator on the face-plate nearest the operator and crank the cross-slide back to the center. The test will show 0 (zero) as it is duplicating the travel of the cut. Now keep cranking to the back side that is farthest from the operator. This where you will see the error and it will be 1/2 the value of what it reads.

TGTool · May 25, 2020

If I'm understanding your description you're finding a repeatability problem with the face being true initially and having a face runout when re-mounted. This isn't about flatness but about wobble.

If that's true, it means that the taper on the backplate isn't true, or that there was a chip somewhere either in the initial mounting or the subesquent re-mount that shifted.

Engineering blue will tell you if it's fitting on the taper correctly. In fact, it should indicate if there's a burr or piece of swarf somewhere preventing correct fit. I can't see it being affected by wear or looseness if the carriage is stationary as you're checking runout of the face. Either that or I don't understand exactly where the error is that you're finding.

Paolo_MD · May 26, 2020

I am not sure as well if I understand the problem correctly or not.
First, I would check if the run-out is repeatible in position and magnitude with separate mountings.
Second, I would test if it's just axial or/and angular, by sticking a rod in the collet and measuring near the collet and a couple of inches away.
Possible culprit could be a less than perfect fit at the key.

Speaking of which, you could check if your run-out disappears by removing the key.

Paolo

dian · May 26, 2020

as tg said, the backplate probably wobbles on the taper.

question: where/how did you get "under a thousandth TIR"? did you put it on once and got one thou, put it on again and got four thou, taped on it and got more? you dont even have to blue it up, you should feel it moving or check with indicator if it moves.

jmm03 · May 27, 2020

If I am not mistaken the L series works by drawing the taper of the chuck onto the taper of the spindle by means of the spindle nut, (or collar) and is located and more or less driven by the key and the friction of the taper. I have taken the chuck on and off a dozen or so times and it repeats around .004 every time. The chuck cannot be moved as far as I can tell independently of the spindle once it is drawn up. If I Dychem up the backplate to check contact how should I do it? Thanks for the help. Jim

Paolo_MD · May 27, 2020

Jim,
Still you aren't answering our questions.
1) Where are you measuring the TIR (a couple of pictures would help)?
2) If you put a mark on the chuck where you have the maximum reading, remove the chuck, install it again a couple of times, do you get the maximum at the same position or somewhere else?
3) Is the TIR in any way dependent upon the tension you're tightening the spindle nut?
4) If you remove the key from the spindle and install the chuck, do you measure the same TIR?
5) Is the run-out the same near the collet as a couple of inches from the collet (e.g. chuck a dowel pin in a collet and measure it in two places)?

For checking the taper it works best using some type of spotting ink (e.g. Prussian Blue, "High Spot blue"), oil colors or, even better, Charbonnel Aqua Wash Prussian Blue etching ink (non-drying water soluble ink): the goal is to have a ink, spread in a thin layer that doesn't dry out and transfers to the mating surface only in the areas of contact.

Thanks!

Paolo

TGTool · May 27, 2020

jmm03 said:
If I am not mistaken the L series works by drawing the taper of the chuck onto the taper of the spindle by means of the spindle nut, (or collar) and is located and more or less driven by the key and the friction of the taper. I have taken the chuck on and off a dozen or so times and it repeats around .004 every time. The chuck cannot be moved as far as I can tell independently of the spindle once it is drawn up. If I Dychem up the backplate to check contact how should I do it? Thanks for the help. Jim

Make sure you're using the right stuff. This isn't the Dykem layout fluid that dries and then you mark on it. This is a paint-like paste with intense pigmentation that doesn't dry. Hi-Spot is one brand at McMaster Carr but there are others. It takes just a tiny bit, smeared smoothly on one surface of the pair of parts you're checking. If you can't see through it to the metal underneath it's spread too thickly. And in this case you'd only need a line of it, say half and inch wide along the length of the spindle. Mount up the backplate, tighten it, remove it and see where the blue has transferred to the inside diameter of your backplate. If you don't see a reasonably uniform transfer from front to back, there's a burr, and error in the taper, or something else interfering with correct fit.

jmm03 · May 30, 2020

Hello all, still working on my chuck problem to get some answers to your questions, that pesky work thing keeps getting in the way.
1. measuring the run out is taken about an inch from the end of the chuck nose, it repeats about the same every time.
2. repeatability as to the same amount of tension on the lock ring is somewhat subjective due to my lack of ability to measure it with a torque wrench, but I would say it is about the same based on marking the ring to spindle and going back to the same spot as close as possible.
3. I have not removed the key or blued it for contact yet.
4. The run out is not affected by the collets that I can see. I tried several collets of varying quality and size, e.g. a 1" older Hardinge, a 1/2" older southbend, a 5/8" new chinesium unknown make and the readings on all of them were repeatable from collet to collet although slightly different between sizes.
5. I will be using Dychem Hi-spot #107 when I can get around to checking it more thoroughly.

Appreciate everyones help so far. Regards, jim

ratbldr427 · Jun 14, 2020

When we first got our well used Regal I started checking things and noticed the chuck had some ro.Pulled the chuck and could see that the top of the key clearly had been bottomed out in the back plate at the front of the key.
Touched the key with a file and found it to be hardened.Pulled it to see if any junk under it,none found.Ground .010" off and blued ,no interference.Don't know if just one chuck or all of them were touching but was probably just a .001" or .002".
Some thing you might check and eliminate as a cause.

jmm03 · Jun 15, 2020

Thanks builder, I haven't gotten back to check some of the areas on the spindle nose by bluing yet but the key was one of them. Jim

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