[How do I?] "map" The Errors On A Older Lathe?

jjtgrinder said:
................What did you think about the uniform scoring on the ways?

Thank You, John
Click to expand...

John,

If the uniform scoring runs the entire length of the bed, it left the factory like that. If it is only for a small length, it's from debree that got caught under the saddle. I would not worry about it. Just stone the ways with mineral spirits and call it good for now. Change out the felts in the way wipers, they collect crud that can cause scoring, too!

On my Sheldon lathe when I first got it, you can see the grinding marks from where it was ground at the factory. It looks like faint scoring marks. You can't feel them, but it's there. Both of my Sheldon's show the same pattern.

Ken
 
I have a hypothesis on the taper towards the chuck end.

As you feed the cut towards the chuck, is it not possible that the heat generated expands the workpiece slightly, meaning that the diameter of it becomes slightly greater as you near the chuck. So you'd be skimming off slightly more material than when you started the cut. When you stop the lathe to measure, enough heat may have been conducted away through the chuck and via IR radiation for it to shrink again, and you end up with a taper when you measure.

Thoughts?

A good hypothesis is of course testable - flooding the workpiece while cutting would provide such a test. Or cut a relief chuckside, let it cool down and cut to the right, although I have no idea if the mechanics of rightward cutting creates any sort of repeatability compared to a leftward cut.
 
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TBH JT, I see some scoring, which goes the full length of the bed, which is odd, and does suggest, as has been said above, that it has been there from manufacture. Having said that, I do not see a lot of wear, but then again I am looking at photos, not the lathe itself. I see from your pictures that you have had the saddle off, so I assume you have cleaned any swarf or dirt from the under the saddle? Is the cabinet a one piece job that supports the bed full length, or is there a gap in the middle like a kneehole desk? Now the million dollar question, have you taken the bed off the cabinet to refurb the lathe, because if you have this could be the problem. Lathes on one piece cabinets are shimmed to the cabinet, and tested to get the lathe turning parallel. If you have had the bed off the cabinet, it will want doing again, indeed, it may want doing again anyway, and you can cure a 002" discrepancy by doing it, but you do need to know if the error is consistent down the bed, that is, as you move away from the chuck the error keeps increasing, but at the end of the day, the magnitude of the error is not much, and it is doubtful that it would impact anything you make in the lathe to a great extent. Having said all of this, the first thing to do is get the lathe on a reasonably level, but more importantly stable, base. As a rule of thumb test, loosen the bolts that secure the bed to the cabinet and re run the turning test, and see if it gets better or worse.
Phil
 
The lathe is just like this one here: (http://www.lathes.co.uk/delta metal/page3.html). It has a separate cabinet under the head and tail portions. There is a chip pan suspended under the central bed between the cabinets. No, I have not taken the bed off the cabinets. I did not see any benefit. I did take the saddle off and clean it and the apron gear box.
I mic'd the carriage vee-way by placing a vee-blk on the vee-way (I throughly cleaned the ground surfaces underneath the vee-way and the vee-way itself.) i started by also mic'ing the extreme end where I doubt there is any wear (2.9824"). I mic'd ,from under the chuck, every two inches (the length of the vee-block) for eleven iterations.
Here are the numbers from left to right with position "A" under the chuck.
A(2.9809"), B(2.9798"), C(2.9792"), D(2.9795"), E(2.9797"), F(2.9798"), G(2.9795"), H(2.9800"), I(2.9800"), J(2.9806"), K(2.9815") ------------------------- tail (2.9824").
Diff ------ .0010 ------- .0007 ------ .0004 ------ .0002 ------ .0001 ------ .0003 ------ .0005 ------ .0000 ------ .0006 ------- .0009
Direction - ................... - .............. + ................ + .............. + .............. - ................. + .............. n/c ............ + ................ +

I agree, not a lot of wear here in my very inexperienced opinion.

I will proceed to improve the bedding of the lathe to the concrete floor (more stable base) and then go from there. I will report back (may take a few weeks).

Thank You all very much.
 
Hi JT, given that you lathe stands on what are essentially two separate cabinets, I thing the problem is the surface it stands on. From your measurements there is not enough wear on the bed to really worry about. In days gone by, when things were done right, a new machine arrived with instructions on how to do the parallel turning test, and how to impart slight twist on the bed to get the lathe turning parallel, if the lathe was expensive enough, you would get a "works" engineer who would install and commission the lathe. If the lathe has been used on an uneven surface in its previous life, it will over time have imparted slight twist on the bed. Get it on a level, flat surface, loosen the bed holding down bolts and the chip tray bolts, and do the turning test again. If the error is still there you need a shim under the front tailstock end foot, then retest to see if you get any improvement. Using this method you should be able to dial it in pretty much spot on. It looks like a very fine machine, I would certainly be happy to own it!
Phil
 
Guys,
The way the Rockwell 14" lathe is designed, and according to the user manual, you shim up under each foot on the bed. The cabinet is not designed to be un-bolted and shimmed between the bed and cabinet. I guess you could if you really wanted to. Not like some of the South Bend lathes where you do the leveling at the bed and legs of the lathe. I definitely agree on needing a firm foundation under the lathe.
 
Thanks 4GSR that is good info, I am not at all familiar with Rockwell, machinery.

Also to JT
"Nice looking machine! What is the "bar" running behind and overhead of the bed?"
Sorry, missed this question, you slide the bar left and right to start/stop the chuck, it it operates a clutch on the headstock input pulleys. Means you can easily stop the machine from any work position along the bed. Looking again at the pics of your lathe, are they adjustable feet on the cabinets? if they are you will be able to untwist the bed using careful adjustment on these.
Phil
 
Thanks to each of you for the excellent encouraging words. I am anxious to get on with the foundation improvements. My wife "volunteered" me for some charity work this weekend. Oh Well. I do have adjustable feet under the lathe but the wood platform is not firm enough to make them effective. (that's my theory.)
The previous owner was not too particular with the installation from what I saw when I purchased the machine. I may very well be working with some "induced" twist. I bought some steel to use to firm up the foundation. It will take me a week or two to complete that. Wife, children, mother and a job keep me very busy.

JJTgrinder
 
Firm bedding in place, a precision level indicating bed is twisted down at the front tail end and low at the back head end. This indicates a twist which would cause the tapering as indicated earlier in the post. Initial adjustment will not move the bed much, the Rock-Delta 14" has a "beast" of a deep wide bed!!!


Sent from my iPhone using Tapatalk
 
Just put a little weight on the high side of the bed to push the twist the other way. let it set for about a summer, it should be un-twisted by then. It's a little more complicated than that, but basically what you have to do to get the twist out of the bed.
 
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