MT5 Test Bar

mikey said:
Tim, there are some of us who have been aligning headstocks for decades without a single calculation or test bar, relying instead on test cuts on test bars held in the spindles of the lathes that are being adjusted. I am one of them, and I feel that this is the most accurate way align a headstock. I won't go into the other methods but know that anytime you use a MT test bar you are relying on the accuracy of the bar and the fact that a perfect interface between the bar and your spindle must be accomplished, something that is not likely to happen with a cheap bar from India. My advice is to return the bar for a refund and do some simple test cuts as below.

  • Find a bar of easily cut material; an 8-10" long piece of 12L14 or 6061-T6, about 1.5" OD, will work well. Stick that in your 3 jaw chuck so about 4-6" of it sticks out and lock it down.
  • Using a freshly sharpened GOOD HSS tool, take a 0.010" deep cut from the end and turn up near the chuck. Repeat this with a 0.003" deep cut, then with a 0.001" deep cut and strive for a good finish. Note that the tool must be ground well by someone who knows what they're doing. A square tool with a 1/64" nose radius as described elsewhere on this site works well for this purpose. If you cannot grind such a tool then I suggest you PM @Z2V or @ttabbal and have them grind one for you. Either can do it for a very reasonable cost and it will be worth it.
  • Once your test cuts are done, measure the OD up near the chuck, in the middle and at the end of the rod. This will tell you if the headstock is out of alignment and will also tell you which way to rotate the headstock.For example, if the OD on the tailstock end of the bar is larger than the chuck end then the tool is farther away from the spindle centerline on the tailstock end and you have to rotate the headstock in a CW direction to correct it.
  • Repeat your test cuts and rotational adjustments until there is zero deviation in the OD at either end of the rod. At that point, the headstock is aligned with the ways. How close you get this adjustment is up to you; both my lathes are at zero.
  • Once you align the headstock you can proceed to level the lathe and then align the tailstock.
Hope this helps.
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This method neglects the required leveling of the lathe bed ways to eliminate twist in the bed ways before attempting to align the headstock with the ways without twist; personally I have never seen or experienced a lathe that there was any adjustment to rotate the headstock into alignment, other than scraping or shimming of the Vee ways into alignment to eliminate taper.
 
I think Mikey assumes a preliminary level check was done.
This means check the HS end and TS end with a precision level to make sure there is no deviation. Do not introduce intentional twist to get the lathe to cut without taper.
I would also add once you take a cut turn off the lathe. Move tool back to the beginning and take a spring pass without moving the cross slide.
 
The beds have been leveled, I'll check it again before performing a cut like Mikey explained.
 
ddickey said:
I think Mikey assumes a preliminary level check was done.
This means check the HS end and TS end with a precision level to make sure there is no deviation. Do not introduce intentional twist to get the lathe to cut without taper.
I would also add once you take a cut turn off the lathe. Move tool back to the beginning and take a spring pass without moving the cross slide.
Click to expand...
I think we should not assume ----
 
To be fair to everyone I never asked about checking the level or the alignment of the lathe. I did make one comment, kind of a rhetorical question about using the bar that wasn't true and zero to align the headstock.

I purchased the bar thinking it would be a convenient way of checking the headstock and tail stock for alignment. It's not very convenient when the tool is not concentric.

A lot of times I learn a lot about the techniques and measurements from just posting and describing the photos. I was trying to decide if I was doing something wrong or if the bar was bad. And after a few of your comments and a couple of retests I truly believe the bar is bad.

I really do appreciate all the comments and help I receive from you guys. And as @benmychree stated I guess you can't really assume anything.
 
benmychree said:
This method neglects the required leveling of the lathe bed ways to eliminate twist in the bed ways before attempting to align the headstock with the ways without twist; personally I have never seen or experienced a lathe that there was any adjustment to rotate the headstock into alignment, other than scraping or shimming of the Vee ways into alignment to eliminate taper.
Click to expand...

Leveling of the lathe before aligning the headstock is, to me, backwards because you are influencing the 2 collar test with a potentially off-axis headstock. It is better to align the headstock with the ways first, then level the lathe, then align the tailstock ... in that order. This has been my personal approach and works best for me.

As for never having seen a lathe with adjustments for headstock alignment, I know some lathes have jacking screws for exactly this purpose. My Emco lathe does not have these screws but has adequate room for minute adjustment that allows precise alignment of the headstock. As a result, my lathe cuts a 6" test bar with zero deviation in diameters. It also has zero deviation between the 2 collars of a test bar over 10" and the tailstock is precisely aligned with the spindle when tested with a test bar cut on my lathe.

As I said, this works for me and my results may differ from that of others.
 
@mikey I think we've talked about this before.
Our definitions of leveling differ and I may be wrong what leveling is.
To me leveling is checking to make sure the lathe is level as far as no movement of the bubble from HS to TS and that's it, over, done.
 
It just makes no sense to me to unload a new lathe from the trailer and immediately start taking cuts to check for HS alignment.
I'm going to level it first to take undo stresses out of the casting. Probably let it sit for a few days and check again. Then I'll start taking test cuts.
 
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