How can this be?

[RSG]

Continuing the discussion on my floating reamer holder I finally had time to address the numbers.

I'm totally shocked at my findings, especially since I did the alignment last year and it tested well. I did it using the chuck and machining a center out of steel while it was chucked, as you can see this test was using the headstock center. Do you think this makes a difference? Pete mentioned sweeping the top of the tailstock quill fully extended to see how much it's out. I did the test and it drops 7 10ths at the front. Not sure if that's bad and if so should I shim it to correct it?

Also, I thought I'd check the parallelism of the tailstock to the head stock and I was shocked! The frtont disk was .015" smaller than the back. (See pic)



I assume this means the tailstock needs to shift toward me .0075" I plan to do a test on the chuck end also as Pete mentioned using the faceplate. I'll do that first. If its out I assume I need to tweak the headstock to align it before doing anything else.

As usual, I'd appreciate some input.

Regards
Ron

[Harold_V]

Also, I thought I'd check the parallelism of the tailstock to the head stock and I was shocked! The frtont disk was .015" smaller than the back. (See pic)

That won't determine parallelism. It determines tailstock concentricity (with the spindle), and that's usually adjustable by altering the screw settings at the base of the tailstock.

Note that the set-over may or may not be consistent when you move the tailstock.

I'd suggest you extend the quill of the tailstock, then run an indicator along the side (using the carriage) to determine if the tailstock is parallel to the ways.

Headstock alignment?

You can't use the tailstock for this. Best fast and easy way to determine if the headstock is parallel with the ways is to turn a large diameter piece of stock that is chucked. Use aluminum --- as it's free machining. Take a VERY light pass once you're made a cleanup cut. It the cut is tapered, and the tool is dead sharp, then the headstock is not parallel to the ways.

When you do this test, make damned sure you observe the three times the diameter in length rule. That's why you use large diameter material, so you can take a long enough cut to determine parallelism, and not worry about deflection.

H

[pete]

I think you might have found at least part of that reaming problem Ron. Any somewhat large temperature swings in your shop from when you last checked your lathe and now? Using a MT shanked dead center in the head stock is always going to be a combination of the condition of both the the male and female MT's, the lathe bearings and any inaccuracy's on all of the machined/ground surfaces. Since nothing is ever "perfect" there's going to be some combinations of those measurable inaccuracy's. I much prefer machining my own dead centers held in any chuck, and as long as it's not removed from that chuck, it's then as good as the bearings and your machined surface finish will allow. My best guess is it's slightly more accurate than using a hardened and ground MT center. Tool post grinding your own in a chuck or even the head stocks MT might gain slightly better accuracy. I don't yet have that ability.

7/10ths drop at the front of your tail stock quill isn't much when just turning a part between centers, the cutting tool point is moving up and down on the parts radius as it's cutting along the length of the lathe bed. So the larger the part diameter, the less the diameter change along the part. It takes a fairly large up/down error to be measurable compared to a side to side misalignment of the tail stock. Side to side is a direct 1-1 measurement if there's any misalignment. But that downward tilt can and does make a real difference when using any tooling in that tail stock because there length continues that misalignment all the way out to the tool tip with everything else being equal. Longer tools literally magnify that inaccuracy. If it were me I'd shim for zero/zero on the tail stocks quill AND along it's side so it points directly at the head stock C/L. Once all that's correct and the bed is known to be in a level non twisted condition repeat the same turning test. At that point you "might" need to make a minor correction on the bed leveling bolts to compensate a fraction due to component deflection under cutting loads.

With a soft center machined in your lathe chuck it's on the head stock C/L, turning and measuring a part between centers is then checking the lathe bed for parallelism and any bed twist. Any wear your lathe has I can't comment on because I don't know how much you may or may not have.

Doing that face plate test I mentioned is mostly an indicator that both the cross slide and the head stock are ok. If there is an issue it can't really pin point which part or a combination of both any problem might be. So if that test does check out, you can figure the head stock and cross slide are still correctly aligned and there's not yet enough wear in the cross slide dovetails to show a measurable effect. If it doesn't check ok? I'd probably then try that two collar test bar cutting without using any tail stock support. But the lathe bed has to be 100% known to turn parallel between centers first. I'd also really analyze any problems you find and moving the head stock would be the very last thing I'd do before exhausting every other possibility. Even then I'd want a good hardened and ground MT test bar in the head stocks taper and checked by indicating it's top and front side to 100% confirm and guarantee that head stock is in fact out before I would be willing to move it at all. I'd also be checking the head stock bearing pre-load first just to be sure it isn't time to snug them up a bit due to enough wear. In my opinion the whole lathe has to be already known to be checked and passed as rock solid correct before I'd ever touch those head stock bolts.

[GlennW]

Also, I thought I'd check the parallelism of the tailstock to the head stock and I was shocked! The front disk was .015" smaller than the back. (See pic)

Not sure I understand that, as they are side by side. Is the headstock or tailstock end smaller?

I ask because there is a much greater chance of the headstock being rotated away from you from cutting pressure making the left disc larger, than there is of it moving toward you making that disc smaller.

I did it using the chuck and machining a center out of steel while it was chucked, as you can see this test was using the headstock center. Do you think this makes a difference?

It wouldn't make a difference since the axis of rotaion of the spindle would not change.

[Harold_V]

In my experience, it would be unusual for the headstock to lose orientation. Those that offer the possibility are usually pinned once properly located. Might not hurt to explore how yours is mounted to see if it is possible to move. If it mounts on the ways, it most likely can't.
H

[GlennW]

Mine is actually adjustable with two bolts similar to the table stop arrangement on a surface grinder as the V ways do not extend under the headstock. A horizontal adjusting bolt on each side of a fixed vertical pin. The headstock must be set down on a pivot point like the work head of a universal grinder allowing it to swivel a minimal amount.

Reading RSW's post reminded me that I should check mine for squareness again and check the bed for "level", as I haven't done that in a while! I usually work with short parts and the longer stuff usually needs grinding anyway.

[RSG]

I'd suggest you extend the quill of the tailstock, then run an indicator along the side (using the carriage) to determine if the tailstock is parallel to the ways.

Good idea, I'll try that

Headstock alignment?

You can't use the tailstock for this. Best fast and easy way to determine if the headstock is parallel with the ways is to turn a large diameter piece of stock that is chucked.

Ya, I may not have conveyed myself clearly but that a what I plan to do, then go back to the tailstock after if it checks out. I hate to say it but last year I was messing around with the headstock but don't think I actually moved it but had the bolts loosened off. Now I'm concerned.

[RSG]

Any somewhat large temperature swings in your shop from when you last checked your lathe and now?

No, I'm careful to try to maintain a consistent temp in the shop. The headstock however heats up a lot during machining which I've come to learn will change my dimensions so I usually run the lathe without cutting for about 10 minutes before starting any large intricate parts.

I much prefer machining my own dead centers held in any chuck, and as long as it's not removed from that chuck, it's then as good as the bearings and your machined surface finish will allow.

This is what I did last year so I thought I needed to use the dead center in the spindle instead, I didn't think it mattered but figured I'd try it.

Once all that's correct and the bed is known to be in a level non twisted condition repeat the same turning test. At that point you "might" need to make a minor correction on the bed leveling bolts to compensate a fraction due to component deflection under cutting loads.

That's one thing I've been very conscious of all along is bed twist and check it regularly

moving the head stock would be the very last thing I'd do before exhausting every other possibility.

As mentioned above to Harold, I did loosen the head stock bolts last year but didn't actually end up doing anything and tightened them back down. Now I think they may just have moved.

[RSG]

Mine is actually adjustable with two bolts similar to the table stop arrangement on a surface grinder as the V ways do not extend under the headstock.

Same as mine

[RSG]

Also, I thought I'd check the parallelism of the tailstock to the head stock and I was shocked! The front disk was .015" smaller than the back. (See pic)

Not sure I understand that, as they are side by side. Is the headstock or tailstock end smaller?

I ask because there is a much greater chance of the headstock being rotated away from you from cutting pressure making the left disc larger, than there is of it moving toward you making that disc smaller.

The headstock end is smaller Glenn!

I'm going to do some work today based on all your comments Harold, Pete & Glenn. I sure appreciate your support and can't thank you guys enough for the advice.

I'll report back with my findings latter.

RG

[RSG]

So I finished my testing today and am very relieved to say it's only the tailstock that is out.

I started with testing the spindle with a bar and to my surprise it was with a tenth or two both times I made a cut.





I then swept the tailstock quill as per Glenns suggestion and it came out with the following:
Top - front to back - .0005" low at the front end
side - 1/10th over 3.5"



I then checked squareness of the cross slide. I'm not impress with this and want to know if it can be corrected?



Its' out .002" from the front to back (were the DTI sits)

And lastly I dressed the centers on my test bar and machined a center in the chuck and started tweaking the tailstock.



It took a while since it was so far out but I got it witnin a .0005" then pulled the bar, moved the tailstock and reset it for antoher cut and it read .0008" which is waaay better than before.



So, thanks for your help guys, I don't mind saying I was panicking thinking the worst. I still scratch my head how the tailstock could shift so much from last years tests. I guess it was out then and I just never saw it.

[armscor 1]

I use a 2" brass bar with 10 inches of stick out and very lightly machine both ends with a sharp HSS tool.
I aim for less than 7 tenths after adjusting the jacking bolts on the headstock.
My cross slide machines about a thou concave which is good enough for me.
Off course I check for level before adjusting headstock so there is no twist on the bed which has a huge impact.