More Questions About Tailstock Alignment

[Luminast]

I recently embarked on a project to fine tune the alignment of my lathe in preparation for my most ambitious project to date, WRT to accuracy. Previously, I've only been working to "farmer-repair" accuracy levels. Now I want to turn some parts to real fine accuracy.

I have the headstock aligned now. That was a big job, but it's done, and its nearly perfect.

I've finished alignment of the tailstock. It's about as good as I can get it, with about .001" horizontal variation when I unclamp the tailstock, move it 18 or 20 inches on the ways, and bring it back, re-clamp, and re-measure. It comes back to within about .001" (horizontally) of the same spot each time relative to the spindle, and within about .001" of matching the headstock centerline.

I also find that the tailstock centerline is about 10 to 12 thousandths above the centerline of the spindle. I've read a couple of places that this is intentional on the part of the manufacturer to allow for future wear. Is that correct?

I can understand how that vertical alignment error is not of serious concern if our turning/cutting tool is set on center, but my real question is what this means for center drilling operations. If the tailstock center is 12 thou. above the spindle center, will every center drilled hole be 24 thousandths oversize? Or will a drill tend to 'hunt' and find the center of the piece? Will the geometry of the center drilled hole still be correct to fit the tailstock center?

Can someone explain? I expect that once you explain this, the answer will be obvious, but my mind is getting twisted around the geometric implications, and I don't know which way it goes, and I can't seem to find this answer in a prevous thread.

 

[Doubleeboy]

I believe 10 to 12 thousands hi on the tail stock is quite a bit. Might take a hobbyist a life time or two for that to come down to center. I could be wrong but I thought the goal on a new or rescraped and shimmed tail stock was just a few thou hi, maybe 2-4. You could call Monarch and ask them what their spec is on their rebuilt 10ee toolroom lathe. They still rebuild them and they are extremely accurate. I spent days working on the shimming and adjusting of my 10ee tail stock. I have .002 high and pointed down as my happy medium. My center drills drill nice round holes as do my high quality USA made drills. My Chinese drills are used for roughing when I am going to then bore and ream. When I turn between centers on a 6" long 1" stock my variance end to end is less than .0001". Not too bad for a 59 year old lathe.

 

[ortho]

Luminast,
10 to 12 thousandths might sound a bit much. Keep in mind that when you turn down the work, you are normally cutting at 9 o'clock, not twelve o'clock (top dead center). If you could adjust the tailstock down where it should be (zero thousandths), it's extremely difficult to measure the change/difference. You probably will not see any improvement in accuracy effected by the adjustment.

 

[Luminast]

I believe 10 to 12 thousands hi on the tail stock is quite a bit. I spent days working on the shimming and adjusting of my 10ee tail stock. I have .002 high and pointed down as my happy medium. My center drills drill nice round holes as do my high quality USA made drills. My Chinese drills are used for roughing when I am going to then bore and ream. When I turn between centers on a 6" long 1" stock my variance end to end is less than .0001". Not too bad for a 59 year old lathe.

Your lathe sounds fantastic. Unfortuantely, I only have an engine lathe, and not a toolroom lathe. Surely the two are built to different specs. Maybe I will one day . . .

It will be interesting to see what kind of taper I get now when I turn a test bar between centers, and how that compares to your .0001". Yesterday, after finishing the headstock alignment, when I turned an 8" long by 2" barbell centered in the 4-jaw, I got end to end variance of about .0001". I'll try to get the test between centers done tomorrow and post the result.

BTW, I grew up in Eugene. Does it still rain there?

 

[Luminast]

Luminast,
Keep in mind that when you turn down the work, you are normally cutting at 9 o'clock, not twelve o'clock (top dead center). If you could adjust the tailstock down where it should be (zero thousandths), it's extremely difficult to measure the change/difference. You probably will not see any improvement in accuracy effected by the adjustment.

Yes, I understand that the vertical alignment is does not have a big impact on turned taper. I have read it in a couple of different forums that engine lathes (surely not toolroom lathes) are built with this much extra height at the tail end. I don't know if it is true, but one fellow who sounded knowledgable wrote that it would take .022" of vertical misalignment to have the same affect on taper as .001" of horizontal alignment. I think that would depend a lot on the diameter of the turning. It seems to me that a small diameter would reveal vertical misalignment much sooner than a large diameter.

 

[george wilson]

Normal extra tailstock height is .002",not 10 or 12 thou!!

 

[Bill Gruby]

The tailstock is two pieces. One upper one lower. Take them apart and check for shims, yes it does happen.

"Billy G"

 

[w9jbc]

could it be possible that the tailstock was not a mate to that particular serial number? I know on screw machines all the drill saddles are bored and stamped with a machine serial number.

 

[Doubleeboy]

Your lathe sounds fantastic. Unfortuantely, I only have an engine lathe, and not a toolroom lathe. Surely the two are built to different specs. Maybe I will one day . . .

It will be interesting to see what kind of taper I get now when I turn a test bar between centers, and how that compares to your .0001". Yesterday, after finishing the headstock alignment, when I turned an 8" long by 2" barbell centered in the 4-jaw, I got end to end variance of about .0001". I'll try to get the test between centers done tomorrow and post the result.

BTW, I grew up in Eugene. Does it still rain there?

Still rains in Eugene. The Pineapple Express is here for the weekend, very warm and we are expecting 3 inches of rain. Good Luck with your lathe. Its always a challenge getting a new lathe dialed in.

michael

 

[Luminast]

The tailstock is two pieces. One upper one lower. Take them apart and check for shims, yes it does happen.

"Billy G"

I've had the tailstock off and apart this week already, as it was not moving freely side to side, perhaps from not being adjusted for 25 years. (Actually, what I mostly found was that I was not able to adjust side-to-side because I did not fully understand how the various parts were holding it tight. Once I understood that, it now moves easily, and then still locks tight.) There were no burrs, or ridges, or wear of any kind that was apparent. Still shows nicely frosted scrape marks. The lathe is a 4800-pound Webb-Whacheon 17x40 with almost no signs of wear on any surface.

It sounds like this situation needs some more investigation. Thanks for all suggestions.