Another lathe leveling question

[ddickey]

Do not use the TS when doing a two collar test.

 

[Clunker1]

Denney,
Great explanation. I understand now since you're using the tailstock after aligning it with the spindle. Others do a two collar test using a stout relatively short bar without tail stock to check for twist and then a two collar test with a bar between centers to check tail stock alignment.

Would you check for twist with a two collar test between centers or just chucked on one end and centered on tail stock end?

I like your idea of razor blade pinching with tail stock retracted and then extended to test if it is turned (yaw).

 

[rwdenney]

I do a two-collar test using an Edge Technologies test bar, between centers. They call it a tail stock alignment bar, which it is, recognizing that tail stock alignment is affected by bed twist as much as the lateral adjustment.

Tailstock Alignment Bar 27-000

The Tailstock Alignment Bar by Edge Technology is used to align the tailstock to the headstock. Accurate alignment is critical to eliminate any taper in work pieces that are supported by the tail stock. Our Tailstock Alignment Bar makes the process of tailstock alignment fast, easy and accurate.

www.edgetechnologyproducts.com

Rick “learned that the hard way” Denney

 

[gard]

I do a two-collar test using an Edge Technologies test bar, between centers. They call it a tail stock alignment bar, which it is, recognizing that tail stock alignment is affected by bed twist as much as the lateral adjustment.

Tailstock Alignment Bar 27-000

The Tailstock Alignment Bar by Edge Technology is used to align the tailstock to the headstock. Accurate alignment is critical to eliminate any taper in work pieces that are supported by the tail stock. Our Tailstock Alignment Bar makes the process of tailstock alignment fast, easy and accurate.

www.edgetechnologyproducts.com

Rick “learned that the hard way” Denney

I am not convinced that bed twist can have that much of an effect on a 2 collar test when the part is between centers. Consider if you have a long part between centers and the bed is twisted. You cut or measure the right collar with the apron all the way to the right. The apron will be mostly sitting on the twisted part of the bed so the distance from the center to the cutting tool will remain almost the same regardless of the bed twist. I can see where there could be a small change with twist but nothing like you can get by adjusting the sideways location of tailstock.
It seems like any bed twist would have more effect on diameter between the 2 collars.

The more conventional way to check headstock alignment to the bed is with a test bar which allows checking along the length in both the vertical and horizontal planes. The test bar is checked each time it is installed by rotating it and doing measurements only at the midpoint between the highest and lowest reading. Even a relatively crappy test bar can be used. Tailstock not used for this. Bed si leveled first. Rollies Dad is an example showing a precision test bar and taper is not necessary but a uniform diameter sure makes it easier.

I am not suggesting your way is wrong, do whatever makes sense and works for you.

 

[WobblyHand]

The carriage rides on the ways, along with the cutter. If there's twist, even if the stock is perfectly aligned between the head stock and tail stock won't the cut be affected by the twist?

 

[rwdenney]

I am not convinced that bed twist can have that much of an effect on a 2 collar test when the part is between centers. Consider if you have a long part between centers and the bed is twisted. You cut or measure the right collar with the apron all the way to the right. The apron will be mostly sitting on the twisted part of the bed so the distance from the center to the cutting tool will remain almost the same regardless of the bed twist. I can see where there could be a small change with twist but nothing like you can get by adjusting the sideways location of tailstock.
It seems like any bed twist would have more effect on diameter between the 2 collars.

The more conventional way to check headstock alignment to the bed is with a test bar which allows checking along the length in both the vertical and horizontal planes. The test bar is checked each time it is installed by rotating it and doing measurements only at the midpoint between the highest and lowest reading. Even a relatively crappy test bar can be used. Tailstock not used for this. Bed si leveled first. Rollies Dad is an example showing a precision test bar and taper is not necessary but a uniform diameter sure makes it easier.

I am not suggesting your way is wrong, do whatever makes sense and works for you.

Try it and let us know.

I check headstock (or, more often, the tailstock) using a bar, too. For the OP, though, a really straight morse-taper test bar isn't that easy to find, but the approach I took can be done with any bar if turned for the two-collar test.

Rick "if the bed is straight, and the tailstock centered, then one doesn't have to worry about which problem is worse" Denney

 

[rwdenney]

The carriage rides on the ways, along with the cutter. If there's twist, even if the stock is perfectly aligned between the head stock and tail stock won't the cut be affected by the twist?

Bed twist isn't linear. It's constrained on the headstock end by the headstock being clamped to it. The cutter is at various positions between the tailstock and the headstock, so the error will vary. Most of us with old lathes are already having to deal with a dip in the ways close to the headstock.

Rick "Blondihacks has a good video about bed twist" Denney

 

[Clunker1]

Had to pull off of this for a while due to a bad foot and could not stand at the lathe.

I used the facing method to align the headstock on my 13×40 enco lathe and got the variance down to below .001". So far so good. Not easy to do though since the set screw alignment can change while tightening the headstock bolts.

I did not have stock to do a two collar test for bed twist so I used Rollies Dad's Method with a motorcycle fork tube chucked in a four jaw chuck un-supported on the tail stock end. Horizintal alignment measurement indicated about .0015" difference from head stock end to tail stock end about 18" apart. The vertical alignment, on the other hand indicated a difference of .0075" over 18" down the tube. Now the vertical alignment could be due to the headstock or the bed. The bed would require shimming both legs the same but the headstock adjustment would likely require headstock removal, cleanup of faces and shimming one end.

I suppose the vertical can be corrected on a critical part wth use of tail stock? I'm not sure how far to go down the rabbit hole.

 

[rwdenney]

Work on lateral—that’s at right angles to the tool path and has a big effect. Vertical works on the tangent of the tool path aand has a much smaller effect.

Rick “who would do the razor-blade test to initially align the tail stock before anything” Denney

 

[Clunker1]

Thanks. Guess I'll start turning chips and see how it goes. This has been a great help and experience.