Leveling the lathe for twist

B will not give you a reference for "leveling"the lathe. You can compare readings down the lathe but not for level just twist. Those two V surfaces are different heights measure them to the flat surface.
A would give you two surfaces on the same plane. Keep you blocks on the same side down the whole length of bed do not mix during reading trying to position in the same spots to take variables out.
 
I use method C myself. I prefer to level the lathe using the surface upon which the tool post rides. This reduces the influence of wear, mismatched blocks or whatever. I remove the compound and put the level on the chuck side of the cross slide where the tool will be located. Using this method, I can usually finalize my level with a few cuts in a 2-collar test.
 
I would use C as it is spanning the bed ways and the saddle can be cranked and you need not move the level by picking it up and not setting it back down in the exact place of the ways on the other end. I would put an equal amount of pressure on al the leveling screws and hopefully the screw in ontop of a leveling plate that has a counter-sunk hole in it. Then zero the level bubble on the head stock end and move to the tail-stock end. Then crank it back to the headstock end and read it again....then move to the tail stock end and only adjust down there. The head end will change a little so you can re-check the pressure on the plates by tapping on them with a hammer. This way you are aligning the bed using a level and your saddle will be following the same path your tool bit follows. Then you can get the final tweek doing the 2 collor method as Ben said.
 
My lathe ways are different heights and I considered using method C . It seems the most obvious and makes the most sense. But I never seen anything that said so. Now, I respect what mikey says because he has always given good advice here and seems to be quit knowledgeable. So, could you please elaborate a bit further on it. Dan S, feel free to jump in here as well as you seem to concur. Now, most of my work is within 6 inches of the chuck. My lathe is a PM1020. Two mounting bolts at the chuck end and one at the tailstock.
 
Tom, thanks for the kind words. Many lathes have front and rear ways that are not level with each other, my Emco Super 11 and your lathe included. Even if my ways were level I would still use the cross slide as a platform for the following reasons:
  • My cross slide is flat along its full length and is accurately machined.
  • It is the reference surface that I use to support my tool post.
  • It more accurately reflects and magnifies the geometry of each way in relation to the other.
  • It is quick and easy to do, and it is, for me, accurate. My level is sensitive to 0.02mm/M and sitting the level on a surface that accommodates its entire length adds to the stability and accuracy of whatever it is reading. Plus, once I put the level on the cross slide, it doesn't move until I am done with the leveling process; this eliminates any error induced by moving the level around to different spots.
Typically, this allows me to more quickly level the lathe. I admit that some days God smiles and I'm done in a few minutes; some days he doesn't smile and I can be at it for several hours. In the vast majority of cases I can level the lathe quickly and take a few quick cuts with my 2-collar bar to finalize things and I'm done. I guess what I'm saying is that this works for me and that I'm not guessing that it works; I've proven to myself that this is the best way for me.
 
While I have used method C (well like only twice that I can remember), I like to use method A cause it's quicker. Leveling for twist can sometimes be a time consuming chore. I only have a 36" between center bed but cranking the carriage back & forth gets old really quick. Especially if you have a big lathe, say like 60" between centers, I'd hate to crank the carriage back and forth from end to end multiple times.

Method A saves me a lot of time & gives me equally good results. Just pick up the level, move it over, wait till it settles. Test cuts are a part of my leveling process. After leveling I'll tweak the leveling feet with test cuts. I usually get down to 2 tenths over 10" & stop, anything less than 3 tenths is good enough for me & cause it may not last long.

I relevel my lathe once a year no matter what as part of my maintenance routine but sometimes more often. I live in earth shake country & the ground likes to move here. Anytime there's a quake big enough where I can feel it I'll relevel. Anything that helps me get the process done quicker I'll do as I hate doing it as it is.
 
Just an academic question;
once a two collar test has been done and the results are acceptable, can we not use that piece as a test bar with a tenths DTI on the cross slide for future twist checks?
 
If you mean to use a 2-collar test in lieu of using a level, yes, you can certainly do that. In order for that test to produce acceptable results the lathe must be level.
 
Tozguy said:
Just an academic question;
once a two collar test has been done and the results are acceptable, can we not use that piece as a test bar with a tenths DTI on the cross slide for future twist checks?
Click to expand...

I have done this before, but sometimes it's quicker and easier to take a light cut, after getting the test bar indicated close, rather than taking the time and care to indicate it in perfectly and just use the DTI alone (without taking a cut). Getting that test bar indicated in within a few tenths can be an arduous task. But if you did, then checking between the two collars with said DTI could help you get things true without taking a cut.

Ted
 
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