You should take a spring pass.
I did on retracting the carriage. Plus the dimension was smaller on the tailstock side. That cannot be caused by deflection as that end was unsupported..002 at slowest feed. No spring pass marks when cranking handle back.
this would be my strategy. If it is twisted it takes time, you cannot rush, if you believe it is twisted support the head stock end off the table a half inch or so and place another support the same thickness under the front or the back based on which direction it is twisted then ad a little extra weight on the opposing side. Check it daily, it will relax gradually provided it wasn't twisted when is was originally machined and doing it this way will insure it stays flat.May of made some progress! I previously maxed out adjusting the cabinet to the point of looking like it will rip itself apart. I decided to shim the rear tailstock end casting again. I’ve got it down to 4 thou at 16” and 1 thou at 8”. Clearly it’s not linear from bed wear I’m guessing. I’m going to let it sit like this over night and see if it changes. If it doesn’t should I see if I can add a little more shim to it and bring it closer?
Fingers crossed that the bench can hold back the shim I put in and it doesn’t stress back
Also I’m having trouble visualizing it will the 4 thou difference cause the part to be 4 thou smaller or 8?
Is the taper in the same direction at both 8" and 16"? If so, tweak it a little more to flip the direction of the taper at 16". you should be reducing the taper at 8", hopefully to under .001" while not introducing a terrible taper at 16".I think we made it boys! I’ve got it down to 1.25thou in 8” and .0002” at 16. I would love to bring 8” in at the expense of 16 going out but to get the 8” measurements in it would really throw out the 16”. I can change the end quite a bit with minimal change at 8”.
Unfortunately its a hump. 0.00 to -1.25 to +.0002Is the taper in the same direction at both 8" and 16"? If so, tweak it a little more to flip the direction of the taper at 16". you should be reducing the taper at 8", hopefully to under .001" while not introducing a terrible taper at 16".
Knowing what your lathe is actually doing, you can make some dead reckoning corrections while turning to get your desired results.
Few things come to mind. Some may not apply since they are already checked.Hey all I am trying to level out my sheldon lathe. I dont have a precision level, I figured I would use my construction level to get things close after placing the lathe. I am "close now" but I have ran into a problem, I cant seem to get the twist out. I mounted a level on two flat surfaces of the carriage and moved it from end to end. I am using the adjusting nuts on the cabinet(steel desk construction not cast) and have gotten to the point that I need to raise the rear leg at the tailstock but the front leg at the tailstock is currently floating. I dont have a test bar or even a long piece of metal to play with to see but I did turn a patch on a bar about 1.5 inches long and got 4 thou of taper. It tapers smaller towards the tailstock end. This was done unsupported with a 1-2 thou cut at the slowest feed. This is repeatable on cuts.
This leads me to believe either the front tailstock adjuster needs to lower or the rear needs to raise but it is currently floating on the front. I suppose I could bolt down the front leg to the floor? Right now I left it floating so maybe it wants to relax itself down while resting.
Most of what I do isnt "high precision" its always as precise as it needs to be. But 4 thou seems like a lot. I have a ram from a hydraulic cylinder that is in good shape but scrap. I am thinking of measuring it to see how consistant the size is and if reliable chucking it up as a test bar equalize runout along the bar and use a indicator on the carriage to sweep it and see if the issue is just bed wear near the front or real twist. I have basically confirmed it is bed twist as I cant get it level but figure I would get more info.
So after all that mess of words I am hoping for some advice on how to level it more and if my thought on the test cut matches my thoughts on which leg needs to move which way.