Tips on leveling a lathe.

D

D.sebens

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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.
 
You might need to shim the front foot and continue leveling. If the cut tapers smaller towards the tailstock then you're right - the ways are twisting towards the back bringing the tool away from the part as you move towards the headstock. Following the process on the last page of the SB leveling manual has worked for me:

 
I finally got my lathe cutting without a taper. What it took for me is buying a test bar (not expensive on Amazon) and running a DTI along it. Adjust the leveling so the DTI reads the same at each end. If you adjust with it you'll know immediately if you went the right or wrong way.

I can't recall any official lathe leveling instructions recommending that, but it sure worked better for me than using a level.

.004" over 1.5" sure seems like a LOT of taper. Are you sure there isn't something else going on?
 
Before buying a test bar, it might be worth noting that it seems the general consensus (unless my reading is off) of opinion on here, does seem to be that with test bars, there's a pretty sharp expense cliff between cheap and bad and ineffective on the one hand and expensive but good and usable on the other.

I also noticed that on Amazon UK at least, the less expensive test bars (and some of the middling expensive ones too) have enough negative reviews regarding quality that provide actual measured deviations from expected parameters to make me doubt the positive reviews.

For the needs of the 'home gamer' when levelling the bed, Rollie's Dad's Method seems to be the go-to recommendation:


No need for perfectly straight, perfectly round bar; just a bit of reasonably tidy 8" round bar and some very simple maths.

(I expect it's available as a download on here too but that was the first link I found)
 
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If you're having an issue with a leg floating off the floor shim the lathe where it connects to the base not the base feet.
 
ddickey said:
If you're having an issue with a leg floating off the floor shim the lathe where it connects to the base not the base feet.
Click to expand...

Yes, shim between the legs (cabinet) and bed.
 
There are multiple reasons why leveling a lathe is not sufficient to reduce/remove a tendency to cut a taper. This discussion has recently been discussed as nauseam in a recent thread https://www.hobby-machinist.com/threads/master-precision-machinist-level.108832/ and in previous threads. There is a lot of useful information there.

Leveling solely with a construction level is pretty much a n exercise in futility. If you don't have a precision level, you will need to use the RDM test or two collar test to make adjustments. Even so, it is possible that your lathe is absolutely level but it still cuts a taper. Headstock misalignment, manufacturing error, or wear are some reasons.

Using bed twist to correct a tendency to cut a taper will depend upon the lathe. A large industrial lathe with a heavy cast frame id different than a small bench lathe mount on a sheet metal or wood bench. Generally using twist to correct for taper involve applying enough force through the use of bolts and shims to twist the casting. When you place a shim under one corner of the tailstock, the other corners have to be bolted down to effect a twist. On a lathe with four mounting bolts on the tailstock shimming should be more or less equal left too right to avoid tilting the nose of the tailstock. The shimming differential would be front to back.

On a lathe without a sturdy integral stand, you have to realize the adding a shim under the tailstock feet also introduces a twist in the stand. you can keep adding shims and not see any change in taper. This is the reason why a sturdy stand, preferably one made of steel is used.

I did a fairly thorough discussion in this thread. https://www.hobby-machinist.com/threads/on-the-level-further-adventures-with-the-g0602.72338/ If you search on lathe leveling by me (RJSakowski) there are numerous posts on the subject.
 
Pro tip, take your time and don't force anything....

John

P.S. I don't know anything other than what I've read here but I'm pretty sure trying to force it won't end well.
 
If I recall correctly, this is an older Sheldon. Anecdotally speaking, I have found that on my 4.5 ' 1941 SB9, and 4' 1928 SB Junior 9, I can get them nicely level with a Starrett 6" level. However, I would still get almost .001" (more on the Junior) taper on a piece of 3" -4" unsupported steel (if I recall correctly). In order to get it down to less than .0001" over the same distance, I have to introduce a slight twist in the bed. I placed a piece of feeler gauge (around .015 thick) under the rear cast iron leg on my SB9. I attribute this to some way wear.

Point I am trying to make is that with my older lathes with way wear, in my limited experience, I have had to add a slight twist to compensate for the way wear. Again, this is just anecdotal with my 2 Southbend lathes, and I don't know if it is the proper way to reduce taper.
 
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