Datum for Lathe Leveling

That would make sense if you had a lot of twist in your bed. Until gravity worked on it you would have 2 feet off the ground.
 
The lathe bed was ground lengthwise on all surfaces in one setup at the factory. All the ground surfaces are parallel after grinding. Find areas that do not have wear from use on them and you can use those for reference surfaces after cleaning and deburring them.
 
By using the top if the ways, you make the assumption that they are in the same plane and parallel with the ways. Since those surfaces only function is to provide clearance for the carriage and tailstock, that is a bit of a stretch. It may be ground but that may just be to look pretty. To be useful as a datum when using a machinist level, the tolerance should be sub-thousandth.
As has been pointed out by others on this forum, an uncalibrated surface plate, square, or straight edge is of diminished value. Before using those surfaces as datums, I would want verification that they are true.
Those surfaces on a G602 are definitely not in the same plane. The tailstock vee ways are smaller than the carriage vee ways. I use a pair of 1-2-3 blocks as risers on the flat ways and my measuring points are close to the headstock and the far right of the bed where there is no wear.
 
ddickey said:
I think what I'm going to do try to get all six feet to bare load. Take some cuts and see where I'm at.
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That sounds like a good plan. In the end its all about making a a straight cut. If the machine has wear in the bed, the level might not get you where you need to be anyway.
 
I decided to level my Sb 13 today.
I don’t have a precision level. I do have an accurate construction level.
The way I approach this is, it’s better than nothing.
I observed something interesting. Cast iron moves. I watched several YouTube videos on how to do it.
After about an hour of doing my best, my construction level showed a decent days work.
I checked later, the day is warming up, all four bolts are touching and the level is right on.
I used the best surfaces I could find, ways at several points proved my level is just not sensitive enough.
I will continue to look for a real level, they are expensive. I see the imports run about $125-$175 for a 12”.
I do feel better though, I have been reading through, Machine Tool Reconditioning, the section on leveling does mention, permanent damage can occur if a precision tool is left too long un balanced/leveled. I’m paraphrasing here.
I have been chasing a taper, maybe this will help.
 
Have a look at 'Build something cool' on the you tube. has a simple pendulum level very simple and accurate. Then,(opening can of worms), try Rollie's dads method to check alignment.
 
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