Vertical alignment of headstock and tailstock.

[PeteHB]

I have a record Coronet Regent lathe that is 10 months old which I haven't used for 5 months, workshop too cold. last week I moved it to a new workshop and spent a lot of time getting the bed level as the concrete floor has a slope. It was level when I finished with the headstock feet being a good 3 cm higher than the tailstock feet. However given the size of the bed I think that there is unlikely to be any significant deflection in the bed. This morning I decided to do the final alignment and found a vertical separation between centre points of 3mm. I am pretty sure that this was not present prior to moving the lath but it's 10 months since it was last set up when the centres were perfectly aligned. I am at a bit of a loss as to how this has happened and am wondering if I drop the headstock end will it pull everything into alignment, I would have thought that unlikely with such a heavy cast iron bed. The bases of the headstock and tailstock are clean.
Any suggestions?

 

[Orraloon]

I would look for machine leveling feet. Sitting on an unlevel surface will always cause problems. Being able to adjust all 4 feet with a spanner is easier than messing about with shims.
Regards
John

 

[sawtooth-9]

Something does not sound right
Even though the headstock end and tailstock end may be 3 cm apart, this should NOT result in the 3 mm centre difference - if the lathe has a reasonably solid construction.
Certainly, level the lathe, but if you still have a problem - look elsewhere

 

[PeteHB]

Yes it's the elsewhere that has me scratching my head. Having adjusted the feet to take account of the floor to get the bed level longitudinally and transversely I can't see any other reason for it to be out of alignment. going to have a play this morning by lowering the headstock end to see ifs it changes the relationship between the centres.

 

[ChaiLatte]

You do not say if tailstock is higher than headstock or lower. It does not really matter, but would be good to know for completeness.

How are you measuring the difference? Are you putting a centre in the headstock, a centre in the tailstock and bringing the two together?

Do whatever test you have done with the tailstock both fully retracted and fully extended. Try to verify that the tailstock barrel moves parallel to the bed.

Make sure both headstock and tailstock tapers are clean and also verify that both centres run true. Mark the tailstock one, eject it and reinstall 180 degrees rotated. Do the same to the headstock one.

Scratch a block of wood resting on the lathe bed with the headstock centre. Rotate block 180 degrees, move tailstock to right hand end of bed with quill fully retracted. See if scratch mark lines up.

Check for burrs on the bed under the headstock.

 

[Inspector]

The lathe being level does not actually matter. What does matter is that it is in the same plane. For example if the tailstock end of the bench was 100mm lower than the headstock end and the bench leaned away from you 50mm, it would't matter as long as there is no twist. Think of the lathes on big ships. The boat is moving all the time but the deck the lathe is bolted to is flat.

I think what you have done is introduced a bend, I assume you have bolted the lathe to the bench. Lossen off all the bolts holding the lathe down and see if the alignment changes. If it improves than get the bench top flat. Your level can be half a bubble off as long as it is the same at both ends. Now position the lathe and see how the centres line up. Shim as needed to correct any twist. Now if the headstock is too high you are going to have to determine if the shaft of both the headstock and tailstock are parallel to the bed or if indeed one is higher than the other. Or if one is pointing up or down. Those are harder to fix but it can be done by shimming or worst case machining. Before doing the latter if there is any warranty left get Record to correct it.

Pete

 

[Fergie 307]

Not clear from your post how it is mounted. If it is bolted directly to a wooden bench then you need to allow for some movement. I would probably simply use bolts that are a bit smaller than the mounting holes, say an M8 bolt in a 10mm hole, and large washers. It just needs to be nipped down, use nyloc nuts to make sure they won't come undone this way the bed can move as it naturally expands and contracts without stress. And the areas where it is bolted down need to be perfectly flat and level. Personally I would probably mount it on some fairly thick steel plates rather than directly to the wood. If the plates are securely fixed to the bench and the lathe nipped down into them then it can move about fractionally as it expands and contracts with temperature etc. I suspect if you bolt a cast iron lathe tightly straight onto a wooden bench you might have issues caused by the different expansion and contraction of the two materials, especially if the bench itself is not perfectly flat. You also need to be sure the bench is capable of adequately supporting the weight, if the lathe is distorting the bench itself that will not help. You might be surprised how much even really heavy castings can distort. Usually with a lathe it's twist rather than it bowing. As Pete says levelling a lathe bed is really nothing to do with it being level in the conventional sense, but rather making sure everything is correctly aligned end to end. If it has indeed bowed then you need to try and work out why, it can only really have happened if it has been subjected to some stress. As ChaiLatte says I would certainly check everything else first. It is for more likely, and probably much less hassle to fix, that your misalignment is caused by something else rather than the bed being bowed, especially if it's by 3mm, if it was indeed bowed to that extent I would expect to be able to see it with a straight edge laid along the ways.

 

[Peri]

Might give you some ideas, you'll need to watch to the end where she aligns the tailstock.

 

[Fergie 307]

Apologies. I realise now that you don't actually mention a bench in your original post. Is it mounted on the standard legs? If so I can only think, if it is indeed bowed, that this could only be caused by the legs being pulled together. Is it bolted to the floor, if so you need to make sure that it sits on the mounting easily, any tweaking to get the holes to line up is going to introduce stress that may cause problems. Oraloon is spot on, machine feet with ball and socket ends so the actual footpad can swivel a bit. These will make life a lot easier.

 

[PeteHB]

Thanks for all the replies.
It is mounted on its legs on a concrete slab which unfortunately whilst being flat is higher at one end than the other, the lathe was trued up longitudinally and across the bed so no twist. I was using two centre points to check the alignment and checked they were true in the tapers. All faces were cleaned and lightly lubricated with light machine oil.

Now the good news, yesterday I first moved the headstock and the tailstock as far to the tailstock end of the lathe bed as possible and the gap was the same. Then I moved them back. The tailstock like the toolpost is clamped with a short fixed handle that raise the slide underneath and clamps to the bed rails. It is the same arrangement on the headstock but it uses a short Tommy bar. When I was clamping up the head stock I noticed that as I gave it a final tweak I could see the headstock move. I slackened it off and brought the tailstock and centre up to the head stock and they were in line but if I really tightened or probably over tightened the headstock it it deflected out of alignment.Slackening of and then tightening with the tailstock and centres in place just to the point at which the headstock seems to deflect and then checking the headstock to see if it is well clamped showed that it was and as remains so and aligned after roughing out a large bowl.
So problem solved either I was over tightening or something was not quite right but seems to have moved in place. I will never know but suspect it was the former. Lesson learned and thanks again for taking the time and effort to respond.