I,ve had my super 7 for about thirty years it,s never moved and it,s bolted to an angle iron stand

Concrete and steel have very similar cofficients of expansion. Lucky, that, or a lot of reinforced concrete would not survive long…

This is a guess!

You are adjusting the lathe by twisting the lathe bed. The bed stores energy like a spring and will return to 'normal' if it possibly can. The problem may be that time and vibration gradually move the lathe, shimming, and/or stand such that the lathe bed relaxes and goes out of alignment again.

If so the cure might lie in finding out why the lathe bed needs to be corrected in the first place.

The problem may not be with the lathe at all. For example, if the floor or cabinet base aren't flat, then firmly bolting the cabinet down will twist the cabinet out of shape. This in turn could upset the alignment of a lathe balanced on top.

Some detective work is required.

Or:

Occasionally threads pop up questioning the need for lathes to be installed level. Some recent reading suggests that levelling isn't done because lathes 'must' be level. Rather, the installation process of any structure uses levelling at each stage as a way of ensuring that all the parts are fitted in proper alignment. Unpredictable things happen if they aren't.

It's much easier to get alignments correct when everything is orientated with a common reference like a level. You could try the same: make sure the floor is flat; make sure the cabinet base is flat and evenly seated on the floor; make sure the cabinet sides are vertical and the top flat; make sure that alignment is maintained when the bolts are tightened; make sure the lathe sits flat on the cabinet top. Then apply any shimming needed to get the lathe spot on.

Good luck,

Dave

I leveled the 2 lathes I have 15 years or so ago, checked them now and then but no movement at all. They stand on non reinforced concrete on sand, with ground water level at around 10 m. Niko.

The words "bolted securely to a concrete floor" ring alarm bells. The manual for my lathe (a Viceroy) details that the anchor bolts should be finger tight. If the lathe is pulled down hard onto a concrete floor then there is a good possibility that it will twist everything. Think about it, if the floor is out by just 1mm over the length of the machine (and how many pieces of concrete are this level?), then pulling it down hard can transfer this into the bed of the lathe. The anchor bolts are only there to stop the machine from falling over and don't need to be tight to do this. If vibration etc is a problem then use a rubber or similar pad around the anchors.

Edited By Martin Cargill on 05/11/2016 10:55:54

The concreter floor is moving,small lathes should just sit on the floor i.e. not bolted ,if the lathe continues to "move " try mounting it on three pads,precision tools such as grinders only have three pads cast on the bottom of the machine ,with three pads it is bound to sit down without rocking.My myford has sat for 40 years on a home made sturdy timber cabinet, with a 7 inch wide length of channel iron mounted on top under the tray,the iron is very stable and is stiff enough to align the bed as per Myford instructions i.e. adjust it at the tailstock end. My large Colchester 7.5 in does suffer from alignment problems as the clay subsoil does move and the sheds concrete floor is a bit thin,I never thought I would have such a big lathe,the solution to this problem would be to dig out about 1 ft and make a "floating " base of reinforced concrete but I have got past it. The instructions for my surface grinder state that for the best operating conditions a it should stand on a concrete block 2 ft thick. A large Cincinnati Cnc mill I was involved with years ago sat on a concrete block 4 ft thick.So do not bolt a machine tool down to floor which is not stable,let it float.Unstable machines such as drills & power presses are bolted down as they are top heavy.

The cabinet is not rigid enough. I doubt if any modern ones are really. Lathe beds are pretty stiff things. Sheet steel plus bits of angle iron aren't and will give over time. The lathe wins eventually. Really the technique is from days when lathes were mounted on very stiff and rigid cast iron cabinets of one sort or another. Those days from what I can see are long gone.

John

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I may have overstated the problems a little but this gives some idea of the amount of correction that may be needed.

If it's any more than these sort of figures suggest it may well mean that the bed is worn or the headstock is out of alignment. Bearing wear / looseness will also cause taper – similar to the bar bending when cutting – larger towards the end. In short the lathe aught to cut to 0.001 / ft as it comes freely mounted and that is all the bed stressing is intended to fix. I have my doubts about if it will last though. Even I beams take a set eventually under their own weight.

What I would do if it was more than this and not due to wear is look at the headstock alignment first. 7's have some cap head screws coming in from the side which should allow minor adjustments. I'd guess if people have a lathe that doesn't meet these sort of figures there is a "problem" some where. It doesn't take much of one to exceed 0.001 / ft.

John

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I am amazed to read some of the methods to get a lathe to align, a small lathe does not need bedding down on concrete. With a stand just level the bed both ways and get rubber pads to fix to the stand first.

If you had a 14 foot bed lathe then, I agree that you need hard standing. The same thing applies to a mill or a shaper, their own weight is adequate for stability on the sizes that model maker work with!

Bolting down should be that the head or nut slightly clamped and backed off half a turn, job done. Why all the finesse. A good way to disperse ground force from a machine is set it down on lead sheet where it contacts a hard floor. All my optical stands were set on 2 thicknesses of lead sheet and after setting never moved, I worked to less than a half sec and a Collimator set and tested stayed the same year in year out.

Spend a bit more time turning or milling instead of fussing about where the machine is walking.

Clive