Hi,

I have a Clarke CL500 lathe which sits on the stand (also provided by Clarke and the right one for this model) on a concrete floor. I've been trying to eliminate twist in the bed by shimming up one corner of the lathe. The stand is made from sheet steel with welded and bolted construction.

my problem is that when the corner of the lathe is shimmed up, the stand rocks on the concrete floor. The stand sits pretty flat, without rocking, when there are no shims used, but then there is a slight twist in the bed.

Should I bolt the stand to the concrete floor? Has anyone any recommendations of the best way to tackle this? I had thought of adding weights to the stand, might this be enough?

i think the twist is quite small but as the corner of the stand lifts, it needs a big shim to affect the lathe bed by a small amount.

the lathe is firmly bolted to the stand, and I have slackened/re-tightened all of the bolts in the stand itself.

thanks!

Tony

Many thanks to you all for your replies and thoughts, all very much appreciated.

The stand is quite flimsy and what I think is happening is that the lathe, being heavy cast iron construction, pulls the stand to conform to the shape that the underside of the lathe has. The amount of twist in the bed is quite small and this is noted with a bar held in the chuck at headstock but not supported at tail end, just making DTI measurements along the bed.

To eliminate the small amount of twist in the bed (only a few thousandths – I forget the exact amount), I've put shims between the lathe and the stand. What seems to be happening is that this bends the stand a lot more than it bends the lathe. The net result is that one corner of the stand lifts off the floor, making the whole think rock when given a push.

Even though the twist reads only a few thou, it needs a stonking great shim (2 mm) to eliminate it, again I think this is because the stand hasn't got the strength to fight against the lathe stiffness, so the lathe more or less stays where it wants and twists the stand, unless the shim is big enough to put some real stress into the stand.

What I think is needed is a way to prevent the stand from lifting one corner (preferably preventing it lifting any corners at all), which is why I thought of bolting it to the floor or weighing it down. Then, when shimmed, the lathe will have to twist itself or twist the stand together with the garage floor as well, which is considerably heavier and not very flexible at all.

I don't really want to move the lathe off the stand as it weighs so much, otherwise reinforcing the stand could be a possibility.

I think I'll have a go at bolting the stand to the floor and see if this improves things. I'll post the results when done.

Tony

Hello Nick

You ask if I'm sure the bed is twisted. The truthful answer is "no". What I am doing though is attempting to set up the lathe for turning parallel, as described by Harold Hall in his book "Lathework – a complete course". In the book, and in numerous YouTube videos and other on-line sources, methods are described whereby a check is made that the tool cuts the same diameter when it is both near the headstock and when moved via the carriage to near the tailstock end (no tailstock used). The suggested cause of inconsistency here is that the lathe bed may not be aligned for best result, and that by putting deliberate movements onto the lathe bed, the ability to turn parallel can be adjusted. None of that means, I suppose, that the bed is actually twisted – the headstock could perhaps be a bit out of line and I might be effecting a compensation for that.

What I do know is that the mean value of the DTI moves as the carriage moves, and I'd like to eliminate this, if I am to complete the project in the book.

There is considerable run-out which is also greater at the tail stock end than at the head end. That's why I'm going off the mean value for assessment of parallelism. Once I've got the bed sorted, I'll see if I can reduce the run-out. I have a 4 jaw independent chuck with which I can pretty well eliminate run-out, but the DTI reading still changes as the carriage moves along.

The bar came from a printer, it used to have a rubber sleeve over it as a support for the paper when the impacting through the ribbon. It's not a special test bar but is beautifully straight, smooth and parallel according to my micrometer. I was glad to get this useful bar out of the printer, which was being scrapped.

Tony