Levelling a lathe..yes that old chestnut again

Edited By Jon Cameron on 03/03/2018 17:35:42

By "bolt it down" do you mean bolt the feet of the bench to the floor? If so, slide a feeler gauge under each foot first and if there is any measurable gap there, slide a U-shaped piece of shim that same thickness in around the bolt before tightening it down. This way the bench is not under tension and will not tend to distort the lathe bed bolted to the top of it as the bolts are tightened into the floor.

Position of compound slide is not important for this test. It is best if it is locked in position, either by locking screws or by tightening the gib screws if no locking screws are fitted.

Your piece of tube sounds like it will suffice for a turning test under light cuts. How much taper do you have over the 100mm length?

Edited By Hopper on 04/03/2018 07:32:21

Mak.e sure your test cuts are very light and using a very sharp tool. You might be surprised how much the work bends under the cutting load if the tool is at all blunt. A finely honed HSS tool is probably best.

Russell

Hello, well ive just managed to get a slight improvement by changing to my 4 jaw chuck, as my thoughts were, the lathe has come from a school, so i don't know if it has suffered any abuse, i have got better results but still a little bit of taper, (larger end at the chuck) from memory i had the 28mm did tube sticking out about 75mm, (my 4 jaw is 250mm dia... think i got 25.34 tailstock end, 25.56 next to the chuck... i still need to bolt the lathe down and shim the feet, but this will have to wait till this week

Chris, I don't think you will get a result with all these turning tests until you have a firm foundation to work from i.e. the lathe is in it's final position and the cabinet stand bolted firmly to the floor. Only then can you start to make adjustments, if necessary, by shimming the lathe feet. At the moment any changes you make will simply distort the stand to fit the lathe!.

John

Like John says, even bolting the lathe to its stand will give you variations, in fact I when I bolted my lathe to its stand I had to take multiple cuts and adjust the tension on the bolts to get it to cut within an acceptable tollerance.

I recently did a test cut having left my lathe all winter in the dark shed. (She was tucked up). I was 2thou out. Will adjust one of the feet my ML4 is setup on and hopefully get it a little closer, the tenth of a thou is approxmate I can only measure 1thou with my dial indicator.

Quite impressive, but the surface finish doesn't look so good. I think I would attend to surface finish before I made other adjustments for run-out.
BobH

Why do you use a dial indicator to test for parallel turning? I thought the test was turn both parts of the bar and use a micrometer to measure.

I am not quite sure that you can measure a taper using a dial indicator, surely if set in the toolpost it will simply follow the same path as the toolbit and therefore will show no difference from end to end as the carriage is moved. You would normally measure with a micrometer or at a push with a dial/vernier/digital caliper. Once the lathe is turning parallel then a dial indicator could be used to make measurements.

John

Edit: Typo

Edited By Journeyman on 22/03/2018 09:39:32

I'm sorry to have to agree. That finish is appalling. To such a degree it probably affects "tenths" in a reading.