Some questions:

What tooling are you using HSS or Carbide?

Is your tool on the workpiece centreline

and are you certain its Mild steel as it sounds like it's tearing?

Paul

Another book is "Using the Small Lathe" by L(eonard) C Mason. Old it may be, but it is written in simple everyday language. Borrow it from the library for an initial read, then buy it!.

Regards,

Peter G. Shaw

This may sound stupid but are you sure the lathe is not running in reverse?

Hi Myles

All the above plus you say your material is "Mild Steel" – but where did you source this mild steel and what size piece are you working on? If it's a bit of what looks like MS but is in fact a bit you picked up somewhere then it could be hard and that will give you problems, Your Colchester is a far more rigid machine than many here posess and should be able to perform well.

Cheers

Norman

Hy Miles

When I first started I stuck a piece of black iron that I got from the local blacksmith in the chuck and had the same problem. Try with a bit of bright mild or similar and a sharp tool on centre height.

Nick

I think your main problem is the cheap carbide tool.

I got a set with my lathe and threw them down the garden.

they are generally rubbish, get a high speed steel cutter and see the difference.

Roy.

Should be no perceptible shake at the spindle/chuck.

Could be the headstock spindle bearings need adjusting – something that requires a handbook/manual to be done properly.

If perceptible shake on the toolpost or cross slide, you might be able to adjust the gib strips – small strips of metal that fit against the ways and can be adjusted with three little grub screws on many lathes.

Best to get hold of a handbook/manaul first though and have a good read until you understand how it all works. See the page on http://www.lathes.co.uk on your lathe. It has a link at the bottom to a manual you can purchase.

http://www.lathes.co.uk/colchester/page17.html

But first thing is to get a good tool in place, quality carbide, new, or correctly ground High Speed Steel finished off on an oilstone and set at centre height with minimum overhang. (see those two books I recommended.)

Some pics of your set up would help.

And what model/year of Master is it?

Edited By Hopper on 19/02/2013 02:16:43

Edited By Hopper on 19/02/2013 02:23:40

Myles,

While possible I think it unlikely that the problem is due to headstock bearings or anything else that is loose. I did have an issue on my lathe (Harrison M300) where one of the bolts holding the cross slide down had sheared, but this resulted in a barely perceptible spiral pattern not a torn finish.

I would suspect that the problem is down to tooling and/or material. I'll second the advice to throw away the cheap insert tooling. If you want to use insert tooling buy quality holders and inserts. Youve got a decent lathe with some horsepower behind it, so run insert tooling fast, the chips should be coming off blue. For steel a decent depth of cut helps too, at least 1mm. It's no good pussyfooting around with insert tooling when turning steel! See here for some results on turning:

**LINK**

Try steel from a different source. I've had poor quality steel from commercial suppliers that was impossible to get a good finish on.

Where are you based?

Regards,

Andrew

Hi Myles,

That sudden change sounds suspiciously like a chipped tool. Take a close look under a lens.

I had a similar problem with a tiny inserted tool boring bar (3/16" shaft!) that wouldn't give a decent finish. It wasn't until I rotated the insert and got a good result that I was convinced the old corner was damaged at all!

Neil

Myles,

A good finish that turns (oops, there's a pun) bad is exactly what I experienced using poor grade steel.

Some metals, like aluminium and free cutting stainless, produce good finishes with carbide tooling, even at small depths of cut. This doesn't seem to be the case for low carbon steels. However, the finish is not badly degraded with depths of cut in the order of 0.25-0.5mm. I would regard anything up to about 1mm depth of cut as a finishing cut. Roughing cuts are up to 6mm, depending on the material.

If I put on a depth of cut of 0.5mm I expect the lathe to take 1mm off the diameter, so I try not to sneak up on dimensions.

Regards,

Andrew

I'm new to this lath and milling thing, but I had a smiler problem with my Bantam lathe and it turned out to be the chuck not holding tight enough do you have a different chuck to try.

Al.