Poor cutting

So after finally getting the lathe set up accurately I got a chance to make first cuts on some brass I had but it's coming out like so when facing

Edited By Curtis Rutter on 21/03/2017 15:30:32

Edited By Curtis Rutter on 21/03/2017 15:31:05

Pic of cutting tool would help, hand or power fed? Speed? feed? grade of brass? diameter?

Edited By JasonB on 21/03/2017 15:32:12

The speed I'm trying to work out, excuse my ignorance but I'm still new! But this is the belt configuration. Diameter of brass is 40mm and I believe it's cz108The cutting tool

Looks like you have too coarse infeed if you are hand feeding / power x traveling; the tangential tool is an excellent tool for just about everything...but try putting a small stoned radius on the front corner to take the needle point off, or use a HSS / insert RH knife tool with a small radius on the tip...e.g. .02mm.

George.

Because brass is so easy to machine, we gwt lazy and attack it with whatever tool is set up in the lathe at the time.

Tools that cut brass do not need top rake and to get a better finish, a rounded tool is prefered. Try sticking a bit of mild steel in the chuck and repeating what you have done on brass.

If you are on an ML7 use top speed and if you are on a super 7, one down from top speed would give you a good start. assuming your lathe is bolted down

CZ108 is a cold forming brass, usually supplied in sheet form rather than bar. It can be machined, but with slow speeds and light feeds. The colour of the bar seems all wrong for brass?

Bin it and get some CZ121; it machines beautifully, hard to mess it up!

Andrew

The colouring is due to the lighting in my workshop, I assure you it's brass in colour

ML7 it is, will get hold of some mild steel and attemp that

Also if hand feeding use two hands on the wheel, don't crank away on the handle if things are not tight you will lift then lower the tool as the handle revolved upwards and then downwards. Aim for a constant feed.

I like the tangential tools very much but there is still a bit of a nack to orientating them to get the best finish.

When using the tangential tool for facing IME it's better to rotate the tool to have just a small clearance behind the cutting tip (against the face) so that the point leads or is perpendicular to the cutting "front".

HTH

Jon

Are you seriously suggesting that a model engineer, the most impecunious of all archetypes, bins a 40mm brass bar?

Neil

As I've not seen anything quite like them before, can anyone explain what's causing the marks I've highlighted on Curtis' photo please?

In Red, the parallel lines running across the diameter, one through the centre, the others offset from it.

In White, the periodic nicks around the circumference.

My guess is that Aliens did them like the Nazca lines or crop circles! Please put me right.

Ta,

Dave

I'd noticed the ones marked white and could not think what they were unles sits a scrap bit of lacquered brass and the lacquer is being flaked off.

Red could be old saw marks if only a light skim has been taken and not enough to remove all saw marks

Possibly a shallow facing cut on a previously sawn/dinged end, which hasn't entirely removed either saw marks or dings.

Andrew

Edit: Too darn slow yet again; back to machining, slow there too, but at least I'm being paid for it.

Edited By Andrew Johnston on 21/03/2017 17:12:45

Somewhere on this forum I posted the grinding angles for a tangential tool to give zero top rake for brass. You can grind a bit with the conventional angle one end and reduced rake the other, then just reverse the tool when turning brass.

Found it in this thread, third page I think.

**LINK**

If he's gonna chuck it out I'll have it.

I am guessing that the marks across the face are made by the cutting tool being dragged across the face of the brass after the spindle has stopped.

I'm also guessing that the circumferential marks are made by the cutting tool being advanced into the material when it is stationary, then the lathe is being switched on.

Excellent suggestions Sherlock! I wonder if Curtis will confirm your theory. Even if it's wrong I like it!

Ta,

Dave

In which case why aren't they all radial?

Andrew