Poor cutting

This topic has 38 replies, 14 voices, and was last updated 1 April 2017 at 15:16 by Curtis Rutter.

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21 March 2017 at 15:28 #289890
Curtis Rutter
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@curtisrutter61973
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
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21 March 2017 at 15:28 #8624
Curtis Rutter
Participant
@curtisrutter61973
21 March 2017 at 15:31 #289891
JasonB
Moderator
@jasonb
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
21 March 2017 at 15:54 #289895
Curtis Rutter
Participant
@curtisrutter61973
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
21 March 2017 at 16:05 #289901
mechman48
Participant
@mechman48
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.
21 March 2017 at 16:06 #289902
old Al
Participant
@oldal
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
21 March 2017 at 16:06 #289903
Anonymous
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
21 March 2017 at 16:13 #289906
Curtis Rutter
Participant
@curtisrutter61973
Posted by Andrew Johnston on 21/03/2017 16:06:53:

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
21 March 2017 at 16:14 #289907
Curtis Rutter
Participant
@curtisrutter61973
Posted by old Al on 21/03/2017 16:06:46:

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

ML7 it is, will get hold of some mild steel and attemp that
21 March 2017 at 16:17 #289908
JasonB
Moderator
@jasonb
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.
21 March 2017 at 16:22 #289910
Jon Gibbs
Participant
@jongibbs59756
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
21 March 2017 at 16:30 #289913
Neil Wyatt
Moderator
@neilwyatt
Posted by Andrew Johnston on 21/03/2017 16:06:53:

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

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

Neil
21 March 2017 at 17:05 #289918
SillyOldDuffer
Moderator
@sillyoldduffer
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
21 March 2017 at 17:09 #289920
JasonB
Moderator
@jasonb
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
21 March 2017 at 17:10 #289921
Anonymous
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
21 March 2017 at 17:53 #289925
John Haine
Participant
@johnhaine32865
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.
21 March 2017 at 18:08 #289928
John Haine
Participant
@johnhaine32865
Posted by John Haine on 21/03/2017 17:53:59:

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**
21 March 2017 at 18:15 #289930
Brian Oldford
Participant
@brianoldford70365
Posted by Neil Wyatt on 21/03/2017 16:30:44:

Posted by Andrew Johnston on 21/03/2017 16:06:53:

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

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

Neil

If he's gonna chuck it out I'll have it.
21 March 2017 at 18:16 #289931
David Standing 1
Participant
@davidstanding1
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.
21 March 2017 at 19:14 #289938
SillyOldDuffer
Moderator
@sillyoldduffer
Posted by David Standing 1 on 21/03/2017 18:16:55:

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
21 March 2017 at 19:18 #289939
Anonymous
Posted by David Standing 1 on 21/03/2017 18:16:55:

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.

In which case why aren't they all radial?

Andrew
21 March 2017 at 19:38 #289942
John Hinkley
Participant
@johnhinkley26699
Just a quick count – but I reckon that piece of brass is around 78 years old!

John

(I don't have enough experience with brass to make a sensible contribution. Sorry.)

Edited By John Hinkley on 21/03/2017 19:39:18
21 March 2017 at 21:37 #289958
David Standing 1
Participant
@davidstanding1
So here's an even more off the wall suggestion – is the tool holder contacting the brass?!
21 March 2017 at 22:19 #289961
Curtis Rutter
Participant
@curtisrutter61973
So to answer some of the points raised….in regards to some of the markings, the initial facing cuts were very light and the material had some rough saw marks on. The outer marks were caused by me attempting to turning across some of the length and not getting that right either! The tool was never dragged across the face after the spindle had stopped, I've always moved the tool away from the workpiece before turning off the lathe. Will check out the post ref angles John, Ta.
21 March 2017 at 22:23 #289962
Anonymous
Posted by Neil Wyatt on 21/03/2017 16:30:44:

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

Yes, precisely because we don't know it is brass, and even if it is, it is almost certainly not CZ108. I suppose it depends if one wants to waste time trying to machine mysterium, or move on and make something useful from known material.

Andrew
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