Screaming brass

Just a simple question - When turning brass, why does it scream?

I apologise if this has been asked before.

JA

Good question!

I would guess it's because it fractures into tiny similar-sized chips that can set up a vibration, rather than longer swarf.

Interested in other people's ideas!

Neil

Leaded brass is the type that can be noisy, and those tiny chips are worse than cast iron dust.

.

I think you are essentially correct, Neil ... but also that the problem can be exacerbated by inappropriate rake angle. Brass is usually 'happier' with either zero or negative rake.

MichaelG.

Yes, perhaps you are making it 'unhappy' JA.

IanT

I accept that. I am cutting it.

I use a very slight positive rake. This cuts well and cleanly.

JA

Edited By JA on 04/09/2019 22:37:24

I've just found this old thread from 2012, which might be of interest: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=65244&p=1

MichaelG.

Hi. I turn brass pretty much every day and have never ever had it make any noise - nothing. I can only assume its a special grade or that your tool is rubbing not cutting. I find tips for steel useless as they sheer rather than cut, prefering very sharp inserts instead. Im making a batch of chimney collars today, all brass.

fizzy

What grades of brass do you use?

I have always expected brass to squeal or scream irrespective of the lathe. However I am beginning to realise most of my experience is with CZ.121 bar (leaded free cutting brass).

JA

JA

Its cz121, it gets used on my boilers for burners and chimney parts and I use a lot of it up to 3" diameter down to 1/4" diameter. It honestly never makes so much as a squeek and I sometimes run it extremely hard in terms of cut depth and feed (you know its OTT when the 3/4" boring bar starts to bend!). What I have learned is to cut it at a relatively low turn speed. Ive got a fixed high speed lathe which refuses to cut brass. I now always use ccmt super sharp inserts, they cut very cleanly. If you are near me I would gladly help you resolve this issue hands on?

Nigel (Pendle Steam Boilers)

Perhaps the younger members are more ‘prone’ to notice this phenomenon?

I cut brass at times and rarely have had more than normal chatter at extremes of the cutting envelope.

But, there again, I am oblivious to anything much over 8-9kHz, probably due in part to shooting, driving D8 Caterpillar earth movers, working in an extremely noisy industrial environments, along with probable genetic and age related hearing impediment!

I was often dragged in as the college ‘dummy’ when audible range (and colour blindness tests) were carried out for the student’s demonstrations! The physics and biology GCSE tutors would carefully organise those lessons for when I had free time, if they could!

Have you tried reducing tool protrusion or increasing its thickness or stiffness to reduce the risk or resonant micro-deflections causing the squeal?

I've certainly heard brass squeal but if I do it's because summat ain't right, and I'll fix it before carrying on. IME rake angle within normal limits for general use doesn't make a lot of difference, although a zero rake platform on twist drill lips cut the risk of snatch on breakthrough. I can't readily think of a case where it hasn't resolved to a rigidity issue and/or a blunt/rubbing tool edge.

I'm minded to think of Kundt's Tube which relies on a brass rod and a rosined cloth.

Neil

If i am looking for a mirror finish on brass off the tool i use HSS with either zero rake or negative rake for an even better finish still. If not being quite as fussy on finish but still a very good finish indeed or roughing down brass i use the excellent aluminium inserts.

Many thanks for the comments.

As already stated I do not have a problem machining brass. It is easy and the finish is good to excellent. It is just the noise.

When I have a spare moment on the lathe (not in the next few days) I will put a 1" diameter bar in my biggest four jaw chuck and take a number of 0.030" deep cuts using my existing tool (left hand knife with about 5 degrees of top rake) and a similar zero degree top rake tool at various speeds and tool overhang. Photographs of the finish will be taken and I will report back.

I don't really want to spend time on this since it is not a problem!

Nigel, thanks for the offer but I am just outside Bristol.

JA

Edited By JA on 05/09/2019 17:26:36