Problem turning copper.

Hello all.

Been turning some copper sleeves today, no problems until I came to turn the last one tonight,

When I came back to the machine to start the last one, touched the tool on the grinder to restore the edge, same as I have done many times before but the finish is awful, material just tearing away,

Machine is a myford 7

thank you for any advice you could offer.

Edited By Brian Abbott on 01/06/2014 23:12:57

hi brian,

tool looks fine for copper but think the side cutting angle should be much less ie negative instead of positive, and less end cutting angle. hope this makes sense.

ive done a fair bit of machining copper recently.

cheers,

julian

Brian,

I think I'm basically saying the same thing as Julian:

It looks like you are using only the extreme point of the tool. ... If you have literally only "restored the edge" then the basic shape should be right [it worked before]; so I would first try moving the tool a couple of degrees anti-clockwise [as viewed in your photo] ... the cutting action needs to be "slicing".

The other possibility is that the tool is now a few thou' low, and is digging-in a little.

MichaelG.

Hello both,

Sorry have just confused myself, 

If I draw a line from the point of the tool back towards me, them rotate this anti clockwise from the point, would this be the correct line to grind the tool back to, ?

i have downloaded a drawing and added it to be album but this does not seem to be right.

thanks for any help

Edited By Brian Abbott on 02/06/2014 00:37:58

First thing is you have no nose radius, you are cutting with a sharp corner so you will get tram lines.

Next thing is and I'm going to get slaughtered for this is I reckon all the books are wrong on copper. They always say no top rake or 5 degrees max but years ago I used to make laser cutting nozzles, that many I even bought a brand new Myford C7 capstan to do them on.

Getting these right was a steep learning curve to be fast and make money. Two things I found really helped and none was in any books.

First the top rake was ground at 30 degrees, side rake was 5 to 10 and the edge had a radius honed on.

Second I ran on neat soluble oil, no water added at all and within a few hours this oil had turned green from the copper.

That job and lathe has long gone but I might still have some tools left as I used to grind a few up at a time so if needed it was only a tool change and not wait to regrind. I'll look tomorrow.

One thing that I have since found that confirms this, is that there is a dedicated service industry for the motor rewind game, generic fans, bearing sleeves, new commutators, brushes etc.

One of the things they offer is reground lathe tool tips in various formats for skimming comms. Just a normal brand new tip that has been re profiled on a diamond wheel to suit comms and the main feature is that the top rake is 25 to 30 degrees approx.

Thanks again,

need to educate myself on tool grinding and fully understand the terms used I think..

.

Brian,

The confusion is probably my fault, not yours

All I was suggesting was that you reposition the existing tool in relation to the work ...

That said; John is of course correct in pointing out that the tip should have a slight radius.

MichaelG.

Edited By Michael Gilligan on 02/06/2014 06:39:00

Brian,

I've just found this handy crib-sheet

... probably worth putting a copy near the grinder.

MichaelG.

You just can not have the tool too sharp to cut cooper. It does need a nose radius unless you want to feed it very fine. Some grades of HSS just do not hold as sharp an edge as others. Just like some grades of carbide do not hold a sharp edge. Using a fine hone stone makes a very big difference when turning soft materials.

Making a guide up so the stone is not rocked as the edge is being honed is also a big help in getting the tool sharp. When you look under a powerful loupe at the cutting edge you will see the various marks from grinding and the hone. Getting it as fine a finish and smooth makes all the difference. It should look shiny to the naked eye.

They now make carbide inserts with very high positive rakes for copper, and they are very shiny on the surface finish, and expensive.

Vege oil like canola or olive oil works very well with most materials including copper.

When everything is right, you do not need it to be going really fast to get a good surface finish.

Neil

Quick thank you to everyone.

Ground the tool as instructed in the link supplied by Michael, did the trick a treat.

must have been a lot more heavy handed than I thought.

thanks again..

Brian

Edited By Brian Abbott on 02/06/2014 22:23:46

Nicely done, Brian

That looks good.

MichaelG.

.

For your reward, you may now watch this

Hello Michael,

Just watched your link,

I think my 50 year old S7 would struggle but just shows what can be done.

I remember as an apprentice doing my spell in the machine shop I had a job which included tapping 5/16" whit holes in copper. I think I broke 18 taps!