Parting off 25mm copper

[GingerLatheParticipant @gingerlathe]

For the first time I have a need to do some work with 25mm copper. I've come to the parting off stage and I can't get my lathe to part off without the typical screaming and chatter you read so much about. The setup I use works will all other materials to a reasonable degree. From what I can google, copper can be a bitch to work with. I'm using a HSS Parting Off Blade 3/32"x1/2"x4.1/2" and even with the parting off point 1cm from the chuck with minimal blade overhang it refuses to part. My lathe cannot accommodate a rear tool post and I don't have a tool bit holder to mount a blade upside down from the front. From what I have read this may be about having the correct tool geometry. I've tried a number of options with my current failure having a 5° front clearance with a 20° back rake.

Any suggestions would be most welcome.

[GingerLatheParticipant @gingerlathe]

[Chris Evans 6Participant @chrisevans6]

Some grades of copper are really difficult to machine/part off. The hard drawn ones being the worst (HDHC hard drawn)

In my working years I operated spark erosion machines and made a lot of copper electrodes. 90% of them in free cutting copper, I think sulpher was added to the copper.

[GingerLatheParticipant @gingerlathe]

To be fair, I'm not sure what grade of copper this is so it might be my own doing! Ebay special…

[J HancockParticipant @jhancock95746]

Flood lubricating with diesel ?

[bernard towersParticipant @bernardtowers37738]

+1 for WD40

[Clive HartlandParticipant @clivehartland94829]

personally I would cut with a hacksaw. then face in the lathe.

[David George 1Participant @davidgeorge1]

What lathe do you have. I suppose you have set the center height and locked the compound and saddle locks to make sure all movement is reduced. I would use an oil based cutting liquid driped on to the blade during cut. I use Rocol RTD liquid.

David

[Howard LewisParticipant @howardlewis46836]

Try Zero top,rake. It will be less likely to try digging in or chattering.

Being copper, i would try to cut dry. Any lubrication may prevent cutting for a time until the pressure builds up and then, having broken through the lubricant film, will grab. And then with the pressure relaxed, it the cycle of "rub then grab" will repeat.

Howard

[Jon LawesParticipant @jonlawes51698]

There are times when you need to be brave and part off, and times when you pick the quicker and less stressful option and grab the hacksaw! For me personally this would be one of those times. I've made a small bit of wood that fits snugly over the bed under the chuck to protect it for exactly these times.

[GingerLatheParticipant @gingerlathe]

Many thanks for everyone's reply. I'll try everyone's suggestions later today although I feel the hacksaw will be making an appearance…

[Niels AbildgaardParticipant @nielsabildgaard33719]

From what I have read this may be about having the correct tool geometry. I've tried a number of options with my current failure having a 5° front clearance with a 20° back rake.

Any suggestions would be most welcome.

Is 5 degree to little?

Many carbide inserts run 7 degree or more

[JAParticipant @ja]

I am with Clive on this one.

I avoid copper unless I have to use it (very rarely). We had a research project at work which needed a copper block with 60 reamed 1/4" diameter holes in it. The project was terminated when thousands of pounds had been spent on removing broken and jammed reamers from the block.

JA

[noel shelleyParticipant @noelshelley55608]

WHY not use a tube cutter ? What wall thickness is being used ? Noel.

[larry phelan 1Participant @larryphelan1]

Dont see any mention of a tube there, I assumed it was a solid bar.

[Nigel McBurney 1Participant @nigelmcburney1]

This may be one of those occasions when an old style parting tool is required,ie ground from a square HSS toolbit where looking at the top of the tool the sides taper slightly inwards from the front to give side clearance,parting blades do not have this side clearance and tend to rub in difficult conditions,drops of Rocol lubricant would help.

[GingerLatheParticipant @gingerlathe]

Posted by noel shelley on 26/04/2021 09:50:22:

WHY not use a tube cutter ? What wall thickness is being used ? Noel.

It's a 25mm solid copper bar which I'm beginning to regret choosing…

[Howard LewisParticipant @howardlewis46836]

Tool geometry is likely to have a big effect.

Front clearance is obviously essential, (Probably 5 degrees will be sufficient ) possibly zero top rake to reduce any tendency to dig in.

Most parting tools taper from top to bottom so clearance is there.on both sides, giving just a line contact along the sides of the newly cut groove.

I would feel inclined to start by using a fine feed, and only increase if cutting is intermittent.

HTH

Howard

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