Very high positive for copper
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    Default Very high positive for copper

    I machine a lot of oxygen free high conductivity copper that is very gummy. I found a few of these very high positive 1" shank tools and wonder if anyone knows of a source for them. I'm on my last one. They are the only tools that really work for turning this copper. The bars of copper are 3 1/4" dia and 42" long and finish at 3.000" with a finish for "O" ring sealing. The mat'l is over a thousand per piece. Any other cutter has a tendency to quickly gum up and dig in, creating a deep pit or groove out of the blue when turning. I'm using the high Sulphur dark cutting oil. I am not allowed to weld or fill a defect and even with a lot of cutting oil it is scary watching it cut, knowing any second it can grab and destroy the part. I trust this cutter in the picture and need several more.
    Attached Thumbnails Attached Thumbnails img_20200530_064025965copper.jpg   end.jpg  

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    What's the tool? .HSS? Carbide?

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    Quote Originally Posted by Limy Sami View Post
    What's the tool? .HSS? Carbide?
    I could be wrong.. VERY wrong ... not the best fotos, even "zoomed".. but are we looking at a brazed HSS-Cobalt... or even a Stellite .. rather than brazed Carbide?

    Cost of the workpieces, I'd be using such as a "solid" Tantung-G instead.

    And as a "tangential".

    Much easier to do a consistent "extreme rake" ..sharpen & re-sharpen it...and still be as predictable-rigid as some flavour of religious fanatic.

    Not to forget, serious pos rake wants to draw the topslide into the work! And/or draw the work into the tool. Gots be be beyond "razor sharp" to keep it cutting, not digging..

    Serious-challenging Copper work is. ISTR some folk even cryo-chill it whilst in the cut.. much like workin' certain non-metallics?

    Others might not "single point" it for grooves and such at all. Live-tool a saw-tribe cutter at it, rather.

    Copper - especially when optimized for Electron-pushing has ALWAYS been a right BITCH!

    Was busting some very competent English chops for multi-cavity RADAR magnetrons.

    Yanks cheated. Stamped a whole stack of THIN high-precision laminations. Furnace-brazed the stack.

    And we had 1940's "mass production" to put SHORT rather than LONG wave RADAR to work. More portable, that way, as it were..

    2CW

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    Looks pretty simple to make, whether HSS or carbide tipped. A little time on a mill for a steel blank for brazing, or a large piece of HSS and send it out for wire edm if you don't want to spend half a day grinding. I think I'd try one tipped with PCD (polycrystalline diamond).

    What rpm and depth of cut do you use? I've seen a similar operation where the rpm was pretty slow, maybe 30 rpm. The chip came off unbroken, and the operator coiled it into a box while it was running.

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    Quote Originally Posted by gbent View Post
    Looks pretty simple to make, whether HSS or carbide tipped. A little time on a mill for a steel blank for brazing, or a large piece of HSS and send it out for wire edm if you don't want to spend half a day grinding. I think I'd try one tipped with PCD (polycrystalline diamond).
    Can't argue with the PCD. Surely should last a long time!

    Just happen to have the Tantung layin' in the drawer..

    In fair-sized rectangles.

    Meant to reduce risk of wreck-tangles.

    Fair-decent at not bonding non-ferrous to itself as it does its work....

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    Machining copper contact bases and annealed 97% silver, 3% copper contacts, I got a lot of practice at cutting gummy materials. I agree with the high rake, large clearance, and as sharp as you can get it is still not sharp enough. Never give the tool a chance to rub against the copper because your primary enemy is buildup on the cutting edge. Another feature that seems to be the case in your bits is giving the chip a place to escape. No chip breakers! you can have a chip curler as long as it is a gentle continuous polished curve to allow the chip to slide easily over it.

    Another large factor is the coolant. Contrary to usual practice on things like steel where high film strength is undesireable because you don't want the cutter to skate on the surface and cause work hardening, the soft material is easy to penetrate, regardless of film strength and the higher it is, the less likely to allow buildup. We wound up using a Mobilegear lube, I would have to look up the number, which we had to lubricate the gears on a sheet roller that had very high pressures on the gear teeth.

    Another suggestion, you might try a coolant nozzle under the tool aimed up into the cutting edge.

    Bill

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    The ones pictured are brazed carbide, but now that I think about it, HSS is probably the way to go here. Easy to get the extreme angles and copper is forgiving for wear. Another thing, the 42" long 3" bar has to have a 2" hole bored through it and the part has a tendency to chatter due to harmonics when putting the final od finish on it. I took a piece of thick walled rubber hose and pushed it into the hole and could hardly believe how much it dampened the vibration. Two pieces of the copper side by side, one with the hose inserted and one without, when tapped with a hammer, one would ring like a bell and the other sounded like you were hitting a piece of lead. It was a dramatic difference. Before the rubber hose, I would dread hearing the sound of the part beginning to ring on the final finish cut.

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    Bluechipx - some thoughts

    I'd polish the top rake of that tool as much as I could - I'm thinking fine white Arkansas stone like ''polish'' ...and also hone the ground cutting edges with a similar oil stone, ............….the smoother and sharper the cutting faces the les friction and change of a pick up.

    Machining tubes, ...BTDT and I feel your pain, ………….loading the rubber hose ''trick'' with lead shot is another vibe killer.as is replacing the hose with a piece of rectangular or square wood that just fits across the corners, ...and again more lead shot to fill the gaps.

    Plasticene (playdoh) makes a good ''bung''to hold the shot in

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    We also used to machine oxygen free copper using conventionally recommended inserts.
    Two things cut machining time by a factor of 1/6th.

    The first was a recommendation for "Shear Geometry" inserts and holders.
    Shear Geometry(R) Cutting Tools
    The depth of cut and especially feeds were unbelievable. I've talked before here about this, the CNC lathe enclosure sounded like a gravel storm driven by a tornado inside, the size of the chips went from thin twisted birds nest type chips with the old tooling to what looked like nothing like conventional chips but instead like gravel, big pieces of copper gravel.
    The biggest problem I've had with these inserts is getting employees to use Robinson's feeds and speeds, it goes against normal common sense.
    The other problem is that feeds of .035 per rev tend to push the bar back into the collet, we went through a game of increasing collet pressure, then feed, then pressure etc. Looking back on that time I think we were ignoring the fact that as the diameter gets smaller the helix angle increases and we were pushing the tool beyond its relief.

    Next was a material changed to tellurium copper, quite a bit more expensive but savings on machining time made it far cheaper. If the customer can accept tellurium you will never look back at nasty oxygen free pure copper. Tellurium copper actually worked against our best use of Shear Geometry inserts because it has 6-10% tellurium (or close to that) that allows the chips to break much MUCH easier, so my operators backed off to closer to normal feeds and speeds and got away with it.
    SG inserts also work well with aluminum alloys.

    Sorry to sound like a salesman but the change to SG really opened my eys and filled both the customers and my own bank accounts.

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    I can see many of you have real world experience with copper, insanely sharp and polished tools really make the difference. Carbide with the standard honed edges and negative rake are instant disasters with copper. I can still recall my early learning days machining copper, everything going smoothly then the sickening sound of the drive motor loading, followed by a horrible buildup in front of the cutting edge and another scrapped part. Yuck!

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    Quote Originally Posted by Bluechipx View Post
    I can see many of you have real world experience with copper, insanely sharp and polished tools really make the difference. Carbide with the standard honed edges and negative rake are instant disasters with copper. I can still recall my early learning days machining copper,
    Aye. Main reason I prefer to work it the way the ancients did.

    With a hammer!

    OTOH? I've been accused of being outright queer for some of the Bronzes!

    Loved working Nickel-Aluminium-Bronze back in the '60's with my HSS-Cobalt near-as-dammit microtome blades.

    Because I could.

    And others - neg-rake Carbide lovers who were carelessly indifferent HSS End-Losers - thot' if it looked like Brass it hadda WORK like Brass.

    They just "didn't GET it." It got THEM, rather!


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    Partsproduction, The link on SG was incredible, .05 ipr! I don't have the pecking capability they advised on a manual Axelson lathe unfortunately. I can see why employees are reluctant to try those methods. I manually apply the dark sulphur based threading oil on certain operations but get by with Trimsol on plain turning. Thanks for the info.

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    Quote Originally Posted by Bluechipx View Post
    I can see many of you have real world experience with copper, insanely sharp and polished tools really make the difference. Carbide with the standard honed edges and negative rake are instant disasters with copper. I can still recall my early learning days machining copper, everything going smoothly then the sickening sound of the drive motor loading, followed by a horrible buildup in front of the cutting edge and another scrapped part. Yuck!
    You could try talking to Korloy about these, they worked like a charm on the copper and a very stringy nasty soft sticky gunmetal (no idea customer supplied material) I've used them on, ...oh and they are mega sharp, .and being Korloy easy on the $.

    Korloy CCGT-AK Carbide Inserts (Finishing) | Cutwel Turning Inserts Cutwel Ltd

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    Quote Originally Posted by Limy Sami View Post
    You could try talking to Korloy about these, they worked like a charm on the copper and a very stringy nasty soft sticky gunmetal (no idea customer supplied material) I've used them on, ...oh and they are mega sharp, .and being Korloy easy on the $.
    Korloy AK chip breaker and H01 grade is always my first attempt with anything gummy and nasty.
    You need to pay real attention also to HSS sharpening if you want to get it even as sharp as these are.

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    Quote Originally Posted by Bluechipx View Post
    I machine a lot of oxygen free high conductivity copper that is very gummy. I found a few of these very high positive 1" shank tools and wonder if anyone knows of a source for them. I'm on my last one. They are the only tools that really work for turning this copper. The bars of copper are 3 1/4" dia and 42" long and finish at 3.000" with a finish for "O" ring sealing. The mat'l is over a thousand per piece. Any other cutter has a tendency to quickly gum up and dig in, creating a deep pit or groove out of the blue when turning. I'm using the high Sulphur dark cutting oil. I am not allowed to weld or fill a defect and even with a lot of cutting oil it is scary watching it cut, knowing any second it can grab and destroy the part. I trust this cutter in the picture and need several more.
    I have a lathe bit with that kind of rake et al, but it has no markings. These kinds of lathe bits are intended for turning soft plastics.

    Metal Lathes Tool sharpening and shaping for plastic

    If I recall, the traditional coolant-lubricant for turning copper was whole milk (full fat).


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