PDA

View Full Version : Turning copper



scott in NM
09-21-2011, 09:43 PM
I have a Taig Model 4500 Micro Lathe and am new to turning metal. I got it to make specialized copper grinding heads for gem cutting. Copper is a bit of a pain as I'm sure you all know, but I have a few basic questions for the more experienced:
1. Should I use HSS or some other material for the cutting head?
2. RPM - I need a good, smooth finish. Go as fast as possible?
3. If I wanted to make a 1" diameter wheel on a 1/4" diameter shaft, and I don't want to turn down a 1" rod, how would I attach the two pieces?

I need to use copper as I will diamond impregnate it for grinding purposes, and it sucks up diamond like a sponge in water.

Can't tell you if it is hard or soft copper, if the two are different I'll take suggestions for both. Can always email me at scott@museumdiamonds.com. Any help greatly appreciated, my skills and knowledge are in working stone, not metal. I have skills in "materials management", but still treat me like I don't know nuthin' and let's go from there. Thanks!

Scott

So much to learn, so little time!:D

RussZHC
09-22-2011, 12:06 AM
3] I'd be tempted to solder a copper "disc" to steel (?, sorry not enough experience to specify material)

Machinery Handbook keeps it simple, "Copper can be turned easily at 200 feet per minute."

Atlas "Lathe Operation" gives a bit more detail, highlighted by:
...combination of toughness and softness...recommend tool angles as Front relief 12*, Side clearance 14*, Back rake 16.5*,
Side rake 20*...turning speed recommended at 120 sfpm or slightly less for wide face tools...fine finish cuts at .0035 inch feed w DOC of .030 to .050 for roughing and finishing about .010...round nose tool w 1/16 radius for finishing and edges honed as sharp as possible...chips will be tough and stringy...cut-off on soft copper is difficult as the chip wants to spread and jam in the groove... [tooling HSS]
[FYI: AFAIK neither is specific as to type of copper ("Ops" does talk about harder copper alloys later), I am assuming neither is discussing beryllium copper...whole different kettle of fish from what I have heard]

tdmidget
09-22-2011, 12:50 AM
Russ is onto something. Make yourself an arbor and be able to change wheels. You will need a positive location method, which is this biz means a tapered fit. What SFM are we talking about here?

dp
09-22-2011, 02:17 AM
When you've gotten your answer I wonder if you could elaborate on your diamond-sucking copper experience :) There has to be something interesting about that. I have a feeling if copper can suck up diamonds then it should also hork garnet as easily. I have several buckets of garnet blasting media and am always looking for interesting ways of using it.

DATo
09-22-2011, 04:38 AM
I asked this question of an "old timer" when I got my first copper job long ago ... his answer: "Keep it wet."

Tel
09-22-2011, 04:56 AM
I asked this question of an "old timer" when I got my first copper job long ago ... his answer: "Keep it wet."

...... with milk!

davidwdyer
09-22-2011, 05:15 AM
I can't exactly tell if your 1/4" is the working part or the 1" part, but I assume that it is the 1" part. I think you might consider drilling out the copper and pressing a 1/4" steel shaft into the copper for two reasons.

First, it is easier. And second, if you are putting pressure on the 1" part with a 1/4" copper shaft, the shaft will bend.

Are you doing concave faceting or something else?

Circlip
09-22-2011, 07:52 AM
Cut with honed HSS tools (Sod Carbides), radiused end, cut fast and wet - Milk or WD40 or even Parraffin.

Instead of bar stock, you could Silver Solder (British terminology) blanks from sheet to a smaller dia mandrel, which is going to anneal it anyway and turn to a disc.

Regards Ian

Rustybolt
09-22-2011, 10:03 AM
1. Should I use HSS or some other material for the cutting head?

2. RPM - I need a good, smooth finish. Go as fast as possible?
3. If I wanted to make a 1" diameter wheel on a 1/4" diameter shaft, and I don't want to turn down a 1" rod, how would I attach the two pieces?

HSS is fine. Keep it sharp,SHARP. I had good experience grinding my tooling the same as for alum.


As fast as alum. Copper is a lot 'gummier' so a finer feed is called for.


Silver solder the copper. Steel, brass, stainless, it doesn't matter.


If I were doing it I'd ss the blank to its shaft and then machine the copper to the final dimension.

mochinist
09-22-2011, 11:24 AM
Maybe its because the smell of rancid milk makes me gag, but I've never understood the fascination of home type machinist wanting to use milk on copper. It will no doubt help and be better than trying to turn/mill/drill the copper dry, but you could also use water soluble coolant/wd-40,kerosene, or even plain ol cutting oil and not have rancid milk all over your machine.

When the milk thing may have been more common(whale oil and lard also for tapping) I dont think they had as many options as we do now. I would imagine all of the above would also attract critters to your machine.

P.A.R.
09-22-2011, 12:23 PM
Turning copper is a pain, if you have a hard drawn alloy a lard,graphite,turpentine,cutting oil mix may be needed.Whole milk works well the fat helps keep your edge lard,milk, whale oil high fat types work best.Cutting tools with a positive rake seam to work best.To anneal it heat then quench.For a material that is supposed to be soft this stuff will dull your tools and ruin your day until you find the right cutting oils and tool combo.
Make a steel shaft with a tapered end with a nut on the end as your soft copper diamond imbedded tool wears tighten the nut.

Tel
09-22-2011, 04:54 PM
Maybe its because the smell of rancid milk makes me gag, but I've never understood the fascination of home type machinist wanting to use milk on copper. It will no doubt help and be better than trying to turn/mill/drill the copper dry, but you could also use water soluble coolant/wd-40,kerosene, or even plain ol cutting oil and not have rancid milk all over your machine.

When the milk thing may have been more common(whale oil and lard also for tapping) I dont think they had as many options as we do now. I would imagine all of the above would also attract critters to your machine.

Perhaps 'cos the milk works so well!

Hmmm..... 'and arf a pint of whale oil please!' - in this country you'd probably get lynched!

mochinist
09-22-2011, 05:34 PM
Perhaps 'cos the milk works so well!

I dont know, I've been turning, milling and drilling copper for years and never had any problems using the modern methods and no rancid milk smell to deal with. Drilled a bunch of .025" holes .5" deep in 101 copper yesterday, using a acid brush and some kerosene.

Tel
09-22-2011, 06:40 PM
Possibly with a heavier machine? Mine is a Myford ML7.

I use kerosine, or WD40 for aluminium, but have never had much luck with copper. Another thing that works OK with copper, tho', is a smear of Trefolex paste - but I didn't say that, it tends to give off nasties if you get it too hot.

Video Man
09-22-2011, 10:00 PM
+1 on what P.A.R. said, I've been playing lately with making lard oil compounds from lard oil extracted from grocery-store unsalted lard. (Another post for another time). Tried a mix of lard oil and turpentine on brass, copper and aluminum bronze and was amazed at the quality of the finish with all of these on lathe turning. Slightly round-nosed tools, rake appropriate for the material. Non-staining oil, and gleaming smooth finishes....mixed with kero, it works great on steel, and with trichlor (don't ask...) makes the greatest aluminum threading and reaming results I ever accomplished. One poster here referred to one of the new synthetic threading compounds as "about as effective as warm spit." Maybe those ole boys back in the day really knew what they were doing....

The mix is not a lot of help drilling aluminum bronze, however, it still binds and squeaks.:)

DATo
09-23-2011, 02:50 AM
I have to agree with mochinist. I never heard tell of using milk on copper till I came to this board and I've been in the business 40 years. Totally agree with just using a kerosene and oil mix off a paste brush. I've done it often myself and it managed to get the job done efficiently.

With regard to the "warm spit" post : An old guy I worked with long ago mentioned a machinist he worked with when he was a just starting out in the trade who chewed tobacco. He said the guy was so proficient in the use of tobacco spit as a cutting lubricant that when threading he could hit the thread just in front of the tool as it was cutting from his normal standing position at the lathe. Said he saw him do it often with his own eyes and that the guy never missed. The guy who told me this was pretty much a straight shooter so I believe his story.

scott in NM
09-24-2011, 12:01 PM
Sorry guys, haven't visited in a few days, little busy. A few answer to questions asked, and other clarifications.

1. Diamond has an affinity for copper so it just "sticks" to it. It gets impressed into the metal and just stays there. Makes it easy to create and use your own cutting heads. Wouldn't try to mill a battleship out of a single block of steel, but it works wonders at the smaller scale.
2. I am using my creations primarily for fantasy cutting. For those not familiar, that is the art of placing dimples, V channels, U channels, and other forms on the surface of a stone. For what I like to do, no one makes what I need, so I need to make my own. Hence the lathe, and the questions about turning copper.
3. My heads will be less than 1" in diameter (a ball, wheels with rounded edges of different radii, wheels for creating a V with different side wall angles, etc), the shaft can be up to 3/8" diameter. To create a head attached to an arbor, I can do solder, milling out of solid stock, drilling and tapping to insert and end screw similar to Dremel, anything is possible. I care about the destination (finished product), not the trip itself (process to make it). So I wanted to see what you guys recommended.

So, from what I gather, copper gums things up (already knew that). The use of a cutting liquid, ranging from milk to petrol products to whale blubber to fairy wings would probably work, I just need to see what works for me. Not unusual, every gem cutter cuts stones, and every one of them does it differently. Same things you pros go through, we just work rock and not metal.

For a good finish, use high speed and a light touch.

So I shall experiment, and if anyone can recommend a good book on metal machining (I can actually read AND look at pictures!), I would be greatly appreciative. Send the suggestion to scott@museumdiamonds.com if you would please, I don't do much web blogging.

Thanks for your inputs.

Scott

P.A.R.
09-24-2011, 03:01 PM
+1 on what P.A.R. said, I've been playing lately with making lard oil compounds from lard oil extracted from grocery-store unsalted lard. (Another post for another time). Tried a mix of lard oil and turpentine on brass, copper and aluminum bronze and was amazed at the quality of the finish with all of these on lathe turning. Slightly round-nosed tools, rake appropriate for the material. Non-staining oil, and gleaming smooth finishes....mixed with kero, it works great on steel, and with trichlor (don't ask...) makes the greatest aluminum threading and reaming results I ever accomplished. One poster here referred to one of the new synthetic threading compounds as "about as effective as warm spit." Maybe those ole boys back in the day really knew what they were doing....

The mix is not a lot of help drilling aluminum bronze, however, it still binds and squeaks.:)
Add a tablespoon of powdered graphite to the lard and kerosine.

RussZHC
09-25-2011, 12:46 AM
Not knowing exact details and that the end product it the thing, for you, I would suggest not duplicating items already out there that may be close enough

http://www.leevalley.com/en/wood/page.aspx?p=31018&cat=1,130,43409

that is just a quick found example from Lee Valley,

Suitable for all woods, hard metals, bone, alabaster, glass, gemstone and plastic, the bits keep their shape, even when working metal
and that is without any looking at jewelry sites.

At the very least a look at the general shapes of those and other types of burrs could give you ideas as to what is needed or what is just nice but seldom used (there are what, 100s of shapes ? in mounted points for example but only maybe a couple dozen have common usage, rest are used but only for specialized needs)

davidwdyer
09-25-2011, 05:08 AM
You will probably find that copper cutters are a bit slow, even with coarser diamond, especially for the "V" grooves where it is difficult to hold a sharp edge.

You probably will have better luck doing your initial grooves with diamond coated (or scintered) "V" or "U" shaped little wheels which some lapidary shops make. They do leave quite a bit of "subsurface damage" and later need more work to remove the scratches in the gem material. The the finer work can then be done with other kind of materials like copper. If you are concaving, copper rods stiffened with steel inserts (if the your cutters are thin) works well, but are slow.

If you are using shaped copper discs for your cutting, you will need to change them often due to the copper becoming misshaped. You might consider a small sort of arbor, like dremel has, where you drill your copper and then change frequently on the arbor.

The grinding wheels which RussZHC suggested will not hold up for very long under lapidary use.

You biggest challenge will not be cutting the shapes, but polishing.