Machining Copper

This is a followup to my question about tellurium copper. I don't want to mess with toxic materials.(I realize that copper can be toxic) The tellurium copper is also hugely expensive.

I Want to build a small copper rocket chamber. The nature of the beast is such that I will probably have to build several as it is easy to make an error and burn one up on the test stand.

I've been working with some local rocket people. (Most notably the Flometrics/SDSU rocekt team) and I've been bitten by the rocket bug.

A number of amateurs have successfully built and tested small biprop rocket motors. Very few people have succesfully bult small motors that are regenerativly cooled.

Any one that has been following the armadillo aerospace sage as they've tried to build a small regen motor out of aluminium willrelize that is a difficult endevour. They have gotten very close, but not quite succedded.

The problem with aluminum is that is rapidly looses it's strength when heated. It also has less than half the thermal conductivity of copper.

Thus it's clear to me that the chamber needs to be made of copper.

The aproximate shape of what I want to machine looks a lot like

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This is a personal project, not a business proposition so time is not a huge issue.

I was planning to do most of the work on a Lathe and then move the chamber over to my CNC Taig mill with a 4th axis to cut the slots.

Is this possible?

If so what tooling/methods would you reccomend to machine copper?

Reply to
pbreed
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Flometrics/SDSU rocekt team)

Give this link a try:

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this link:
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above links show the thermal conductivity of various copper alloys in general and alloy UNS C18700 specifically. Pure copper, OFHC, has a thermal conductivity of 2660-2710 measured as BTU-in/hr-ft squared- degrees F. Alloy 18700 has 2620. So the C18700 alloy has about 96% of the thermal conductivity of pure copper. Using Free machining Brass as

100%, alloy C18700 has a machinability rating of 85%. You'll have to decide if this alloy will work. ERS
Reply to
Eric R Snow

Machining copper comes up occasionally on alt.machines.cnc, about 4 or so threads in the past 6 mos or so.

Reply to
Proctologically Violated©®

If you have any choice at all in the matter, I'd recommend that you fabricate stuff from sheet metal/tubing/rod instead of machining from billet.

And consider the various brasses/bronzes too.

Most of them braze pretty easily (heck, most brazing rods are made out of brass/bronze variants), many are weldable, and they'll have significantly better strength than copper.

Not sure exactly how these other materials do as rocket engines but I have a hard time imagining them doing any worse than copper and they've probably got nearly the same thermal conductivity.

Tim.

Reply to
Tim Shoppa

Flometrics/SDSU rocekt team)

Reply to
David Billington

Flometrics/SDSU rocekt team)

Unless you are ready to pay for an expensive learning curve... I'd figure out a way to cast to near finished part then chem mill the rest to final. I cringe at the thought of putting a cutter to pure copper. Brass and bronze no problem. But lead and copper simply don't lend themselves to traditional chip making tools. A file will fill in one stroke, a two flute cutter on a mill will load in a second and just won't let go the chip. Single pointing on a lathe may be possible but you'll never get better than an RS120 surface finish even with luck. Think of investment casting and a final .002 ream in one revolution.

But I may be wrong... my machine shop experience goes back to before CNC and there may be better solutions today.

Wayne...

Reply to
Wayne Lundberg

Actually Tim, brass has way lower thermal conductivity than copper. Some are worse than aluminum which has about half what copper does.

Reply to
Eric R Snow

Wayne, Copper and lead, each machined alone, are terrible, as you pointed out. But leaded copper machines nicely, and a good finish is easily attainable. Eric

Reply to
Eric R Snow

If it were my project, I'd seriously consider raising heavy copper sheet or tube to rough form, then machining from there. I've never machined copper, but I have raised it. Raising is slow work, and there is definitely a skill you have to learn (if you don't already have it), but it is quite doable, once you get the knack. Actually sort of fun, in a restful way. (A great way to get tennis elbow, though, if you don't keep your body position right.) I welded and ground a couple of my raising stakes, that wasn't too tricky. They're pretty expensive to buy.

I like the idea of hydroforming, but have never done it, so can't comment on feasibilty.

Adam Smith Midland, Ontario

Reply to
Adam Smith

Where can you get C18700?

What are th hazards of machining something with 1% lead in it?

Reply to
pbreed

Prolly way less than using 60/40 solder and I've been doing that since I was 8.

And I'm still smart enough to design single- board computers (:

Reply to
Jim Stewart

Me to,

I don't however make solder dust.

I've been doing electronic/soldering things since I was 10 or so. At my last physical I asked the doctor if he could add a serum lead reading to the standard tests. It came back normal, no lead and I want to keep it that way.

No food, drink etc.. near where I solder wash hands between soldering and other ...

etc...

Paul

Take a look at ours ;-)

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Reply to
pbreed

I wouldn't worry about the small amount of lead. Like any metal, don't breathe the dust. Wear a respirator if you are worried. And do a google search for the copper. It is available from many sources. Try Thyssen-Krupp. ERS

Reply to
Eric R Snow

Oh, what the heck - take a look at the conductivity properties of silver before you settle in too hard on copper ;-). And then there was an interesting demonstration of vapor-deposited diamond I once saw...

Reply to
Ecnerwal

...

I use alloy 101 copper to make my EDM electrodes. Available from McMaster Carr, page 3418 of #110 catalog. Its "not too bad" for both lathe and CNC machining. Its gummy and wants to stick to the tool. WD-40 makes a great coolant/lubricant. Sharp HSS tools, 0 rake angle seem to be best.

I see alloy 145 tellurium copper is about the same price, far better machinablility. List is $108.34 for a 1 foot 2" OD rod.

Good Luck

Karl

Reply to
Karl Townsend

Recently I saw a microwave guide made of copper by electroplating. It was about 5 inches long with 1/16" wall thickness. One end was about 1/2" bore tapering to 1 and 1/8" at the other end. An aluminum plug the exact size of the cavity was plated with copper for about half a day to build up the wall thickness. Then the aluminum was dissolved with lye leaving a cavity the exact size the plug had been. The outside was thicker at the corners because of the way the electrical field worked. The plug can be any shape but very long thin sections take a long time to dissolve. Regards, Charlie

Reply to
chlessig

After Ernie L. recommended it I got some pure d-limonine, the active ingredient in citrus cleaners. It is by far the best cutting fluid for copper, copper alloys, aluminum and aluminum alloys that I have ever tried and I've tried lots.

Ted

Reply to
Ted Edwards

I would definitely try metal spinning on a two-part form and then braze with a copper filler rod (or whatever a welding shop would reccomend) to attach the fins/side plate things. It would be nasty on a lathe to machine the finished piece, with the internal tapers and such, but machining the form for the spinning should't be too hard. After spinning the form, measure the profile that the fins have to attach to and imput the profile into the CNC to make a piece ready for brazing that will match perfectly with the finished piece. Another thought: what heat loads does this thing have to withstand? Copper, especially leaded copper, melts at not very high temperatures, compared to steel. Aluminum is even lower.

Reply to
woodworker88

...

Anything that Ernie recommends and you second is worth a try. Never heard of it. Where do I order?

Karl

Reply to
Karl Townsend

Here's a Canadian outfit that sells it.

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mentioned a source in Seattle but I didn't bookmark it.

Reply to
Ted Edwards

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