Cutting tiny slots in copper

Hey guys, I've worked around machines in the model, pattern, and mold industries for almost a decade. That said, what I'm doing on my own as a gov't project has me a bit uneasy as far as how to do what I need to do.

At the bottom of a roughly 1.5" square flat pad, I need to cut a number of slots that are about .018" wide and as deep as I can realistically make them. (.020" at the least, would like .030"). I'm out of my wheelhouse here. I ordered a couple of different half mil carbide cutters... And plan on running them at just a couple IPM, so slow slow slow. Lead ins will be shallow and stepdowns miniscule at maybe a thou. I'm limited to 6500 rpm. 3 axis vmcs. They're accurate as I take good care of them.

Is there anything I can do to be careful here? Any tips or tricks? Am I looking at this the wrong way? Make it not take a lifetime to cut? Being a rotational mold guy, my daily job is making big things, and any small details just have to look good, not be good. I need to cut at least 40 of these slots per piece, and at this rate it'll take a whole night, assuming the cutter survives, to cut, and I essentially relegate all my free spindle time to one toolpath.

I've heard some other methods of doing this thrown around, but I can't for the life of me remember the names. I eventually want to take this into production once my prototypes mature, and I don't want to shop it out. Any and all help would be super appreciated.

Thanks!

Can you use a type of free cutting copper? That will make a world of difference, standard copper will be nightmare.

There are companies like Harvey that specialize in smaller cutter size and different coating. Try contacting them and see if they have a cutter with a coating that might be beneficial.

Can you stand it up and use a slitting saw to remove most of the material, then finish the corners with an endmill? Even with two setups, might be quicker than endmilling the whole slot.

"at the bottom of a roughly 1.5" square flat pad" do you mean it is recessed? how deep? I'll second TeachMe, any slotting you can do is going to help. if you have a lot to do, make a die and mash it in there?

Thanks for all the replies, guys. The part will have already been machined. It is 2.2"x2.2"x0.355" and the pad in question is recessed roughly 0.16". Already several things have been brought up that I hadn't considered since I have my head somewhere dark when it comes to materials anymore. Being in a basically all aluminum shop, with some steel and stainless tossed in here and there, will do that.

Luke.kerbey said:

Can you use a type of free cutting copper? That will make a world of difference, standard copper will be nightmare.

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A long time machinist where I work mentioned that C110 would be fine since it's readily available, which obviously isn't the case with such a low machinability index. What I need to do is maximize my material with the absolute highest thermal conductivity compared to something that won't be ridiculous to machine. I know we have some cutoff pieces of 3.5" copper bar that I can use that were turned. I'm assuming that this means it is one such alloy that can be machined with relative ease. It's all about thermal conductivity for this project. Any tips?

TeachMePlease said:

Can you stand it up and use a slitting saw to remove most of the material, then finish the corners with an endmill? Even with two setups, might be quicker than endmilling the whole slot.

Click to expand...

Hmm, interesting. I would be able to cut around 70% that way looking at a quick solidworks sketch using a 1" diam 0.020" thick slotting saw. No issue with standing it up, it would take less time than the direct route I think.


110 copper is everywhere, and apparently not what I need. I think what needs to happen is that this specific part, which is part of a larger assembly, needs to be redesigned to drastically reduce the amount of copper that comprises its mass. The thermal conductivity of copper cannot be matched, not even close, so I can't get around using it... but I can greatly diminish my reliance on anything larger than something 0.1" thick and maybe 1.75" in x and y.

Any recommendations on copper that can actually be machined? Seriously guys, thank you for the input here.


EDIT: Does 145 work okay? I did some forum searching here and otherwise and it seems like this may be the way to go. Going to be rough to find it and not pay an arm and a leg as I simply cannot find rectangular bar stock in this alloy. I'll have to get round which causes there to be a bit more waste, but all in all I can order a two inch cut of round 2.5" 145 for around $45 which gets me 7 parts (assuming I don't screw up the band saw cuts). That's all I need for my prototype runs. The new design I just drew changes the base of my design into two pieces: a frame and a copper core. The copper core is now only recessed .070" and the idea of using a slitting saw gets more enticing as I'll be able to cut around 85%+ of the slots with a 1" diam .02" thick slitting saw and then endmill the rest. The slots don't have to be dimensionally perfect, but they do have to be deep enough to carry fast flowing water from one end to the other. I'm playing a surface area game here for heat conduction from heat source to copper to liquid and out.

thenrz said:

The thermal conductivity of copper cannot be matched, not even close, so I can't get around using it...

Click to expand...

Silver will see copper's conductivity, and raise it .... not too expensive, maybe, if you consider machining time. Sterling silver could be even better, conducts well and easy to machine. Just go melt down the teapot

If you had to make a whole bunch of these you could think about investment casting.

EmanuelGoldstein said:

Silver will see copper's conductivity, and raise it .... not too expensive, maybe, if you consider machining time. Sterling silver could be even better, conducts well and easy to machine. Just go melt down the teapot

Click to expand...

Well, you certainly have me there. Let me augment my statement: "The thermal conductivity of copper cannot be matched without moving to much more expensive metals, so I can't get around using it..."

I'm hoping 145 copper will work for me. I'm going to buy a two inch piece of 2.5" round bar stock and try this week when I can get some more free spindle time.

Copper 145 is a dream to machine Vs 110.

Haven't seen a drawing, but it seems like you're making a finned heatsink? Instead of machining, can you fabricate it, with solder? Or do that fancy skivving/shaper approach, as shown on the video from a few weeks back?

(I usually spend a good bit of time looking for something that I could modify first.)

What is your eventual production volume target? Is extrusion or casting an option?

thenrz said:

Thanks for all the replies, guys. The part will have already been machined. It is 2.2"x2.2"x0.355" and the pad in question is recessed roughly 0.16". Already several things have been brought up that I hadn't considered since I have my head somewhere dark when it comes to materials anymore. Being in a basically all aluminum shop, with some steel and stainless tossed in here and there, will do that.

A long time machinist where I work mentioned that C110 would be fine since it's readily available, which obviously isn't the case with such a low machinability index. What I need to do is maximize my material with the absolute highest thermal conductivity compared to something that won't be ridiculous to machine. I know we have some cutoff pieces of 3.5" copper bar that I can use that were turned. I'm assuming that this means it is one such alloy that can be machined with relative ease. It's all about thermal conductivity for this project. Any tips?

Hmm, interesting. I would be able to cut around 70% that way looking at a quick solidworks sketch using a 1" diam 0.020" thick slotting saw. No issue with standing it up, it would take less time than the direct route I think.


110 copper is everywhere, and apparently not what I need. I think what needs to happen is that this specific part, which is part of a larger assembly, needs to be redesigned to drastically reduce the amount of copper that comprises its mass. The thermal conductivity of copper cannot be matched, not even close, so I can't get around using it... but I can greatly diminish my reliance on anything larger than something 0.1" thick and maybe 1.75" in x and y.

Any recommendations on copper that can actually be machined? Seriously guys, thank you for the input here.


EDIT: Does 145 work okay? I did some forum searching here and otherwise and it seems like this may be the way to go. Going to be rough to find it and not pay an arm and a leg as I simply cannot find rectangular bar stock in this alloy. I'll have to get round which causes there to be a bit more waste, but all in all I can order a two inch cut of round 2.5" 145 for around $45 which gets me 7 parts (assuming I don't screw up the band saw cuts). That's all I need for my prototype runs. The new design I just drew changes the base of my design into two pieces: a frame and a copper core. The copper core is now only recessed .070" and the idea of using a slitting saw gets more enticing as I'll be able to cut around 85%+ of the slots with a 1" diam .02" thick slitting saw and then endmill the rest. The slots don't have to be dimensionally perfect, but they do have to be deep enough to carry fast flowing water from one end to the other. I'm playing a surface area game here for heat conduction from heat source to copper to liquid and out.

Click to expand...

If it’s for flowing water, You aren’t going to get any meaningful flow in the corners you would make with the endmill. Completely a waste of time and effort. Just use the slotting saw,

Got a shaper?

I keep accidentally deleting my posts somehow. All the input is much appreciated. I'll repost a drawing of the part in question later.

No shaper. Slitting saw is a good possibility. Would have several of pieces cut and do the slitting all at once since it will be a more complicated setup. I think for the first two prototypes, I'm going to just cut with my half mil cutters. My tooling rep comes out late this coming week, and he's going to bring some stuff with him. Hopefully I can fit a vice in somewhere... Going the 145 route is a huge boon to all of this. You guys are awesome.

We used to make similar products by the thousands. I would go to great lengths to use a saw, even for prototypes. A small endmill out that far will be an exercise in frustration. If I recall correctly, the more machinable the alloy, the worse the thermal conductivity. We also had to make some compromises in the aspect ratio of the slots for manufacturability. I think we finally settled on a about .040" wide slots about .080" deep.

In full volume production, we went with a metal injection molded process. The only machining that we had to do was to get the bottom as flat as humanly possible, and cut some interface surfaces. It wasn't cheap, but we were also spending taxpayer money (thank you for supporting our bad ideas).

G00 Proto said:

We used to make similar products by the thousands. I would go to great lengths to use a saw, even for prototypes. A small endmill out that far will be an exercise in frustration. If I recall correctly, the more machinable the alloy, the worse the thermal conductivity. We also had to make some compromises in the aspect ratio of the slots for manufacturability. I think we finally settled on a about .040" wide slots about .080" deep.

In full volume production, we went with a metal injection molded process. The only machining that we had to do was to get the bottom as flat as humanly possible, and cut some interface surfaces. It wasn't cheap, but we were also spending taxpayer money (thank you for supporting our bad ideas).

Click to expand...

I'm losing around 8% w/mk going to this alloy (getting conflicting values, so averaging them), but being able to cut slots for surface area will more than make up for the loss. I wish I had the cash to shell out for a process like that, but I have what I have which is access to 3 and 5-axis machines, CNC lathes, and plenty of tooling. I purchased the tiny cutters myself obviously...


I redesigned the base. Now I only need 70 thou overhang plus my slot depth until I can get a slitting saw. Tool rep should give me a deal. He always does for my gov't projects. I also chamfered the ends of the slots so the cutter isn't running into a wall at the beginning or end of travel. Walls of slots are slightly drafted, .0015 from top to bottom. Copper core will be within a brass or acrylic base. Going to try both and see if casted acrylic will be rigid enough at this size. Would be great if it is.

OP, check out this video @ 1:20. Hell of a lot faster.

The internal shop at my last job used the slitting approach when I had parts with 12x 1mmx4mmx300mm slots. Cleaned up the ends with an end mill. Way faster.

Yes, for sure on being faster. Gwizard pretty much agrees with my own manual feeds and speeds calculations. I won't get breakage level tool deflection past 4ish ipm at my max spindle speed of 6000rpm and a .0015 depth of cut. I could probably get away with 3.0 ipm running at a .002" depth of cut and save some time... Keep in mind, this is all for prototyping. An actual production run would utilize slitting saws and fixtures. Getting the proper saw wouldn't even require the endmill cleanup since my inlet and outlets for fluid are within the ends of the cut.

Quick photo below:

Why wouldn’t you just use the saw from the getgo? If you are determined to try the endmill go ahead, and do let us know how it goes, but the 5% additional area at the ends of the cut won’t see any significant flow so are pretty much useless. (use a smaller dia. Saw, say 3/4?)

If you are hellbent in taking 5x longer to create useless features have fun.

thenrz said:

Well, you certainly have me there. Let me augment my statement: "The thermal conductivity of copper cannot be matched without moving to much more expensive metals, so I can't get around using it..."

I'm hoping 145 copper will work for me. I'm going to buy a two inch piece of 2.5" round bar stock and try this week when I can get some more free spindle time.

Click to expand...

Any chance you could have them silver plated?

Martindale Electric, where I work, makes slitting saws designed for cutting copper in both HSS and solid carbide. We have a wide range of standard sizes, and can also manufacture custom saws to your specifications.

Another thing you may not have considered is stacking several saws with spacers on your arbor. That way you can get more slots done in one pass.