Machining metal.

S

SpasticTeapot

Limp Gawd
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Sep 21, 2004
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I'm looking to build a few amplifier enclosures, a lot like these:
http://vikash.info/audio/chipamp-lm3886/

I have copper bar stock, and I'm looking to get the heatsinks. However, I'm still trying to figure out how I'm supposed to tap those tiny little holes into the ends of the aluminum bars.

Any suggestions, folks?
 
Any tricks for making the holes? Nine times out of ten, copper snaps drillbits that small no matter how much oil you use. And how do you clamp something that precisely?
 
Machining a ductile metal like copper requires a different approach than steel.

Use a thin weight oil - clear the chips often. Do you have the ability to sharpen your drill bits? Figured I'd ask.
 
Not really, no. All I have is crappy drill bits from the hardware store.

I've been using 3-in-1 oil liberally, and it seems to help a bit.
 
I would never use oil to drill copper. Copper is very soft as metals go. Use slow speed and only light to moderate pressure. Put your drill on its slowest gear and press the trigger no more than half way. That will reduce the heat buildup.

In a perfect world you should see 2 thin spirals coming out of the hole, but more than likely large chips. If metal stops coming out or comes out in small globs or dust, your bit is too dull or too hot. If your bit gets hot, just take a break. When you are about to break thru the backside, ease off on the pressure a lot to keep from forcing metal out of the back.

You can also cover your piece with masking./painters tape to protect the surface shine around your hole while working.

Here's a Tap and Drill Bit chart I googled.
 
The main thing I have learned in my copper machining experience ,has to do with it's thermal properties rather than it's mechanical properties.Especially when drilling holes.

Here's the deal ; when you drill holes in copper , the heat from that process immediately transfers to the work piece.This causes problems , as the piece will expand in all directions.This can jam and break a drillbit in no time flat , not to mention that if you let it heat up too much , it will throw off any precise hole locations.

Here's my only advice ;

-cooling the piece while you are machining it is mandatory.The best way to do this is a circulating coolant/lubricant pump system (~100$ if yer thrifty).You can just use lots of 3&1 too....but that's only a short term solution.

Typically , copper is also machined with fairly high speeds (to reduce time,and therfore expansion due to heating.)

:D
 
BrainEater said:
Typically , copper is also machined with fairly high speeds (to reduce time,and therfore expansion due to heating.)

:D
Click to expand...

Therefore, if you use very low speeds, you reduce the heat and expansion. If you're going to drill a few 3/16" holes thru 1/4" plate, high speed and lubricant is unnecessary. Keep it cool by drilling slow and taking breaks to let everything cool down between holes.

He's right, the fluid is for cooling and chip removal. And if you work in a machine shop turning out dozens of pieces a day, its worth the trouble.
 
I'd agree fully.

Go slow or go fast.There is no 'medium'

:D

It really does depend on the amount of work you want to do , and the speed you want to do it....If you only need a couple holes , and you have the time , slow machining is the way to go.

If you are doing milling or multiple holes , fast with coolant works very well.

I'm still learning myself tho .
 
Good discussion here.

Let's expand the conversation to cutter (bit) rake angles. Problem is most drill bits are pre-ground with the intent they be used on ferrous (iron/steel) materials. Which is why I asked about the sharpening ability.

For copper alloys, which have a high ductility, can be a problem with cutters which have been ground for machining ferrous materials. As a general rule, the clearance behind the cutting edge should be sufficient to prevent a rubbing or burnishing action. In other words, more of a shearing or scraping action than digging. A quick grind of the cutting edges can help a lot.
 
BrainEater said:
the piece will expand in all directions.This can jam and break a drillbit in no time flat
Click to expand...

Except that heat causes the holes to expand, not contract, so they will not bind the drill bit. If you've got jamming, it's from some other problem.

To the OP - avoid trying to drill with a handheld. At the minimum, get a right angle drill guide; best is to use a drill press. If you are hand holding the drill, you will have to hold it very steady to get a good hole.

Also, unless your bits are sharp, the holes will be bigger than you want - an old machinist's trick for drilling a loose hole is to use the right sized bit that's a tad dull.
 
The misconception may come from the fact that you can actually melt the metal (aluminum for sure) onto the drillbit, causing the bit to seize up as if the hole got smaller.

And also, IRL, the metal will not be heated evenly, so the diagram in your link dosen't take that into account. If the mass on the outside of the heated area is larger than the mass of the heated metal, then what?
 
Well of course. The diagram is just a generalization.

And if anyone has a problem with metal melting onto their bit, they are doing something seriously wrong. Blue chips are bad.
 
Susquehannock said:
Well of course. The diagram is just a generalization.

And if anyone has a problem with metal melting onto their bit, they are doing something seriously wrong. Blue chips are bad.
Click to expand...

It's suprisingly easy to do with thicker aluminum stock. I don't mean turn to liquid and run on the floor, but soften to the point where it'll stick to your bit and you'll see small flattened globs on the inside wall of your hole.
 
Yeah, you are right. I know what you mean. Anyone who has ported an aluminum intake or cylinder head with a carbide burr has
experienced that. Good solution is some "Cut Lube".
cut_lube.jpg

http://www.silversupplies.com/catalog/tools/saws/index.shtml
 
upriverpaddler said:
I would never use oil to drill copper. Copper is very soft as metals go. Use slow speed and only light to moderate pressure. Put your drill on its slowest gear and press the trigger no more than half way. That will reduce the heat buildup.

You can also cover your piece with masking./painters tape to protect the surface shine around your hole while working.
Click to expand...

I'll take your word for it. I might try the fast approach, though - I'm machining pretty large pieces of copper.

Michael Daly said:
Also, unless your bits are sharp, the holes will be bigger than you want - an old machinist's trick for drilling a loose hole is to use the right sized bit that's a tad dull.
Click to expand...

Actually, I have a drill press. I'm not quite that desperate.

I have noticed the holes are a bit big, though.

Any suggestions for cheap drillbits that might do the job?
 
IMO, it would be quite foolish not to use some type of lubricant when machining Copper. That is asking for trouble. Trust me. I have machined enough Copper over the years. Try working with the "101 OFHC" copper (Oxygen-Free High Conductivity). Sometimes called "electrode copper". Can be expensive, well as harder to work with.
 
IMO, it would be quite foolish not to use some type of lubricant when machining Copper. That is asking for trouble. Trust me. I have machined enough Copper over the years. Try working with "101 OFHC" copper (Oxygen-Free High Conductivity). Sometimes called "electrode copper". Can be expensive, well as harder to work with.

Try using the Cut Lube above. Will be well worth the $5-$6 expense. You'll be amazed how much easier it is to tap the Copper with that stuff.

Also, try to use a "starting tap" (aka-taper) first off. They have a more gradual taper than the typical "plug" taps sold.

tap.jpg
 
SpasticTeapot said:
Any suggestions for cheap drillbits that might do the job?
Click to expand...

Cheap tools are a luxury that few can afford.

IOW - how much does it cost when the cheap drill bit trashes your work and you have to start over with new materials?

Buy a decent set of drill bits. They aren't that expensive and good ones will last a long time if taken care of.
 
I have found that drill bits made out of cobalt seem to work better than others. They are harder than anything else I have found, and seem to last longer. Check out:

Home depot . com
in the upper search box type in cobalt
It should bring you to a page with where you can choose your catagory, pick powertools, that should bring you to the drill bits and accessories list containing approx. 16 different sizes of drill bits.
 
Michael Daly said:
Except that heat causes the holes to expand, not contract, so they will not bind the drill bit. If you've got jamming, it's from some other problem.
Click to expand...

Cool ! ya learn something new everyday.I'd have sworn it was the other way round.

Last time I did copper work I was getting jamming for some reason , and only when the piece had heated up substantially....After seeing the comments about rake angle , however, I'm thinking that might be the issue:the bit is not removing the material from the hole properly.

Although it could be my POS drill bits too.

:D
 
Jarod888 said:
I have found that drill bits made out of cobalt seem to work better than others. They are harder than anything else I have found, and seem to last longer. Check out:

Home depot . com
in the upper search box type in cobalt
It should bring you to a page with where you can choose your catagory, pick powertools, that should bring you to the drill bits and accessories list containing approx. 16 different sizes of drill bits.
Click to expand...
Cobalt alloy bits are a good choice. Harder than HSS (high speed steel) bits if my memory serves.

I would humbly suggest one stay away from those gold colored TiN (Titanium Nitride) coated bits. Once the TiN wears
off the cutting edge what you have left is nothing more than a pretty colored HSS bit.
 
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