[Shea al'Thor]

I've been trying to drill some very small and deep holes in copper for the last 2 hours.... I've had to restart 4 times now due to broken drill bits...
The project requires me to drill a hole 1.5" through the center of a half inch copper rod. The hole diameter is a #55 bit (.052").
I've been using a lathe to turn the copper with the bit in the quill. I can usually get the hole drilled in about half an inch on either side before the bit snapps...
Any suggestions?

Thanks
al'Thor

[txcncman]

What RPM are you trying? My only success with copper is slow, slow, and slower and lots of pecking.

[txcncman]

Also, do you have to maintain that drill size all the way through the part? Could it be 1/16" drill 1/2" deep on each end and 0.052" through the center section?

[handlewanker]

Yeah, lube the drill with kerosene, and run it at 1000rpm, if you run it slow you will get a thick chip....peck the hole not more than 1mm deep after you are in about 3mm as the chips that come out will pack into the drill flutes and seize up.

You can drill from both sides as you are already doing and this will prevent deep hole chips from getting welded to the drill.

If you neglect to peck at 1mm intervals the swarf will weld to the drill and bang goes another drill bit.

It goes without saying the drill must be very sharp, not previously used on steel etc.

I use a Wishbone type drill sharpener that I have made, and I use this to sharpen small drills of 1mm diam etc, and with Copper you can sharpen the drill slightly off centre making the drill cut oversize and so preventing a seizure.

The Wishbone type drill sharpener was on the market about 50-60 years ago, but I made my own to a slighly different design.

I have a sketch or two and a photo somewhere if you want to make one.
Ian.

[mc_n_g]

Make a small flat with a sharpening stone on the cutting lips. When the cutting lip is sharp in copper it grabs. By 'stoning' the cutting lip it makes the cutting lip a little more neutral to the copper so it flows better up the flute without grabbing all the time. When it grabs suddenly it draws further into the copper snapping your drillbit.

You might want to check out this post about it.
how to drill brass without drill grabbing? - Home Model Engine Machinist

[fizzissist]

Does anyone understand that the problem of "grabbing" the drill is a function of backlash??
I've drilled hundreds of thousands of holes in brass, and the only time I've broken a drill is when the chips packed up or if it was just too dull for the job.

On a drill press or lathe set some drag on the quill so the drill can not just jump into the material and break.

Stoning the edges helps with chip control, longevity, and finish (if you kiss the corners). I do that a lot anyway.

Copper is a different story, no more so with the grabbing than brass, but it acts like it's nasty abrasive. .... I shouldn't be giving this away, but....
Use 1/2 & 1/2 or heavy cream (WITHOUT SUGAR!!) for drilling and tapping.

[handlewanker]

Make a small flat with a sharpening stone on the cutting lips. When the cutting lip is sharp in copper it grabs. By 'stoning' the cutting lip it makes the cutting lip a little more neutral to the copper so it flows better up the flute without grabbing all the time. When it grabs suddenly it draws further into the copper snapping your drillbit.

You might want to check out this post about it.
how to drill brass without drill grabbing? - Home Model Engine Machinist

This is not correct.

The method of having a negative rake on the cutting edge, which is what you get if you make a flat, will only work for materials like brass or cast iron, but for ductile metals like steel, alluminium, bronze, alluminium bronze and copper etc you NEED a sharp cutting edge, otherwise the soft metal will build up on the flat, no matter how small you make it, and weld itself to the tool.

The back clearance of a drill determines how fast it burrows into the metal and the correct clearance, approx 2 degrees, will be average.

It is true, as already pointed out, that backlash in either the tailstock barrel feed screw or the crosslide feed screw will allow the tool to be pulled into the job, IE, self feeding, BUT ONLY IF YOU HAVE EXCESSIVE FRONT CLEARANCE.

You can control the feed rate of a drill by reducing the front clearance so that it will NOT burrow into the metal uncontrollably.....for ALL metals.

If you can't understand this, take a parting tool in the lathe and give it a 1 degree front clearance, then with a top rake of 10 or 15 degrees dig it into a piece of 25mm diam steel........the tool will feed into the cut without digging in.

Now increase the front clearance to 3 degrees and be carefull....the tool will be pulled into the cut as fast as the backlash in the crossfeed crew will allow it, virtually self feeding.

If the crosslide and compund slides are both loose and the jibs are not adjusted properly, you will get disaster every time.

This will happen for all cutting tools in all circumstances when you have excessive front clearance.

In a turret lathe where the form tool in the crosslide tool post can be 25mm wide the top rake is zero and the front clearance is not more than 1 degree, but in this case there is no compound slide and the crosslide is very long.

The 90 degree included angle countersinking drill bit, made from a standard 2 flute drill bit is a typical example of what front clearance can do to the job......if you have the standard 2 to 3 degree front clearance and both flutes of the drill cutting, the drill will leave a chattery finish, but if you stone one cutting edge to prevent it form cutting and you also have 1/2 degree front clearance you get a smooth almost polished countersink finish.....using the usual soluble oil cutting fluid of course.

It is a good idea to make the cutting edges of a drill bit of unequal lengths so that it will cut a small amount oversize and so make the drill less prone to seizure in the hole when the lands at the cutting edge wear, especially for copper or alluminium, and very much especially when cutting bronze and alluminium bronze.

Cutting alluminium bronze with a blunt drill will make the hole open up as the metal rapidly heats up and as soon as it cools it grips the drill and ....kaput.

NEVER drill alluminium bronze with a drill that has previously cut steel without resharpening it.....sometimes you have to cut the drill point back to ensure the lands at the point are not undersize or it will seize.
Ian.