Drill Press Questions

[MikeH]

Does anyone here think that a certain number of RPMs are essential for driling PCBs?  I've noticed that drill presses meant to drill with very tiny components, like dremmel presses, go up to 35,000 RPMs, but your typical budget desktop variety only does 3500.  Are higher RPMs more likely to cause bit breakage than slower ones, or is it the other way around?

[John Lyons]

Faster is better for drill PCBs but my delta DP200 10" drill press seems fine at 3100 rpm.
If you can find a faster one it will drill smoother holes...

John

[R.G.]

In your mind's eye, magnify the cutting edge of a 0.03" drill bit up to where you can see it biting into the circuit board stuff. The edge of the drill bit sweeps along, cutting out chips.

The edge does this by locally exceeding the shear strength of the material it's cutting. That's why sharp edges cut better - the area over which the shear force is exerted is made as tiny as possible, so that the total force to shear the material there is as small as possible.

If you take a cutting edge of any kind and force it into material it can cut, where the cut-off material goes is important. It does not matter if your cutting edge is infinitely sharp if the cut-off junk builds up on the non-edge part of the blade. That part of the blade cannot cut, so forcing it to push along material is no longer cutting, it's pure force. And if you get enough build up, you will break the part of the blade that supports the edge, no matter how well the edge is cutting.

Long experimentation with cutting edges has found that there is an optimum amount of depth of cut and speed of cutting in feet per minute/meters per second that will shear off a chip cleanly with little wear on the edge and making chips small enough to be cleared away without breaking the holding part of the blade.

What is the cutting speed of the blade of an 0.030" drill bit? The outer edge is moving through a circle of 0.03"*3.14159 = .094" every revolution. So it takes 127+ revolutions to move a foot. Good drilling rates for metal cutting metal is in the 200f/m range. Getting to there with an 0.03" drill takes 200*127 = 25,400 revolutions per minute.

Carbide tends to cut metal best at about twice that, around 400f/M. But then it's hard glass fibers being sheared, so the speed goes back down.

When it's all said and done, you need to be running the thing up at 20k-50k rpm to do best cutting depending on whether you're using high speed steel or carbide bits.

If you can't turn the bit fast, advance it slower. That makes the depth of bite smaller per revolution and keeps the build up down so you don't break as many bits.

By the way, my experience is that high speed steel bits last about 100 holes in PCB stock before they are too dull to continue.

[MikeH]

Oh man!  What a comprehensive explanation.  It actually made me giggle with delight.   

[Hiwatt25]

I too have a little benchtop Delta and I've had no problems using it to drill my pcbs.  I drill through the copper too.  I get ten packs of bits from Drill Bit City and in the six months I've been drilling pcbs I've only broken one.  I was bringing the deck up on the press and slammed it into the bit.  Heck, at seven bucks and change I don't tend to worry too much, I just drill nice and slow and everything seems to work out. 

http://drillcity.stores.yahoo.net/10pacresdril.html

[MKB]

Another part of the eqaution is how nice you want your drilled hole to be.  If you look at the holes you drill with your home drill press, often the hole has a white ring (slight delamination of the PCB stock) and some fibers sticking out.  This is not a problem with a single sided home made PCB's, but in commercial multilayer boards it would be a complete disaster, as the tolerances for holes are in thousandths of an inch, and nasty holes like that would cause many problems.  You have pads on inner layers that have to be drilled through properly, and then you need a well plated through hole that makes contact with all those internal pads.  Plus the hole has to be an exact size as the plating will reduce that finished size by a controlled amount.  So you need the optimum speed to get the properly toleranced hole in a standard manufacturing environment.

There is also the manufacturing speed issue, faster drilling=faster PCB construction, more throughput, more money made per hour of machine use.  This may be a smaller reason though.

[Paul Perry (Frostwave)]

Lubrication REALLY matters when drilling metal.
Does it make any difference for PCBs? I don't know.. but even if it doesn't, I consider it worth using to keep the dust from getting in the air. Any glass fibre dust you breathe, is still there when you are buried..

[coxter]

What kind of lube do you use when drilling Alluminium ? May i ask?

[MikeH]

They have this stuff at hardware stores called "Tap Magic" that works really well.  But any "household" (All purpose mechanical type) oil will work.  Even motor oil if it's all you've got.

[markm]

I have yet to hook it up and use it but, I lucked out and had this baby donated to my cause by an older fella I work with!
Have a look;

[Seljer]

caught this earlier today:
http://www.instructables.com/id/E5ENZWHF2FRVIYM/

[drano]

They have this stuff at hardware stores called "Tap Magic" that works really well.  But any "household" (All purpose mechanical type) oil will work.  Even motor oil if it's all you've got.

WD40 works in a snap.  even Water will do.   anything to keep the temperature down.  Heat is the enemy.  burns your material and dulls your bits.

but as for PCB,  that stuff drills like butter, its so brittle and heat-resistant. i dont think you have to worry about your bits at any speed or feed.

on that note,  you dont really even have to worry about  Aluminum enclosures either,  its so soft that your can feed even HSS bits  down pretty hard without damage.    (if you drill steel, you need slow speed, slow feed)

I have yet to hook it up and use it but, I lucked out and had this baby donated to my cause by an older fella I work with!
Have a look;

ive had bad luck with those.  hope your luck is better.

[Chuck]

R.G. has drilled a few circuit board holes.  You can tell.   

[markm]

I have yet to hook it up and use it but, I lucked out and had this baby donated to my cause by an older fella I work with!
Have a look;

ive had bad luck with those.  hope your luck is better.

Really?
Care to elaborate a bit?
Maybe that's why it was free?!