Re: Drilling dilema

clay wrote:
Michael wrote:

clay wrote:

Gary wrote:

On Fri, 17 Feb 2006 06:15:51 GMT, clay <a_design@xxxxxxxxxxx> wrote:


So I have been drilling these .080 thick copper sheets, Ø.093 holes. thanks to everyones suggestions, I finally eliminated the entry & exit burrs. peck drilling at 2-4ipm @ 6000 rpm. Holes were nice and shiny, carbide drill, no coolant. Drilled about 2000 holes, when I noticed that the top edge was starting to get a little ragged, and the inside was tearing somewhat. So I figured the drill was starting to wear at the corners, etc..... changed the drill, no difference. Slowed down the feed, no difference. reduced the Rpm, nothing. Dropped the rpm to 3K, nothing. Chaged to a different dril AND tool holder. No change.

So what could it possibly be? Vibration (belt drive spindle), spindle bearings, runout in the spindle taper? how can I detect vibration, anyone????


What is the material sitting on top of when you drill?
Have you shutdown the machine? Is it a VMC? If so, did the cnc realign slightly off a thou or so and the drill is walking very slightly to follow the holes drilled through into the subplate?
The first peck is ok, as you said, as you go deeper the burr develops, just a thought. In a vmc it only takes a chip to get on the limit switch to change a thousandth. Is the vmc, if that is what you are running this on, possibly an older machine?
The inside tearing may be that the drill is pushing material down into the drill tip holes vs drilling firmly against a subplate.
If that is the case you may need to look at the fixture you are drilling into, mayve 1500 parts is where you would want to consider resurfacing the fixture/ subplate.
Michael



I do need to check the hole size, something I haven't done yet.

ca





Material lot change?



Nope.

I'll buy anthony's chip drag, as the top edge is pretty raggedy, but how do you correct for that? It seems to be created in the second or third peck. I am taking really shallow .020" pecks. deeper or no pecks, makes it worse. Standard carbide circuit board drill. Sticking out only the flute length.

ca




the material is part of a thin web, there is some clearance between the subplate and the material. the hole in the subplate is significantly oversize, and there are 12 holes. I haven't noticed a pattern, yet. they all seem to be uniformly bad. I am suspecting spindle vibration as the prime suspect. the belt is starting to get noisy, but I haven't noticed a change in the bearing tone. So I am wondering if I have a taper burr also.

How do you detect taper problems, and vibration problems?

clay

Clay,
Indicate the spindle for runout. If it has some degree of "slop" in it, that may very well be the problem, but, why would it show up after drilling 2000 good holes?
Michael



--

Michael Gailey
Artistic CNC Mill, Router and Engraver Programming
3D modeling for Product Design and Development
http://www.microsystemsgeorgia.com/toc.htm
.

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