Comments on: PCB Layout and CNC Drilling Problems (and Solutions)

By: sumedh

sumedh — Thu, 15 Jul 2010 06:21:28 +0000

Hello
i want to more information on pcb drill bit tool life optimisation for single and double layer coating. So pplease guide me.

By: Michael

Michael — Mon, 18 May 2009 19:35:59 +0000

Keith,
Thanks for the response. I shortened the bit to .15″ and turned the RotoZip up to full RPM. These changes have cured the problem to a large degree. I will try to increase the Z feed rate on the next go around.
Thanks again,
Michael

By: Keith Neufeld

Keith Neufeld — Sun, 17 May 2009 19:18:25 +0000

Michael — a machinist could probably answer this better than I, but I’ll take a stab based on my experience.

First off, I assume you’re drilling with the #65 bit, not milling. I know you refer to drilling, but I just want to be sure.

Second, I have a RotoZip but I haven’t used it for PCB work, so I don’t know how bad its runout is. Runout is how much radial play there is in a drill’s axle — that is, how far the bit wiggles from side to side as it spins. When you power it up, does the bit stay in a perfect vertical line and you just lose sight of the flutes, or does it become a wider, blurry object? If the latter, I’d be pretty certain that the play in your RotoZip’s bearings is moving the bits enough horizontally to break them off in the holes. Try using a Dremel instead — I’ve had very good luck with their bearings. Or you might look for higher-quality replacement bearings for the RotoZip.

Third, I don’t know what the spindle speed on a RotoZip is. Because it’s made for 1/8″ – 1/2″ cutting bits, I’m guessing the speed is lower than that of a Dremel (5 000 – 30 000 rpm). The smaller the bit, the higher the speed you need to maintain the same linear speed on the cutting surfaces around the circumference of the bit. If the RotoZip is running slower, it’s possible you simply need higher rpm.

Finally, if I’m reading your plunge rate fo 2″ / minute correctly, that seems slow to me. When I’m hand-operating my Dremel drill press, after positioning the workpiece it takes me about a second to drill and retract each hole. My friend Cort refers to “punching” the drill bit through the PCB, and I don’t go quite that fast, but it sounds like I probably use quite a bit faster Z axis feed rate than you are. On my friend Joel’s CNC drill machine, I think we’re using about .5 ips (30″ / minute) feed rate with a Dremel tool.

Of course you don’t want to feed faster than the tool can cut; but once you’re slower than the cutting speed, a slower feed rate just gives the bit more time to heat up and to be subject to radial stress from imperfect bearings. After checking your spindle rpm, it might be worth increasing your plunge rate.

I hope something here helps!

By: Michael

Michael — Sun, 17 May 2009 13:41:04 +0000

Hi,
Liked your posting. I have a few questions. I built my CNC machine am using a CAD program to make the PCB holes and traces. Using mach3 Lazy cam for the CAM and Mach3 for controlling my machine. It took a while to get the mechanical set up routines down for milling traces. The drilling is straight forward but having a problem with bits walking and breaking.
Machine setup:
plunge rate: 2 inch a minuet
feed rate: 5 inch a minuet
drill size .035″ #65
cut depth – .07″
I shortened a bit to where there was .35″ out of the chuck. The bit stilled walked and broke around 20 holes were drilled first. Using a Roto Zip for the spindle and installed a variable speed on it. It seams to have not helped much.

What can I do to resolve this?

Thank

By: Keith Neufeld

Keith Neufeld — Mon, 29 Sep 2008 13:43:50 +0000

Namita, I have no experience working with commercial, multi-spindle drill machines.

By: NAMITA

NAMITA — Mon, 29 Sep 2008 10:17:01 +0000

hi,i am about to by a 4 spindal cnc pcb drilling machine.and u know i don’t know anyting about it.what i know is that it drilles the hole in pcb.i need to know every thing about it if any one can help me i be great full.being a woman it is a very big yet mad step to take but i want to do it.so pls help me