problems drilling small holes in G10

[kentw]

I am trying to drill .039dia holes (+0/-.0005)thru 3/8" thk G10 material. Some of the hole arrays have only a .006 web between the holes. I am having problems getting them to stay straight. I am center drill them all and have tried almost every conceivable speed/feed combination. I am drilling these on a Mazak CNC mill with a 10,000 spindle (I know, I need more RPMs). I have stub length carbide drills, I am using solid holders (no collets). The plate I am drilling is lifted off the table so the drill does not touch anything as it exits. They just will not exit out straight. Hole size is coming out spot on. I am considering a spindle multiplier, this would give me about 40,000rpm. I really dont want to spend $80k+ for a good router. Any ides??? We have do fixtures here routinely with 3000+ .025dia holes thru 1/4" cast alum with no issues. We cut composite materials here day in and day out (Durapol, Durastone, G10, Glastic, WaveMax, etc.) but this is a new product and these holes are kicking our tails.

[beege]

First, are you using center drills or spot drills? I like the accuracy of a spot drill. And what about circuit board drills? Tried them? And what are the parameters / ipr / peck? Here I like a peck of half a drill diameter. Have you tried half-round drills? I don't know that more rpms are going to be your solution. Good luck with it all...

[kentw]

Actually it is a spot drill not a center drill, my bad. I cannot find any half rounds that small, I have looked everywhere. Have not tried circuit board drills, I'm using stub length carbide "Harvey Tool" drills. Speed/feed Ive used ranges from 8000-10000rpm, feeds of anywhere from 6.0ipm-20.0ipm, and per pecks of down to .01 all the way up to just G81 thru. Ive tried drilling the entire array to .100 deep, then coming back drilling to .200 deep and so on until thru, instead of drilling each hole thru then to the next hole. I am using flood coolant and have a 1/8" diameter stream right at the drill.

[beege]

Perhaps try:

Spot drill to .030 diameter (90 deg spot). slight dwell at the bottom. Make sure no runout on the bit.

Drill w/carbide. Either circuit board drill or single flute of some variety. No runout either.
4800 RPM, 3 IPM, .080 first peck, .020 subsequent. Slow the spindle after the first .200 to 4000, 2.5 IPM.

Some of drill wander is an imperfect spot placement. If there is a bump, or the spot wandered on entry, the drill will walk a bit, too.

Hope this helps. Someone else will chime in with different, but this is how I would approach this.

[kentw]

I think I figured it out. The plate I was drilling is suspended in a picture frame fixture so all thru holes can go thru. I took another pc of G10 material and mounted inside the fixture so it contacts the bottom of my plate I am drilling. This keeps the drill from ever "exiting" any material, I think the drill was wandering as it broke out the back side. I will have to use a new pc (or the backside) for every plate I drill. But the holes are coming out great now. Ill keep my fingers crossed that this is not just a fluke. I drilled about 700+ holes today in 1 plate and no problems.

[ViperTX]

I suspect that it has more to do with board flex.

[kentw]

I dont think it was flex. The plate is about 20"x20" and the area to drill is only about 6"x8" and was the only area not supported in the beginning. Material is 3/8thk G10, so I dont think an area 6x8 would have enough flex to cause the drills to wander as much as they did.

[beege]

What were the final parameters that you are having success with? Happy to see you having that success!

[kentw]

Spot drill to approx .03-.04diameter (material thickness varies across the pattern). 9500rpm, 7.0ipm, .030per peck.

[kentw]

Here is a photo of the unit we were having the drilling problems on. What you see are pogo pins installed thru the 3/8thk G10 plate. This is a test fixture we build that is used to test circuit boards. As you can see, it was very important to have the holes straight due to the tiny and tall pins pressed into the plate. After the fix, they installed straight and none came into contact with each other. The pogos in the .039 diameter holes are not installed yet, what you see are the .059 diameter pogos.

[Monnie]

How are the pogo pins pressed into the G10? is there a special tool, or do they press in easy with your hands or a pair of pliers?

Thanks for the help, guys.

I'm working on a bed of nails test fixture and I am trying coming up to speed.

[kentw]

The pogos have a "crush Ring" on the socket part (female) that presses into the plate, basically about a .0005 bump on the outside of the socket. There is a really tight tolerence on the hole diameter, only +.0005/-0. The crush ring is what holds the socket in place once installed. There is a special tool that must be used to install these with, it can also be used to set the height. We get our pogos and tools from QA Technology Company (603) 601-0110. If the hole is too small the probe will not float inside the socket properly, if it is too large the socket will not hold in the plate you mount them in. These are also a "1 time use", if it gets pressed in wrong, it must be removed, tossed away and a new 1 installed. Good luck, with the right tools thse are not that big of a problem, BUT with the wrong tools, they can & will be a major pain.