Any tips on drilling glass limbs?

[Appalachian Hillbilly]

My first set of limbs are out of the mold! Now it is time to drill the limbs for the pins.

Kind of weary about drilling. I know to use a backing block but should I use a block on each side?

When drilling my mold for the stop pin, the bit jersey up a glass strip that I had to repair.

Just don't want to kill my new limbs!

[kennym]

If you can use a block on both sides and be accurate as you need, do it!  A brad point with the cutters on edges helps too, but they don't seem to last long for me...


Slow and steady too...

[OldRawhide42]

I have been using a 2 flute end mill bit . With a backing board under the limb   

[Appalachian Hillbilly]

I will probably use my milling machine and backers. Just irritated when I boogers up the form...

[Crooked Stic]

I have heard a solid carbide bit works well.

[OldRawhide42]

Go slow

[EvilDogBeast]

Like Stic said, carbide bits are your friend when drilling any composite if you don't want to replace them every 10 holes.  Brad point bits at all times, 135 degree bits will grab and tear.

[Mad Max]

I use a carbide Forstner bit and a .2505 Carbide reamer for the pins

[Flem]

I have never drilled holes in a bow, but have drilled hundreds of holes in snow skis. My preferred setup is to spot the holes with a centering bit and then mill/drill them out with a 4 flute, bottom cutting carbide end mill.
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Leaves a clean hole in glass, plastic, metal and wood found in a typical ski lay-up. Brad point and Forstner wood bits are better than twist bits, which are worthless, but none of them are made to abrade glass. A diamond tip abrasive bit would be best, but I have not seen one that did not have heinous runout.

[Mad Max]

Flem The hole will be over sized plunging a end mill, always.

[Appalachian Hillbilly]

I used a 4 flute carbide end mill. I center holed it with a carbide drill first. Worked good. No tear outs.

[Flem]

Flem The hole will be over sized plunging a end mill, always.

I noticed that also. Not a deal breaker, I'm not looking for an interference fit. I am already drilling undersized because of having to deal with drill press runout, as anybody with a press has discovered. Fortunately end mills come in 1/64" increments, so sizing correctly should be easy to achieve. I'm using a 9/64th for a 11/64th hole.

[Arlo]

Carbide tipped end mills are hard to beat. i use one on location pins on limbs and risers both. but drilling larger holes like the bolt hole using a std steel drill bit is fine...

The key to success is the angle of the drill bit cutters and having them razor sharp.  I use a knife grinder and sharpen my own.   

Google drilling plexi glass sometime and it explains this theory well. It works excellent for fiberglass too. But you should always tape your glass first, and use a backer board on the bottom side....

   Arlo

[Flem]

Arlo, are you sharpening carbide end mills on a knife grinder?