Narrow Burrs

[Mr Bill]

I recently purchased some FG329 pear shaped carbide burrs. Normally I use FG701 burrs which make a wider hole .
After I drilled a hole at the end of a long crack using the Pear shaped burr I used the slide hammer and it was bigger than the hole so I chipped the glass.
Fortunately this was on a practice windshield.
I want the hole to be as small as possible for minimal scarring of the glass.
Would I be better off using a needle to pop the bullseye in this case, rather than the slide hammer?

[Jonathan]

Mr. Bill,

The slide hammer tip was designed to be used with the FG701 bur. It makes just the right size of hole for the slide hammer to fit in.

[Brent Deines]

Mr. Bill,

We did a lot of testing on different sized points and have found that smaller points or needles do not provide the consistent results that you get when using the point that comes with the slide hammer. Smaller points will sometimes fracture the glass at the bottom of the drill hole and will not always produce a perfectly round bullseye. I'm not sure why, but making the point smaller or larger by just a few thousandths makes a big difference. We also did a lot of testing to find the best possible bur size and shape to work with the slide hammer point, and found that the FG701 to be ideal if the rotating technique is used during the drilling process. As you have discovered going to a smaller size creates chipping and/or fracturing of the glass surrounding the drill hole, and of course there is no benefit than going larger than necessary. We tried the same shape bur in one size larger to see if we could eliminate the need to rotate during the drilling process, but for some reason that does not work as well either.

I understand not wanting a larger than necessary drill hole, but when weighed against the benefit of having a perfect mini-bullseye to terminate a long crack, I feel it is worth it.

I should also mention that all of our testing was done after the inventor of the slide hammer sent me one to try. The one he sent me worked perfectly but we had to be sure there was no better combination of size and shape that would work better, so we tested, and tested, and tested, but in the end we really could not improve the way the too performed, so we used the same size and shape of point that came in the original sample. It was very clear that the inventor did his homework on the slide hammer.

A lot of windshield repair technicians still use the needle and tap method so they can drill smaller holes, but I just never could produce desirable results consistently until I was introduced to the slide hammer.