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Have drilled hundreds of saddles like you are talking about, since I am a sprinkler guy myself. I have found that when drilling the hole and you are almost through don't push so hard and the coupon will stay on the pilot bit.
Victaulic did make a pilot bit that had a small wire brazed on the end in one of the flutes, so that when the pilot bit made the hole and advanced in the spring would compress, go through the hole, and then expand again thus trapping the coupon on the end of the pilot. I looked on victaulics web site but did not have any luck finding them.
When ever I use a hole saw I always drill the pilot hole with out the hole saw attached. I have seen too many people push really hard and then the holesaw bites on the material and shears the drill bit off with the holesaw marking the job surface.
My best suggestion about not letting the piece fall in would be to drill a pilot hole and then have a seperate mandrel made.
The new mandrel would be a 1/4 rod with a 90 degree bend on it that you could thread into the pilot hole, drill the hole and with any luck the piece will stay on the bent piece.
Wow, does this bring back memories of when I used to do these before retiring. Murphy's Law's state that if you drill a pipe in the shop, on the floor, the coupon (correct term) will always find a way to stick into the hole saw. BUT, once you climb that proverbial ladder (before I saw my first mechanical lifting device) and drill out a hole for a saddle, the coupon will fall into the pipe being drilled even if you are drilling from the bottom. Have you had the experience of tieing in a 2" saddle to a 6" pipe using ladders? NO cutting torches allowed! Are plasma cuts allowed nowdays? Had I ever had the opportunity to get into my possession one of those pilot bits with the little "fingers" I would have kept it in my pocket so no one else would know my secret. Yes, our local Fire Marshall, and IRI Inspector wanted those coupons tied close to the new tie-in. The IRI Inspector would have us damage the coupon so we couldn't use it again, he had worked in the field, he knew. Thanks, David
After your hole is 90% cut remove the 1/4" pilot drill and replace it with a special 90 degree Allen Key, which is described below. Put a mark on your drill chuck where the right angle is on your Allen Key. Hook the Allen Key back into your pilot drill hole and continue cutting. If you are cutting a vertical pipe almost cut through, line up the Allen Key upright in the pipe and then wiggle out the cut piece by rocking the drill up and down. Lightly file the hole saw hole to remove the burr.
Buy an extra Allen Key and grind it down the right angle to 3/8", which will be good for 3/4" and larger hole saws.
For larger holes grind down a second Allen Key to 1" which will be good for 2" and bigger size holes.