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Spencer Lapidary Archive Page
Thursday, July 16, 2009
Tina & I get asked all the time about drilling rocks, slabs and gemstones. Most questions concern the problems people experience while trying to drill with diamond drill bits and not having very good results or life from their expensive bits.

First ask yourself a couple of questions. Are you using sintered or plated diamond drill bits? At what speed are you drilling? Are you withdrawing the drill bit often to allow for flushing and cooling?

Sintered diamond bits have the diamonds mixed directly into or embedded in the steel tip. As the metal tip wears down, new diamonds come to the surface. Sintered diamond drill bits tend to hold up better than plated diamond drill bits; however, they are initially more expensive. The life of any type of diamond drill bit depends upon the hardness, abrasiveness and thickness of the material being drilled and the specific drilling techniques used (drill speed, pressure and lubrication), however, the diamonds of a drill bit don't actually wear out as much as they wear off due to heat and friction caused by the extreme hardness and abrasiveness of the material drilled. Plated diamond drill bits tend to shed their layer of diamonds more easily and you are soon left with nothing but a blunt steel rod with which to drill.

SPEED KILLS: Reduced drill speeds, low drill pressure and increased use of water lubrication will extend drill bit life considerably.

We DO NOT recommend drilling metal. When you drill metal with a diamond drill bit, the metal will build up on the diamond drill bit covering the diamonds that actually DO the cutting for you. You CAN NOT dress a diamond drill bit with a grinding wheel, because the diamonds on the drill bit are harder than the grinding wheel. About all you may accomplish is to knock off more of you precious diamond particles. Sintered diamond drill bits have a much thicker layer of diamonds so that when one diamond is knocked out in the drilling process, the one below with take its place.

Tina & I find that we are able to drill dozens of holes by following the rules below.

  1. Use a good quality sintered diamond drill bit if you can afford them.
  2. Drill only hard rock or glass, no metal.
  3. Drill at fairly slow RPMs.
  4. Use lots of water as your coolant.
  5. Withdraw the diamond drill bit from the hole often to allow the fresh cooling water to flow in and flush out the waste material.
  6. Use a small drill press. You'll put less stress on you diamond drill bits and your hands by using a drill press rather than hand drilling using a flexable shaft or electric drill.

Happy Rock Drilling!

Tina & Mark Bennett



by: Spencer Lapidary





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