part 3: drilling action, use personal protective gear when drilling...ear plugs, safety glasses etc.
Now is the time to talk about heat. Heat is the enemy. Heat destroys the cladding that holds diamonds onto the drill bit. Heat will destroy the cladding faster than the stone wears out the diamonds. If enough heat is generated, the stone can crack or the bit can expand and get lodged in the partially drilled hole. Everything you do in the drilling operation is to slow the buildup of heat and help remove waste heat from stone and bit. The cooler everything is kept the longer your bits will last and the faster the drilling progress
Some things to keep in mind: more RPM=more heat, more pressure=more heat, deeper hole=slower heat removal
In general, use the coldest water your fingers can stand in your water pan. If you are drilling a heat sensitive material, put it in the freezer overnight to get a head start on the heat (no I am not kidding)
The tips above are only stopgap measures to help with initial heat buildup. The real heat control is in the RPMs, the applied pressure and the cleanout rhythm.
RPMs. The numbers below come from my personal experience. If you are burning up bits quickly, try a lower RPM setting or a lighter touch or both
1mm-->9000 RPM
2mm-->4500 RPM
3mm-->3000 RPM
4mm-->2250 RPM
10mm-->900 RPM
Don’t worry if you don’t have the exact setting, just try to get close. Remember the bigger the diameter, the slower the RPM.
Pressure…Remember the bathroom scale? Try to use less than 20lbs, lighter is better. Let the bit do the work.
Cleanout rhythm…you will get a feel for this. I watch the swirl of dust that appears during the drilling action and listen to the noise that I hear to tell me when to raise the bit so that it can cool in the cold water bath.
First contact
Starting to dig in
Good cutting action
Time to lift the bit and have it cool
This whole process should take only a few seconds. Let the bit spin in open water for a few seconds then reengage and repeat. If the ‘smoke’ coming out of the hole turns black, stop the operation and check the bit. It is likely that the cladding is starting to fail or has failed. Swap bits and continue. You don’t want large chunks of cladding coming off in the hole as they are nearly impossible to get out and the piece will be ruined.
Use your ears as well as your eyes during the drilling process. You should hear a distinctive grinding sound. Increase the pressure and the pitch changes. Learn the noise your system makes when the drilling is good.
still to come, drilling deep