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Unread 04-18-2020, 09:25 PM   #36
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Join Date: Apr 2020
Location: Dupont, Washington
Posts: 38
The Corner Holes

Thanks everyone for all your assistance. It has enabled me to solve the problems I was having and keep this job moving.

Speed - Short story: The higher speed is the way to go with this 3/8" Milwaukee diamond coring bit. I start the hole slow with a variable speed drill and using a jig consisting of a metal bar with a 13/32" hole in the end. Then once it's started I remove the jig, put the bit into a high speed drill running at 3000 Rpm (A Phillips Red Head 606 Hammer drill - with the hammer turned off, of course). Drilling this 3/8" thick porcelain the times I've clocked were:

500rpm: 40minutes
1000rpm: 15 minites
3000rpm: 4-6 minutes (not sure where the variation comes from)

What I'm seeing is that the higher the speed, the higher the vibration - but for me, even in this delicate situation, the vibration is still tolerable at 3000 rpm (This phillips Red Head drill is a beauty). I suppose it would also be the case that a 1/4" bit would have less vibration than this 3/8" bit but I haven't tried that's still tolerable. I think some of the vibration comes from the hole saw rubbing against one side of the hole as it goes down into the bore (not sure).

Vibration control: throughout the duration of the cut, the tile itself is sitting on one of those foam cushions that you can buy in a plant nursery intended to cushion your knees when you pull weeds in your garden - seems to work perfectly! (a variation on CX's "scrap of carpet" idea)

Cooling/WaterLube: The water is a continuous stream that comes from my garden hose. The Ryobi Handheld wet Circular Saw comes with a hose connector to squirt water continuously on the circular diamond blade I just disconnected it from the wet saw and used it to squirt water onto this hole saw. (it includes a regulator to reduce the water pressure from the hose pressure to about 5 psi - similar regulator to the ones used for drip irrigation in gardening)

I don't know if the bit I'm using is "electroplated" or not. It is a Milwaukee "Diamond Plus hole saw".
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