How I make Step Drills w/pics!

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rherrell

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Joined
Aug 22, 2006
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Location
Pilot Mountain, NC
The first step is grinding the correct diameter and length. I use my Themac toolpost grinder for this...

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It has a 4" CBN grinding wheel and in the background you can see my dust collection. I use my Festool shop vac, I ran a 30' long hose to it and I have a remote control to turn it on and off. The lathe runs at 500rpm and the grinder runs at 4,200rpm but they run in opposite directions.


I hold the drill bits in a Set Tru er40 collet chuck that I can dial in to less than .0002" of runout.

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After the lathe they need to have the relief (clearance) ground on the flutes, I use my Tool and Cutter Grinder for this...

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I had to modify the machine to do this operation.
First I had to make my own er32 collet chuck to hold the drill bits, it came with 5C collets but they wouldn't work for all the different diameter drill bits I'll be grinding.

Then I had to make an extension (the round aluminum piece in the center) so I could get the drills on the other side of the grinding wheel. This machine is made for grinding end mills and that's done on the left side, in order to grind drill bits I needed to be on the right side.

The last mod was getting the grinding wheel to run clockwise instead of counter clockwise. To accomplish this I used a trick the old belt driven steam operated shops use, I put a twist in the belt. You can barely see the green belt behind the grinding wheel, it has a round profile so putting a twist in it was easy.

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This pic shows a close up view of grinding the flute relief. The machine has precision dials to get the bit in position but I have to twist the collet chuck by hand to get the correct grind. Basically the machine is a precision holding device, all the contouring is done by hand.

Here are some pics of some step drills using this method...

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