Spotting drill

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Friday, Apr 7 2017

The mill is working well and meeting my needs. I also use the mill for drilling. It’s slower to crank on the Z axis than a drill press (or larger mill) with a quill that can be lowered) but it gets the job done. I do, however want some spotting drills to start holes and keep drill bits from wandering. Since most of my drill bits have 118° angle points a 120° spotting drill would be perfect. Hmmm.

Truing stock in the 4-jaw

Truing stock in the 4-jaw

Truing stock in the 4-jaw

That’s some 3/8" W-1 tool steel being centered with the 4-jaw chuck in the lathe. Once centered I cut a 60° taper on the end for a 120° included angle. When that was done I cut off a small (but large enough) section of the tool steel and moved to the mill.

Milling the bit

Milling the bit

Milling the bit
Ready for hardening

Ready for hardening

Ready for hardening

I used the collet block I made to hold the piece and milled off just under 1/2 the diameter. That leaves a bit of material to grind off after the bit has been hardened. The collet block was then rotated 90 degrees and a slight radius milled along with a relief under the cutting head to make sharpening a bit easier. It’s ready for hardening.

Hardened and tempered

Hardened and tempered

Hardened and tempered

The above was done yesterday. Today I picked up some Map gas (I was out). I put the part on some bricks and got it cherry red before quenching it in water. I cleaned off the resulting scale and heated the part again, this time slower and not as hot. When my thermometer said the part was about 500° I turned off the torch and let the part cool.

It works

It works

It works

Once cool I honed the face on a stone. I didn’t think I needed to use the grinder at this time. As the picture shows, it works. At least it works in aluminum.

If I had use of a D-bit grinder I could have made this out of HSS and got a proper relief ground behind the cutting surface. No matter. This is likely good anough for my needs.

 

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