Making pin drills

[David HaynesParticipant @davidhaynes53962]

What am I doing wrong with my pin drills. I have a silver steel round, say 3/8″, drill for pin size, create a cutting edge, harden and temper and yet it won’t cut very well.

 

Any advice, thanks

 

Dave

[David HaynesParticipant @davidhaynes53962]

Advice on improving pin drills

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

The most common problem with silver steel tooling is running them too fast . This causes the hardening to go and the tool to become blunt at practically first contact .

 

For a 3/8 inch pin drill cutting steel you may have to run as slow as 50 rpm to get any sustained cutting life .

 

Post hardening sharpening is in any case essential as is use of at least basic coolant .

[David HaynesParticipant @davidhaynes53962]

800rpm may be ok for turning but not cutting! I’ll try the slower speed. Any advice on getting the best shape for cutting edges?

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Very simple tooth shapes work best – just a straight cutting edge with about 15 degrees backing off . More important is chip clearance – with small teeth on a cutter working in an effectively blind hole there is nowhere for swarf to go unless some provision is made . There is no entirely effective solution to this on small cutters but it is worth trying double backing off of the cutting edge ie 15 degrees for the cutting edge but with a steep angle behind which forms a relatively deep gully for chip clearance .

 

 

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