The Murphy Builders Site

Folks,

I am having a heck of a time drilling large diameter holes in the seat frames (which I think are 4130?). Drilling #30 and #40 holes is a cinch. However, I am buggering up my drill bits drilling 1/4 inch and larger diameter holes. I am using generic 'high speed' cobalt drill bits.

I have tried also drilling the holes out in stages as well, with no luck.

Any suggestions of the best practices to drill larger diameter holes in steel? Speed? Should I use cutting fluid? etc?

Thanks, -Jason






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Jason,
My first guess is that you are using to much RPM. Think about the speed of the outer most part of the cutting end with respect to the work. You can use much higher rpm on the small bits as the speed of the cutting interface is lower. Yes, do use a cutting fluid. It cools as well as lubricates. Also apply sufficient pressure but let the drill do the cutting (don't try to force it through with pressure). A smaller diameter pilot hole is a help as well as is a drill press.

When drilling stainless steel use slower speed yet and more pressure. You must avoid spinning the drill bit without cutting or the work piece will harden, the drill will quickly dull and restarting much more difficult. In my case, learning this resulted in no recreation and more education under the 51% rule in the US.
Raalph Baker



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