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Countersink Feed and Speed

RMW864

Plastic
Joined
May 9, 2017
I am having trouble finding the right feed and speed for a 60 degree 1-1/2” single flute countersink for my haas mini mill.
Material is 1018. There is a 13/32 hole that is pre drilled. I am having to go about 1” deep with the countersink, bringing the largest diameter to 1.2”.
To be safe I am currently running 300rpm and .5” IPM. It’s putting a high load on the spindle and surface finish isn’t good. Any help would be appreciated. Thanks
 
1018 is not known for it's machinability.

The first thing I would try is a good cutting fluid; one with good lubricative properties. Tap Magic or perhaps a good lubricating oil like LPS. Cooling is not the only function of a cutting fluid.

And, of course, is the CS sharp? DEAD SHARP? Many are not even when factory new.

And the obvious fact that this sounds like a bit of a heavy cut for a mini mill.
 
If you need to do a lot of them,interpolate with an end mill

Or, rough with a ~3/8 ball endmill (or whatever) spinning as fast as you can. Don't worry about finish, only edge breakdown, lower the RPM if you get excessive wear. Keep to around .02" between cusp heights, min .01" finish material at the shallowest section of the cut.

Finish by interpolating with a good, sharp 1/2" x 60* countersink, perhaps a carbide 4-flute. Starting at the top, drop in by .25" depth, adjusting cut radius to suit as you go successively .25" deeper (or whatever you decide is best).

Now you've got your geometry AND cutter selection that works well within the stiffness and speed capacities of a Mini Mill.
 








 
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