Drill bit speed question?

[cuervo]

I know large bits should be used at a slower RPM and smaller ones at faster RPM but does anyone have a guide or link to what RPM is best for what size bit?


Thanks.

 

[Snowman1000]

depending on what material your cutting

Rpm=Cutting Speed x 4 / Diameter of the drill bit

Some general cutting speeds are

100 I.p.m. Steel
75 for S.s. Steel
150 for cast Iron
150 for Brass/ Bronze
400 for Aluminum

So for a 1 inch drill bit in steel

(100 x 4) / 1.0 so 100 Rpm if your using carbide you can double your rpm

This is what we use for figuring rpm on machine work but yes bigger bit slower speeds.

 

[cuervo]

Thanks that's great info.

I do have one quesition, because I math good.


Isn't (100 x 4) / 1.0 400 rpm not 100 rpm as you posted?

Or am I not understanding you.


If I was doing stainless with a 1/4 bit it should be.

(75 x 4) / .25 = 1200 RPM

Am I understanding this correctly?

 

[Snowman1000]

yeah your right, not quite with it today sorry for the confusion

 

[cuervo]

Thanks for the pointers, Snowman! I'm sure to save some bits with it.

 

[BlazerBud]

When drilling steel, make sure the bit is cutting. As long as you are getting flakes of steel or curly cues coming off the bit, you will be drilling good and the bit will stay sharp and last a long time. The steel flakes carry away the heat. If you are just spinning on the surface, the bit will overheat and loose its edge and temper, no amount of resharpening will be able to fix a softened bit. Also, a squeeze bottle with cutting oil will help. Basically, a slow speed will be better for steel, and moderate bit pressure during the cut, but right before penetration ease off some.