Flakes instead of chips when drilling steel structural tube

[tominboise]

I helped a friend drill some 11/16" holes in structural tubing (2X4X1/4") and the drill bit was putting out flakes instead of chips with some length to them. I pilot drilled with a 1/4" bit and used thread cutting oil while drilling. We were not feeding the bit very hard, so I am wondering if the slow feed rate was the cause of all the flakes in lieu of a more normal chip? If we fed the bit too aggressively, we would stall the press (It's an old Buffalo drill press from WWII that my dad bought after the war, and I inherited from him).

 

[woodchucker]

I helped a friend drill some 11/16" holes in structural tubing (2X4X1/4") and the drill bit was putting out flakes instead of chips with some length to them. I pilot drilled with a 1/4" bit and used thread cutting oil while drilling. We were not feeding the bit very hard, so I am wondering if the slow feed rate was the cause of all the flakes in lieu of a more normal chip? If we fed the bit too aggressively, we would stall the press (It's an old Buffalo drill press from WWII that my dad bought after the war, and I inherited from him).

yes, the slow feed rate was not cutting. you want to put pressure on big bits, and make them cut. If you do stainless and don't put enough pressure you harden it and then can't drill it.

Also a sharp bit is important. You should push as hard as possible, and if it's stalling the the press, then go to a lower RPM, the lower RPM have more torque, and with large bits will not burn them up. With small bits you need high RPM, with big bits, slow is fine... I prefer low RPM and more gronk, but don't bend the bit.

 

[tominboise]

yes, the slow feed rate was not cutting. you want to put pressure on big bits, and make them cut. If you do stainless and don't put enough pressure you harden it and then can't drill it.

Also a sharp bit is important. You should push as hard as possible, and if it's stalling the the press, then go to a lower RPM, the lower RPM have more torque, and with large bits will not burn them up. With small bits you need high RPM, with big bits, slow is fine... I prefer low RPM and more gronk, but don't bend the bit.

I'm running the press on the lowest speed it has, so I can't go any lower. Nature of the beast, I guess.

 

[Provincial]

A harder steel is more brittle, and the chips have to curl as they are removed. At a certain combination of feed and speed, this can cause the chip to fracture completely along the cracks formed when the chip is curled. This happens because the ductility of the steel is exceeded.