Drill/tap steel after cutting

[gamble]

It's been my experience that everything I have cut and tried to drill out is a bear and ruins a bit. My last experience was some 1/4" SS trying to drill out a hole and it chewed up a brand new bit.

I have to cut out a piece on 3/8" steel. Should I just pierce the holes and if so will it be able to be easily drilled? It needs to be tapped which is my reasoning for doing it

[acourtjester]

There have been posts about this it seems the metal gets hardened when plasma cut, seems to also be mild steel too.

[gamble]

There have been posts about this it seems the metal gets hardened when plasma cut, seems to also be mild steel too.

Yep that's what I'm trying to see if it's still drillable if i just pierce the hole or even if I just cut the outside edge and drill all the holes by hand if it gets hardened.

Also curious if i have the water really high if that makes a difference

[jimcolt]

Dry cutting with air or nitrogen nitride (case) hardens the edge of most mild steels to a depth of .006" to .010". Cutting with water in contact with the edge can add hydrogen embrittlement as well. Industrial plasmas are designed with liquid cooled torches and special gas delivery systems so they can use pure oxygen for cutting steel...instead of air, this eliminate the nitriding.

You can drill out the nitride hardenened holes using a good quality solid (not plated) cobalt drill bit, these bits are even available in Home Depot....or you can buy them from industrial tool suppliers....always seem to work better!

Jim Colt Hypertherm

[Gamelord]

Get some rapid-tap and use it a lot. As jim said, a good quality cobalt bit, not the plated crap. Learn to re-sharpen the bit because it will chip if it hits a bad spot. Also, drill at a slow speed and let the bit cut the metal out - high speed will burn the bit up in less than 1/16". Once it starts to bite into stainless it will just bore right through with slow steady light pressure. Feel the bit cut through the steel, don't try to smash it through the hole or you will burn it up faster than you can back off. I drill 1/2" holes through 3/8" stainless (304) all the time. I can get many holes without dulling the bit as long as I go slow and steady with plenty of rapid-tap. It seems that once the bit hardens up a bit (after a couple holes) it cuts better and won't dull out for a long time. Just guessing I would say my press speed is between 150 to 220 rpm. If you are drilling at 600 rpm or more forget it.

Hope that helps.

[lockeyone]

Gamelord pretty much drilled it (pun intended). If you are free hand drilling, you could try Crisco shortening as your lub. Had an old timer that used to install lots of lab equipment and when he needed to drill lots of stainless they used Crisco. He did this for over 30 years.

[jason.jason.p]

I set up my job in sheetcam, I put any holes I'm going to drill on a separate layer. I run a "Drill" operation on all the holes which will pierce the hole centers, then a jet cutting operation to cut the outer shape. Here's the important part... while its running the "Drill" operation, I babysit the machine. when the torch moves to pierce a hole center i manually turn off the torch in mach3 just as the plasma arc fires. The goal here is to barley and I mean BARLEY!! mark the plate where the hole center is. it takes some practice getting the timing right but when I do, I have a very small divot similar to a center punch. This hardens just a tiny amount. It's still hard on my drill bits but once i get through the first 0.06 of the hole its smooth sailing from then on. This is much easier than piercing a hole clean through the plate which hardens through the entire plate thickness.

[hsolve]

Good morning gamble.
I believe there is a 'soft peck' for the purpose of center marking holes in the candcan posts. This has to be checked however it was something that I looked at some time ago. I just added a plate marker and in sheetcam just move the hole centers into a different layer and mark them with the air scribe. This feature 'the sir scribe' has many uses apart from marking holes. You can put text on your parts, label, idetify, mark bend lines etc. It is something that can be worth it's weight in gold

[tcaudle]

To take that one step further, if you have the Hypertherm with the RS485 and the interface kit the peck process can be even closer managed so you can back off the amps automatically. Nothing to keep you from doing manually if you peck all of the holes as a separate process. A combo of lower current, precise torch on times, and a higher pierce height can peck small divots in the metal. We just finished up some projects using 18ga mild steel and got centering pecks with no blow though.

[Metriccar]

I use m42 cobalt bits. They work good. I also bought a drill doctor. If you're going to do a lot of drilling you will need to sharpen bits to save money.

[hsolve]

Good morning gents.
The quality of the sharpen is vitally important especially for stainless steel and 316 is worst still than 304. The early small drill doctors were OK however still fiddly to get the correct grind, the newer small ones, don't know, however the XT3000, now that is a drill sharpening machine. Accurate, easy and repetative results, which is what you want. It still only does split point to 3/4" which is a shame.

[Metriccar]

The Drill Doctor is still fidgety. I've only used it to sharpen maybe 15 times (it's already paid for itself), but rarely does it correctly sharpen the first time. Usually takes about 3-5 times to sharpen. But an XT3000 is a $3300 machine.