Counter sinking holes

retiredcpo · Post by **retiredcpo** » Tue Apr 03, 2012 8:40 pm

I find that the holes I cut Are extremly hard and can not counter sink them.
How do you guys deal with counter sinking your holes
retiredcpo

I Lean · Post by **I Lean** » Tue Apr 03, 2012 9:43 pm

Cut them undersize, drill them out with a cobalt drill bit (this will remove the hardened edges) then countersink as normal.

gary42095 · Post by **gary42095** » Wed Apr 04, 2012 5:11 pm

i know nothing about work hardened from plasma but i drill and countersink ar550 plate with solid carbide countersinks and bits

Post by **jimcolt** » Thu Apr 05, 2012 10:22 am

The key to drilling and countersinking air plasma cut holes is with using the correct drill or countersink. Low cost, off the shelf drills and countersinks are designed for drilling on standards grades of mild steel. The nitrogen content in air with an air plasma produces a nitride hardened edge....too hard for regular drill bits.

Solid cobalt (not plated or coated) works well, as does carbide. The cobalt drills are easily resharpenable and work very well.

Picture shows a part that I did a while back. Many of the holes were plasma cut at a .187" dimension, then drilled with a .201" cobalt drill....then tapped 1/4"-20. Others were countersunk....again using cobalt.

Keep in mind that industrial high definition grade plasma's use oxygen instead of air for cutting steel. There is very little hardening when oxygen is used......however you cannot use oxygen in a torch designed for air plasma cutting!

Jim Colt

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Post by **ggeh** » Wed Jan 18, 2017 6:23 pm

Can you tell me what settings I should use to mark the steel where I want to drill later. I tried for the first time and first mark blew a hole through and the rest where better but still about an 1/8 inch wide and 1/8 inch deep. I have a hypertherm powermax 85 using sheetcam and mach3

Brand X · Post by **Brand X** » Thu Jan 19, 2017 12:02 pm

Depends on the size of holes.. I picked one of these up for larger then .500" Amazon is pretty cool, if you know how to look for deals.. $136.22 for this unit.. Nitto are top quality too..Normal price is a bit much, but still top quality..They do sell a chamfer bit,and a thin plate attachment below .250

https://www.amazon.com/gp/product/B00NV ... UTF8&psc=1

Unless you have the correct hardware, and software. it's hard to mark correctly.. I use to do it with zero issues with my Esab 1600 with it's 15 amp low end.. Real nice.. I tried a bit with my 65, and got nowhere fast.. I think with some work I cold get it to function ok .. Now on to my last try without any programing, other then the drill mode in SheetCam.. (Victor A-60 with the valve in torch) Marks the same from first hole to last.. I turned the machine down to 20 amps,put a 120 amp nozzle in the torch for the marking.Good work around, without buying a new machine/hardware.. The 45 XP will mark, but you still have to change consumables to do so.. Real nice marks with a round bottom, to set your drill or punch in (perfect really)