Cutting holes question

[plain ol Bill]

I have a job that I need to cut a bunch of (32) holes into 1/4" plate. I have been experimenting some and the closest I have come to get a pretty decent looking hole using my Hypertherm 1250 is:
80 amps
134 arc volts
23IPM
straight in & out leads in's
pierce height .125
cut height .0625
kerf width .080

What recipe would you use for a .375 hole in 1/4" ??

[I Lean]

I'd probably use a 3/8" cobalt drill bit after whatever plasma settings I used, to make sure the holes are round and straight. Once the hole is there, it wouldn't take long at all on a drill press to do all 32.

[I see spots]

I remember Jim Colt saying "low and slow" for holes less than 1" and use the lowest amp possible for the material.

I'd have to look at the shop, but I think i'm cutting holes in 1/4" @ 40a, 15 ipm and .055 cut height.

drawing bolt holes .010" oversized at these settings has worked well for my Powermax 1000

BUT

Ima Newbee

[jimcolt]

If you are looking for best quality holes.....use the 40 amp shielded process. Folow the specs listed in the Hypertherm manual......your lead ins should be half the diameter of the holes (start in the center).....the holes should be cut at 60% of the optimaum recommended cut speed at .06" cut height with .12" pierce height. Cut all of the outside contours at optimal speed settings.

if you are looking for the best quality holes.....use the above specs but size the holes about .015" undersized and drill them with a good quality solid cobalt drill.....not coated cobalt.


Jim Colt Hypertherm

[WSS]

I have used Jim's pdf on hole quality on a regular basis. Anti-spatter will help on small holes like that. A 90? lead in from the center is essential, a 10? or 12? arc on the lead out that is twice the kerf diameter in length works pretty good. Make sure you freeze the torch or it will want to kiss the plate at the slower speed. I would go .1" arc start height and .18" pierce and a .1" cut height just in case you encounter a stuck pierce booger on the loop around. Holes will be very close to size if your machine has good accel and clean motion. Go by the Hypertherm book specs for amps, speed and volts. LOW AND SLOW is a good rule of thumb. I am going to make a sign for our table that says that!

WSS

http://plasmaspider.com/viewtopic.php?f=45&t=3306

(Jim's pdf on hole cutting a must read!)

[Dawgonhawg]

This is good info for us beginners.

[aicomp]

Hi,
I second what Jim said. I use the 60 amp shielded consumables and cut at 86 ipm on 1/4 with my HT1250. I get great holes and almost no dross. I use the settings from the manual on everything I cut. The Hypertherm recomendations are pretty spot on. I do cut holes slightly undersize and finish with a cobalt drill.
My $.02
Mike

[plain ol Bill]

Guys thanks for all the replies. I need to do some more experimenting with lower settings I think. I do not generally do holes that need to be very close in tolerance. I know the 1250 is more than capable.