torch or plasma?

[rmcphearson]

I need to cut about 15 holes from 1/2" to 3" in diameter in 1/8" increments in a 3/4" steel plate. My o/a cutting skills are fair. I may be able to borrow a plasma but I've never used one. Will I get better results with my fair o/a skill or with my first-time plasma experience?

If the edges come out rough I may have them cleaned up on a CNC mill.

My thinking is to turn a disk 3" diameter and "trace" around it with the torch or plasma, then turn the disk down to the next smaller size, repeat and so on.

I haven't found a place around here yet that will laser cut it. I'm sure that would be cheaper than having it cleaned up on a mill. Any advice would be appreciated.

Roland

[metalmagpie]

You will get similar results as long as you know how to use both setups *and* you have a circle cutting attachment and are reasonably good at using it.

There are a million waterjet guys out there now, though. Just have the part cut. It will need slight deburring but will otherwise be essentially perfect.

[Pherdie]

While I'm not an expert in metals, I would think an O/A setup would put more heat into your work than a plasma, thus possibly having a greater perimeter of hardening around your cut (depending on your steel).

Can anyone knowledgeable comment further?

[hardtail]

You should get way better results from plasma, make sure it's rated for that thickness and try a few parctice cuts first.......

[Dr Stan]

The plasma will produce a much smaller heat affected zone, a cleaner cut, and more precise holes. While I'd recommend some practice the techniques for plasma cutting by hand are not dramatically different than those of OA cutting.

That said, I think the recommendation to have them cut with a water jet is is an excellent idea. Zero heat affected zone and precision of around .005"

[macona]

I wouldnt say way better cuts with plasma. A good oxy-fuel cut will look like a plasma cut. But oxy-fuel has a much bigger HAZ as mentioned.

3/4" thick is very heavy for laser. Thats a big machine.

[dave5605]

I'm just a home hobby guy with a plasma that cuts up to 1/2" so take this for what its worth.

Rather than trace around a disc I'd drill appropriate oversized holes in a piece of 1/4" plywood (or similar material) and drag the plasma tip around the inside. It would give you a lot more control of the finished line and much easier to clamp in place.

Less opportunity to 'sneeze' and end up with holes that look like they were chewed out of the plate. Once that plasma arc starts any deviation in moving the tip is instantly reflected in the finished product.

You want to practice a little (piercing and cutting the actual holes) on scrap before doing the actual cuts.

[lazlo]

I have both, and plasma leaves a much cleaner cut, and takes almost no skill.

Both leave a hardened kerf. I cut a knife blank out of O-1 tool steel with my plasma cutter and it was a PITA to grind off the profile.

[tsmartin_98]

If it were me, and I could use a mill, I'd use drills and hole saws then finish bore. That would avoid any heat generated issues.

AB

[tmc_31]

I have and use both. If I was going to burn the holes, I would use the plasma cutter. It will yield a smoother cut and a smaller heat affected zone. My plasma cutter has become my go to offhand cutting machine. The O/A torch has been relegated to heating and gas welding duties. A tank of gas lasts me a long time.

All that said, if I wanted clean holes that might need machining later, I would consider "Annular Cutters". They are like grande carbide hole saws and are made to cut 2" and deeper in steel. I have a small mag drill (Champion RB32) and regularly use an annular cutter with it to cut 1" holes in 1.5" plate.

http://www.championcuttingtool.com/rotobrute.html

Tim