Precision part with an entry level cnc plasma!

[jimcolt]

Today I needed to make a fairly precise mounting bracket....and my buddy with a machine shop was away on vacation. I had to get the bracket done today....so I imported the .dxf file of the drawing into my PlasmaCam software. The part needed a bunch of 1/4-20 tapped holes in 1/4" steel plate, as well as 4 countersunk holes for 1/4" bolts.

I resized all of the holes that needed tapping to about .187", as the proper drill size for tapping 1/4-20 is no. 7, or .201". After plasma cutting the part using the PlasmaCam machine and a Hypertherm Powermax45....I went to the drill press and ran the #7 drill through all of the holes (I used a high quality cobalt drill bit as the air plasma cut holes have a nitride hardening on the edge....if it was an oxygen cut, there would be very little hardening). The four clearance holes were countersunk for flathead socket screws. Here are a few pictures....The tolerances for the part are pretty tight...about .005", more than adequate for the job! Amazing what you can do with the wrong machine when you put your mind to it!

Jim Colt

By the way....this bracket is to hold two different z axis slide assemblies for a cnc machine that will be equipped with a Hypertherm HPR260xd plasma and a new 1.5 kW Fiber Plate Laser. Plasma and Laser on the same machine.....this will be the demo machine in the Hypertherm booth at the upcoming Fabtech show in Atlanta.....should be a great demonstration showing how plasma and laser can work together on one machine. The plasma can cut from gauge to 1.5" thickness, the new Hypertherm laser can cut from gauge to 1/2". Kind of ironic that the little Powermax45 air plasma is cutting out parts for these high end industrial machines!

[DanOSB]

Nice job..

you are going to fabtech?

Erik and I are considering going will visit hypertherm booth if we decided that we are going for sure

[jimcolt]

I have been at every Fabtech and AWS show for 30 years.....I'll be there this year. You will hear me on the PA system at the Hypertherm booth talking about the Laser and the HPR (high definition) plasma...

Jim

[DanOSB]

sounds good.. hopefully ill make it this year..

[multiplex]

damn thats impressive! can you post a close up of your entry points? speeds and torch config?

can i come to your house for a private lesson?

[jimcolt]

The speed setting was right out of the Hypertherm manual for 1/4" steel, 60 inches per minute, although the PlasmaCam software automatically performs a slowdown of approx 60% on holes under a preset diameter (I have mine set at 1")....nice feature that helps minimize taper in the holes.

The hard part, cutting holes that are smaller in diameter than the thickness of the plate requred a few tricks....in order to make the holes round with no lead in divot or ding. Since the holes were to be .187" diameter, I made the lead ins .09" (so the torch would start dead center), and sprayed mig anti spatter spray on the top of the plate....this makes the top splatter (from piercing) blow away, which minimizes arc deflection (if the torch runs over a small glob of top splatter...the plasma arc will wander...this is a common cause of out of roundness on small holes).
Pierce height was set at .22", cutheight at .06"....the PlasmaCam machine has a very nice torch height control that accurately finds the surface of the plate before every pierce (using ohmic contact), retracts to pierce height, pierces, then lowers rapidly to cut height while still in the original pierce location. It is critical with plasma to get to cut height while still on the lead in...this allows the plasma arc to stabilize before getting on the actual cut path contour.....if this is not done, holes will be out of round as well.

The holes were very round, but had a slight taper, as I would expect. Next step....simply drill them to the right size....this drilling takes the hardness out of the edge (approximate depth of hardness with air plasma on steel is .005") so the holes could be tapped.

Jim

[multiplex]

jim, when you say "then lowers rapidly to cut height", how fast is fast?

50ipm, 100ipm?

thanks

[jimcolt]

The z axis speed is currently set at 100 ipm.

Jim

[WSS]

Originally Posted by jimcolt The hard part, cutting holes that are smaller in diameter than the thickness of the plate requred a few tricks....in order to make the holes round with no lead in divot or ding. Since the holes were to be .187" diameter, I made the lead ins .09" (so the torch would start dead center), and sprayed mig anti spatter spray on the top of the plate....this makes the top splatter (from piercing) blow away, which minimizes arc deflection (if the torch runs over a small glob of top splatter...the plasma arc will wander...this is a common cause of out of roundness on small holes). Jim

Now that is a trick! I will try that Monday. I just cut some .5" plate with some close tolerance holes and had some wander. I could see the shield stick momentarily and jump a little, never even thought about the arc shifting when it ran over it. I just painted the parts but will take some pics anyway and post em.

WSS

[MBG]

So you built this plasma machine and will be displaying it at fabtech? I have to see it as I am building a CNC plasma.

Also, have to talk to hypertherm about the plasma cutter for the machine.

See you there.

[jimcolt]

No, I have a PlasmaCam cnc machine....with a Hypertherm Powermax45 mounted on it. I was cutting some parts for the Hypertherm demo machine that we (Hypertherm) will be using to demonstrate one of our high definition class plasma systems as well as our new Fiber Laser cutting system.

Jim Colt

[Weminuche]

I've seen videos of a Komatsu unit that auto sprays anti-splat. Would be a nice feature to have on your HD versions