Torch Height Control Tips

[jimcolt]

Actually....if you look at the specs in the Hypertherm manual under "machine torch" and optimum settings you will see real world cutting specs for cnc machines. If you set your setting exactly the way the manual suggests, you will get a good cut.

The specs listed by virtually all manufacturers for hand torches are the absolute fastest speed, with a new set of consumables. They can be achieved, with a new set of consumables, but not with the best cut quality.

Why do manufacturers list their hand torches with these barely achievable specs? Because the hand plasma cutting business is very competitive.....many buyers make their purchase decisions based on price and cut thickness and cut speed. If you don't list the maximum speed, then you don't get the orders!

Jim Colt

[jeepsr4ever]

Thanks for the explanation! We have tried very hard with TD to get close but havent gotten close enough. We are setting up another powermax 45 unit, good to know we are closer with Hypertherm than with TD!

[sadisticiron]

ya mines an automated 101. not sure if that matters but seems to be pretty good so far.

thanks for the knowledge

[sadisticiron]

i got it. i added the .250 to the pierce and the cut height as stated before due to the z axis limit switch, turned my cut speed to 60, set my amps to 60 and BAM... . the cut was so clean with almst no dross on a worn nozzle.

thanks guys for the help

[Creepy]

Actually....if you look at the specs in the Hypertherm manual under "machine torch" and optimum settings you will see real world cutting specs for cnc machines. If you set your setting exactly the way the manual suggests, you will get a good cut.

Jim Colt

I've been able to produce finished parts on the first cut in different thickness steel, aluminum and stainless with the basic PM45 machine torch cut variables entered straight from the chart.

Made a grill for a guy, never had aluminum OR stainless on the table before.....came out near perfect.

I say they work!

[sadisticiron]

are you adding that .250 or so to your cut and pierce cuts.

[sadisticiron]

bump for the last post

im having a problem cutting holes no matter what size or thickness of steel being cut. the holes in the 3000thc come out as "U's" and in the 1000thc they come out oblong almost like a "d". not sure if its the post or the gantry's motor turn or speed. any help would be nice.

[jimcolt]

Good holes with plasma requires that everything is set up pretty close to right...and the torch height control plays a major part in hole quality...

Rules of thumb for good hole quality with plasma, and these apply pretty much to all holes under 1.25" diameter.

1. Cut speed for holes should be set at 60% of the optimum speed you are using for larger contours on the same materials. This slower speed allows the plasma arc to be more straight, yet will produce a little low speed dross on the bottom of holes.

2. Lead in for the hole should be as close to the center as possible, for a few good reasons. a. Piercing often produces a puddle of resolidified metal on the top of the plate...if this material is in the cut path of the hole, the torch cuts over it and it will cause some instability in the arc which will change the shape of the bottom of the hole.b. Starting near the center allows for more time for the torch height control to index from pierce height to cut height before getting to the hole contour. c. Starting near the center allows for more time for the plasma gas (air) to reach proper pressure and flow in the torch, which is critical for a good cut.

3. Accceleration on your machine (x and y axis) should be set at the highest rate that still allows the machine to stay on path. Plasma cutting of holes is always best at higher acceleration settings.

4. If your cutting machine is tight (good accel, no backlash) then a straight lead in for holes works best, and will leave a minimal ding/divot on the contour of the hole. If your machine is sluggish in the acceleration department, or may have some slop in the drives, a radial (curved) lead in may work best. Plasma likes to cross its own kerf at the end of the cut at 90 degrees, there is less arc instability when the straight lead in is used, however if the machine is sluggish a straight lead in will cause a divot in holes where the meachine has to decell to turn on to the hole contour.

5. Make sure the software programs your holes to cut in the counter clockwise direction. Plasma is directional. If cutting a ring, the ID cuts ccw, the od cuts cw.

6. At the end of the cut profile for a hole....never use a lead out that goes back into the center scrap material...this is bad for hole quality and bad for consumable life. Lead outs are normally used for oxy-fuel cutting. If possible program an overburn of about .200" where the arc off signal shuts off the plasma at the 360 degree point of the circle, but the motion stays on the hole radius and travels .200" past the 360 degree point. If the previous cannot be easily done with your software just cut the hole with no lead out...let the torch extinguish on the radius at 360 degrees. An air plasma is exothermic, meaning it does not instantly extinguish when the off signal is issued, so if motion stops at the same time the plasma stop id issued...there will be a divot in the cut edge.

7. Pierce height must be at the plasma torch manufacturers spec. If your torch manyufacturer does not supply this info...then pierce at 2x the recomended cut height.

8. Pierce delay time must be set at manufacturers specs. If your torch manufacturer does not provide pierce delay times...then just be sure the delay is long enough so there is no x, y or z movement until the plasma arc has fully penetrated the plate.

9. AVC (arc voltage control) should not be active on hole diameters smaller than 1.25". The THC should find the surface of the plate, set and accurate pierce height, once the pierce is complete index down to cut height...and remain at the cut height until the hole is complete.

10. Last, but certainly not least, worn or damaged consumables will screw up every hole shape. Nozzle orifice must be sharp and perfectly round, same goes for the shield orifice. If the above specs are followed carefully...you will get good holes as well as good consumable life.

The above assumes that the machine motion can maintain constant speed, and stays on pathe for hole cutting. A simple test with a pen in the torch holder, and a piece of paper on top of the plate can show your machines ability to cut a circle.

The best plasma torch in the world will not make a round hole if all of the machine motion is not optimized to work together. Incorrect torch height is the single biggest cause of ugly plasma cut holes.

Jim Colt Hypertherm

bump for the last post

im having a problem cutting holes no matter what size or thickness of steel being cut. the holes in the 3000thc come out as "U's" and in the 1000thc they come out oblong almost like a "d". not sure if its the post or the gantry's motor turn or speed. any help would be nice.

[sadisticiron]

gotcha. i think i got it all figured out. is it best to run your holes in your part as a seperate g code or just manually edit the gcode to cut holes at different speeds and cut heights. i manually edit but when u have 300+ lines of code for one part its kinda a pain.

i got my hole cutting thing under control to with the new post from the guys at candcnc. i had a problem with only the lead ins and outs being cut. also the gantries steppers gears were coming loose from the set screws. oblong circles from that aswell from that slight miss step.

i also changed my kernel speed to 25000 and turn my velocity down to 600. that helped alot with cutting. i just now have to figure out how to have over burn on my holes

thanks jim

[jeepsr4ever]

You should not need to interpolate a hole twice.