Hypertherm and cut sizes

Hi Guys,

I have a hypertherm powermax 1650 cnc and am entirely self taught. As such I am having trouble with some things.
My struggle today is getting holes and squares to cut the right size. I am attempting to cut a 50mm square with several 10mm holes inside the square.
Trouble is the holes end up 12mm and the square ends up 48mm. The holes cut counter clockwise and the square cuts clockwise. Kerf value is set to 0mm. I did try setting it to 2mm but for some reason the holes then cut elongated.....maybe a different problem?
I am using 60amp consumables with 3mm plate, 1.5mm cut height and 138volts.

Any help would be appreciated.
Thanks,
Richard.

I am no expert but I have a week in on my new machine and plenty of other experience.
I also have no idea what software or control you are using.
I do know that with my Powermax 105 I would chose 45 amp setup to cut 3mm (maybe even go with finecut).
If Kerf comp doesnt work (your oblong holes sound like a software issue to me) - just draw your part manually to compensate.
Here is Hypertherms kerf est chart from my manual.

based on your numbers , it sound like you should have the kerf set at 2 MM, about .080. When you are cutting the circles, you are cutting on the inside so you will add the kerf width to the diameter. When you are cutting the square, you are cutting on the outside so you will subtract the kerf width from the length and width.

I don't understand the elongation problem but without the kerf width entered in your software, you'll never get the correct results. The software (Sheetcam in my case) compensates for the kerf width so you get the correct dimensions.

Good luck.

Willy

Thanks for the replys! Yes I should have mentioned that the controller is Hypertherm EdgePro and the shape I am cutting was drawn in Autocad and brought across to the machine in 2010version .dxf

The majority of the cut work I am doing/going to be doing will be in this format of being drawn up in autocad. How do I tell the machine what parts in the drawing are to be cut on the inside or on the outside of the line? Especially when there are lots of parts in a drawing. I have read about putting text inside the drawing itself, but reading about it and actually doing it and getting it to work....well....

Autocad is the cad portion. The dxf file should represent exactly what you want the part to look like. The CAM software takes the DXF (or other CAD files) and converts it to Machine Code ( G code) to run the CNC machine (plasma , mill, lathe, etc.). The CAM software adds calculations such as kerf width, lead ins and outs, etc. to the G code.

If you were cutting a 1" circle inside a 2" square, the circle would normally be cut first. The CAM software should determine that the first cut, the circle, is inside the major part and would subtract 1/2 the kerf width from the absolute torch positioning in order to give you the correct final value. Likewise, on the final cut of the square, the CAM software would add 1/2 the kerf width to the cut position all the way around the square. You shouldn't have to specify which cuts are on the inside or outside. Some software will let you determine the order of cut but the result is the same.

So if you have a 1" circle and a .050 kerf width, the torch center will rotate in a circle .950 in diameter ((.025 from the final circle edge). This is the classroom explanation. I'm sure there are other variables but this is the basic stuff.

Don't forget that with Plasma, as the consumables wear, the kerf width will increase and it can also change with cutting height. If you need a precise diameter or exact shape, leave enough to do a final machining operation.

willy

Willy

I agree and disagree with Willy.
What he says is true (and IDEAL) accept the fact that he makes it sound like that is the only way.
The one g-code converter (CAM) in my machine does not do Kerf compensation (that I have found anyway). As I mentioned earlier, draw it with factored sizing for this scenario.

My troubleshooting mind says that if your machine cuts round holes with kerf comp off and egg holes with kerf comp on. Then something is wrong with your software.

If it is always cutting egg holes, could be as simple as worn electrode.

Normally with an industrial cnc control such as the Hypertherm model you have....a post processor software (such as ProNest) is used. The .dxf file (from AutoCad) is then imported and the lead ins, lead outs , kerf compensation and cut direction are automatically set.

With the Edge Pro...if your are importing a .dxf file directly...then you must manuall setup the lead ins, lead outs, kerf compensation and in some cases cut direction. I would suggest going back to the OEM or dealer that supplied the EdgePro for training....as it should be included with the sale. With specific questions you can also contact Hyperther technical support....and they will help you out as well.


Jim Colt

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Originally Posted by richard75

Thanks for the replys! Yes I should have mentioned that the controller is Hypertherm EdgePro and the shape I am cutting was drawn in Autocad and brought across to the machine in 2010version .dxf

The majority of the cut work I am doing/going to be doing will be in this format of being drawn up in autocad. How do I tell the machine what parts in the drawing are to be cut on the inside or on the outside of the line? Especially when there are lots of parts in a drawing. I have read about putting text inside the drawing itself, but reading about it and actually doing it and getting it to work....well....

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