increase of cut quality

[betamot123]

Hello friends,

so far my DIY table runs well, but to be honest id expected a better cut result. Mechanicly the table is perfect, I orientated me on many industrial manufacturers and picked double linear bearings on each axis, belt drive strong steppers and so on. Plasma source is a Powermax 65.
My main troubles are holes( oval never round), dross, V formed angles although using Hypertherm parameters.
Latest improvement on the machine was the Proma THC which helped a bit.
Lazy as I am, I dont want to invent the wheel twice. Do you guys have suggestions what kind of improvement can be done?
My thoughts are: air dryer, extra pressure regulator in front of plasma source, fine cut consumables. Or may be anything else that helps.
Thanks in advance

Dieter

[acourtjester]

if your holes are not round you need to re-calibrate the X and Y steps per.
Make a pen holder attachment and use it to check your work.

[jimcolt]

There is no motion control that is perfect. The plasma as well is not perfect and will always produce a certain amount of taper.
Here are a few things you can do to help troubleshoot your issues:

- Install a spring loaded pen in the torch holder and trace some of the parts that you are having issues with. Look carefully at fine features and holes, and run the trace at the same speed that you would plasma cut at. If holes are out of round with the pen tracing then expect them to be out of round when cutting.

-Assuming the holes appear perfect with the above tracing....but are not round with the plasma....then you will need to look carefully at the functions of your hole design (lead in location and length) your height control functions (pierce height, pierce delay, transition from pierce height to cut height) as these all have a huge effect on the shape and quality of the hole. Some height controls work better than others and hole quality is the first thing affected.

- Choose the correct consumables and process cutting specs. For best edge angularity and fine feature (small holes included) use the lowest amperage process that the cutting charts (in the operators manual) suggest can be used for the material and thickness being cut. As an example....if you are cutting 3/8" holes in 1/4" steel plate....use the 45 amp shielded consumables. The 65 amp consumables (and larger) will certainly cut holes but will demand more from the motion control and height control.....expect out of round and taper.

- A rule of thumb for holes under 1-1/4" is to cut them at 60% of the recommended (best quality) speed from your cut charts. This assumes all of the above issues have been addressed, and it assumes that the height control transitions completely from the pierce height to the cut height (physical height, not arc voltage feedback height) before the cut path reaches the hole contour (this is why lead-ins and pierce delays are important).

- I have a presentation that describes the necessary "best practices" for hole quality with plasma cutting. I will send a .pdf copy of it to anyone that emails me directly.

Here is what holes can look like on 1/4" steel with a Hypertherm plasma when the height control, motion control , part program and plasma cutter are all operating properly. The dimensions show nominal top and bottom measurements....these holes are sized to accommodate normal taper...so bolts will drop through with no secondary rework. Cut with a Powermax85 with 45 amp shielded consumables paying careful attention to the above issues.

Best regards, Jim Colt Hypertherm

dimensions.jpg (106.35 KiB) Viewed 1149 times

dimensions.jpg (106.35 KiB) Viewed 1149 times

[Brand X]

I might cut the hole, and trim up with my ironworker punch. Gets a real nice hole that way..(depending on the part) I like the idea of zero taper for best overall strength of the fastener. I also use my mag.drill and SheetCam plasma drill/marking to get the quality I want..

[jimcolt]

I agree with Brandx if the holes need to have no taper. Probably 98% of the bolt holes I produce are fine with the amount of taper shown in my previous picture. If I need better holes I plasmacut them about .020" undersize and then drill them with a good quality Cobalt drill. I have successfully done 3/16" diameter rivet holes on many occasions with plasma as wel...no drilling required. On low cost entry level cnc machines good holes do not cut themselves....you must pay attention (as previously posted) to the plasma, the height control, your part file and your cnc machine settings.

Jim Colt