Torch crashes when cutting thicker material

[gamble]

Was playing around tonight cutting some 3/8" steel. Seems everytime I had height control on the torch would crash.
Why is that?
Is it because of the slow speed? Was cutting 25-29ipm

[sphurley]

That's a little slow for 3/8 with a PM45. 32ipm is book.

[gamble]

I always slow down book spec a little. I think their values are too fast sometimes

[beefy]

I always slow down book spec a little. I think their values are too fast sometimes

Do you compensate for the reduced speed by increasing the Set Volts ???

When you slow the speed down you are allowing more metal to be burnt away in a given time. This effectively increases the arc length and thus the voltage at the torch will be higher than the book Set Volts. Thus the torch may dive down to correct this too high voltage.

Now, as to WHAT Set Volts should you use at a different feedrate, you can find that out with a test cut with THC off. Simply do a straight line test cut at the correct height (THC off) and note the voltage on your screen. Use that value for your Set Volts.

I sometimes reduce the feedrate too and it has given me improved edge quality in the past. My thinking is different systems may not be precisely calibrated or accurate so even though the cut charts may be bang on, some system may not actually be cutting at those parameters. If different speeds etc give you better results, why not.

Keith.

[gamble]

Didn't get a chance to play with it yet, but noticed after changing the settings the holes and overall size are much larger.
night and day larger. I really doubt the .005 cut height made that big of a difference.

[jimcolt]

I use exact book specs on 3/8" when cutting with 45 amp shielded consumables. If the torch dives or runs closer than .060" (ideal height for best quality) then increase the arc voltage until the height is at .060". Things that affect voltage and height relationship:

1. Electrode wear. As the hafnium emitter develops a pit, the torch will move closer to the material....increase the arc voltage to maintain the suggested cut height. Note that some height controls that use "voltage sampling" will automatically do this (Plasmacam is one).
2. If cutting at speeds slower than book settings...then you will need to run a higher arc voltage (than the book setting) in order to maintain the correct height.
3. Changes in cut air pressure will affect height.....this changes the resistance of the arc, which changes the voltage drop across the arc.
4. A slug of moisture that gets from your air system to the torch mid cut....will alter the height (resistance change in the arc).
5. Poor contact between the material being cut and the work cable. (dirty slats, poor connection between slats and material, loose work cable connection, etc. will cause the torch to dive.
6. Incorrect corner AVC (arc voltage control) setting in your cnc...or having this function shut off will cause diving when the torch slows in corners and fine features.

Jim Colt Hypertherm

[motoguy]

Always useful information, Jim. Thanks.

[edclayton1]

I am having the same difficulty too. I was cutting 12 gauge diamond plate one night this week (first time) and the DHTC worked just fine. I had set the Z axis from slow to medium just to be safe before I attempted that. It cut perfectly. Then the following night I went to cut plain flat 3/8 mild steel and my torch would dive into the work or sometimes it would not even pierce the work and would abort the task altogether. I connect my ground clamp from the PM45 straight to the work every time. I do not rely on the slats to pass the current. I also was trying to cut clean steel and I tried replacing my nozzle and my shield but I did not try replacing my electrode as it seemed to look pretty good. I tried raising and lowering my voltage and turning off my DTHC as well as experimenting with the manual automatic button, (whatever that's supposed to do). I tried slowing down the IPM too, also no help. I use the DHTC4 CandCNC system. I have had some problems with height control from time to time ever since I got this equipment. I am new to all this stuff though so I cant seem to figure out whether my problems are operator error or the system doesn't do height control all that well and reliably or some of both. I plan to try some of the other things I read here tonight if time permits. I cant help but think there has to be a better way of DHTC than this whole arc voltage sensing concept. In my manuals from CandCNC they say the torch doesn't have Radar. Well I wish it did. Because It would work a whole lot better if it automatically knew how many thousandths of an inch it was above the surface and it would help if you could dial it up and down with a knob to override it when it seems to decide to get a mind of its own.

[tm america]

Sounds like you have your thc set to low.if the torch is to low you need to raise the set torch voltage on your thc.if the torch is to high when cutting you need to lower the set voltage on your thc.. So raise volts to raise torch and lower volts to lower torch.. Conductivity, cut speed, and many other things effect torch voltage so be mindful changed in material,material thickness,cut speed and cut volts,tip selection all effect torch volts ..Even electrode wear while cutting will cause the torch volts to go up thus making the torch go closer to the material