Changed consumables, then what?

[WinterFabrication]

So I swapped the consumables for the first time today since I've had everything working. Hypertherm45 with 45 amp consumables.

Cutting before, the DTHC was (in my opinion) dialed in pretty good, with no top dross and minimal dross on the bottom.

I changed the tip and electrode, and took a scotchbrite to the shield. I have been, and still am using 16 gauge HR, so none of that changed.

When I went to cut the sign, I notices it had a huge ARC gap! It was still cutting, but was .5" above the surface. I let it finish, but I lost a lot of details since it was so high.

Settings are .15 pierce, .06 cut height at 116 volts

I resort back to doing 30" test cuts from when I initially set up the DTHC IV and found that around 94 volts put it at .06 cut height, but when I changed the "tool" in SheetCAM to 94 volts, it made the torch drag

What am I missing here? Something simple I hope

[WinterFabrication]

Air is 85psi, I "drain" manually every day. Northern Tool filter on the wall, filter at the inlet of the Hypertherm

[acourtjester]

were the consumables you used to replace the same parts number made by Hypertherm??

[jimcolt]

Increase the voltage until the torch to work distance is correct. The voltage does not matter , the height does. As an electrode wears a pit develops, which causes the arc voltage to increase. In order to maintain the correct height through the full life of a nozzle and electrode you need to increase arc voltage by 10-15 volts, other wise the height control will run the torch closer and closer to the material as the electrode and nozzle wear. Some height control systems auto calibrate before every cut cycle so you do not have to reset voltage, most don't.

Here are a few things that affect the voltage/height relationship:
-speed changes. Slower speed will make the torch run closer at a given voltage.
-Air pressure changes.
-Air purity (moisture or oil)
-Worn nozzle
-Worn electrode
-Aftermarket consumables
-Poor work cable connection


Jim Colt Hypertherm


quote="WinterFabrication"]So I swapped the consumables for the first time today since I've had everything working. Hypertherm45 with 45 amp consumables.

Cutting before, the DTHC was (in my opinion) dialed in pretty good, with no top dross and minimal dross on the bottom.

I changed the tip and electrode, and took a scotchbrite to the shield. I have been, and still am using 16 gauge HR, so none of that changed.

When I went to cut the sign, I notices it had a huge ARC gap! It was still cutting, but was .5" above the surface. I let it finish, but I lost a lot of details since it was so high.

Settings are .15 pierce, .06 cut height at 116 volts

I resort back to doing 30" test cuts from when I initially set up the DTHC IV and found that around 94 volts put it at .06 cut height, but when I changed the "tool" in SheetCAM to 94 volts, it made the torch drag

What am I missing here? Something simple I hope[/quote]

[tcaudle]

Increase the voltage until the torch to work distance is correct. The voltage does not matter , the height does. As an electrode wears a pit develops, which causes the arc voltage to increase. In order to maintain the correct height through the full life of a nozzle and electrode you need to increase arc voltage by 10-15 volts, other wise the height control will run the torch closer and closer to the material as the electrode and nozzle wear. Some height control systems auto calibrate before every cut cycle so you do not have to reset voltage, most don't.


Jim Colt Hypertherm

Jim we used to have the "auto learn" on our systems over 3 years ago . It is what you call "sample and hold"

We finally removed it because:

1. the cut needs to be relatively straight and at the feedrate from the chart and the material needs to stay flat . Since most cuts start with an arc lead in, neither the speed nor the voltage was right. The longer you sample the better the average but also the more opportunity for the material to not be flat and the arc gap to move outside nominal

2. If you do it on every cut you get different results depending on the toolpath. Cutting a decorative piece with bunches of details and text caused it to get wrong settings part of the time. It works great if all you cut is larger flat pieces and simple parts

3. On our system you could elect to perform it on every cut or once per job. If the first cut was not a longer straight piece it screwed up the whole cut

4. If for some reason the cut or any cut was off on voltage it would mess up. The only way to make it work was to have a preset voltage from a setting and only let it deviate off that by a few volts. So you still needed preset values. Some systems don't have stored presets

In our POSTS for SheetCAM we have added some checking so that if the total length of the cut is less than the setting you define, the DTHC just does not turn on. This works great on things like small holes or small objects by keeping the DTHC off.

Some of my users though that all you had to do was punch the Auto Learn button and no matter what the problem it would just set the height. A lot though you did not even need to set any parameters and it would fix it for you It actually created more support calls.

So for a commercial shop cutting out larger pieces on thicker material I can see where it would help but it all depends when and where you do the sample and hold in a cut, and what kind of cut it is

We cut 10 sheets of 4 X 8 Saturday for a big architectural job and changed consumables once

[jimcolt]

Sample and hold works only if the sample voltage is taken when the torch is at the correct physical cut height...the plasma gas (air pressure) has reached steady state, and the cut speed is within about 5% of stead state programmed speed. If the cnc machine always has the same mass, the same motors, the same plasma, and an accurate method of finding the surface of the material, then sample and hold height control settings work very well and are repeatable.

With homebuilt machines of different sizes, masses, acceleration rates, etc., I could imagine that this process may not always work perfectly!

Jim Colt

[SeanP]

Rightly or wrongly I am always looking at the z axis motor connecter as it comes off the dthc delay, as long as the sheet is flat and not to far/close to the pierce, ideally there should no movement, if it drops - increase the volts a little and if it lifts at that point lower the volts, it seems to be working well for me.

[beefy]

I was taught to do test cuts with the THC off. The important thing is to have steel which is flat / parallel with the X & Y axis. Forget it if you haven't got that. Even if your slats are very accurate height wise, a bit of slag stuffs that up.

So once I'd got my flat bit of steel (no good if the heat will warp it too), I'd do a straight line cut at the proper cut height with the THC off. You should get a fairly constant voltage reading at that torch height and travel speed. If the cut is good use that voltage and travel speed. If it's not good, try a different travel speed and note the new voltage.

I'll repeat again though, you need ACCURATELY flat steel for this test, you are trying to maintain that exact 1.5mm (my machine) torch to steel distance for the test distance.

The benefit of testing this way is you are checking the voltage at the set gap, regardless of whether the nozzle, electrode or whatever is worn.

I do wonder if it's easier to just do a run with THC on then measure the torch to metal distance at the end of the cut. No need for a perfectly flat sheet that way.

Keith

[WinterFabrication]

Thanks guys for all of your input!

Still a newbie fresh off the "Burntable" rebuild so just have these "non-issue" issues is still great! haha...

Lowered my voltage, good to go