Bad cuts with Hypertherm 65 (Finecuts are the problem?)

[ajk2004]

Good morning everyone,
I have a problem with my CNC machine that is making me go crazy. I can't seem to find out an answer and every forum I look at, I see something different. I have and C and CNC setup (bladerunner). I spoke with Luke on the phone and he is a nice guy, pretty helpful. The problem I get is when doing a longer cut, sometimes the torch will rise off of the material when it is cutting so high it will eventually stop cutting through the material. The settings I have are 85 volts. The torch will ride just above the metal at this setting and the cut looks wonderful. When cutting longer, it will be at 85-90 volts and start climbing. I've seen it get to around 165 volts and the torch is probable 1" or more off of the metal. When doing a big piece, sometimes it will screw it up so bad I don't feel like using it and it is costing a pretty penny to ruin that much material. It also happens about 75% through the job, naturally! I was thinking that mach isn't running right, but after talking to Luke, he said mach isn't responsible for raising/lowering the torch, he said that was their system that should do that. I told him I was using finecut consumables and he said that was likely my problem. He said it was because I likely don't know my table and my settings weren't right? I wasn't offended as I don't know my table but this baffles me as I hear from a lot of you that use finecuts with no problem and I was confused hearing that from him. I have a TM system where I work at and I DO know that table and have never had issues like this before. Have any of you experienced this before? Thanks.

[motoguy]

Is your Tip Saver turned on? I was having nearly the same issue. The torch would randomly lift up to about 0.20", and just "hang out" there. Sometimes it would eventually drop down, some times it would not. Either way, I had a long line that was not cut all the way through, and presented problems. Looks like the Tip Saver was causing it for me. On your Mach screen:

New Bitmap Image.JPG (285.17 KiB) Viewed 1411 times

New Bitmap Image.JPG (285.17 KiB) Viewed 1411 times

press the "Tab" key on your keyboard. This "flyout" screen will open:

Mach3_TAB_Screen.jpg (118.47 KiB) Viewed 1411 times

Mach3_TAB_Screen.jpg (118.47 KiB) Viewed 1411 times

In the bottom 1/4 of that screen, you'll see where it says "Tip Saver". It has a black box to the left of it, an "On/Off" button to the right, and another black box.

Is box on the right green, instead of black? If so, you have your tip saver turned On. When you have this problem, if you open this flyout screen, you will probably notice the box on the left is flashing yellow/black. This means the tip saver has been activated and engaged.

I'd do one of two things:

1) duplicate this cut again, but leave the flyout open. See if the box on the left starts flashing yellow/black when the problem arises. If so, it's the Tip saver. Click the On/Off button, to make the box on the right black (Off).

2) Shut the Tip Saver off, using the On/Off button. The box on the right should be black. Continue cutting, and see if the issue goes away. If so, it was likely the tip saver, bit without doing the step above, you may not know for sure.

Shutting off the Tip Saver seems to have fixed it for me. According to the guys at CandCNC, the DTHCIV is fast enough that the Tip Saver should not be needed, anyway. Not sure HOW it's being activated, but it is.

[WyoGreen]

Another thing you might watch is the up/down lights on the Mach screen. Is the up light lighting when the torch is heading up? If so, that would indicate that the controller is telling the Z to rise. If not, then something else is going on.

Steve

[ajk2004]

I should add to that I tried it with the DTHC on AND off and it did the same thing each time. So to be correct, I want the tip saver OFF? I have not checked to see if it was on/off. I would assume it is on by default. Thanks Motoguy

[motoguy]

Here is a link to a similar discussion on CandCNC's support page:

https://www.candcnc.com/supportforum/vi ... f=3&t=1641

and what CandCNC says about it:

"Its the TIp saver. As long as the voltage is the & ABOVE the preset voltage it locks DOWN motion. Once it sees ti fall below again its happy. Either raise the % value or turn off the Tip Saver. Its there to prevnet diving at theend of a cut but the DTHCIV is so much faster than the DTHCII it seldom has a chance to save you from a dive . That is better handled on a MACH system by turn off the DTHC with a Cut rule in SheetCAM at about 1/2 inch before the end.
So change the TIp Saver % up or use the button to turn it off on any cut that has a a lot of vertical changes. The other thing is you may have the DOWN Velocity (on the DTHC tuning in the Hub Utility) set a little low . If its too low the Z will not react to a rapid change inthe material height and then the tip saver DOES lock on."

[sphurley]

If the DTHC is off then it is not the tip saver.
What does the DRO read for the Z height when it's up an inch off the surface? Sound more like he is gaining/loosing steps.

[tcaudle]

Losing steps does not raise the torch....indeed it justs raises the DRO and the torch stays low and the voltage stays close. I ts onoly on the next cut it causes mysery bebause the Z thinks its way up in the air and its not. The DTHC doe snot care about height as reported by the DRO...its imply moves the torch up or down to try and make the voltage go up or down. If the voltage starts to climb the toruch SHOULD go down and the DOWN indicator will come on. The TIp saver can (ad does ) get locked on and that results in it refusing to go down evenif the voltage is increasing.

The other option is that the Z is going the opposite direction from the direction the DTHC is telling it to. that would cause it to climb when it thinks its going down. Your close observation of the DRO value and what is doing verison the UP and DOWN LED's will help,


Fine cut requires that EVERYTHING be perfect. You have to be cutting at the right speed as per the chart. YOu really need to use the shieled consumables and shield. The % of tip saver needs to go up. 3% fo 85 volts is less than 3% of 135V

Another ting I have seen is the MAX and MIN faul voltages have been messed with and it will stop sending up or down if its out of range (nornal is 200 max and 50 min. In MACH there are THC corrections that need to be set at +1" (or 25mm) max and -1" min . Other wise it will lock from going below the min .

[ajk2004]

Everyone, Thank you for your time and insights. I am going to be out of town for the next few days and will get back to my table on Sunday. My inkling is it is somehow the DTHC. Tom, if my DTHC is off, will the tip taver engage? The guy that posted above you said no. I tried cutting a piece and the machine wanted to raise quite a bit. I shut the DTHC off and was still getting the issue. That one surprised me. I understand what you are saying about the z being wrong, when the torch wants to lower it will raise and visa versa. Wouldn't this happen ALL of the time if this were the case? It doesn't happen all of the time, but when it does it is at the end of a project when the outside of the piece is being cut out, which is generally the longest cut. Thanks.

[tcaudle]

You have to be careful about "OFF" on the DTHC" You have to put it in MANUAL mode and turn it off via the button. If its left in Auto the G-Code turns it back on again at the start of the next cut.

The Z should not move (Up or Down) with the DTHC off and while its cutting.

[tcaudle]

The only way you can move Z DURING a cut is if you have the older DTHCII that uses the internal THC in MACH and you have the "Use THC even when THC is off" option tin the Mill Settings.