corrugated roof panel cutting suggestions.

[Rister]

I have not had very good luck trying to figure out how to cut corrugated roof panels. The girlfriend found some artsy stuff that she want me to cut out and i have been having a rough time trying to get everything dialed. 29 gauge is thinner than crap and the dthc is working its hardest but cant seem to keep up. I tried to turn off the thc and just run it without and base the cut off of the ridges.
i tried 50 ipm and it couldn't keep an arc, appeared that the cut was ahead of the machine or something, loosing arc
then i moved up and bounced around and made my way up to 150 and i still didnt have much luck.
i am running a powermax 105 with fine cut consumables and candcnc for controls. my voltage is off, which i still have to figure out, but i am running 62 volts which looks good as far as cut height, until it gets into the waves.

[elvenhome21]

Why not just cut it with a hand torch and straight edge or a tin snips. Tin snips go pretty quick and you wont have to worry about messing up the paint from torch heat.

[Rister]

sorry I should have stated that the picture was an example. I figured if I could make one I could sell a few to her friends, this is why I am trying to figure out how to cut it out on the table.
Thanks for your reply though

[muzza]

If you use the search function up the top right and search the word corrugated you will find a few threads where this has been discussed before, will work with some systems and not with others.
Murray

[JJsCustomDesigns]

I did this one with no THC on. The ribs were short enough the torch still fired. 25amps, 55psi 70ipm. Occasional misfire. Not fun. I tried to talk em into flat steel but they wanted this...

If you get er figured out- post up your results. Good luck.

[plain ol Bill]

I have tried and tried to cut corrugated and finally just gave up and put my hand torch on. Relieved a lot of frustration.

[beefy]

I'm sure I read somewhere that the Z-axis needs a servo motor to get the necessary speed for the THC to follow corrugated.

My system is Candcnc and under THC control there is no accelleration / deceleration control so there is a THC Rate % setting. My is set at 15% (think this is 15% of max z-axis velocity). Because of the leadscrew the z-axis motor has to spin fast to get any decent speed. A servo has position feedback via its encoder and they can spin faster than steppers. Ask a stepper to spin above a certain speed without any accel / decel buildup and you'll get lost steps. With a servo the feedback system tells the driver if the motor is lagging behind the position it's supposed to be in and if it's lagging the driver will send a boost of current to increased its torque and speed so it can catch up. Up to a limit that is, too much position error and I think they fault. Stepper don't have this "catch up" luxury, if a step is commanded and it can't do it, lost steps is the result.

Could changing to a servo motor solve your problem.

When the THC Rate is set higher you can get a situation where the z-axis becomes a jack hammer and bounces up and down like a sewing machine needle. It's caused by the correction movement overshooting in the opposite direction, then the THC corrects again the other way, and on and on it goes. You can help reduce this effect by increasing the span setting in your cut profile. This is a "dead band" zone where the THC doesn't cause any movements if the voltage is within it.

Tom at Candcnc is certainly the guy to ask about this situation, but try searching on the Candcnc Yahoo support site. I bet this subject has already been discussed there. I try not to bother Tom if I don't have to so he has more time to develope more great plasma systems.

Keith.

[BTA Plasma]

You can most certainly cut metal like that with your CandCNC system. The THC rate is the acel and decel for the Z. Between 18-25 is a good setting depending on the thickness and amperage your cutting. You should have no problems with a stepper if it is properly sized for the Z axis. Any backlash you have may or may not work against you in Z motion and a steps per of 9000 to 14000 works well for raised sheetmetal pieces. But anything under will not work well and anything over wont like the stepper RPM unless your running an ultralight Z axis and a 180oz stepper.

[beefy]

Hi BTA Plasma,

since being involved with Candcnc equipment, all I have ever been told by Tom himself is that under THC control, there are NO acceleration and deceleration moves applied to the Z-axis, and the THC Rate setting is a speed percentage, not an acceleration or deceleration setting.

That is why THC Rate is set relatively low, because it's easy to get lost steps when the z motor cannot ramp up to speed.

The only acceleration and deceleration settings that I know of for Z are in Motor Tuning.

These are 4 examples of Toms very words I've copied and pasted from posts on the Yahoo Support site:

"THC RATE is the speed the Z moves at (Velocity) when it is under THC Control."

"THC Rate controsl how fast the Z responds during cutting under control of the THC. It does not effect the speed of the Z moves under any other condition."

"raise the THC Rate will make the Z perform quicker moves while it is cutting under THC control BUT too fast is worse than too slow. It will drive that motor to lose steps (stall) and you may be little or no movement at all. The telltale sign is that at the end of a cut and the Z lifts to Rapid height (whatever you have that set at) if the Z DRO shows the rapid height but the actual Height is a lot less then you have lost position on the Z. Most stepper based setups will not handle a 40% THC Rate."

"THC RATE is the speed the Z moves at (Velocity) when it is under THC Control. Default is 30 (%). So if your Z is tuned to move at 100 IPM normally it lowers that to 33 IPM during THC moves."

Keith.

[SignTorch Vector Art]

the velocity in motor tuning is max speed for that axis

just as you can limit homing speed to a percentage of velocity to not overshoot the limits

you can limit thc travel speed to not move faster than thc can sense and control

acceleration (and deceleration) in motor tuning is always applied whenever travel speed is changing

if any axis ever loses steps it's because of incorrect acceleration and velocity settings for that motor with that load at that speed

thc rate calibration should be based on what's best for thc stability,

after motor tuning is calibrated to avoid lost steps during normal operation

[MidAmericaIron]

I'm waiting for the owner of TruCut CNC to jump in on this one. I have watched the video that he has posted on his web site that shows his table cutting corrugated metal, and it looks like it does a great job. That is one of the main reasons when I get ready to pull the pin in a few weeks for my table I will be going with his set-up. As far as I'm concerned, you get a lot for your money with him. His team will even deliver the machine, set it up and give me a full day of training for a few dollars more than other companies want to charge just for shipping!

[beefy]

Hi Signtorch,

regarding acceleration and decelleration always being applied, it is NOT applied with the Candcnc THC control on the z-axis. Here are more words from Tom, the designer of the Candcnc systems:

"The condition of overshoot is part of the issue but THC Rate controls the VELOCITY of Z while it is under THC Control (only). When the Z is running THC moves it ignores the normal Z ACCELERATION setting. The concept is that the THC moves are mostly lots of quick short moves (often in opposite directions) so apply an acceleration curve to the motion would make response suffer. Because a motor can only physically accelerate so fast to a given velocity if the velocity is lowered the motor can achieve faster acceleration. The complex part is that what velocity a motor can run at without stalling with virtually instant acceleration varies based on the motor, the final drive configuration (leadscrew pitch, etc). The 30% default we use covers a lot of configurations."

As Toms words show, he has designed the system to purposely ignore the acceleration setting when under THC control.

That is why Tom says most stepper systems cannot handle a THC Rate of 40%, and high THC Rate settings will cause lost steps. The z can travel at the max speed set in Motor Tuning yet may quite well lose steps if it's asked to go at only 40% of this under THC control.

Keith.

[SignTorch Vector Art]

I'll be darn. I keep forgetting the thc controls the Z,

no acceleration doesn't seem logical to me, especially if driving a lead screw

but really the thc self-compensates for lost steps

[beefy]

It will compensate as far as still maintaining the correct gap (voltage), but the actual z position will be lost.

The Candcnc system keeps track of its true z position even while the THC is moving the z up and down.

I've often wondered what sort of a difference it would make if the normal accel / decel could be applied to THC moves. My z seems to react plenty fast when I jog it a max speed, there's no perceptible "build up" of speed. But maybe decel would make overshoot worse ?

Keith.

[SignTorch Vector Art]

that's got me wondering to, I'd've never imagined it was like that, with a servo maybe (no lost steps), but not with a stepper... I would shy away from using a lead screw driven Z axis for that....

[vmax549]

Going to a courser feed screw will help here, it allows the speed you need for Z and still stays in the operational RPM range of the stepper motor/drive.

Just a thought, (;-) TP

[trucutcnc]

I'm waiting for the owner of TruCut CNC to jump in on this one.

Been so busy lately with our new product line I've been neglecting the forum.

There is no accel/decel in the CandCNC THC. That's not a limitation of the THC, it's a limitation of Mach3. Mach can only apply accel/decel if it knows where it is stopping. That's not the case with the Mach3 THC inputs. The THC Feedrate setting is a percentage of the axis velocity setting. If your Z velocity is set at 100IPM and your THC Feedrate is set at 10, the Z will make THC corrections at a fixed 10IPM. As you raise the THC Feedrate, you get more overshoot which makes the torch "bounce". Any THC using the Mach3 THC inputs will exhibit this effect to some degree.

THC's that incorporate a PID controller to adjust feedrate proportional to the difference between set volts and tip volts are stable at all speeds up to max axis velocity. Any of the industrial THC's such as models by Hypertherm, Promotion, Burny, etc. all use PID controllers. Our new TruTrac THC also uses a PID controller. The PID controller essentially provides the deceleration needed to run the Z axis at a high feedrate but still stop right at your target set volts. It does this by slowing the feedrate as tip volts approaches set volts.

[BTA Plasma]

As you raise the THC Feedrate, you get more overshoot which makes the torch "bounce".

If it is bouncing your rate is too high for your axis speed. The thinner the material the faster the rate should be. THC in Mach 3 works from 3" steel to 28 gauge material and everything in between. Settings are often misunderstood and so are mechanics of the actual Z axis. There are many variables that must work together and if the machine mechanics and dynamics are properly engineered then Mach 3's THC capability will meet or exceed the capability of many industrial controllers THC units.

[trucutcnc]

As you raise the THC Feedrate, you get more overshoot which makes the torch "bounce".

There are many variables that must work together and if the machine mechanics and dynamics are properly engineered then Mach 3's THC capability will meet or exceed the capability of many industrial controllers THC units.

You can't overcome the basic laws of physics, and without deceleration there is no way Mach 3 is going to stop on a mark (IE: exactly at your set voltage). We ran a THC through Mach3 for years. I'm well aware of how it works and it's limitations. For the low cost to set up a THC using Mach inputs, it works OK, but it's no where near that of a industrial PID controlled THC. The bouncing effect is a well known phenomenon amongst Mach3 plasma users. There are ways to minimize it but it will always be there to some degree.

That said, we did have some success way back cutting corrugated with the Mach3 THC by turning the THC Feedrate way up. As long as the material height is always in a state of change...IE: The torch is always either climbing or descending....it will work OK, but as soon as you hit a flat spot it will bounce like a jackhammer.

[BTA Plasma]

Any Z axis courser than 4TPI will bounce at any THC setting. Are you sure your minimum Z movement wasn't overshooting the target voltage? A course Z axis leads to bounce for sure. Mach is plenty fast enough to read and hit target voltage however if your mechanics aren't capable of getting to that voltage they overshoot and you will get torch oscillation all the time. I have seen ranges from 5TPI to 12TPI work great with no overshoot or bounce.

[trucutcnc]

I have seen ranges from 5TPI to 12TPI work great with no overshoot or bounce.

Our old THC worked fine with an 8TPI screw, but it was no where near responsive enough to track corrugated at a decent cut speed. If you turn the THC Feedrate down low enough, the overshoot becomes unnoticeable, but it IS always there. Mach3 can not stop dead on set volts without deceleration. The faster it's moving the more it will overshoot the target.

Apply the same logic to driving your car. The same laws of physics apply to both a moving Z axis and your car. If you were driving blindfolded and I told you to stop just as you passed a line in the road, you would not be able to stop on the line. If you were to slow down, you could stop closer to the line. Now if you remove the blindfold so you can see the line, as you approach it you can slow down and stop on the line. This is exactly what a PID controller does. It reduces the feedrate as it approaches the target. You just can't stop a moving mass on a mark without decelerating. It's simple physics. If you could then there would be no need for acceleration/deceleration in CNC control software.

With the CandCNC THC, at what feedrate can you accurately track corrugated material?

[BTA Plasma]

At 8TPI we found one could never get the speed where it needs to be to be effective on materials that need to be cut faster than 200ipm. Thats a step per of 16000 which is just a couple thousand over what we have tested for good response time with Mach with a Z axis. At that TPI you may well have been under your target voltage. I think if you were to do more testing youll find the magic numbers work wonders in Mach but once you step out of that range you will have endless struggles with THC. Weight of the actual Z axis also has alot to do with running a stepper. I understand what your saying Ross I really do but what you have said so far shows you didnt have the R&D into making it work well. Maybe I will get to shoot some video next week of a machine running over 200ipm on corrugated.

[trucutcnc]

At 8TPI we found one could never get the speed where it needs to be to be effective on materials that need to be cut faster than 200ipm. Thats a step per of 16000 which is just a couple thousand over what we have tested for good response time with Mach with a Z axis. At that TPI you may well have been under your target voltage. I think if you were to do more testing youll find the magic numbers work wonders in Mach but once you step out of that range you will have endless struggles with THC. Weight of the actual Z axis also has alot to do with running a stepper. I understand what your saying Ross I really do but what you have said so far shows you didn't have the R&D into making it work well. Maybe I will get to shoot some video next week of a machine running over 200ipm on corrugated.

Should have mentioned that those screws were 8TPI with 2 starts, which effectively makes them 4TPI or 1/4" per turn travel. Our Z can easily run at 175IPM. The bouncing effect with Mach3 THC's is a well known and very common thing. We did tons of R&D and still do, but through that R&D we quickly realized that Mach3 THC is a good and inexpensive hobby solution, but not an industrial solution. As cheap as it is to implement, If it were it would be used on industrial controllers.

Our new THC uses the same technology as the high end industrial controllers and meets or exceeds industrial performance standards. You claim that we didn't do the R&D. The fact that you think that CandCNC and Mach3 can exceed industrial standards shows your inexperience with industrial plasma. We develop our own product lines and are constantly doing R&D to develop better products. Other manufacturers simply buy the parts and bolt them together.

I'm not putting down CandCNC or Mach3. We use and like Mach3. Just saying, if it were the industrial wonder that you claim it is, there would be no market for the controllers offered by Hyperthem, ProMotion and Burny costing upwards of $40,000. If you had a better understanding of the physics behind inertia and motion, you'd see why a Mach3 THC does what it does. You've found some settings that minimize the effects as did we, but our end goal was to eliminate them and our TruTrac Pro does exactly that.

I'll bet a lot of people would like to see a video of a Mach3 THC cutting corrugated at 200IPM. Cut a square with an edge parallel to the corrugated. That will demonstrate cutting corrugated and flat with the same settings.

[BTA Plasma]

We found 4tpi too course for any good fast movement with THC and Mach. I would tell you the real secret to it but then again it wouldnt be a secret anymore. You cant really bundle all controllers together and generalize which one is a hobby grade and which one is industrial. You can put the most expensive control with the largest servos on a machine incapable of stability and have terrible results. That term "industrial grade" is from the eye of the beholder meaning... take an early version of Burneys control. I can tell you from experience the early controllers were the gold standard and left much to be desired. Ask around to folks who have "industrial" controllers and ask them how many times a week they have to lie to the controller to get it to cut the part correctly. Their is a simple definition of an industrial control and that is one that is used in industry. Everything else is sales jargon. Most are labelled and made to isolate the control and keep simple the operation of a large plasma machine and to use multiple gases but there really isnt much more to them if you strip them down with exception of a simple geometry scan. Mach 3 THC works in a small envelope indeed but inside that envelope the right THC is superior to 95% of every single THC out there whether or not it is labelled as a industrial grade THC or not. Sorry if I did say you didnt do the R&D I assumed you didnt because you didnt get your Mach THC to work like you wanted. It is a long road with Mach to figure out what works best but you have moved on from there now with a new THC.

But I dont think CandCNC's THC meets and exceeds the majority of the THCs out there. I know it does through 4 years of effort with CandCNC. For every machine using CandCNC's THC correctly there are 10 of them out there that dont. Its not their fault its an open source collection of hardware with a ton of misunderstood info out there on it. Just like Mach 3 an open source software with millions of options.

[beefy]

The statement about Mach3 THC always having bounce to some degree should not be true with the Candcnc system, which has a SPAN setting in addition to the THC RATE setting. The span setting is a dead band area where the THC makes no adjustment. Granted this dead band area gives a voltage range where the torch voltage can change without any z height corrections. Overshoot (bouncing) in the Candcnc system only occurs if the THC RATE setting gives a z velocity which makes the z drive right through the dead band zone to the "other side", then it all reverses and happens again. Or likewise if the SPAN setting is so narrow that even a small THC RATE setting is not low enough to prevent this overshoot through the dead band.

The statement that Mach3 THC always has some bouncing leads me to guess that Mach3 on it's own doesn't have such a SPAN setting, and I can see this making it susceptible to overshoot and bouncing if there is no accel & decel as the torch voltage is approaching.

The Candcnc system is a plug-in for Mach3 so it customizes Mach3 for the plasma process. Seeing as Candcnc is being mentioned in this thread, we need to be careful that any of Mach3 shortcomings are not equated to the Candcnc system if it's not the case.

Keith.