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Shielded torch wants to be too low.... solutions?

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jazzkramer
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Shielded torch wants to be too low.... solutions?

Post by jazzkramer » Wed May 11, 2022 7:56 pm

Hi, i read many posts here and I leart many things, THANKS YOU ALL!!

It's the first time I write, i built a (diy) plasma CNC driven by LinuxCNC, mesa 7i96, THCAD10 (for THC), cutter Lotos 5500D-CNC. (Ok, strange thing I'm temporarily using the 1.5m X axes turned 90 degrees so the Z axes move horizontal like a 14cm Y, and I mounted a small Z (6cm) on top of the Z to work as the real Z.... It works!)

Recently I switched to a vertical torch (PTM60) and I bought shielded consumables because I wanted to add a Ohmic sensor to get precise sensing of the materials height position.

First problem/question: the Lotos cutter has a recomended height cut of 1.5mm and at that height it performs good vertical cuts, but the shielded torch has the consumable 1.02mm inside the shield... so, I have to set the cut height from the material at 0.48mm.

Is it enough clearence?

What actually happens is that the torch moves up and down (THC) during the cut and it often touch the material so I have to stop the cut not to damage the torch.

What cutting distance do you have on your shielded torch?
Does it means I can not use the shielded consumables with this Lotos because the cutting 1.5mm is too near for this?

I don't have the Ohmic sensor yet, so,
a possible interpretation of the problem could be:
1) The torch goes down before the cut, to sense the material position (by the floating switch).
2) The material flex a little (or maybe being not perfectly plane on the supporting grid because has some dross and cuts from previous cuts) and the torch thinks it's lower than it actually is.
3) The torch goes to the "correct" piercing height BUT actually it's lower.
4) LinuxCNC starts the torch ON and lower the torch to the cutting height (too low) maybe already touching the material.
5) After 0.X (did not remember.. 0.2 ... 0.3 seconds) the auto voltage of the THC decide that's the correct voltage for the cut... but it measured it with the torch too low on the material, so it wants to
keep the height on this voltage
6) eventually the THC corrects the height crashing in the material AND I have to stop the CNC to
protect the torch.

Do you agree with the above interpretation?

Do you think that adding the ohmic sensor to the shielded consumables, will solve the problem and that the clearence is 0.48mm only will be enough?

Do you maybe have other suggestion (a part from adding a torch collision detector which I'm doing soon)?

Do you think unchecking the "Auto Volts" on Linux CNC and set a correct voltage manually could
tell the THC to go to the 0.48 correct height?




SECOND "Problem":
This is not a real problem (I hope so), it's more a question:
Because of the fact that I was in a hurry to cut some 2mm thik parts, I decided to use the unshielded 60A nozzle that came with the torch at 1.5mm height (instead of crashing an possibly damaging the torch on the material).
I cutted the parts with the machine at 55A (it's maximum even if an online guy says it measured it and it's really 48A on the Lotos), 75 PSI and they came VERY VERY good. No Dross, almost perfect cut, a part for a small miniZ axis vibration.
So the question is: is it normal? A material that in theory wants to be cutted with 35A, cutted with 55A came so good?
I mean: can I cut every material at the maximum and I will get always this so good result?
So why bother with lowering the amps??

I'm a bit confused about all that.

I apologize for my bad english, and the "many questions" in this post, but I'm really new in Plasma cutting world and I did not find an answer to these questions.
Thanks for every answer you can give me,
have a nice day, happy cutting!
Alberto.

jazzkramer
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Re: Shielded torch wants to be too low.... solutions?

Post by jazzkramer » Fri May 13, 2022 4:42 pm

:Sad

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acourtjester
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Re: Shielded torch wants to be too low.... solutions?

Post by acourtjester » Fri May 13, 2022 5:31 pm

Hi Alberto
What I think will help you with cutting height is to not use the THC until you know at what height is correct for your torch.
This will mean making test cuts maybe about 140 MM long and do an edge start (place torch at the very edge of the metal) so you don't have to have the pierce height involved. Also do not change the torch height at the end of the cut, when you have good cuts measure the distance from the tip to the metal surface. This will give you the correct cut height for your torch. Now most torches will cut 2 MM steel at about 1.6 MM if you measure and find a difference this will tell you how far off your torch is working. You may be overthinking the design of the torch's inside and trying to correct for it. Actual cutting distance is more important.
With the MiniZ axis could it be your THC could be causing these movements.
Cutting with to high amps will make a wider kerf and will put to much heat in the metal and can cause warping as you cut.
Your English is not a problem The info is there for us to help :Like
DIY 4X4 Plasma/Router Table
Hypertherm PM65 Machine Torch
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Miller Mig welder
13" metal lathe
Small Mill
Everlast PowerTig 255 EXT

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Re: Shielded torch wants to be too low.... solutions?

Post by adbuch » Fri May 13, 2022 8:34 pm

Tom gives good advise. I agree to do some testing without our thc to see what specific torch to material cutting distance works best for your particular metal thickness and cutting speed.

David

jazzkramer
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Re: Shielded torch wants to be too low.... solutions?

Post by jazzkramer » Sat May 14, 2022 10:22 am

Thank you. I will do some more tests,
Alberto.

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