Rods "Spaceship" Scratch built Plasma Cutter build

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25 May 2019 04:05 #134872 by rodw
The same warpage also happened further down the sheet. I don't think it respects your retries so it seems to continue indefinitely.

I don't think the float switch would work in that situation. If you watch again, you will see the material is pushed down a fair way and then the ohmic sensor takes a fair while on the upstroke before it breaks contact as the material springs up again. I think the float switch would baulk at that and give wrong results.

What would be good is if this happens a few times, the probe height was increased by say 10mm each subsequent attempt. To set it at 50-60mm to fix this would slow cutting down a lot.

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25 May 2019 04:28 - 25 May 2019 04:28 #134874 by phillc54

rodw wrote: The same warpage also happened further down the sheet. I don't think it respects your retries so it seems to continue indefinitely.

I don't think the float switch would work in that situation. If you watch again, you will see the material is pushed down a fair way and then the ohmic sensor takes a fair while on the upstroke before it breaks contact as the material springs up again. I think the float switch would baulk at that and give wrong results.

On my probe test rig I got good results with float switch and light material. The probe up is only one offset count per period.

What would be good is if this happens a few times, the probe height was increased by say 10mm each subsequent attempt. To set it at 50-60mm to fix this would slow cutting down a lot.

That sounds like a reasonable idea.

I was thinking along the lines of an initial quick probe to find the approximate material height then use the Probe Height value to do any further probing. This height could be offset on the fly by the component from the THC motion during a cut. The problem here is that you may end up with a pretty high probe height due to warpage (I honestly didn't know that it would warp that much).

It may be better to get some input from John and Tommy and anyone else that has a fair bit of cutting experience to see if we can come up with a viable solution that suits everyone.

Cheers, Phill.
Last edit: 25 May 2019 04:28 by phillc54.

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25 May 2019 05:02 #134876 by rodw
What about this?
When probing, if the ohmic sensor is triggered before the probe height is reached, save the Z height (as material height) and change the probe height to be material height plus probe height and retry.

There is really 2 things that can go wrong here with ohmic sensing that are totally different to each other.

1.Ohmic fails to light up inside the probe height. Thats really going to be when the float switch should provide a fall back
2, Ohmic is triggered earlier than it should be. This signifies the material has warped upwards so the probe height needs to be reset for that probing event and retry.

I think I experienced case #2.

But they both need to be dealt with separately .
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25 May 2019 22:12 #134936 by tommylight

phillc54 wrote:
It may be better to get some input from John and Tommy and anyone else that has a fair bit of cutting experience to see if we can come up with a viable solution that suits everyone.

Cheers, Phill.

I can not help much as i never use ohmic probing, i just make the floating head that need about 1 KG of force to trigger and be done with it. It never fails. On an Esab industrial machine we did make a different type of holder without magnets and with a proximity switch, round shaped with 3 springs, so that one requires roughly 2.5KG of force, still i never got complaints about bending the sheet while probing, although i think it is because of very fine mesh on the table ( something like 4x4cm squares all over). The minimum thickness cut on it is 1.5mm.
From a lot of reading on the net i had made up my mind on avoiding any other type of probing ( ohmic, high frequency sensor floating around the torch) and use only floating head.
The above mentioned Esab has 2 fully functional high frequency sensors disabled and disconnected.

Reading all your posts regarding this and the probing complications with different speeds and skipping probing for some distance/cuts etc, i feel i should mention once more, all those complications and trouble for Phill could have been avoided with two simple hardware solutions, 1- a fast Z axis and 2- a sensitive floating switch. The result would have been a much simpler and much more reliable functioning of software and hardware. Also worth mentioning after reading about disabling THC, i did have a chat with 4 of my costumers and none of them ever needed disabling it. I did read Icelanders reason for needing it, he did say it is for his use case only.
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25 May 2019 23:46 #134943 by islander261
Guys

First of all I am an extreme corner case. All I do is cut wall and yard art out of 14Ga steel (about 1.9mm). No long straight lines, very rarely fitted parts. That said I do work at getting good cut quality to minimize secondary operations. I also try hard to get good consumable life. My franken torch is the business end of a HT Duramax torch grafted onto a TD SL100 Automation torch. I use almost exclusively the Finecut consumables. I use the Copper Plus electrodes and get over 3,000 pierces consistently. This combination works better for me than any combination of the original TD torch and consumables. The HT consumables are a good value to me because of the service life.

My table has 6Ga (about 6mm thick) expanded metal (nonflattened) welded over the slats to support small dropouts and keep them out of the water. I replace this about 4 times a year when it gets too nasty. The water table is only filled when cutting. The water is stored in a stock tank under the table. The table is filled with a cheap submersible sump pump located in the tank.

My work lead goes to a star point on my table frame. Other connections to the star point are the slat frame, work piece lead and ohmic sensing connection.

I tried to use a float switch only. When I had the torch down pressure set as light as Tommy's the torch couldn't keep up with the Z axis down and tended to bounce when moving from G0 height. Even at that the probing wasn't consistent over the whole sheet of the thin material I cut. So I use ohmic sensing. On my old setup I had retro fitted a CandCNC Feathertouch sensor and it worked well with my hacked THC SW, at least better than the old TM smash and stall sensing that came with it. I use the IHS skip feature because I often have a bunch of pierces very close together and don't like probing onto an old slag pile. It is hard on the shield/nozzle sometimes and always not accurate. The IHS skip feature also really speeds up production when you have many close starting points. I also clamp my work piece to the slats with pinch clamps (metal clothes pegs) to hold it down. I am really picky about IHS because the Finecuts want to pierce at .09" and cut between .06" and .075" height. I will say that if you have good true slats and cut material more than 3mm-4mm thick you will never need to use ohmic sensing YMMV.

I am still using an older edition of the Plasmac branch, around May 6. I did have trouble at one point with the torch doing a pogo stick routine while trying to probe. Getting the correct Z axis settings in my .ini file and the probe distance and probe speed on the GUI fixed it for me. The probe tripped before reaching probe height was fixed with a slower probing speed, the rest of the time it is usually caused by debris caught between the nozzle and the shield. Finecuts have a big gap between them. I am very happy with the Plasmac ohmic probing now.

I use different cutting parameters to vary the appearance of my work pieces. It is very important to me to be able to disable the THC and cut at a fixed height for some of the effects. Job shops need this to for cutting small to size holes with little bevel. At the time I was the only one that bothered to post that was testing the Plasmac branch on live cutting. I figured to ask for features that make my life easier if I was going to test. BTW I haven't lost a part do to a cutting error since my latest Plasmac update.

SheetCam really doesn't do cutter offsets like a real milling (VMC) CAM solution. It generates an offset cutting path instead of just sending the part outline and a tool number/offset side. I have no doubt that a PP for it can be configured to produce the correct code. If all else fails using a code snippet will always work.

John
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26 May 2019 01:20 - 26 May 2019 02:24 #134945 by rodw
I think we are missing a bit here. I would have probing issues with plasmac even if I was just depending on the float switch becasue the problem I had with probing was to do with the probing algorithm Phill has created. The real issue is the material warped more than it what phil was expecting so hopefully there is a learning from tis that can improve his plasma solution.

Skip distances don't have anything to do with ohmic probing.

NOw I've got Ohmic probing working on my table I won't be giving it up.

And Tommy like you I don't bother turning THC off.
Last edit: 26 May 2019 02:24 by rodw.

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26 May 2019 02:54 #134948 by islander261
Rod

Clamp your work piece to the slats and you will have much less trouble with warping. Yes, it will warp in the cut but when free both the part and the stock tend to lay flatter.

I have no idea how much treasure HT spent developing their "True Hole" technology. Plenty I suspect. One of the few things that has been publicly disclosed is that they cut smaller holes (< 37mm) at a fixed cut height (no THC) at a slower speed to get less bevel. The other part I have picked up from PS is they use a perpendicular lead in with no lead out just a slight overburn (motion) combined with early torch off. I have no need to go down this road but there has been plenty of discussion on PS. SeanP has posted a bunch on this subject.

John

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26 May 2019 04:23 #134952 by rodw
John yes, Jim Colt had a presentation about hole cutting which is quite informative. See attached.

This browser does not support PDFs. Please download the PDF to view it: Download PDF



I did find a fair bit about holes including finding SeanP's rules.

I think a lot of the PS stuff is based around a basic controller that can't operate as smart as Plasmac. I ended up turning off the hole rules

And yes, I did clamp the material down
Attachments:

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26 May 2019 22:26 #135034 by tommylight
John, you are responsible for confirming that Linuxcnc can do anything you think off, and do that in several ways, usually. My complaints are regarding new users and the ensuing workload for Phill and the others here in the forum. It would have been much better to have a simpler version, ready for use by them by now, and continue working on the actual version. That would have left users the option to choose, and not be thrown on the deep end to start with.
Just noticed, sorry for hijacking your thread, Rod.
Personally i can use anything and modify it to my liking, but i can not use Plasmac on clients machines anymore since people here where i live do not wait for a week or two to have their machine fixed, at encountering any issue, i have to leave whatever i am doing and go check and fix whatever is needed.
Back on topic......hmmm.... at last,
Regarding holes, usually i avoid anything under 30mm for a good cut, and making small holes and later drilling them to size is not an option as it tends to mess up drill bits on short notice. This is for parts cut on a water table, have not tried to do that with cuts on air, maybe that will work as the material would cool down slower so the inevitable hardening of the cut would have to be less of an issue.
Also will have to make 2 holders for the new torch heads i got several months back, but had not time to put them to use. Unfortunately derlin or HDPE is very expensive here and finding big parts for those holders is hard and way more expensive. Making an attempt tomorrow, wondering how much of a shock the price will be.
Regards,
Tom
P.S.
In the mean time of doing other things, i am also building a small frame for a plasma cutter with the cheapest parts i can find here, with round linear rails all over, belts and stuff, but trying to make it look better as a whole. Size 55X95CM.

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27 May 2019 08:07 #135045 by Clive s

In the mean time of doing other things, i am also building a small frame for a plasma cutter with the cheapest parts i can find here, with round linear rails all over, belts and stuff, but trying to make it look better as a whole. Size 55X95CM.


I am going to attempt to build a small one as well so looking forward to see yours.B) To gain Ideas .

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