Why LinuxCNC does not need a THC.

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Rodw
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Why LinuxCNC does not need a THC.

Post by Rodw »

I thought this was an interesting question raised on another forum questioning how a $69 THCAD could be better than a stand alone THC
You can read the full thread here https://forum.linuxcnc.org/plasma-laser ... rs?start=0
Some minor edits made for clarity (and to obscure some trade names).

Original Poster (OP)
I’ve asked this question but never really get an answer.

What THCs are there in the market? I only really hear of Price THC, the Mesa THCAd-10 I believe it’s called, and the Promas.

I keep hearing that Proma 150 compact THC (which is what I have) is a cheap option. But all the ones I’ve heard of are about the same price. So there must be others. What are they and what are their advantages?
dvn4life1972 Response:
Using the THCAD-x allows use of THC native to the Plasmac interface. The Price and Promas are standalone if I'm not mistaken. In terms of cost, using the Mesa THCAD card and Plasmac for THC is quite less expensive than, say, the Price. I would argue it works much better as well.
OP:
Yes I haven’t heard many complaints about the THCAD. And I figured it’s quality was good, but when I was buying my hardware I wasn’t knowledgeable enough to realize that. I was too worried it was worse bc of its price. I don’t care for the price thc for some reason. I’ve never used it but I don’t like it.

What other THCs are there though? You also mentioned only the several I talked about
thefabricator03 Response:
Hypertherm do THC;'s but they are not for amateurs. I got a quote for a system and it started at $40,000AUD.

xxxxxxxxx do THC's as well but in my experience they are junk compared to the THCAD. I spent over $10,000 AUD on a xxxxxxxxx system and I scrapped it for a Mesa 7i76e and a THCAD10.

Really nothing even comes close to the features and reliability that the THCAD offers.

Sometimes the most simple solutions are the best and most cost effective.
and thefabricator03 again:
I have over a years worth of heavy duty cutting experience with a Mesa 7i76e and and THCAD10 and they have never let me down. Day in day out they just work!
RodW Response:
I think its important to understand a few things here:
1. The traditional THC's like Proma exist becasue few CNC controllers can manage torch height control internally so must depend on external hardware. But its not possible to get full control over the process as its hard for the two systems to communicate in real time (1000 times a second).

2. The very best plasma controllers (like the AUD $40k Hypertherm system thefabricator03 mentioned ) manage torch height control internally so they can get superior results and full integration between voltage sensing and all seeing all knowing CNC motion controller. They don't need external THC's becasue they can do it all themselves.

3. If the Linuxcnc motion controller knows the torch voltage, it can control the torch height like the very best high end controllers costing AUD $40k. Its just that companies like Hypertherm have a bit of a head start in this area. We are learning what they already know and applying it to Linuxcnc.

4. Neither Linuxcnc or the THCAD are THC's. The THCAD provides a nice, neat, accurate and robust method of telling the linuxcnc motion controller what the torch voltage is. This allows the motion controller to manage the plasma cutting process.

5. With a THCAD in conjunction with Linuxcnc, the concept of a THC becomes obsolete. LinuxCNC becomes a full plasma aware motion controller.

So in answer to your question, the best upgrade you can do is to toss out your Proma THC and buy a THCAD. If you can afford to, also throw out any parallel port BOBS in use and replace with Mesa hardware. That way you are upgrading to a tightly integrated plasma controller.
thefabricator03 again:
Rods correct, the THCAD is not a Torch Height Controller. I had Tom from CandCNC mention that to me and I pointed out that its actually a non proprietary way to measure arc voltage in real time, which is a whole lot more useful than a THC.
The OP:
Wow. I must not have put notifications on this topic. I wasn't aware of all the replies. I haven't read everything but from what I read I gather this: the THCs mentioned in the initial post are about the only THCs that are accepted in the realm of "cheaper" builds. And out of all of them the THCAD is the best. My next build will be a THCAD (and I'm currently using and will continue to use the mesa 7I96 board). Its very strange to me that the cheapest option is the best though.
RodW:
Its more that the THCAD is the enabler for Linuxcnc to be the best!
PCW owner of Mesa Electronics the THCAD Manufacturer:
Its not the THCAD that's the enabler. Its LinuxCNCs HAL
and all the THC work that people have done in the open and
collaborative real time structure that LinuxCNC and HAL provide.

A functional THC A-D could be made for $2.00 with a
555 Timer VCO and an optoisolater.
thefabricator03 again:
Thats what I love about the open source movement. In a industrial environment most thing are very expensive. Using your THCAD or something similar and some very clever coding we can make a plasma cutting system for very minimal cost.

It really is pretty awesome. I was skeptical of the reliability at first but with over 1500 hours of cutting on my machine it still has not failed and continues to work everyday.
The OP again:
Yes, I’m definitely switch for my next build. Now just to make this one as perfect as possible and sell it.
Full disclosure. Posts from RodW above were written by me.
dvn4life1972
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Re: Why LinuxCNC does not need a THC.

Post by dvn4life1972 »

I'd have to look at my statistics in LinuxCNC, but I believe I've made close to 1000 cuts on both versions of my table using the THCAD and PlasmaC interface within LinuxCNC and never ever any kind of hiccups with the THC. In fact the only hiccups using the software have been instigated by their human.
asuratman
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Re: Why LinuxCNC does not need a THC.

Post by asuratman »

Hi Rod,
Now, to start with linuxcnc 2.8, we need only 1 ea 7i96 (for linux2.7 we use 1 ea 7i76), 2 ea THCAD10 (or THCAD5) and THCAD300, that's all. Nothing else from linuxcnc side ?
Rodw
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Re: Why LinuxCNC does not need a THC.

Post by Rodw »

asuratman wrote: Sun Oct 25, 2020 12:58 am Hi Rod,
Now, to start with linuxcnc 2.8, we need only 1 ea 7i96 (for linux2.7 we use 1 ea 7i76), 2 ea THCAD10 (or THCAD5) and THCAD300, that's all. Nothing else from linuxcnc side ?
V2.8 is required for plasma as the plasmac config uses some features that are not present in earlier versions. Most people are using a Mesa 7i96 and a THCAD (Plus a second THCAD-5 for ohmic sensing.)

IF you tell me what plasmacutter you have, I'll let you know what THCAD version to get.
asuratman
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Re: Why LinuxCNC does not need a THC.

Post by asuratman »

IF you tell me what plasmacutter you have, I'll let you know what THCAD version to get.

I will use : https://www.aliexpress.com/item/4001248 ... hweb201603_

It is chinese plasma cutter 50A with pilot arc.
Rodw
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Re: Why LinuxCNC does not need a THC.

Post by Rodw »

There are some notes here http://linuxcnc.org/docs/2.8/html/plasm ... cad_to_use
I think I would shoot for around a 200 volt full scale with a Mesa THCAD-10.
Per the THCAD manual, http://www.mesanet.com/pdf/analog/thcadman.pdf
This requires a (200-10)/100 = 1.9 M scaling resistance.
Its best to split that on both electrodes.
thats 950k per side but the closest is a 910k resistor which if you work backwards will give a full scale of 192 volts. That will be perfect!

So put a 910k resistor on wires connected to each electrode inside the plasma cutter and place the THCAD-10 inside your control panel.
The voltage coming outside of the plasma cutter will carry non lethal voltage and current using that method.

So just to be clear the cutting volts will be around 130 volts max and the THCAD is rated for 500 volts indefinitely so by using around 200 volts gives a better resolution and we will never care about volts > 192 as we will never need to monitor it that high!

The wattage of the resistor does not matter 0.25W to 0.5 W is fine.

I'm not sure if you can use Hypersensing/ohmic sensing with the exposed tip like that though.
asuratman
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Re: Why LinuxCNC does not need a THC.

Post by asuratman »

So, its only 1 ea THCAD 10 needed and ohmic sensor or floating head. The ohmic sensor is not from mesa, it can be used the one from ebay.
Rodw
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Re: Why LinuxCNC does not need a THC.

Post by Rodw »

asuratman wrote: Sun Oct 25, 2020 9:01 am So, its only 1 ea THCAD 10 needed and ohmic sensor or floating head. The ohmic sensor is not from mesa, it can be used the one from ebay.
I'm not sure there. I think the THCAD-5 with my hypersensing arrangement will work. I just can't test it as I don't have one of that style of torch. Some of them are shorted out inside the torch tip while not cutting to create the blow back ignition so it won't work as the tip is already connected to the material. Any ohmic sensing circuit where the torch tip is not shielded (like yours) means there will be the full force of the plasma torch voltage in the circuit so you want to make sure it can withstand that. The THCAD can.
VlakHund
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Re: Why LinuxCNC does not need a THC.

Post by VlakHund »

I'm building my first table and am now searching for the best hardware software solution. This is a very interesting topic. It sounds like this would be the way to go for me. ALL of this is very new to me. Would you please, help me with a shopping list here? I have motors, 2 NEMA34s and one Nema23 on the vertical piece, I have 3 drivers 2 MA860Hs and one M542T, the table is 4x8 with a rack and spur gear, and the motors are held into the rack gear by spring force. I did buy a few years ago ( huge procrastinator) the Proma THC. Just because I have it doesn't mean I have to use it though. Any help would be HUGE! Gracias!
Rodw
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Re: Why LinuxCNC does not need a THC.

Post by Rodw »

Well you don't need much. At the bottom end a ordinary BOB and a PC that can run Linuxcnc with appropriate latency and your Proma.
The next step up would be to buy a Mesa THCAD-10 ($69) and use a BOB. Discard the Proma
Then best performance would be a Mesa 7i96 ($119) and a THCAD-10
If you go the Mesa route, you could add a Meanwell 24v 40 W power supply for field power and a 5V power supply (not a USB plug pack), Meanwell would be better.

And a 3 pack of Mesa Din rail mounts and a Mesa COMM2X terminal block will make life easy to mount things up.

There are still a few variables regarding your plasma cutter that may change things slightly.
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Re: Why LinuxCNC does not need a THC.

Post by VlakHund »

Great response, exactly what I was hoping for! What other table related variables are you referring to? Is the Mesa 7i96 also a BOB? So, ultimately a Mesa 7i96, Meanwell 24v 40 W power supply and the 5V power supply is what I need then. I'm going to have a significant learning curve with the CAD/CAM software anyways, might as well learn to use Linux too. Hopefully none of it is too painful.
Rodw
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Re: Why LinuxCNC does not need a THC.

Post by Rodw »

I would not call a Mesa card a BOB as that implies it can connect to a parallel port..
I'd probably call it an industrial quality ethernet interface board. It 5 stepgens, an encoder input used by the THCAD and some inputs and some 2 amp relays onboard for outputs. Motion control is still managed on the PC by Linuxcnc but the stepgens are offloaded from software to the Mesa hardware. This substantially relaxes the latency requirements of the PC's operating system. The Mesa cards can run the stepgens up to 10 Mhz, way faster than you have time to create discrete steps!

The other major advantage is that while the logic and stepgens run on 5 volt, all I/O uses 24 volt power which is much more immune to being affected by noise. Eg the noise has to change the signal by 12 volts before anything is affected.

I have no experience with other platforms/hardware but a number of people have commented on how much of an improvement the Mesa card makes with stepper based machines when they convert from another motion control method.

If you let me know what plasma cutter you have, I might be able to make some other suggestions.
Does it have a arc OK signal?
Does it have a voltage divider output?
Does it have a RS485 input?
VlakHund
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Re: Why LinuxCNC does not need a THC.

Post by VlakHund »

Thank you Rodw. I do not know the answer to any of your 3 questions, but I'm guessing the answer to all of them is, no. So, the plasma cutter that I have now is pretty old, and I've only ever used it by hand. It's a thermal dynamics 75xl. I think it's called Pakmaster. I am completely open to purchasing a new machine which, I have to do some more research on that, too I guess. A friend of mine has an Esab he would sale cheap that he bought about 10 years ago and has never used it. He said it would cut one inch easy and that it came with a torch for a plasma table. I do lots of welding on the side and its usually heavy duty structural work like 30' automatic gates and the spans above them, my regular job I work in a chemical plant. I will want my machine to be able to cut at least one inch preferably more and the one I have now won't do that. I also want to use this table to cut out patterns from 1" plate for prototyping a tool. I am fully aware that the cheap guy often pays twice, so I'm open to spending some on a newer machine. At this point I would say that my budget for completion of this table is $2k so definitely won't be jumping for a new machine just yet. I do have an adapter for the pakmaster that I bought several years ago when I decided to build a cnc.
dvn4life1972
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Re: Why LinuxCNC does not need a THC.

Post by dvn4life1972 »

Rod, did anyone mention Hypersensing with a THCAD-5 yet?

:geek:
N2 Welding
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Re: Why LinuxCNC does not need a THC.

Post by N2 Welding »

Some good things no in here :)
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