Next steps

Hi all;

Firstly let me say that I have posted this under Plasma Machines but I know there are a few different areas that I am asking about, so please excuse this. I have a number of questions as detailed below.

Q1 Can I use the computer I am running Linux CNC v2.7.0 on to also run v2.8.0/2.9.0 and PlasmaC?
Does the GRUB file need to be edited for boot options, i.e. I can run both 2.70 and 2.9.0 (PlasmaC) on the same HDD and use GRUB to select the version I wish to run or do I need a separate drive for each version of Linux CNC (I hope this makes sense)?

Q2 RodW (many thanks Rod) provided me with a MESA 7i96 and MESA THCAD5 (Ohmic sensing) cards.

• I have read a few articles on the fact that these cards don’t lend themselves well to a water table, is this true?

• Does the Ethernet connection need to be a cross over or straight through to connect the MESA card to the PC?

• If I change the 10 resistors on the MESA THCAD5 card from 10K to to 4.99K (0.1%) I can effectively change the card to the THCAD10 configuration, thus allow the 20:1 voltage divider, rather than the 50:1?

Q3 I would appreciate some advice/clarification in the fact I currently run SheetCAM and have configured it to slow down on curves, circles etc. Does all this extra code get ignored when using PlasmaC? How does the relationship between these two products work?

Q4 I notice there doesn’t seem to be an ESTOP function on the MESA card (well at least in the same way that my LPT1 BoB does) how does/does this function work/exist in PlasmaC or via the card itself?

Q5 I have been using an older CIG Cut40i for my initial build. It seems to have died but in close inspection of the boards they look alright and fuses etc have not been blown. I look at the electrode and see that it is badly scorched and the pilot arc doesn’t fire. I have included pics of said unit. Does anyone have any ideas where to look? (I have no circuit diagram, nor can I seem to find one on-line). Is there a replacement torch assembly that is available, or do I just write it off as learning and wait for the new Hypertherm to turn up?

Thanks all for you valuable guidance and input, I doubt I would have made it this far without the contributions of this forum.

Cheers

John

• I have read a few articles on the fact that these cards don’t lend themselves well to a water table, is this true?

That does not make any sense to me...

• Does the Ethernet connection need to be a cross over or straight through to connect the MESA card to the PC?

Either will work

• If I change the 10 resistors on the MESA THCAD5 card from 10K to to 4.99K (0.1%) I can effectively change the card to the THCAD10 configuration, thus allow the 20:1 voltage divider, rather than the 50:1?

That would change the range to 2.5V full scale.
The easiest way to convert a THCAD5 to a THCAD10 is to add an external 100K 1% resistor.

Q2, I think from memory you were keen to get going and were talking about buying a Hypertherm 45XP and the THCAD-5 is perfect for the 50:1 divider out of the box. Alternatively, as PCW has alluded to you can still calibrate it to any voltage by reading the manual and following the formulas.

Q2. Ohmic sensing. Islander261 donated a proven circuit using a couple of relays that is published here in the Plasma primer docs. PCW proposed a THCAD-5 could be used for ohmic sensing and offered a free card for someone to experiment with and that was me. I wrote the ohmic component that is now part of the linuxcnc distribution. This proved to be a bit intermittent on water tables (more so with Hypertherm plasmas, than my Thermal Dynamics). I rewrote the component (called ohmic3.comp) to handle this better and it is on the forum somewhere. PCW proposed some circuit changes which also helped. Essentially now the hypersensing method we devised achieves what is impossible on other platforms and that is reliable ohmic sensing on water tables.

Q3 There is a sheetcam post here on the forum. Make sure you use it. You can to continue to operate as you have if you create the relevant code snippets in Plasmac format. Have a look through the Plasma and laser section because I shared some screen dumps from Sheetcam back before Plasmac had a dedicated section.

Q4. Estop is a function of Linuxcnc, not the board. If you have a look in the Hal examples sections here, the topmost post shows how to add an external estop using the estop-latch component.

Q5. If your CIG plasma cutter is anything like my long since binned BOC plasma cutter, its not worth attempting to repair. We attempted to fix a BOSS Cut40 and afterwards it let the smoke out in a spectacular and very loud explosive statement! My advice would be that your plasma cutter joins mine in landfill somewhere!

I'm happy to contact the Australian Hypertherm Distributor on your behalf. I may be able to negotiate a better price than what you can get. Feel free to touch base again.

Thanks for that info re the THCAD 5 to THCAD 10. So if I understand correctly an external 100K 1% resistor would be added to the +IN side of the card?

I will use a straight thru ethernet cable.

As to the watertable issues I think it was based on some old info so apologies I am fairly new to this and so was seeking some clarification.
Cheers John

We actually need a bit more info.
Did you get your plasma cutter going?
or are you going to use a Hypertherm?

If you are going to use a Hypertherm, the default 50:1 divider could be used without any resistors. That will give you a 250 volt full scale (5 * 50 = 250) which will work well.

If you are going to use your existing machine, we need to actually calculate the resistor to suit based on the formula in the THCAD manual.

Hi Rod;
Sorry for the late reply we have been battling Telstra for connectivity, so much for living in the bush (well close to it!)
I have gone the UNIMIG razorcut route, because I wasn't really getting anwhere with the Hypertherm resellers. So thanks for the offer, I'll see how I go and if I need to up the anti I will reach out.
I must admit I am a bit overwhelmed by the info available and whilst there is a lot to read, it is sometimes hard to know what it is you need, therefore sometimes guidance is useful. As to sheetCAM I have contacted Les, I found part of my problem was due to the fact I am running the linux version and some Gnome 2 rendering issues. Les has indicated there may be a new version coming out in Feb, that may address the issues.
As to E-Stop there was an E-Stop on my BoB card, I also have a diagram from AgentWD40 (Kyle) from his lowrider2 plasma build that I will use as a wiring guide. Out of interest what number of sub-steps are people using on their steppers?
Have taken yr advice and now the CIG unit it provisioning parts and scrap metal for recycle.

Thanks Rod; Razorcut is 20:1 voltage division out of the box. I have procedure to change if needed, but 20:1 sounds reasonable. As I mentioned if I need to up the ante on a machine I will reach out re. Hypertherm.
Cheers John

jnwinkie wrote:

Thanks Rod; Razorcut is 20:1 voltage division out of the box. I have procedure to change if needed, but 20:1 sounds reasonable. As I mentioned if I need to up the ante on a machine I will reach out re. Hypertherm.
Cheers John

A 3.3 M resistor by my calcs will give a 170 volt upper range. That will be fine for a machine like that. A 2.7 M resistor will give 140 volts which is still probably OK as I would expect the max voltage while cutting to be 110V (90-95V probably) Start with 170 volts and see how it goes. for the extra 68c, maybe you could grab a couple of different resistors,

www.jaycar.com.au/3-3m-ohm-0-25-watt-car...s-pack-of-8/p/RR1660

Remember, we don't care if the voltage goes off the scale when piercing because we have no need to worry about voltage until it settles down and stabilises.