Another Constant Velocity Question

[nick7251]

Any other ideas on what I can check? I'd love to get my machine to run without pausing at every new start point.

Well I could say use Linuxcnc

I've thought about switching, but I just bought my controller (pokeys57cnc) and I don't want to dump more money into hardware. With that said, Any recommendation for a cheap controller that works with LInuxCNC that has a relay to switch the torch on and off? Just curious to explore what it would cost to change over to see if that solves my problem.

[Rodw]

A mesa 7i96 $119 and a THCAD $69 plus about $50 in power supplies about is all you need. the 7i96 has relays built in.
A second THCAD for Ohmic sensing is handy and frees up a few input pins

[nick7251]

A mesa 7i96 $119 and a THCAD $69 plus about $50 in power supplies about is all you need. the 7i96 has relays built in.
A second THCAD for Ohmic sensing is handy and frees up a few input pins

Does the Mesa work with other THC's? I already have a Proma, and I've been looking at getting a PriceCNC. Also I cannot find any documentation about it having a relay built in already.

[Rodw]

Yes, the Proma 150 has long been used with Linuxcnc and there is a mode in Plasmac that supports it. The Proma SD is still usable but not as effective because it can't be controlled by Linuxcnc.

Here is what Tommy in Kosovo who has used the proma for retrofits for years says.

As for what works, well everything i did test works perfectly, THCAD tracks the material smooth and fast, Proma THC works nicely in mode 2 and the tracking speed can be adjusted to avoid "bunny hopping" the torch, materials work perfectly setting the feed rate and all the parameters, touch off button (when added) works and reloads the part in gremlin makes using a laser for edge finding a single button affair, load sheet works, change consumables works and can be set as needed, pierce/cut feature works and is very usefull for thicker material to save consumables as one can use old consumables for piercing and new ones for cutting. Yes, nozzles will get messed up when piercing, shortening their life.

Ref: https://forum.linuxcnc.org/plasmac/4030 ... ng-plasmac

He makes a living making plasma tables and has done a number of tables over the years with just a parallel port and previously had his own Linuxcnc config for the Proma 150.
He's also done a couple of table with 2 parallel ports and the THCAD.

[nick7251]

Nice info. Just don't want to make the mistake of buying the wrong thing again. The pokeys57cnc is really nice and solved all my issues but this one which isn't pokeys fault. Mach 3 just sucks.

Okay now by you giving me the cheap option from mess it makes me wonder what I might miss out on with the more expensive options?

Another concern of mine is that I don't speak Linux and have only dabbled with it in the past.

[Rodw]

You'd be surprised who is learning to speak Linux on this forum but I'll leave them to come forward when they are ready.

There is also a dedicated Linuxcnc plasmac section here now.

I gave you a cheap version so you could get a taste. Using software based stepping on a parallel port limits the maximum velocity whereas the Mesa solution moves the step generation off to dedicated hardware stepgens.

Linuxcnc is just an application. So the OS does not really matter other than its the right platform for Linuxcnc, BMW and a host of others. Whilst the official install is an ISO that included Linuxcnc on Debian, Linux mint is super smooth and easy to migrate to from Windows and there are simple methods to install it now that the PREEMPT_RT real time kernel is available as a package.

Tommy has explained how here:
https://forum.linuxcnc.org/9-installing ... stallation
But you can follow the first link to download an ISO that does it all for you. After that you will be able to upgrade Linuxcnc without worrying about messing with the OS. (Hint, stick with Mint 19.3 64 bit, away from the bleeding edge)

Everything I do these days is in the cloud so it does not matter if I am on my Chromebook, Linux or Windows day to day. I just install Chrome and keep working... I like to think I am OS agnostic

[sbest1]

I'm not sure if this is relevant, but we just did a new retrofit and had to learn Sheetcam and Mach 3. We had a heck of a time fine tuning to get a decent cut for art. For some reason we had to cut our feed rate to about half of the Hypertherm recommended speeds. We too had our machine stopping during cuts often. We discovered that with constant velocity on in Mach 3, it worked better with no rules (other than loop corner) in Sheetcam. What happened to us was that in Sheetcam when I checked Path Rules "None" in the operation, it still stopped during cutting. I discovered that even though I had Path Rules showing as "None" if I clicked the 3 dots beside there, it took me into another window and I had to change Always Apply Rule Set to None in there as well. Then we were able to cut without stopping.

[nick7251]

I'm not sure if this is relevant, but we just did a new retrofit and had to learn Sheetcam and Mach 3. We had a heck of a time fine tuning to get a decent cut for art. For some reason we had to cut our feed rate to about half of the Hypertherm recommended speeds. We too had our machine stopping during cuts often. We discovered that with constant velocity on in Mach 3, it worked better with no rules (other than loop corner) in Sheetcam. What happened to us was that in Sheetcam when I checked Path Rules "None" in the operation, it still stopped during cutting. I discovered that even though I had Path Rules showing as "None" if I clicked the 3 dots beside there, it took me into another window and I had to change Always Apply Rule Set to None in there as well. Then we were able to cut without stopping.

I'll check that out in sheetcam. Thank you. I have used rules before but for most of what I cut I don't use rules.

I think I am convincing myself to give Linux cnc and plasmac a shot. Looks pretty cool and hardware is relatively cheap. I most look forward to dumping the proma thc for the thcad solution. I don't know how to determine if I need the 5v or 10v variant. Maybe someone here can help me figure it out?

[acourtjester]

I have been snooping into LinuxCNC, being helped by RodW, you may need both one for THC and the other for Ohmic sensing (they call it other things). The one for THC is determined by your plasma unit as to the output of the arc voltage (divided or raw).

[nick7251]

I have been snooping into LinuxCNC, being helped by RodW, you may need both one for THC and the other for Ohmic sensing (they call it other things). The one for THC is determined by your plasma unit as to the output of the arc voltage (divided or raw).

My current plasma is raw. But I hope to upgrade to a hypertherm 45xp in the future so that would be divided. I guess for now I need to plan on having raw voltage.

[Rodw]

I would suggest you get a Mesa 7i96 and a THCAD-10 for best flexibility. You will need to add a scaling resistor as per the calculations in the THCAD manual. Then you can remove the resistor when you get the 45XP and select 20:1 divider. If your torch has a shield on it, you can use ohmic sensing with a THCAD-5 or a relay circuit.

I'm not sure how that would go with an exposed tip but the THCAD ohmic sensing circuit can handle over voltage of 500 volts so it might work as torch voltage won't hurt anything.. You might need to use a float switch..

[Rodw]

Oh and I forgot, if its HF start, you need to connect the THCAD before the HF unit inside the plasma cutter. I've only ever used a blowback start torch.

[nick7251]

How do I tell if my cutter is HF start? It's an older Chinese unit but it has pilot arch (not drag tip). I'm guessing it is HF because of it's age. I've looked for a schematic diagram in the cutter but can't find one. I don't know how to tell where the HF unit is.

For the ohmic sensing could I use a water switch? I already have one of those.

[Rodw]

It should work fine. Normally we use 24V field power for all the sensors and relays but I see the kemo water switch can switch 24v so it would be fine. Use it to switch field power to an input. We also use an ohmic enable output which was intended to leave the ohmic circuit disconnected unless actually probing but you can probably ignore that.

It sounds like you have hf start so the best way forward would be to post on the Linuxcnc plasma forum as Tommylight is the expert with that.

[nick7251]

Thanks so much. I'm getting pretty excited about the prospect of dumping Mach and gaining smooth cuts that don't pause at each new direction and a THC that doesn't bob up and down on a relatively flat sheet. Thanks all.

[acourtjester]

Nick I am not trying to tell you what to do (far from an expert) but you may be better off clearing some problems before you move on. I have built a few table and used different configurations. I have use Mach 3 on most and the table and I am now using UCCNC 400ETH and their software. I have use the Feather touch from CandCNC and the Water Switch for Ohmic sensors. I have used the DTHC-IV from CandCNC and the Price THC. And if I build another table I will use LinuxCNC with the Masa electronics. Each had slightly different configurations and setup procedures but all worked well.
The bobbing up and down can be a setting on the THC being to sensitive or too fast reacting. I assume you will continue using SheetCam to create you G-code, under the tools tab and the cutting rules, unless you have "none" in the bottom box, the cut rules will affect the G-code.
Have you asked for a simple G-code to see how it would run on your table?

[nick7251]

Nick I am not trying to tell you what to do (far from an expert) but you may be better off clearing some problems before you move on. I have built a few table and used different configurations. I have use Mach 3 on most and the table and I am now using UCCNC 400ETH and their software. I have use the Feather touch from CandCNC and the Water Switch for Ohmic sensors. I have used the DTHC-IV from CandCNC and the Price THC. And if I build another table I will use LinuxCNC with the Masa electronics. Each had slightly different configurations and setup procedures but all worked well.
The bobbing up and down can be a setting on the THC being to sensitive or too fast reacting. I assume you will continue using SheetCam to create you G-code, under the tools tab and the cutting rules, unless you have "none" in the bottom box, the cut rules will affect the G-code.
Have you asked for a simple G-code to see how it would run on your table?
rules.JPG

I have the bobbing up and down pretty well fixed with the THC. I cannot get the pausing resolved. I will make sure the rules are set to none next week when I get back to the table and see if it still pauses.

Other than this issue I am really happy with everything. But I don't like Mach or proma. I think I could get better results with a different thc. I'm excited about mesa because I can get a controller and thcad cheaper than I can get the price cnc thc, which is what I was thinking in on buying. Also from what I'm reading it works great too. I'm very happy with what I'm cutting lately. 3/16 and 10 gauge stuff. But when I speed things up for 14 or 16 gauge the pausing is much more pronounced and causes bigger problems. I'd like to make a couple signs for some friends. I don't feel confident doing so right now. I hope seting rules to none fixes the pausing issue.

And yes, I'll still likely use sheetcam if I switch to Linux cnc.

[acourtjester]

Ok I do agree with those changes, and the price of the replacement electronics. When checking the rules setting I would just delete any that are in there to be sure. Another thing to check is in SheetCam look at the start point of one of your cut operations and see if you can move the start point in that cut operation. If you cannot it is an open path and this may be why your not getting a complete cut around the part.

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[nick7251]

Ok I do agree with those changes, and the price of the replacement electronics. When checking the rules setting I would just delete any that are in there to be sure. Another thing to check is in SheetCam look at the start point of one of your cut operations and see if you can move the start point in that cut operation. If you cannot it is an open path and this may be why your not getting a complete cut around the part.
start.JPG
post1.jpg

I am getting complete cuts around the part. My shapes are closed and I can move the start points. So I'm not having a problem with that at all. When I say the torch pauses I mean it just had a slight stop and start at each new curve in the path. I think it is an issue in constant velocity, but everything others have had me try hasn't resolved it to this point.

[acourtjester]

Ok you may have a slippage in the drive assembly, but this generally shows up in the ends not meeting or a jog in the cut path.
With the motor power on see if you can push by hand the X or Y axis in both directions, they should not move.

[nick7251]

I checked for slippage recently and none of the motors move at all when power is applied.

[nick7251]

Also I looked at my rules in Sheetcam. It is set to none in the rules setting. I do have one rule in there to slow down on corners, but I haven't applied that rule to any of the cut files that I have noticed the pauses. So I don't think that is the silver bullet. Good check though. Thanks.

[Nacs Fab]

Nick, can you post up your Motor Config screens showing velocity and acceleration for A, X, and Y axis'. You may have an acceleration issue coupled with a CV issue. When I get a chance, Ill post both my motor info as well as my Config Screen. Mine pauses very slightly but I've got it close to dialed in. I began upping my acceleration a few sheets of steel ago and still working on it.

[nick7251]

X, Y, and A are all set the same.