SOMD - Lowrider Plasma CNC

LowRider CNC Your Builds
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My original build of the V1 LowRider was with 1/4" lauan, which was really closer to 3/16". It was really flimsy stuff that flexed way too much. When I rebuilt everything up to V2, I used 1/4" MDF and painted it.

On my to-do list is to redesign the torch mount. The way I have it cantilevered off the end puts too much bending on the center assembly and it is not very rigid. I have been thinking about implementing a torch mount inside of the DW611 base in the center. It would put any loading directly between the two X rails and prevent any twisting when the torch goes to touch off. Plus by using the DW611 base it makes it that much easier to tool change when I want to go back to routering. The big headache then becomes replacing the water pan with my MDF wasteboard.

I’ve got a lot planned for the CNC upcoming. I’ve been spending a lot of my free time building a powdercoating oven for finishing parts (30"x34"x48" inside dimensions)

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Yea I figured I’d be rigging up a floating torch mount in the center too. Something that attaches to the standard router mount for quick change is an interesting idea.

I had thought the waste board could just slide over the top of the (drained) water pan, no?

Nice teaser, I’m looking forward to seeing it!

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Although it would be nice, I’m afraid that I would lose too much rigidity while routing because then the Z axis is zeroed 4.5 inches higher at the top of the pan (3" for the pan + 1.5" of two MDF slabs).

I just added some pics of the oven to the same shared album

 

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Thank you for sharing your experience and keep it updated ?, I was thinking alot about how i should done it and your topic helped me,

One more thing, i like the way you designed the table, could you please share cad file that on the first photo on your google photo album? I think its fusion 360

Best regards

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  • the cost of separate TB6600 driver boards right? One for each stepper or one for each axis? I’m guessing it’s gotta be one for each stepper and you’re auto squaring in linuxcnc?

What jitter are you getting with your computer?

If you get an opportunity I’d love to see some pictures of your electronics.

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I did order exact parts as your

  • Mesa 5i25 with 7i76

  • Mesa THCad

  • TB6600 drivers

I wired everything as attached photo, and change the 5i25 jumper to provide 5v power to 7i76,

When i use pncconf wizard and hit axis test no motor will move

 

I struggle alot and i read and searched alot i can’t found a solution, please if you can help or anyone i will appreciate it.

 

Screenshot_20190505-231239.jpg
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Glad to hear this has been of some help. I can definitely share the table, but it’s not 100% completed. I don’t really like making assemblies in Fusion 360, much prefer SolidWorks so I kinda gave up on the design once I knew the general idea I was going for. A few pieces are missing, but hopefully it gets you started.

One thing to note, the table was designed for the LR1 with wheels on top and bottom of the Y-axis rail. Because of this, my X-axis table supports lay on two Y-axis stringers. Those stringers have quite an unsupported span being only welded on the two ends, and adding all the weight of the water on top of this was not a great idea. At some point during this summer when I break everything down to throw some paint on and finish some welds, I may revisit this portion of the table.

 

Yes, I think I paid about $10 each. Since the 7i76 allows for 5 independent step/dir signals I split all of the motors out to their own driver. You probably could just use DRV8825s and it would work the same, but I wanted some extra headroom in case I ever implement NEMA23s for extra speed without losing torque and skipping steps during 300 ipm jogs.

I haven’t configured auto-squaring yet, but I have my limit switches already ran and its ready for it, just need to change the software side.

I’ll have to get back to you on jitter. I’m running Linux Mint 18.3 Cinnamon, so not exactly a barebones build. Jitter wasn’t horrible (30,000-50,000 iirc), but it didn’t effect operation so I didn’t bother trying to lower it.

I will upload some pictures of the electronic cabinet when I get a chance. It needs cleaned up, but its serviceable as it is now. I intend to mount the rack on the wall and possible make a DB37 connector to switch from control of the plasma to a separate MPCNC. Anytime I use GRBL on a raspberry pi it’s an unpleasant experience compared to LinuxCNC. :confused:

 

Edit: Cabinet picture here: https://imgur.com/a/riWrbSj All stepper wires and sensors come into the back of the cabinet through 5 pin panel connectors. One or two wires are hardwired into the board (need to update with more quick connectors…) 5 TB6600 drivers, 24v Meanwell PSU, and a ground and 24v positive bus for easier connections. SSRs for router and plasma connections. The whole thing is currently turned on via the power strip, will need to update to an external switch with E-stop.

Table_Assy-v18.zip (33.7 KB)

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I’m not sure if I ever used the test axis button; I briefly used the wizard to setup the general outline of the config files and edited them in a text editor. Once you have the basic lines, its easy to go in and adjust steps/unit and setting it negative if you need the direction reversed, etc.

I’ll upload my configuration files to give you a baseline config that you can tweak to match your setup, but I would highly suggest to go through and comment out/delete lines that don’t deal with the initial movement setup. It can be very confusing trying to adapt configurations. Once you have the basic things working, you can reintroduce the other parts.

My recommendation is to start one axis at a time and go from there. Steppers > Limit Switches > Relays > Rest of plasma stuff

Also, you’d be better off starting a thread over at forum.linuxcnc.org for help getting everything initialized. I don’t know of many here that are using this setup so the help may be limited. I don’t mind helping, but you should start a separate thread and document what you’ve tried.

One more thing, make sure you tie all of your grounds together. The grounds from the drivers and the PSU and the 7i76 should all be connected somewhere. Unconnected grounds have driven me wild chasing down a problem before…

Edit: Upload isn’t working. Posted them to pastebin: https://pastebin.com/psz3q63S and https://pastebin.com/fzXqCJvJ These are the two basic files that should at least get the motors running. You may need to adjust how the axes are mapped, but it will at the very least move the motors. If not, you probably have a wiring issue.

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I don’t know if you’ve had to deal with this yet yourself. How would you handle tiling with a larger plasma cut part? It seems pretty straight forward with a router just dropping in some dowels for locating pins, but with a plasma torch I’m imagining it could be an issue with precision and repeatability. Maybe not. How have you/ or how would you handle tiling?

I’ve tried googling but can’t seem to find any good examples of people tiling on their plasma table.

On a side note, fedex just delivered to me a 7i76e. Time to start compounding the frustration :wink:

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Thank you for posting. While I’m new to cnc I have been playing with mircrocontrollers and ssr for a few years now. I wanted to caution you about the relays being attached to wood. I don’t know what relays you’re using but the chinesium cheapos are known to fail from time to time, when they fail they can go up in flames. Also, if any loosened connections were to arc it could ignite the wood. I’ve read stories of people setting their homes on fire. I know we’re already playing with torches and power tools and don’t leave these unattended, so we take on more risk and but also more precautions than those guys, but I just wanted to get that out there.

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That’s a tricky one. I haven’t seen anyone do anything like that with a plasma, either. Most people either have 4’x8’ (or larger) or 4’x4’. I wouldn’t recommend anything smaller than 4’x4’ just due to sheet stock sizes. If I ever had a request to do something 6’ long, I would probably just pass on it, or cut in two pieces and weld it back together? Yeah, nope, I’d pass. Since I probe the surface and adjust my Z-offset prior to every pierce, I’m not too concerned with how flat my water pan and slats are. The THC handles Z-movement very well, so I don’t have anything easy to index off of for things like pin indexing.

Have fun with the 7i76e, I probably would have dropped the extra for ethernet if I did my research first.

That’s a good point, I did see the huge heat sinks that they come with but didn’t think much about putting them right on the wood. I’m sure they were the cheapest SSRs out there. My only comfort is that there is probably only a few mA running through the plasma SSR since its only purpose is to close an 18VDC circuit on the Hypertherm. Nonetheless, thank you for pointing that out, I do need to come up with a better system.

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Oh yeah, duh. I’m used to running 30+ amps through them. You’re probably fine. (*not an ee)

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Still a valid point for the 7 amps the DWP611 can pull, I just haven’t tried that one yet.

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I’ve tried to reverse engineer your wiring connections based on that photo. Assuming your tb6600 headers are in the same orientation as mine it looks like you simply wire Dir- from the mesa directly to Dir- on the driver, Dir+ to Dir+, Pul- to Step-, and finally Pul+ to Step+?

No need for limiting resisters or jumpers anywhere? The enable signal ports are meant to be left empty?

I’ve seen conflicting information flipping through what docs I’ve found online… No need to worry about this common-anode active low active high business?

 

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That’s correct, no need for anything extra on the 7i76.

I left the enable pins empty and the steppers power up as soon as the rest of the electronics are turned on. In the future I’ll probably wire it to a separately controlled pin so I can turn the drivers off. The motors do get quite warm/hot after they’ve been on for some time. And my current setting was set appropriately for my steppers

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Thanks again for all your help, Bryan. I’m jogging steppers now with linuxcnc!

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I hope you don’t feel like I’ve been hijacking your thread, I’ve tried to keep my questions relevant to your build.

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Awesome! Setting up the ini and hal files can be a daunting task, but you’re off to a good start.

I don’t mind you posting here, it helps others who want to follow along with the same build.

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Just a coat of latex paint? Did you give it a sealing coat first? How has the MDF help up to splash back from the water pan?

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I actually used enamel spray paint. I wanted to use enamel on the steel so I just tested it out on the mdf first. Once it cures its fairly tough, probably acts as a sealant too.

So far it’s held up fine. I’ve been thinking about replacing it with aluminum or skinning the bottom with 16ga powder coated steel. My wood storage shed gets wet during heavy rain, and I’ve had MDF get wet and mold before, so I’d like to avoid that.

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Bryan,

Can you tell me about the design of your floating torch?

I don’t see that you’re using an ohmics sensor, or are you? I’ve read they can be a problem when used with a water pan.

 

[edit]

I think I found it: https://www.thingiverse.com/thing:2516238

I’v made a mockup of this mount on top of a 611 plate to see how I can fit it in the center of the plate and miss the rails. It looks it could work without any changes to the float, it just needs some brackets. Looks like the brackets could use 2 of the existing mounting holes in the plate while drilling a few more. I’ll let you know what I come up with. Any suggestions? (the black rectangles represent space occupied by the x rails)

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