First machine build

[Aaron3309]

Looking to build my first machine, right now my experience is limited to a shapeoko router but I’ve been researching plasma tables for several months. I’m a mechanic and welder by trade so I’m reasonably handy.
I have so far decided on a 4x4 water table design, 20mm linear rails and direct drive rack and pinion from nema 23 or 34 steppers.
For electronics I am thinking Uc400eth controller, Gecko g540 driver and neuron lite thc using Uccnc.
Is anyone using this hardware setup, we any problems or have any suggestions?

[Rodw]

I would not recommend a direct drive rack and pinion. You need a 3:1 to 5:1 reduction drive. If you are accurate, there is no need for a spring loaded pinion. You need about 25mm travel per motor revolution and you will be up over 90mm per revolution. Motion will be very jerky.

There is a Plasma primer document as part of linuxcnc which you may find helpful regardless of your chosen platform. http://linuxcnc.org/docs/devel/html/pla ... rimer.html
Full disclosure: I wrote it

By the sound of it, coming from Grbl, you are not really wedded to the Windows platform. Before you make a decision on hardware, have a look at the Plasmac config which is now part of the Linuxcnc distribution for V 2.8 and up. http://linuxcnc.org/docs/devel/html/pla ... guide.html
It is vastly superior than any external THC can ever hope to be becasue torch height is being managed right inside the motion controller resulting in a superior design. Should you go this way, I'd suggest that you look at the ethernet Mesa 7i96 ($119) and a Mesa THCAD card ($69). The high performance THC is managed within the LinuxCNC PC itself.

Because you will not be using a parallel port breakout board, the Gecko 540 is not a good choice. So using Leadshine or Longs Motor drives will be the ticket.

I get excellent performance from Longs Motor DM542a drives off eBay driving NEMA 23 and small NEMA 34's up to 21 metres per minute using Mesa hardware running Linuxcnc and Plasmac.

[Aaron3309]

Wow glad I joined the forum, I knew i would be able to get the info I needed here. So I have just a few follow up questions if you don’t mind I really appreciate the help.

What method of gear reduction do you suggest? Gear or belt or?

Do you have any power supply you recommend?

Would there be much of a difference between interfacing with an everlast or a hypertherm plasma, I may start with everlast and upgrade later depending on budget.

Thanks again.

[acourtjester]

The are many excellent ways to built a table that will give years of service, do your research a settle on a design you like. Different drive, electronics and controller are some of the differences. There is member who have built their own table and have post construction details. Rodw is correct with no direct drive but ones that had reduction built in. Attached is the way I do the reduction for a rack and gear drive a belt drive is used from the motor to a secondary shaft with the gear mounted. I do use direct drive for a lead screw on the Z axis, with a 10 turn per inch lead screw.
The connection to the plasma unit is made with a plug on the back of the unit, if you Everlast are fairly new it should have one and the manual will show it. You should be using one that has “Blowback” type start for the plasma sequence, Hi Freq of Hi Voltage are not good for CNC work.
I have built 8 table and buy a kit with the Motors (1 nema 34 and 2 nema 23, 2 power supplies, and the drivers for those motors).

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[Rodw]

I use belt drive reductions on gear racks. Power supply is a 10 amp meanwell 48v for motors and you would need a 2amp 24v power supply for a mesa card plus a 5 volt one if you choose the 7i96. Plus another 24v for ohmic sensing. The everlast will work for you but Hypertherm or thermal dynamics is much better. There are some traps with the everlast voltage divider I documented on this forum.

[Aaron3309]

Ok so I’ve gone ahead and went with the Mesa 7i96 and ThCad, I have a couple questions in the wiring, first what components can be grounded together? Is it ok to have 5,24 and 48 volt components on the same ground? Where do I ground them backup? The power supplies? Then for the 24v is that only to supply limit switches and such? And lastly I have used shielded wire for all my connections and I know you only ground the shield in one side, would I just run the drain wires to the common ground? Again thanks for all the help

[Rodw]

Hopefully it helps, but here is a reference pinout I've been working on for the 7i96. I've half built this but run out of time. I should take some photos but its at work. It includes IO for air scribe and a drill.

You need a say 48v power supply for motors, a 24 volt (say 2 amp) power supply for field power and a 5 volt (say 1 amp) power supply for logic power.

7i96 Reference Build Pinout (1).pdf

The grounds are more on the 24 volt side. I was going to use on of the Mesa Common blocks so I had 12 terminals +24v and 12 terminals -24v

I use a second thacad for ohmic sensing which frees up a couple of i/O pins which means you can run seperate home and limit switches almost everywhere. That meant I needed to install a new bit file that is available for download in the Mesa product page.

You can either ground at the entrance to the cabinet or do what I did and use a 5 pin connector so you can pass the ground inside and ground at the motor driver. I used an existing copper ground point in the cabinet for all motor grounds.

[Aaron3309]

ok so I have my base machine now set up, I have the mesa 7i96 with thcad 10, for drivers I have leadshine dm556t. I purchased a z axis already complete with floating head and breakaway. Im running the latest master of linux cnc 2.9 on Debian stretch After much tweaking and searching for settings online I was able to finally get some motion but there seems to be major issues. The y axis moves fine when jogging (now that I found how to reverse one of the motors) but the x an z have some problems. when I try to jog either axis the steppers are extremely jumpy, loud and keep moving back and forth different directions. for example I can hit jog left on the x once and it moved left then the next time I press it may move right same with Z. I feel like the problem is in my settings, the Y was acting similarly until I changed the settings under stepper info from all settings at 2500 to all settings at 10000. I really have no clue what I am doing with regards to the settings.

so what I am really asking is what on earth should I set everything to. I currently am going to run direct drive until I can devise a good gear reduction, the gears are 20 pitch 20 degree angle 15 tooth 3/4" pitch diameter running directly on 20 pitch 20 degree angle gear rack. I have no idea what numbers to use for this in the configurator, I also have no idea what kind of micro stepping I should use to strike a decent balance.

as for the stepper settings I have no idea either. the steppers themselves are 4.2 a 425 oz 1.8* step angle run by individual dm556t drivers.

thank you for any help it is much appreciated I need this machine up and running asap i'm just not well versed in all the computer and electronics details.

[Rodw]

Aaron, I think at this stage it would be best to move over to the Linuxcnc forum and make a post in the plasma section
https://forum.linuxcnc.org/plasma-laser

Also post your hal and ini files when you do that.

That way, you will get much better exposure to experienced helpers (including PCW, the owner of Mesa) to get you going faster than possible here.

The good thing is you have motion, so the rest will be just configuration settings. Plenty of people have used your hardware