Help Needed on a Homebuilt Plasma Table

[epeppard]

I've built a table based on a plasmacam framework. The original controls were not functional and the rails and bearing were wore out. Planned to use the existing motors till I found out they were proprietary servo motors. I used 2 x 2 square tubing with nema 23 steppers with rack and pinion on the x and y axis. I fabbed a z axis which has a floating head torch mount. Mounted a 4" deep pan with 2" slats placed in angle iron with slots cut to accept the slats. Pretty standard table.

I built the controls using 3 48 VDC power supplies, 4 DM542T drivers, and a Mach3 breakout board with parallel port. PC is an older Dell running XP. Control software is Mach3.

The plasma cutter is a Hypertherm PowerMax 380. New consumables have been installed and the cutter works fine when not installed on the table. When the part to be cut is placed on the slats and the work clamp is clamped to the part, I can not get the plasma cutter to strike an arc. I have read through various posts about grounding and also Hypertherms service bulletin "Recommended Grounding and Shielding Practices". I have tried to follow the grounding procedures outlined in the service bulletin. I have driven a ground rod next the table. Mounted ground points on the table frame and ran #6 stranded wire from the pan and #10 wire from the rails, gantry and z axis to those ground points. #6 stranded wire is run from the table frame to the ground rod.

I read Jim Colts recommendations to run the work clamp cable to the ground with a shortend cable. I have done that and then ran the work clamp to the table for connection to the part to be cut. Still can not get the torch to ignite. If I isolate the part to be cut from the slats (place it on a piece of wood) and disconnect the work cable from the ground rod, the plasma torch cuts fine. Connect it back to the ground rod and place the part on the slats, no cut. I obviously do not have a completed path back to the plasma cutter through the work clamp cable but am at a loss as to how I can resolve this problem. Any help would be greatly appreciated. I have tried to email Jim Colt directly at Hypertherm but I'm sure he is way too busy to answer all the questions he probably receives.

Thanks,
Ed Peppard

[weldguy]

Hey Ed

Sounds like a project! There should be no difference between striking an arc on or off the table. The only difference is your not pulling the trigger when on the table, the controller is doing the work. Of course I am only guessing and not familiar with how you wired it up, but it could be that you have it wired incorrectly OR the way it is wired you need to zip tie the trigger so its pulled all the time and allow the controller to turn the arc on and off.

[Joe Jones]

If I understand your post correctly, you did NOT use the PlasmaCam controller box. You did NOT use the PlasmaCam gantry or carriage motors. You did NOT use the PlasmaCam Z motor. you did NOT use DesignEdge software, or the earlier PlasmaCAM 3.xx software.

Did you use a PlasmaCam table frame? You say the rails and bearings were worn out. What did you replace them with? I am at a loss to find any similarity to a PlasmaCam table at this point.

You can set up your machine with the aftermarket controllers etc., from C and CNC, which sells various kits and parts to make anything BUT a PlasmaCam table.

I have no knowledge in the "other guys" systems, or the software, so I hope someone can help you figure out what needs to be done in order to get you cutting!

I wish you great luck!

Joe

[jimcolt]

The Powermax 380 was designed for hand cutting using its hand torch. So to trigger the torch to fire you have to do what the trigger switch does when using the hand torch held in your hand. How is this connection made? Jim Colt

[epeppard]

I appreciate the replies. I guess this forum was not the most appropriate place to post my problem. I didn't realize that this was mainly a plasmacam site. I do have a plasmacam frame but that's about it. Also re-used the plasmacam handheld torch holder since the powermax 380 has a hand held torch. To trigger the torch from mach3, I have an output from the bob to the same connections as the trigger on the handheld torch. That all works fine.

But today I actually figured out what the problem was. I read on another forum that controls and pc should not have continuity to the table. I had continuity but couldn't figure out how. Finally realized that I had attached a metal receptacle box to a frame leg to which I plugged the control and pc 120VAC cords into. Ground wire on the receptacle grounded out the frame/table/pan etc. Fixed that and thought I was good to go. Nope. Still had continuity between the PC and the table. First thought was the parallel cable. Nope. Second thought was the SVGA cable to the monitor. That was the culprit. I had made a mount for the monitor and it was bolted to an extension above a leg. I guess that there is a ground in one of the pins of the SVGA cable that is tied to the monitor chassis and also to the mounting bolts on the rear of the monitor. Who would have thought.
Below are a couple of pictures, first cut and table and monitor mount. Notice the monitor on the stool.

IMG_2919.jpg

IMG_2918.jpg

[Joe Jones]

I appreciate the replies. I guess this forum was not the most appropriate place to post my problem. I didn't realize that this was mainly a plasmacam site.

This is NOT mainly, or even largely a PlasmaCam site. I am just wondering which direction you are taking your machine!

[epeppard]

Thanks Joe Jones. I'll keep that in mind as I continue. I'm sure I'll have more questions but at least I now have a functional table. Plan on using sheetcam to generate gcode. Built a cnc router running with mach3 10 years ago with basically the same controls so that's why I chose mach3. I know there is better out there but it's what I know. Have to figure out the floating torch head programming for pierce and cut height. Need to determine switch offset distance. At least I'm getting closer to cutting.

[acourtjester]

As Joe points out this is a open site for CNC (mainly Plasma, but other operations are talked about). As you know from your experiences a CNC table is a basic step up but can use different software and electronic. If Mach 3 works for you keep going, if you want to change later some things will improve. The connection to the table frame can be used as a common signal, but not a power ground. The connection to the Plasma unit is actually the plus side of the output and is connected to the table frame/metal being cut. There are many DIY types here so what you are doing is in that mind set and help will be given, as it has been in the past. Just ask question

[weldguy]

I would have never guessed that a vga cable would cause this.

So your torch turns on and off as it should now that the vga cable no longer has continuity with the table?

[epeppard]

weldguy, yes, mach3 can now turn the torch on/off with the part laying on the table slats. I plan on isolating the monitor mount from the frame so I can put the monitor back where it was. Hopefully will get that done today.

[epeppard]

Made some wooden bushings to isolate the monitor mount from the plasma frame. Mounted the monitor and everything works as it should.

IMG_2920 (2).jpg

IMG_2921.jpg

[weldguy]

The wooden bushings are a clever idea. I would have never thought this would be a problem but I am glad this is working for you

[epeppard]

Thanks weldguy. I mainly do wood. This is my first attempt at cnc plasma. Got my floating switch offset distance figured out. There are two post processors in sheetcam that have floating head in the title. MP1000-THC and PremierPlasma CNC Floating Head. Edited both of those with my switch offset distance. Will probably try both and see what works.

[acourtjester]

You should be able to use other post processors as a floating head routine is just G-code commands. with a little work you can edit a post processor to add a floating head routing so it is automatically installed in the G-code. It uses the G28 command for the Z axis

function OnPenDown()
if (preheat > 0.001) then
post.ModalText (" G00")
post.ModalNumber (" Z", cutHeight * scale, "0.0000")
post.Text ("\n G04 P")
post.Number (preheat,"0.###")
post.Eol()
end
post.ModalText (" G00")
post.ModalText ("\n G90F30\n")
post.ModalText (" G28.1 Z0.50\n") here it is
post.ModalText (" G92 Z0\n")
post.ModalText (" G0 z-0.035\n") here is the offset distance
post.ModalText (" G92 Z0\n")
post.ModalText (" G0 z0.25\n") I think this is the pierce height
post.Text (" Z")
post.Number (pierceHeight * scale, "0.0000")
post.Text ("\n M03\n")
if (pierceDelay > 0.001) then
post.Text (" G04 P")
post.Number (pierceDelay,"0.###")
post.Eol()
end

[epeppard]

Thanks acourtjester. I will give that a try if the others don't work. MP-1000-THC post processor is supposed to work with Mach3.

[acourtjester]

You may contact Les directly at SheetCam for help, he seems to reply to questions or custom requests, great company.