Plasma cutter, automation project

jimgerken · Feb 18, 2003

http://www.grizzly.com/products/item.cfm?itemnumber=G4011&site=grizzly

This is my machine. It is OK, as I said. I am bending up to 6 inches of 14 (0.078") gauge with it now, even though it is rated for 22 gauge. This is the problem I see with most all these things, there is no full-specification published. To fully describe the capacity they would have to spec the gauge and width limitations, it would take a graph of some sort.
I figure when I break it, I will have to build it up stronger.
I think you do have a good priced one picked out there. However, I would go for the heavy duty 39" 14 gauge one at the bottom of your page, if it were for a bender-only.

jimgerken · Mar 5, 2003

Progress update:
Now running a "new" computer: P2 400 Mhz, Win98.
Have switched to Master5 software for table control, which made a HUGE difference. Master5 uses acceleration/decel ramping on rapid moves. The effect of this additional "intelligence" is that the machine can run almost 20 times as fast as it did with the simpler code. It still cuts at the operator-defined speeds, but while traveling between cuts it absolutely flys, and accuracy is maintained.
I am now converting everything to Gcode for for execution by Master5. Master5 contains a DXF to Gcode converter but it does not always do what it should, so I end up editting the Gcode. Gcode is really quite simple so this is no big deal. I am trying to establish a process to draw mechanical parts with CAD software, saving them to DXF format, converting to Gcode, edit Gcode for torch-specific details, and send it to Master5 for burning out. I am not quite there yet but have had a little success. I drew a simple 50mmX50mm square shape and took it thru the above process to burn it out. I used this as my calibration guide to get the translation and scaling setup right.
But, the coolest thing I'v done is this:
I found and downloaded a file of the "mudflap girl". You know the one I mean. I was able to edit the file enough to get it to cut on my machine, very cool. The curves (very important parts of this model) came out real well. She's got all the features. /forums/images/graemlins/tongue.gif
So the results are encouraging, although a bit slow.

jimgerken · Apr 1, 2003

More progress; All the electrical problems are fixed now, no more false switch-open signals. Added o-rings to the motor shafts to keep the insides cleaner longer.
My Dad came home from a local auction with forty sheets of 0.060" stainless steel (400 series?) which had a little corrosion but can still be polished up nicely. Makes nice fodder for the plasma animal. We cut about ten parts out Saturday, including a part drawn in Catia, saved out as DXF, converted to Gcode by Master5, editted for torch pauses and cut order. It came out great. Here's an action shot attached. Next I will be learning cutter compensation to zero in on the part tolerances a bit better. The plasma machine is now worth painting, so I suppose that will have to happen soon. I was thinking John Deere green and yellow...just kidding, any suggestions, I need something cool and exotic looking!

JimMc · Apr 2, 2003

Rather than using cutter comp, you can just offset the shapes you want to cut by 1/2 the kerf in your CAD program - remember offset outward for outer shapes, inward for holes. Makes programming life much simpler if you're hand coding.

jimgerken · Apr 3, 2003

Yea, I like your suggestion. After asking a few "experts", compensation is too much for me to expect to add to most parts. So I will get into the habit of drawing critical dimensions with built-in comp. Conveniently, its 1 mm diameter, so easy math.
Next issue: lead-ins for the holes and slots so no start-up scarring points. I guess these will be "custom" for each feature. Just have to get accustomed to manually writing these lines of G.

JimMc · Apr 3, 2003

I used to use a 3/8" lead-in on a similar system to yours, with no lead out. On lead-ins for arcs and circles I used an arc lead-in. On a straight line use a straigt line lead-in. I could send you a sample dxf if you like.

jimgerken · Apr 4, 2003

> I could send you a sample dxf if you like. <
I will take all the help I can get! THanks for the assistance. Jim

JimMc · Apr 5, 2003

I'm attaching a jpg of typical lead-in situations. The green is the finished part. The purple is the travel path of the plasma. Obviously for illustration, the offset for kerf is larger than you will actually need. The upper left enlargement is the leadin fo the outside profile, the bottom enlargement is for the hole. While I'm thinking about it, always cut outside profiles in a clockwise direction. Inside profiles, like holes in your parts, are cut in a counterclockwise direction. This reduces the amount of bevel in the kerf on the finished part. The way the gases swirl in the plasma tip cause the cut cone to have more angle on the left side of travel, so keep your finish cut to the right of travel for smoother parts. We have reversed this on purpose when we wanted to produce a tapered hole or a part with tapered sides though and it worked quite well.

jimgerken · Apr 10, 2003

JimMC, Thanks for the drawing. I am beginning to understand that you do this BEFORE feeding it to your Gcode converter, Correct? I will try this soon. I've been trying to add to the Gcode after its creation. Sometimes this can be done, but not for very complicated things. If I understand your method correctly, it would seem to be more efficient. I guess if it was too easy, everybody would be doing it.
What I want to do, is design a solid model, unfold the part to a flat pattern, project it to a 2-D surface (draft it), then (your method, if I understand correctly) add lines for lead-in to this 2-D drawing, THEN feed it to the Gcode converter.
Can I ask, on your production machines, is there an automatic height-above-workpiece control? I am having trouble staying the correct height above the sheet metal, as it is a balancing act between real close for great definition and further away for more reliable starts. One-sixteenth inch works well, but then the sheet stock can decide to warp from heat and ruin my best intention. I understand that some machines can adjust the cutter heigth based on plasma current sensing. I could do this, completely seperate from the 2-axis control system. What do you think, am I on the right track here?
(also, thanks for the bevel vs travel direction thing. I was aware of it, but its good to hear from someone else to confirm what I assumed.)

JimMc · Apr 11, 2003

Our height control reads the arc conditions and adjusts for warpage as well as raising between cuts and lowering back down during rapids (movements between cuts). Some machines use a roller or "presser foot" for thin gauge to keep the workpiece. It sort of glides across the sheet.