@dannym, James told us in class that you want to keep the LinuxCNC machine isolated from Vcarve and I understand that entirely. Oops I goofed up above. What I meant to say is “Should we put Lightburn on the VCarve machine?”. And then I immediately withdrew the question.
Well I came in yesterday night to make my first stumbling attempts at getting the big CNC to be a plotter. Here are some notes and thoughts about what happened.
I removed the dust-brush magnetic lucite plate and attached the pencil and its mount to the router. (See IMG_2530 above for what it looks like). It somewhat fit, but I’ve got to redesign it a bit by making the conical section slightly taller. The wrap-around loop that tightens onto the router housing worked well. However I have to redesign how the ER20 collet and nut is held, because I blocked access to the router shaft for tightening the nut. The plastic spring that’s part of the mount also worked well. I could even use the Z-probe to set the Z-home.
Although the pencil is at an angle and the mount is firmly attached to the router itself, that is, the mount does not move or swing as the pencil is dragged, I had no problem manually drawing simple lines and squares using the handheld CNC controller.
I mounted a scrap 2’x4’ panel to the table and put tracing paper on it. I was ready to plot!
Next I tried a “flattened” SVG file from my CAD system (FreeCAD). Over on the VCarve machine I fed in the SVG file and looked around to see what toolpath I could use. I chose “engrave” and generated the GCode. I “sneaker-net” the USB drive to the CNC machine next to it. When it came up on the CNC screen the origin was off the table. Not good. It had been at 0,0 in CAD. What did VCarve do to it? So back and forth I went from VCarve machine to CNC machine until I had finally positioned it ON the table. Not knowing exactly where VCarve thought home was, i had to again position the CNC home over-and-over until it stopped giving me limit errors on the CNC screen. Next, when I ran the GCode I forgot about the spindle speed and quickly stopped it when the spindle started-up. Luckily I hadn’t been able to tighten the collect otherwise it would have torn itself to pieces. On the CNC machine I overrode sprindle percentage to 0%. Please remember that I’m new to all this so it takes me time to reason out what went wrong and to attempt various ways to correct the issue. Bottom line, after resolving home & spindle the pencil would move, lower but then stop and go no further. Ugh. No matter what I changed it would get stuck in the same GCode. I can’t decode GCode yet so I gave up and I tried plan B.
My next attempt was to just use VCarve directly. In other words, don’t use my SVG, but a simple drawing directly with VCarve. I drew a circle, star, curvy line and text. Then back through the pipeline that I was getting to know quite well: select toolpath, calculate toolpath, save to USB drive, unplug USB on VCarve, plug USB into CNC machine, find mount, load GCode, and attempt to run it. In time I got it to start drawing on the paper. It would draw each geometric shape three times on top of itself (which I assumed was caused by the “engrave” toolpath). It did the text, the circle, and started the star and then it would stop. It never drew the curvy line. But it was beginning to work!
In the meanwhile another ASMBLY member stopped by and suggested I use a Drag Knife Toolpath. So onto Google I go to look up VCarve Drag Knife. I watch a short Youtube video about it. I find it’s a VCarve Gadget and locate it on the menus. I try to use it, but I’m confused about how to save the Toolpath. Finally I find save-toolpath. And then went through my pipeline to the CNC. However when I run the GCode it does the initial move and stops on a GCode line. Nada! Repeat. Same thing! Ugh.
It’s late. I close up, clean up, and go home.
Summary/To-Do’s
- Rework Mount
- SVG to GCode is my stumbling block - do I need specific GCode for this application?
- Be able to interpret GCode when things stop
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When I suggested the Drag Knife tool, I didn’t realize that the pencil was fixed; I through it would rotate behind the motion like a drag knife does. Since it doesn’t, that probably won’t help you.
(That the gcode for the drag knife stops is odd and a concern for me, since I’m considering making one for this CNC.)
It needs to caster so the pencil angle is correct. Otherwise it stabs forward and digs in in some directions. But even with a caster, the drag has problems at high reversal angles- e.g. you go one way with the knife dragging correctly, but if the G-code doesn’t have any special toolpath tricks, it could do a straight 180 reversal that makes the tool dig in then anchor itself at some point and twist around that point, digging in hard, before assuming the opposite drag angle again.
Castering does create its own problems. It is possible to have a servo-driven knife on a cutter that drives its angle to a commanded point.
I’m away for a bit. But I hear ya and need to rethink things based upon your comments.
I’m working on the drag knife I mentioned, and I think something similar might work for this. The upper section with the bearings would be the same. The lower part would be in two pieces with springs in between: one with the shaft, the second holding the pen. See my conceptual part here: Puzzle Prototype - #11 by mgmoore
Though at some point, you’re probably just better off spending the $60 on the Rockler CNC pen mechanism you posted earlier. (The cheapest decent drag knife I came across was around $150, so I can justify a bit more effort still.)
I would look at the dog river model vs donek drag knife. The dog river one is more versatile and less expensive by a lot.
The Dog River was the low price model I saw; I just mis-remembered the price a bit. Still $130.
The Donek cost $250 per and you would need to buy one for an 1/8" cut and a 1/4".
I think you’re missing my point.
Cost of Dog River: too much for me right now
Cost of Donek: WAY WAY too much for me right now
Cost of making my own: so far, some scrap lumber and a few hours of my time. Eventually, probably $10 of aluminum.
Gotcha. I look forward to seeing it
After the comments above about the angled pen/pencil needing a caster. I have re-designed it into a simple vertical pen/pencil mount. (Thanks to Michael Cohen for the basic idea.) The pen is a Sharpie Mini and the stubby pencil has a collet to hold it in place. The mount is spring-loaded with about 1/4" travel. The spindle mount is 1/2" diameter which should just fit our ER20 collet. The mount was 3D printed in PLA on a Prusa MK3S. Hopefully in the next day or two I’ll get time on the Big CNC to try it out.
.
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With that design, you won’t want the special dragknife toolpath gadget in Vcarve. It adds extra motions to re-orient the caster, which isn’t an issue here.
You’ll still need to stop the spindle; the dragknife post-processor is one possibility here. But as I just mentioned in another thread, Danny wasn’t sure if it was installed in the current version.
I had been planning to look for it during my CNC time this morning, but I got delayed and had to reschedule that for after you. (Which means you can go earlier if you want.) But I’ll probably be in the woodshop during your time, so maybe I can help with that.
I’ll show you my drag knife prototype when I’m there. It will give you some idea of how the castering option might work. I’m actually thinking of a modular redesign that would let me do both a drag knife and a pen mount.
Well my pen/pencil mount is working and my tool chain (FreeCAD → svg2gcode along with NC Viewer → our shop’s LinuxCNC) is producing good results. I need to get the pen up & pen down working. The default speed of 300 mm/min was too slow so I increased it by 5 times to 1500 mm/min.
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This continues to be a delightful process to follow
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Thanks Stephannie! Continuing with my next episode…
Over last night I fixed my pen up-down problem by fixing my svg2gcode settings (see postscript).
This morning I finally did all my plotting on paper! I experimented with plotting my proposed CNC paths on both tracing paper and mylar with pencil and mini-Sharpie. The reason I’m doing this whole effort is to save me from having to cut multiple versions/corrections in expensive 4’x8’ maple-surfaced plywood.
The plot below used a light blue mini-Sharpie on mylar. However based upon my experiments this morning my preference is to use a thick strong lead pencil and mylar. The tracing paper wrinkled, was too thin and tore a bit whereas the mylar was flat, stiffer and no tearing. The Sharpie line was wider (2 mm) whereas the pencil was thinner (1 mm).
I completed three plots in my scheduled 2 1/2 hr. time slot. They are for a 18" wide 24" deep 90" tall box unit based on the SEKTION High cabinet frame, white, 18x24x90" - IKEA. The plot I’ve shown is the top/bottom box end panel (plotted in 6 min) and the other two are the left & right side panels (15 min each) having nearly 300 holes and spanning the entire length of the CNC table.
Now I’m home to compare them to an existing box unit I already have. Then it’s adjust the CAD, plot and compare until I have a match. Afterwards I’ll cut wood entailing hopefully less wastage and therefore less expense.
P.S. My svg2gcode Settings file contents to enable pen-up/down, feed rate, etc. for the end panel. The right and left side panels have different offsets of -22.88.
{
"conversion": {
"tolerance": 0.002,
"feedrate": 1500.0,
"dpi": 1.0,
"origin": [
-4.19,
-4.19
]
},
"machine": {
"supported_functionality": {
"circular_interpolation": true
},
"tool_on_sequence": "G0 Z0; Tool On Sequence",
"tool_off_sequence": "G0 Z15; Tool Off Sequence",
"begin_sequence": "G28; Program Begin Sequence",
"end_sequence": "; Program End Sequence"
},
"postprocess": {
"origin": [
-4.19,
-4.19
]
}
}
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