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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Sure! I put them on Thingiverse: CNC pencil / mini-sharpie holder for plotter by bwatt - Thingiverse. If you want CAD files I can send them to you.
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