When the pen tip of my Sovol SO-1 pen plotter descends, it tends to strike the paper with a lot of force which creates an artifact in the drawing. This post will discuss several modifications I tried to decrease the force of the pen tip contacting the paper to avoid this problem and what I found worked and what did not work.
I took the Z axis carriage off by removing the four 3mm diameter 5mm long screws from its back with an Allen wrench and then loosened the set screws that hold the end caps onto the 5mm stainless steel rods.
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I removed the two springs and reassembled and tested (not shown), the pen strike artifact was better but still not as good as I was trying to get it to be. Next effort was to try to reduce the weight of the front sliding plate.
The front plate weighs 46 g.
Next, I tried to make a 3d printed version of the Z axis carriage front plate so there would be less weight resulting in less striking force of the pen tip. I busted out the calipers and was able to make a 3d printed replica with fusion 360 and printed it in pla with captured nuts for attaching the pen holder, which weighed in at 20g.
I printed it vertically for optimal bushing shape. I printed various size holes due to the artifact of 3d printing to make holes smaller, ultimately 5.5mm diameter printed would just slide over the rods, but they were still a little bit sticky and wouldn't slide as freely as I needed them to do so I passed a 5.15mm diameter drill bit through the holes and then it would slide up and down nicely.
Here are some comparison of the 3d printed parts with the original:
The disappointing part was although it made the pla printed part made the pen strike artifact less prominent, there was too much play between the rods and the bushings of the pla so the pen tip tended to drift more with changes in direction, so the 3d printed modification was a bust.
I thought about machining out some of the mass of the sliding carriage but if I do that there is no going back if I screw up.
A couple of other ways to decrease the force would be using pistons, counterweights or springs but I had a different idea which ultimately seems to work pretty well.
From Sovol Facebook group user Paul Alvarez, I learned of a program called juicy code which was created by Lazlo Domoszlai and available at https://github.com/domoszlai/juicy-gcode
Juicy-gcode generates G code from SVG files for pen plotters.
Juicy gcode allows for custom start, end, tool on and tool off code to be inserted in the gcode file.
By experimenting, I found that with M280P0S30 the pen tip would be sufficiently high and with M280P0S20 the pen tip would be contacting the paper. I then created a bunch of steps of intermediate degrees between those two extremes for the tool on which basically brakes the pen so it doesn't hit the paper with as much force when it does make contact. The exact angle others might need for start and top might vary but the gist of it is that you put in some steps in between. Also, it can be bigger steps than one degree at a time.
toolon = "M280P0S29;G4 P25;M280P0S28;G4 P25;M280P0S27;G4 P25;M280P0S26;G4 P25;M280P0S25;G4 P25;M280P0S24;G4 P25;M280P0S23;G4 P25;M280P0S22;G4 P25;M280P0S21;G4 P25;M280P0S20;G4 P50"
So to sum up, removing the springs was helpful and using juicy gcode software to stepwise drop the pen tip is also helpful. This software 'trick' bloats the gcode a bit and makes it slightly slower but minimizes the pen strike artifact.
Someone contacted me and requested the stl file for the 3d printed part which I put below:
zaxisslider.stl on my google drive
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very interesting, thanks
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