Tag: Laser Cutter

The last time around, I used Cart Coins to verify platform alignment (a.k.a. “leveling”) on the Makergear M2. The Prusa MK4 does mesh probing to ensure accurate alignment, so these new Cart Coins exercised the MMU3 and gave me some giveaways for a recent dinner:

The design, such as it is, mashes a PNG found on the InterWebs with a few go-fast stripes added in LightBurn to balance the layout inside a circle:

The motivations for LightBurn:

• It’s convenient
• TroCraft Eco is within 0.1 mm of the proper thickness
• Laser-cut coins proceed with great speed

Normally you’d export the finished layout as an SVG, but OpenSCAD ignores “holes” within shapes, so I exported it as a PNG to serve as a binary height map:

• Import the PNG into OpenSCAD using surface()
• Resize it to 20 mm wide and 1.7 mm tall
• Knock it out of a 24 mm OD × 1.6 mm tall cylinder (which is why the extra 0.1 mm)
• Add the PNG again as a separate 1.6 mm object to refill the hole

Whereupon out pops a solid model:

Export that as a 3mf file to keep the two objects aligned, import it into PrusaSlicer, then get multi-material on it:

There’s a fourth group with different colors in hiding. I printed 12 identical coins at a time, mostly so I could keep track of what was happening, and it ended well enough.

The black coins with the translucent retina-burn orange cart look surprisingly good.

But this is way faster:

They’re the size of a US quarter, because that’s what unlocks shopping carts around here. Feel free to tweak the parameters for your locale.

The OpenSCAD source code is almost a one-liner:

difference() {
    cylinder(d=24.0,h=1.6);

    resize([20.0,0,1.7],auto=true)
        linear_extrude(height=1,convexity=10)
           projection(cut=true)
            surface("/mnt/bulkdata/Project Files/Prusa Mk4/Models/Cart Coin/Cart Coin layout.png",
                    center=true,invert=true);
}

    color("Black")
        resize([20.0,0,1.6],auto=true)
            linear_extrude(height=1,convexity=10)
               projection(cut=true)
                surface("/mnt/bulkdata/Project Files/Prusa Mk4/Models/Cart Coin/Cart Coin layout.png",
                        center=true,invert=true);

Use them responsibly, OK?

Having been viciously nerd-sniped by The Great Dragorn of Kismet, I’m in the process of building a Prusa MK4 3D printer with an MMU3. This has been a generally pleasant experience, although I am beginning to loathe Genuine Haribo Goldbären.

Anyhow, the Y axis motor position puts the belt too close to one side of the pulley, with no further adjustment possible:

The stepper motor stator laminations are the striped gray area on the far left, the 3D printed motor mount is the striped black area on the right, and the belt pulley is snugged up against the motor as far as it can go on the shaft.

Pushing the motor a little more to the left requires a shim:

Rather than fiddle with scanning the motor mount, I imported its STL model from the Prusa MK4 files:

Importing the STL into OpenSCAD and converting the motor face into an SVG file is basically a one-liner:

projection(cut=true)
translate([0,0,-5.0])
import("/mnt/bulkdata/Project Files/Prusa Mk4/Calibration/y_motor_holder_R3.stl");

Import the SVG into LightBurn, round the corners a little, set it up for 1.5 mm Trocraft Eco, Fire. The. Laser. and it fits perfectly and stands out nicely:

Having the right tools for a job makes it easy …