Tag: Laser Cutter

OMTech 60 W Laser: Speed vs. Corner Radius Wobbulation

Experimenting with little squares showed the Y axis has a definite wobble:

Subpixel Zoo – Quattron RGBY Shifted – detail

Which suggested a simple test:

Cornering – overview

I adjusted the laser power to compensate for the speed, with the result being a line burned into white cardboard. The lines are a bit under 0.2 mm wide, roughly the width of the focused spot.

The controller settings for the X and Y axes:

KT332N – X Y Axis Parameters – 2025-02-18

The acceleration values may be affected by the limits in this section:

KT332N – Cut Engraving Parameters – 2025-02-18

Assuming the Y axis acceleration is 3000 mm/s², the RepRap calculator shows the Y axis speeds within the 30 mm distance along the vertical sides:

RepRap Accel Calculator – 3000mm-s2 30mm

Extracting the useful bits and lining them up for comparison:

Cornering – detail

The first column in the test results shows perfectly square corners have no problem at any speed, because the controller decelerates to nearly a stop before changing direction.

Rounding the corner to 0.5 mm introduces a distinct wobble in the Y axis that doesn’t change much, probably because the controller still decelerates as it approaches the corner.

The 1 mm radius corners show a distinct overshoot at all speeds. The peak overshoot doesn’t change much between 250 and 500 mm/s, because the RepRap calculator shows the machine barely reaches 250 mm/s by the middle of the side, so 500 mm/s isn’t any faster.

The first overshoot is about 0.2 mm, the first undershoot is a little over 0.1 mm, and the rest are barely visible.

The 2 and 4 mm radius corners have barely visible wobbles. Whether that is due to the head not flexing as much due to the lower acceleration around the larger radius I cannot say.

The machine may not follow the simple RepRap acceleration profile when approaching a corner, let alone a rounded corner.

I think attempting to reduce the overshoot by fiddling with the belt tension / hardware fasteners / whatever will be unavailing. The laser head runs on a linear rail along the gantry with plenty of unbalanced mass hanging off the bottom:

OMTech 60W beam alignment – head X plane

Moving the beam 0.2 mm on the platform by pivoting around the rail 6 inch = 150 mm above amounts to only 0.08°, far less than anything I can measure while adjusting the mechanics.

Slowing down doesn’t help nearly as much as I expected and rounding the corners makes it worse.

Word has it that much spendier machines behave better, which is both comforting and unhelpful.

2025-02-21
Laser-Engraved CD Stress Cracking

Given the cracking caused by vector patterns on CDs and DVDs, seeing stress cracks open up on large-area engravings came as no surprise:

Laser engraved CD cracking – D

They start smaller in the more closely engraved areas:

Laser engraved CD cracking – A

But eventually spread over the entire surface:

Laser engraved CD cracking – C

They’re not always straight:

Laser engraved CD cracking – B

And aren’t aligned with the engraving path:

Laser engraved CD cracking – B detail

My threat model says those discs are definitely unreadable …

2025-02-07
Thunar WEBP Thumbnails
For whatever reason, the Thunar file browser in XFCE does not automagically show thumbnails for webp images. Some searching produced a recipe, although the displayed webp.xml file needs the last two lines to close the tags:
```
<?xml version="1.0" encoding="UTF-8"?>
<mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
    <mime-type type="image/webp">
        <comment>WebP file</comment>
        <icon name="image"/>
        <glob-deleteall/>
        <glob pattern="*.webp"/>
    </mime-type>
</mime-info>
```
The magic copy-to-clipboard button includes those tags, so I suppose it’s another case of being careful what you believe on the Intertubes.

Going through the steps displayed images of the Subpixel Zoo:

Thunar – webp previews

They’ll turn into layered paper patterns:

Subpixel Zoo – Quattron RGBY Shifted – detail
2025-02-05
HQ Sixteen: Thread Cone Locating Disk

After installing (if that’s not too fancy a term) the horizontal thread spool adapter on the HQ Sixteen, I laser-cut an acrylic disk to keep thread cones centered on the other vertical spool pin:

HQ Sixteen – thread cone base locator – installed

It’s trivial: an 11 mm circle to clear the washer and a 55 mm circle to locate the cone.

However, I cut that disk with a 56 mm OD, because that’s what I measured on half a dozen cones. Come to find out at least some cone bases are juuust slightly oval and they latched onto that disk like they were gonna be best buddies forever.

Rather than cut another acrylic disk, I laser-cut a friction ring from a scrap of stamp-pad rubber and jammed the disk against the chuck with a live center:

HQ Sixteen – thread cone base locator – turning

A few minutes of sissy cuts made the disk nicely round and concentric with the inner hole, with a little file work knocking the edges off the rim.

Done!

2025-02-04

Monitor Mount: USB Hub Clamp

Along with the Beelink PC, putting the Anker USB hub on the monitor mount pole helped tidy the cables just a little bit:

Monitor pole clamp - Anker USB hub — Monitor pole clamp – Anker USB hub

It’s still jumbled, but at least the cables aren’t wagging the hub.

This clamp needs only one M6 screw into a square nut:

Monitor Pole box clamp - solid model — Monitor Pole box clamp – solid model

Again better seen in cross-section:

Monitor Pole clamp - PrusaSlicer preview — Monitor Pole clamp – PrusaSlicer preview

The OpenSCAD code extrudes the shape from a 2D arrangement, then punches the screw through the side:

// Monitor Pole box clamp
// Ed Nisley - KE4ZNU
// 2025-01-23

include <BOSL2/std.scad>

/* [Hidden] */

ID = 0;
OD = 1;
LENGTH = 2;

Protrusion = 0.1;

Box = [22.5,45.5,25.0];         // Z is clamp height
BoxGrip = 5.0;                  // on outer side clearing connectors

PoleOD = 30.5;

WallThick = 5.0;

Kerf = 3.0;                     // clamping space
Clearance = 2*0.2;              // space around objects

Washer = [6.0,12.0,1.5];        // M6 washer
Nut = [6.0,10.0,5.0];           // M6 square nut

MidSpace = 35.0;                // pole to box spacing

ClampOAL = Box.x + MidSpace + PoleOD + 2*WallThick;

//----------
// Build it

        difference() {
            linear_extrude(height=Box.z,convexity=5)
                difference() {
                    hull() {
                        right(MidSpace/2 + Box.x/2)
                            rect(Box + 2*[WallThick,WallThick],rounding=WallThick);
                        left(MidSpace/2 + PoleOD/2)
                            circle(d=PoleOD + 2*WallThick);
                    }
                    right(MidSpace/2 + Box.x/2)
                        square(Box + [Clearance,Clearance],center=true);
                    right(MidSpace/2 + Box.x)
                        square([Box.x,Box.y - 2*BoxGrip],center=true);
                    left(MidSpace/2 + PoleOD/2)
                        circle(d=PoleOD + Clearance);
                    square([2*ClampOAL,Kerf],center=true);
                }
            up(Box.z/2) {
                xrot(90)
                    cylinder(d=Washer[ID] + Clearance,h=2*Box.y,center=true,$fn=6);
                fwd(Box.y/2 - Washer[LENGTH])
                    xrot(90) zrot(180/12)
                        cylinder(d=Washer[OD] + Clearance,h=Box.y,center=false,$fn=12);
                back(Box.y/2 + Nut[LENGTH]/2)
                    xrot(90)
                        cube([Nut[OD],Nut[OD],2*Nut[LENGTH]],center=true);
            }
        }

The alert reader will have noticed I didn’t peel the protective film off the hub, which tells you how fresh this whole lashup is.

2025-01-31

Monitor Mount: Beelink Clamp

Clearing the clutter off the top of the laser put the monitors up on mounts clamped to its wings, which required an adapter between the monitor and the mount’s standard VESA bracket:

The Beelink PC has an adapter plate intended to put it on that VESA bracket, too, but a quick test showed the power button pointed downward in an inaccessible spot. I eventually realized the Beelink would fit neatly on the monitor mount’s pole:

Monitor pole Beelink clamp - front — Monitor pole Beelink clamp – front

The view from the other side:

Monitor pole Beelink clamp - rear — Monitor pole Beelink clamp – rear

The clamps have recesses for an M6 square nut and an M4 brass insert:

Monitor Pole BeeLink clamp - solid model — Monitor Pole BeeLink clamp – solid model

Which is better seen in a cross-section:

Monitor Pole Beelink clamp - PrusaSlicer preview — Monitor Pole Beelink clamp – PrusaSlicer preview

The M6 screw uses the same hex wrench as the rest of the monitor mount and the M4 screw fits the VESA bracket. Sometimes, you just gotta go with the flow.

Pondering those pictures will show why the nut and insert must be on opposite sides. I came that close to building one to throw away.

The OpenSCAD source code extrudes the overall shape upward, then punches the screw holes & fittings horizontally:

// Monitor Pole Beelink clamp
// Ed Nisley - KE4ZNU
// 2025-01-23

include <BOSL2/std.scad>

/* [Hidden] */

ID = 0;
OD = 1;
LENGTH = 2;

Protrusion = 0.1;

PoleOD = 30.3;

WallThick = 5.0;

Kerf = 3.0;                     // clamping space
Clearance = 2*0.2;              // space around objects

Screw = [6.0,10.0,6.0];         // M6 SHCS, LENGTH = head
Washer = [6.0,12.0,1.5];        // M6 washer
Nut = [6.0,10.0,5.0];           // M6 square nut

Insert = [4.0,5.8,10.0];        // M4 insert

ScrewSpace = Washer[OD];        // pole edge to screw center spacing

Block = [4*ScrewSpace + PoleOD + 2*WallThick,PoleOD + 2*WallThick,2*Washer[OD]];       // Z = clamp thickness

//----------
// Build it

        difference() {
            linear_extrude(height=Block.z,convexity=5)
                difference() {
                    rect([Block.x,Block.y],rounding=WallThick);
                    circle(d=PoleOD + Clearance);
                    square([2*Block.x,Kerf],center=true);
                }
            up(Block.z/2) {
                right(PoleOD/2 + ScrewSpace){
                    xrot(90)
                        cylinder(d=Washer[ID] + Clearance,h=2*Block.y,center=true,$fn=6);
                    fwd(Block.y/2 - Washer[LENGTH])
                        xrot(90) zrot(180/12)
                            cylinder(d=Washer[OD] + Clearance,h=Block.y,center=false,$fn=12);
                    back(Block.y/2)
                        xrot(90)
                            cube([Nut[OD],Nut[OD],2*Nut[LENGTH]],center=true);
                }
                left(PoleOD/2 + ScrewSpace) {
                    xrot(-90)
                        cylinder(d=Insert[ID] + Clearance,h=2*Block.y,center=true,$fn=6);
                    fwd(Block.y/2 - 1.25*Insert[LENGTH])
                        xrot(90)
                            cylinder(d=Insert[OD] + Clearance,h=Block.y,center=false,$fn=6);
                }
            }
        }

It’s done in PETG-CF, which looks surprisingly good in a chonky sort of way. I’ll find out how well it withstands moderate clamping forces.

2025-01-30

Hotel California: Vole Edition

Although we had considerable success trapping voles during the last half of the 2024 gardening season, Mary found a description of what might be a better technique: a box with small entrance holes taking advantage of rodent thigmotaxis: their tendency to follow walls. The writeup shows nicely made wood boxes, but I no longer have machinery capable of cutting arbitrarily large wood slabs into pieces.

I do, however, have a vast pile of cardboard boxes:

Vole Box – large

That’s a rat-size trap.

A smaller box has room for two mouse-size traps (one hidden on the left):

Vole Box – small

The general idea: plunk the box in a garden plot, arm the trap(s), close the lid, and eventually a vole will venture inside, whereupon wall-following leads to disaster. Apparently bait is optional, as wall-following inevitably takes them over the trap pedal. I won’t begrudge them a walnut or two, should bait become necessary.

Cardboard is obviously the wrong material for a box in an outdoor garden, but I figure they’ll survive long enough to show feasibility and I can deploy a lot of small boxes before having to conjure something more durable.

Yes, those are laser-cut rounded-rectangle holes: 30 mm and 40 mm, assuming voles care about such things.

Edit: More on voles.

2025-01-28