Laser-cut Cutworm Collars

Mary, having had considerable trouble with cutworms in her gardens, routinely deploys cardboard collars around new plants:

Cutworm Collars - assembled
Cutworm Collars – assembled

It seems cutworms trundle around until they find an edible plant, chew through the stem and topple the plant, then trundle off without taking another bite. A small cardboard barrier prevents them from sensing the plant: apparently, motivation to climb a short wall hasn’t yet evolved.

Up to this point, Mary applied scissors to tissue boxes, but I proposed an alternative with an adjustable fit to any plant:

Laser Cutting Cutworm Collars
Laser Cutting Cutworm Collars

A splayed cardboard box rarely lays flat, a condition enforced by a few MDF stops used as clamps.

Come to find out no two tissue boxes have identical dimensions, even boxes from the same brand / retailer, so lay out duplicates of the collar template to match your stockpile.

That was fun!

The SVG image as a GitHub Gist:

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OMTech 60 W Laser: Adjustable Honeycomb Stops

When you (well, I) get fussy about angular alignment on the laser cutter’s honeycomb platform, an adjustable stop or two may come in handy:

Laser Honeycomb - Adjustable Pins
Laser Honeycomb – Adjustable Pins

That’s a serving suggestion based on a true story, because I really wasn’t all that fussy about precise engraving alignment on those signs.

A more typical situation on a smaller scale:

Laser Honeycomb - Adjustable Pins - engraving
Laser Honeycomb – Adjustable Pins – engraving

The scrap of MDF with three holes provides angular alignment for the little two-color acrylic test coupon, so you can tuck successive squares into the corner, hammer them with slightly different patterns, then compare the results.

The stops are an off-center hole (the ±3 text gives the offset) in an MDF disk with an acetal post:

Laser Honeycomb - Adjustable Pins - detail
Laser Honeycomb – Adjustable Pins – detail

The 3 mm SHCS provides a convenient way to turn the post and disk, so the threading isn’t critical. Sufficiently snug threading will let you turn the screw counterclockwise without loosening it, but that surely depends on how tightly the 8 mm section fits into the honeycomb. The larger top section is 9mm, cleaned up from the rod’s nominal 3/8 inch OD, for a jam fit into the 8.8 mm + 0.1 mm kerf hole.

The SVG images as a GitHub Gist:

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The ±5 mm offset disk may be more useful with larger items and now you know where those three holes came from.

Tour Easy: Terracycle Chain Idler Bushing

It turns out that under rare conditions, triggered by fumbling a front derailleur shift, the upper chain section (out of the picture on the top) can whip vertically enough to jam between the Terracycle Idler’s mounting bolt and its longer chain retaining pin:

Tour Easy - Terracycle idler
Tour Easy – Terracycle idler

Whereupon the chain falls off the chainring, jams firmly between the spider and the crank, and brings the proceedings to a halt.

Having finally figured out the cause, I made a simple bushing to fit around the mounting bolt, reduce the gap, and (I hope) eliminate the problem:

Tour Easy - Terracycle idler bushing
Tour Easy – Terracycle idler bushing

Given its rarity, I will need a few more years to verify the solution.

Might get around to cleaning the chain one of these days, too …

OMTech 60 W Laser: Dual-path Air Assist

A tweak to the air assist plumbing of my OMTech 60 W laser produces much the same result as Russ Sadler’s Super Ultimate Air Assist, with somewhat less plumbing and cheaper Amazon parts:

OMTech Laser - air assist - plumbing
OMTech Laser – air assist – plumbing

The overall doodle shows the electrical wiring and pneumatic plumbing:

Dual-path air assist diagram
Dual-path air assist diagram

The electronics bay now has two solid state relays:

OMTech Laser - air assist SSRs
OMTech Laser – air assist SSRs

The front SSR turns on the air pump when the controller activates the STATUS or AUX AIR outputs; the diode between the (-) terminals acts as wired-OR.

The rear SSR turns on the solenoid valve whenever the AUX AIR output is active. The diode turns on the other SSR to start the pump.

When the laser cutter is idle, both the STATUS and AUX AIR outputs are inactive, so the pump doesn’t run and the solenoid is closed.

The controller has a front-panel AUX AIR button that turns on its eponymous output, which turns on both the solenoid and the pump. I have turned it on to verify the circuitry works, but don’t do any manual cutting. I never was very good with an Etch-a-Sketch and the laser’s UI is much worse.

LightBurn includes an Air Assist setting for each cut layer, which should be OFF for engraving layers and ON for cutting layers. Basically, you go through the Material Library and tweak all the values , then It Just Works™ when you assign that material setting to a particular layer.

The solenoid valve must be a “direct acting solenoid valve“, as the air pump produces about 3 psi and cannot activate a “self piloted” solenoid valve. When the valve is open, the pump can push about 12 l/min through the plumbing to the nozzle:

OMTech Laser - air assist - 12 lpm flow
OMTech Laser – air assist – 12 lpm flow

That’s noticeably lower than the 14 l/min without all the valves and additional plumbing.

The flow control valve is a manually adjusted needle valve to restrict the engraving air flow to maybe 2 l/min, just enough to keep the smoke / fumes out of the nozzle and away from the lens, when the solenoid valve is closed.

I set the controller to delay for 1 s after activating the air pump to let it get up to speed. There’s an audible (even to my deflicted ears) rattle from the flowmeter when the air assist solenoid opens.

The paltry 12 l/min seems to promote clean cuts and 2 l/min doesn’t push much smoke into the surface around the engraved area.

So far, so good.

OMTech 60 W Laser: Improved COB LED Shades

Adding (fake) rivets to the COB LED shade brackets definitely improves their appearance:

Acrylic COB LED Shade - installed
Acrylic COB LED Shade – installed

I cut new shades from vintage clear acrylic sheet, with more aluminized mylar attached to the lower surface: you can barely see the COB LED strip through the reflecting surface.

Depending on how you arrange all the hardware hanging on the nozzle, the shades can collide with something at the home position in the far right corner:

Acrylic COB LED Shade - X clearance
Acrylic COB LED Shade – X clearance

Definitely a step up from cardboard …

OMTech 60 W Laser: Improved MDF Spikes and Stops

A bit of tinkering suggested I needed a way to repeatably position stock sheets on the honeycomb, so I conjured stops that would be slightly taller than the magnetic spikes:

Improved MDF Honeycomb Spikes - first pass
Improved MDF Honeycomb Spikes – first pass

Three of those form a corner into which you can tuck victims of the same general size:

Improved MDF Honeycomb Spikes - stock alignment
Improved MDF Honeycomb Spikes – stock alignment

Those pointy MDF spikes should start with slightly rounded tops, because that’s what they’ll look like after a few uses:

Improved MDF Honeycomb Spikes - alignment stops
Improved MDF Honeycomb Spikes – alignment stops

I also made a low-profile stop for victims lying directly on the honeycomb for engraving:

Please Close The Gate - engraved
Please Close The Gate – engraved

The SVG images include a nested version to tile across random MDF leftovers.

The SVG images as a GitHub Gist:

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OMTech 60 W Laser: Magnetic Honeycomb Spikes

When a cardboard base plate under metal spikes would pose a fire hazard, you can position magnetic spikes where they’re needed:

Magnetic Honeycomb Spikes - acrylic
Magnetic Honeycomb Spikes – acrylic

The 12 mm neodymium magnet is slightly larger than a single honeycomb cell, so it wants to center itself atop a cell. The stainless steel button head screw sits in the magnet’s countersunk hole and protrudes just enough to make sure the spike doesn’t slide sideways unless you want it to:

Magnetic Honeycomb Spikes - parts detail
Magnetic Honeycomb Spikes – parts detail

A cloud of combustible gas doesn’t pose a threat under there:

Magnetic Honeycomb Spikes - MDF
Magnetic Honeycomb Spikes – MDF

The thin red beam comes from the targeting laser on the back of the nozzle.

Storage is easy: just smush a handful of the things against the side of the laser cabinet:

Magnetic Honeycomb Spikes - storage
Magnetic Honeycomb Spikes – storage

Buy all the parts in lots of 100 to have supplies for other adventures!