The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Improvements

Making the world a better place, one piece at a time

OMTech 60 W Laser: Hatch Latch Phasing

The OMTech laser cutter has six access hatches, each with one or two latches. These are not locks, although you do need a triangular “key” to turn the latch plug:

OMTech laser – latch – cylinder point up

Being that type of guy, I want all the latches to have the same plug orientation when they’re closed, so that I can hold the key one way, poke it into any latch without thinking too hard, and have it fit onto the plug:

OMTech laser – latch key – latched position

A quarter-turn clockwise (remember clocks with hands?) then releases the latch:

OMTech laser – latch key – unlatched position

Inside the hatch, the closed position corresponds to a tongue capturing a flange around the cabinet opening (not shown):

OMTech laser – latch – latched position

After the quarter-turn, the tongue releases the flange:

OMTech laser – latch – unlatched position

So, we’re not talking high security here.

As delivered, the plugs had more-or-less random orientations when they were closed and some required a counterclockwise quarter-turn to release.

It turns out the latches aren’t a complete unit that simply drops into a hole in the hatch:

OMTech laser – latch parts

I sympathize with whoever must assemble ten handfuls of parts into ten latches on a production line and I also understand why orienting the plug wasn’t on that person’s to-do / QC checklist. I further understand why two cylinders lacked the big toothed washer under the nut; it’s not essential to the function and nobody will ever miss it.

The plug has a triangle on one end (for the key) and a square on the other (for the tongue), with one triangle point aligned to a side of the square:

OMTech laser – latch plug

To my way of thinking, that point must be upward, as shown in the first picture, when the latch is secured.

The cylinder can fit into the square(-ish) hatch hole in four possible ways, but its symmetry allows only two unique orientations. It must look like this in order to put that point upward when the plug is maximally counterclockwise (my finger is pointing upward):

OMTech laser – latch cylinder

So I devoted a pleasant half-hour to reducing the latch entropy.

The screw attaching the tongue to the plug also controls the friction of that spring against the plug as you (well, I) turn it. All the screws now sport a dab of Loctite to ensure the tension remains mostly constant (at least for a while), as do the two large nuts lacking corresponding toothed washers.

The “key” has no marking to indicate its “point-up” orientation, so I stuck a snippet of label on one side, with a jaunty red highlight marking the point. Something better will surely occur to me, but it’s no longer in the critical path.

2022-03-22
OMTech 60 W Laser: Ventilation

The best place for the OMTech laser cutter seems to be snuggled at base of the chimney, venting into the long-disused fireplace through the steel plate adapting a long-gone wood stove to the opening:

Duct fan installed

The short run of flexible tubing allows some give-and-take at the cutter’s vent outlet. The elbow on the duct fan’s output terminates in a blast gate to cut off the draft blowing up (or down!) the flue with the fan off.

The cutter arrived with a huge high-speed axial blower screwed to its output baffle:

OMTech 60W laser – OEM vent fan

The noise from that fan had to be heard to be believed.

The cylindrical exhaust duct attached directly to the motor with four screws, only two of which matched holes in the baffle plate:

OMTech 60W laser – modified vent

A trial fit revealed the assembly rattled something awful: those two screws let the duct vibrate against the baffle. Match-drilling two more holes into the baffle let me mount the duct with three screws and, in combination with the foam gasket, it is now solid and quiet.

A quick check shows the duct fan draws 10 to 11 m/s through the baffle at full throttle, roughly 400 CFM. That’s pretty close to the flow measured through a long pipe and, with only 6 ft³ of stink inside the laser’s cabinet, ought to exhaust the fumes just fine.

2022-03-21
Huion Tablet USB Cable Realignment

The Huion tablet on my desk has its USB cable sticking straight out of the left side, whereupon it must loop around to burrow under the shelf under my monitor on its way to the port on the back of the PC case. The loop snagged on all the clutter atop the desk and I finally got around to Fixing That Problem:

Huion tablet – rerouted USB cable

Of course, it wasn’t quite that simple.

Right angle USB Mini-B connectors are still a thing:

Huion tablet – USB angle adapters

Which is a “left angle” adapter and which is a “right angle” adapter depends on which supplier you ask and how much you trust their descriptions / product photos, so you should get a set containing both: it’s the only way to be sure.

The one on the right (a “right angle”) shows a bit of carving, which came after the completely unsurprising discovery that the stylin’ curves on the side of the tablet collided with the rectangular adapter:

Huion tablet – misfit adapter

Some diligent X-Acto knife work carved away enough of both the adapter and the tablet case to snugly join them:

Huion tablet – plastic surgery

The hackery over on the far right fits around the USB cable’s molded connector. I simply cut away any parts that touched until the adapter seated firmly in the USB socket and the cable exited parallel to the edge.

Part of this involved not carving deeply enough into the adapter or cable connector to expose the internal wiring. I assumed the tablet didn’t have anything vital immediately inside that fancy curve, so that’s where I dug deepest.

Stick adapter + cable to the tablet with good-quality electrical tape and now the cable points directly to where it should go.

Declare victory and move on!

2022-03-10
Expedient Caster Wrench

Cranked down as far as it would go, a new adjustable height workbench in Mary’s sewing room turned out to be just slightly higher than the other work surfaces adjoining it, so I replaced its 3 inch casters with 2 inch versions:

Sewing bench – 2 vs 3 inch casters

The bench arrived as a kit and included the 17 mm flat wrench required to snug the hex head on the 3/8-16 threaded stem atop the 3 inch caster against the bottom of the bench foot. The 2 inch caster also has a threaded stem, but of course it has a 14 mm hex head.

I traced around a 14 mm open-end wrench on a scrap of aluminum and introduced the outline to Tiny Bandsaw:

Improvised 14 mm caster wrench – rough cut

A little belt sander action cleaned up the outside, some hand filing matched the wrench to the hex, and it came out OK, even before I scrubbed the dirt off its white-ish pebble-finish coating:

Improvised 14 mm caster wrench – finished

The bare steel wrench arrived with the bench and has 13 and 17 mm openings. I briefly considered embiggening the 13 mm end, but came to my senses.

Aluminum isn’t a particularly good metal for wrench duty, but this one had to apply maybe 1/3 of a turn to each of four stems, stopping when snug, and it performed just fine. It’s now sleeping in the wrench drawer, dreaming of another job that may never arrive.

The smaller casters lowered the bench by about an inch, whereupon cranking the surface up a bit less than half an inch aligned it perfectly.

2022-03-07
Work Glove Security Tags

Having worn my work glove collection to exhaustion, the fanciest two pairs in a new selection came with elaborate security tags:

Elaborate Security Tag dissection

Finding a standard tag inside inside the fancy shell shouldn’t come as any surprise, but I’m surprised the retail loss ratio for a pair of $20 gloves can support that much hardware.

I went through the self-checkout area and didn’t do anything special, so either those lanes don’t have tag scanners or the tags are security theater.

2022-03-03
Gidget II Sewing Table: Temporary Juki Insert

Mary’s new sewing table just arrived, but the laser-cut acrylic insert fitting around her Juki sewing machine is still a month or two away. Until then, a simple cardboard replacement must suffice to fill the gap:

Juki temporary table insert

The rectangle just to the left of the needle is a hatch for bobbin changes. Sheer faith and an interference fit between layers of Kapton tape holds it in place with surprising force.

I wanted to tape the cardboard edges to the machine and the table to smooth out the transitions, but her Supreme Slider slippery sheet may solve the problem without adhesives:

Juki temporary table insert – Super Slider

The “insert” is a 1/4 inch thick double-layer corrugated cardboard sheet, utility-knifed from a huge box. She layers cardboard under the wood chips in her Vassar Farms garden paths to discourage the weeds; this seemed like a perfectly reasonable diversion.

2022-03-02
CNC-3018XL X-Axis Recalibration
Plotting the backlash / calibration target on both the CNC-3018XL and the MPCNC quickly showed, contrary to what I expected, the MPCNC was dead-on accurate, albeit with some wobbulation and a trace of backlash:

MPCNC – Backlash test – detail

Although it looks ug-u-lee, the (lower speed) drag knife cuts come out nice and, because the entry and exit moves match the main cut, the minimal backlash wasn’t a problem.

Turns out only the X axis on the 3018XL had a problem:

Cal Target – 400 step-mm – merged

Apparently the longer leadscrew I installed as part of the “XL” conversion has a small thread pitch error: about 1 mm short in every 250 mm of travel. I don’t have any (definite, non-handwavy) method to measure the pitch directly, other than by running the follower nut and measuring the results, but it’s consistently short.

Quite some time ago (after blowing up the OEM controller board), I set up the Protoneer CNC board in 1:8 microstep mode, making the GRBL $100 setting a nice, round 400 step/mm for a two-start leadscrew with 2 mm pitch and 4 mm lead:
```
400 step/mm = (200 step/rev * 8 µstep/step) / 4 mm 
```
After a few more measurements suggesting the leadscrew actually traveled 249.2 mm, the correct value will be:
```
401.28 step/mm = 400 step/mm × 250 mm / 249.2 mm
```
To verify I understood the problem and solution, I set $100 to a few integer values around the goal:

Cal Target – stacked – 399-402 step-mm

The top image shows the leftmost line at the 10 mm mark on the scale, because it’s easier for me to match the ink line with an engraved line, rather than the non-line at the end of the ruler.

The other images show the results for $100 set to 399, 400, 401, and 402 step/mm, respectively. The results last two results bracket the desired 250 mm outcome, with 401 step/mm being Close Enough™. GRBL accepts a floating point step/mm value, so I set $100 to 401.28, but I was unable to convince myself the result came out consistently different than 401.00.

Plotting both the tick marks (green) and the knife path (red) on the 3018XL, then cutting the bare paper on the MPCNC, showed the two machines now agree on where the knife should fall. The outer end of the tick marks extends 1 mm beyond the cut line to ensure small misalignments do not produce an obvious white gap around the edge of the deck.

The Y axis continues to match:

Tek CC – 2022-02-14 – Y detail

And now the X axis looks just as good:

Tek CC – 2022-02-14 – X detail

The drag knife corners are rounded, as you’d expect. The cut seems slightly offset from a small origin touch-off error, but the scales now match.
2022-03-01