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.
If it used to work, it can work again
Because the focus pen worked on the bench, I was certain this had to be true:
There is a break somewhere along the blue wire carrying 24 V to the focus pen. The signal and 0 V wires are fine.
I updated the original post, because I’m going to use that picture a lot whenever the subject of laser machine wiring comes up.
This happened while focusing the laser before cutting the cardboard fixture for the chuck rotary:
The autofocus “pen” = switch did not operate when the rising platform pushed the cardboard against its tip, so the controller continued raising the platform. Seconds later, the platform rammed the cardboard against the laser head and I slapped the Big Red Button.
Those indentations match the focus pen and the nozzle:
Yeah, the platform shoved that pen straight up through its clamp until both punched through the cardboard.
The pen has a red LED (barely visible through the opening around the cable when you’re looking down into it) that did not light up when I manually triggered the switch: either the switch was dead or it wasn’t getting 24 V power.
Having spent considerable time diagnosing similar problems on the LightBurn forum, I was pretty sure the PVC-insulated wire connecting the pen to the controller had failed somewhere in the drag chain.
Update Yup, the 24 V wire was broken:
Another discussion there showed how to dismantle the pen, so I (turned off the power and) cut the cable a few inches from the top of the pen body.
The pen body has three parts screwed together with generous application of threadlock. After demonstrating I lack enough grip strength to break the bonds, I deployed a pair of lathe chucks designed for a death grip on cylindrical objects:
The tip came off readily enough:
The upper joint was more reluctant, to the extent I needed witness marks to show progress:
Dripping Kroil into the slightly loosened joint while twisting it back and forth eventually separated the parts:
I persuaded the last chunks of threadlock out with a stout pin (in a pin vise), eventually letting me screw the pen body together without a struggle.
Contrary to what I originally thought, the switch is a proximity sensor triggered by the reshaped head of an M3 socket-head screw also holding the brass-colored tip. Wiring it to a bench power supply verified proper operation, with the open-collector (actually, open-drain) output going low with any ferrous metal closer than about 3 mm to the sensor tip.
Which put the fault somewhere along the wiring from the controller through both drag chains to the pen, as expected.
Unlinking the X axis drag chain involved a pair of small screwdrivers prying the side plates off their pivots in the next link:
The slightly enlarged opening let me pull enough of the cable through to verify I needed more elbow room, so I dismounted the entire drag chain:
The Y axis drag chain was short enough to pull the cable out without drama.
I guesstimated the overall length from laser head to controller, cut a six conductor 26 AWG silicone ribbon cable generously longer than half of that, peeled it down the middle, then put a JST SM connector where the sections meet at the end of the gantry:
Obviously, those connector halves went on before snaking the other end of the cable sections through their drag chains. I paid considerable attention to keeping the ribbons flat and untwisted throughout their lengths, in hope they’d flex easily as the chain bends.
AFAICT there was no good way to use the old wire to pull the new wire through the chain, so running flexy silicone ribbon cable through a drag chain required tweezers, patience, and persistence. I had to realign the existing wires & tubes at various points so they didn’t twine around each other and block the path.
Another JST SM connector at the laser head allows removing / installing the pen as needed:
The connector pins and sensor wire colors:
GND = blue = common = marked cable conductorOUT = black = sensor output24V = brown = powerWiring the new cable to the controller’s 24 V / GND / LmtU- terminals showed it now worked perfectly.
Reducing the vertical offset between the tip of the pen and the tip of the nozzle was then straightforward …
As fate would have it, the Step2 rolling garden seat took an untimely fall while standing in the garage and broke both its hinges:
It’s been out in the garden for maybe six years, so those chunks of plastic are fully depreciated.
Two hours after loading the solid model into PrusaSlicer:
The SiLite tray is well-weathered, but remains structurally sound: still ready for service in the D-Hall breakfast line on the morning after the Apocalypse.
Living in the future works out pretty well.
Obviously, I haven’t popped the top on this PC for a while:
Some fuzz made it past the grille:
PSA: In the unlikely event you still use a desktop PC, it’s time to pop the top on yours, too.
I have unfairly maligned the TPU snout, because the PETG snout failed the same way:
Seen with the shock cord in place, it’s obvious that combining moderately high temperature with steady compression sufficed to bend the PETG enough to pop those tabs loose from the vent.
So the OpenSCAD model now produces a stiffening ring to be laser-cut from acrylic:
The whole snout builds as a single unit in the obvious orientation:
Because the part of the snout with the tabs is 7 mm tall, I glued a 4 mm acrylic ring to a 3 mm ring, with both of them glued to the snout:
That’s “natural” PETG, which I expected to be somewhat more transparent, but it’s definitely not a dealbreaker.
Mary will sew up another cheesecloth filter and we’ll see what happens to this setup.
As the saying goes, “Experience is what you get when you don’t get what you want.”
Fortunately, living in the future makes it easy to iterate on the design & implementation until experience produces what should have been obvious at the start.
It turned out those window screen splines lasted a dozen years until this happened:
Some rummaging in the Big Box o’ String produced the spool of 1000 pound test Kevlar cord most recently applied to the seat back on Mary’s bike, so this happened:
Having re-confirmed that frayed Kevlar cannot be melted into a blob, another UV-stabilized cable tie at each end will control those tufts.
Those cords should last forever …
The cart in Mary’s Vassar Farm plot returned in need of repair:
Those fractures near the end of the axle let the axle erode the side wall:
This will obviously require some sort of reinforcement on the body holding the axle, but the first challenge involved getting the wheels off the axle:
Some brute force revealed the hub covers snapped over an install-only locking fastener:
More brute force cut those fasteners (a.k.a. star-lock washers) to get the wheels off the axles.
While contemplating the situation, a box of 606 bearings (as used in the PolyDryer auto-rewind spindles) failed to scamper out of the way and produced a victim fitting perfectly on the 8 mm axle:
I regard such happenstance as a message from the Universe showing I’m on the right track. The alert reader will note the axle should not rotate, but does sport scars showing it’s done some turning in the recent past, so the bearing may not be a completely Bad Idea™.
Finding a Lexan snippet exactly as thick as the bearing suggested bolting a plate across the side of the body to support the bearing, like this:
Some layout work in LightBurn produced a template to mark the body for hand-drilling the holes:
In retrospect, that was a mistake. I should have:
Instead, three of the holes in that nice Lexan sheet ended up slightly egg-shaped to adjust for mis-drilled holes in the body.
Lexan does not laser-cut well at all, so that sheet was drilled to suit after using the template to mark the holes:
Then it got bandsawed / belt-sanded into shape.
I squeezed 5 mm rivnuts into whatever fiber-reinforced plastic they used for the body, which worked better than I expected. They’re intended for sheet metal, so I set the tool for 5 mm compression and they seem secure. I hope using plenty of screws across a large plate will diffuse the stress on each screw.
Then I threaded the axles and used acorn nuts:
In this situation, I regard JB KwikWeld epoxy as “removable with some effort”, as opposed to the destruction required with those star-lock washers. High-strength Locktite might also be suitable, but I do not anticipate ever having to remove these again for any reason and do not want the nuts to fall off in the garden.
The re-replaced seat conjured from a cafeteria tray continues to work fine, as do its 3D printed hinges.
It’ll reside in the shed until Spring rolls around …
The Smell of Molten Projects in the Morning 