Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
I managed to slobber some fresh hot melt glue on my finger…
Glue burn – after cooling
It was whoop-dee-do brown carpentry glue from a gun that claims 350 °F output, so what looks like toasted flesh is actually the last remnants of the glue. The advice seems to converge around do not peel the glue (because you’ll rip the damaged skin and leave yourself with an infection) and keep the burn cool.
After a few hours cuddling with an ice pack I figured I was probably going to live through this. The next morning the glue flaked off, leaving a mighty blister behind.
Glue burn – blister
Looks like something Piter de Vries might have enjoyed inflicting, had Frank Herbert only known about hot melt glue guns: “… there’s a sort of beauty in the pattern of pus-white blisters on naked skin, eh, Baron?”
One should don all manner of Personal Protective Equipment before using a glue gun, but I bet you don’t, either.
The aluminum build platform plates remain both flat and level, but the outline and test extrusions are consistently thin by 0.05 to 0.10 mm in the right rear corner and thick by about the same amount in the right front. That means the rear corner is too high and the front corner is too low, but the whole left side is flat to within my ability to measure it.
The effect is significant, because I’m laying down the first layer at 10 mm/s with a layer thickness of 0.33 mm; the first layer looks exactly like all the other layers in the object. With the middle of the plate at 0.33 mm below the nozzle, the fill can be cramped at 0.23 mm and sparse at 0.43 mm. The long-term Z-min switch repeatability seems to be no better than 0.05 mm, so when the midline goes below 0.30 mm, the higher rear corner really crowds the plastic.
Given that the left side is level front-to-back, the only way a flat plate can appear non-flat is if the X and Y axis rods aren’t quite parallel: the stage rolls or yaws as it moves.
That could indicate a bent rod, but the last time I rolled those rods on a surface plate, they’re perfectly straight. Maybe something horrible has happened, but any stress capable of bending one of those rods will wreck the printer in passing.
Alas, a static platform adjustment can’t fix a dynamic motion, but tweaking the rods to be (more) parallel could reduce the problem. I tried visualizing the possible causes and cures, then decided to stop thinking so much, just change something, then measure the results.
Why my head exploded:
The thickness varies from front-to-back, so the Y axis rods are non-parallel, which should affect both the left and right sides. But the left side is perfectly level and the right side is not.
The thickness varies from left-to-right, so the X axis rods are non-parallel, which should affect both the front and back sides. But they vary oppositely: the front tilts down to the right and the back tilts up to the right. The midline from left to right, however, is level to within my ability to measure it.
I had shimmed the rear X axis rod quite some time ago, so I decided to try a simple adjustment: move the shim from top to bottom. The picture shows the 0.4 mm shim in its original location at the top of the rod; the edge is barely visible. For lack of anything smarter, I moved the shim to the bottom of the rod to push the end upward.
Shazam! The results of a test extrusion in units of 0.01 mm:
39
35
40
35
40
33
36
[Update: Typo in the rear-left was 49, should be 39. Drat!]
Which says it’s give-or-take 0.05 mm around the middle, with the rear-left corner now a tad low; bear in mind that 0.05 mm is about the limit of my measurement ability. It’s off to a good start, anyway, and we’ll see how it fares over the next few weeks.
Methinks if you’re serious about this 3D printing thing, you need a printer with real axis alignment adjustments and enough stability to make them meaningful. Nophead uses custom code that tweaks the G-Code’s Z-axis coordinates on the fly based on an initial three-point probe, which is a wonderful solution that’s not in the cards for RepG. EMC2 could incorporate that in the kinematics module, but at the moment it does just XY leadscrew mapping. It’s simpler, albeit more expensive on a per-machine basis, to get the mechanical alignment right the first time.
The thermoplastic (who knew?) pads melted right off my long-reach clamps while calibrating those thermocouples, leaving the thermoset (who knew?) clamps behind. I tried a few of the obvious candidates for the job with no success, but (while fiddling around with something else) I came upon an unopened tube of Permatex Ultra Copper copper-loaded silicone gasket glop.
The cured silicone rubber is very flexy, which is sort of what you want in a pad, even if I’m not convinced they’ll stay in place. They seem securely mounted in the recesses of the pad tips; I worked the glop in with a screwdriver tip.
Using the pressure washer to blast the crud off the propane grill has become an early summer ritual around here. I’d reconfigured the extension pipes to reach up the side of the house, so I started by swapping the connectors around to put a shorter pipe at the handpiece. Surprise: those connectors were firmly affixed and a rubber strap wrench on the pipe lacked enough grip.
Rather than wreck that nice chrome plating with a pipe wrench, I clamped two pieces of scrap plywood in the drill press and poked a half-inch hole right down the midline. Add a dab of rosin to improve traction, crunch everything in the bench vise, and spin the connector off.
Well, that’s the way it went for the first connector, with the PTFE joint tape I remember adding last time around.
The connector on the other end was more recalcitrant, perhaps because it still had the manufacturer’s joint compound in place. It eventually yielded to the gentle persuasion of a propane torch, applying just enough heat to wreck the compound’s grip.
The good thing about a plywood clamp is that I don’t form a deep emotional attachment to it: make one when it’s needed to fit the pipe at hand, don’t worry about a precision fit, regard it as a consumable, and move on.
Having managed to mislay my dingy yellow kickstand plate, I made two more and this time hit ’em with fluorescent red paint. Ought to be unforgettable for another few years…
In theory, you’re supposed to apply a white undercoat. I hosed ’em down with many drippy, runny coats of red and it’s all good. This ain’t art and they get thrown on the ground, so what’s the point of being fancy?
The backside of the Lenovo N5901 Mini Wireless Keyboard (which arrived with the aforementioned Q150) has a black-on-black power switch with ON and OFF legends (yes, I think they’re backwards, too) embossed in the matte black case: under anything less intense than enhanced interrogation lighting, you (well, I) can’t determine the switch position.
Of course, the myriad certifications / ratings / labels required for compliance with all the regulations are perfectly legible:
Lenovo Mini Keyboard – enhanced labels
Working a dab of white correction fluid into the letters makes them blindingly obvious; the smudges around the letters will wear off in short order.
I should probably add a bit of white to the switch background as well.
The Smell of Molten Projects in the Morning 