Sunday, 21 February 2016


One E3D hotend coming in from RepRapUniverse. I was tempted by the Volcano powerpack from e3d-online, but until I know it an e3d even works for me, that's overkill.

A couple of thoughts on what makes jam

And not the nice kind of jam you spread on bread.

I would really like to know why my extruder jams. Otherwise I'll just go on replacing things and having more trouble - and I've sure had enough trouble already.

I had a stripping back when I used the old bolt. At around the same time, I left the extruder at 220 for 20 minutes without extruding, moved the printer to a less stable surface, added the fan, and eventually changed the bolt.

I've been able to clean it enough to get a half-way decent print, but it slowly extrudes less and less again.

I had to relevel the bed, it has become almost a full millimeter "higher" - or the extruder head lower/longer. I did one successful print after the overheating incident without having to relevel, though, so at least it didn't immediately become longer.

One possibility is that there is now a little gap between the top of the hotend and the extruder. When doing prints with backpressure, this gap gets filled slowly either with stripped-off dust or squeezed-in filament.

Alternatively, there's something further down that causes slow filament buildup. I can atomic out the buildup, but not whatever is causing it.

I would get a newer hotend, but they're all so much shorter that I'd need a different fan shroud, which I can't just print. Obviously I need a printer to make parts for my printer.

I don't get why hotends are being made shorter at the cost of increased complexity. Having 1cm more extrusion height doesn't help much if you can't print because your hotend overheats. A long-necked hotend ought to have an easier time keeping the hot end hot and the cool end cool, but instead it's all cooling ribs and extra fans and fancy materials, just to get a little extra vertical space that 99% of people won't ever need.

Saturday, 20 February 2016

This One Weird Trick will stop jams forever... or will it?

I've been looking at getting the E3D hotend (maybe even the Volcano, since I tend to print larger items rather than fine detail), but from a number of sources, including most importantly +nop head , heard that it's not so good for PLA. Plus I'd be unable to use my fan until such time as I may be able to print another.

On the other hand, I got a few tips, in particular a number of people had luck adding a bit of canola oil to the filament to grease the inside of the hotend slightly. Also, guitar strings are supposedly helpful, as is a bit of string with metal cleaner. I'm skeptical of the last one, as I don't know what it might leave behind.

Nop head suggests a 0.4mm (or probably 0.5mm in my case, as that's my nozzle diameter) drill shank while doing the atomic, I should get one. There's also the toothpick holder method, but I can't print the holder until my printer works:) Then there's "Korneel's Method" of carefully burning it with a kitchen torch and dipping it in alcohol. Not trying that one just yet.

After reassembling, when trying to center X/Y, I got "Printer stopped due to errors. Fix the error and use M999 to restart!.". Thank you for the informative error message. I tried turning it off and on again, as per IT Crowd. Worked. Sigh.

When extruding 5cm, it underextrudes quite a bit, but getting closer to the right amount, up to 3.7cm, then 4.5, then 4.725, then 4.7, then 4.8, then 4.4 (!), then 4.5. At this point I figured the difference might be due to too little tension on the extruder idler, so I tightened that. Results: 4.8, 5.1, 5.0. That's within my margin of error on this crude measurement, so I'm claiming it has gotten its problems out of the system.

An attempt at printing the test piece crashed into the bed, stripping up the kapton. Fortunately, I acquired some blue tape, which is a lot easier to apply. I did some proper levelling and calibration of extrusion (consistently extrudes 6% too little). After adjusting for that, I finally got correct extrusion. That was a lot of wasted filament there. The whole recycling filament idea seems more and more appealing. As part of testing, I extruded at 195C, at that temperature the PLA was drooling.

First test print (done without fan due to a short - I was lucky I didn't blow something) looked OK at the bottom but became increasingly stringy at the top. A sure sign of a jam coming on.

Maybe when I accidentally left it one high heat for a while I melted some of the interior and now it slowly builds up filament until it jams.

My coworker +Tom Riedl pointed out that the new hobbed bolt, being curved in its teeth, would move said teeth at different speeds, thus effectively carving out filament. My guess is that it doesn't carve enough to actually tear it off.

Saturday, 13 February 2016

End of the hot-end

After last weekend's failed print I ordered some blue tape, but in the meanwhile (it's been four days, and it's still not here. FTW, Trijexx?) I happened to poke at the bed, and it turned out the corner that the print head starts in was loose. Now I should recalibrate, just to be sure. And since the backpressure was high enough that no filament got pulled for a while, check for stripping.

But first, clean. Atom. Clean. Atomic. Clean... I'm coming to the conclusion that indeed this hotend is also pretty crappy quality. Here's what it produces when I press filament through:

Very uneven. And the atomics are black and dirty. I admit defeat, and now need to find a quality hot-end for a Wade's Extruder on a Mendel90. It would appear my current hotend is a J-Head Mk II. RepRapSource has Mk V's available, but I'm not sure the shorter length is a good thing given the fan shroud. On the other hand, they look pre-glued, which is good, as gluing was a pain. Not sure if e3d or hexagon are compatible with my (2013) Wade's while being not much shorter than 71.5mm. More research is needed.

Thursday, 11 February 2016

Pop! Goes the Hotend

Coming back after a week of "how on Earth am I going to get the nozzle properly cleared", I was surprised when I homed Z and the right side got stuck when I tried to move down to take out the bolt. Not sure what had happened, but the right side had gone higher than the left and was wedged, unable to move by motor power. Turned the motors off and manually screwing it down again helped, and after re-levelling it seems to work. But now I'll have to keep an eye on whether the right-hand threaded rod mount has gotten loose/worn.

With that repaired (for now), I got out the hobbed bolt and cleaned the stripped PLA off it. (Mistyped that as "striped PLA", doesn't look like anybody has tried that:) Also used a trimmed-down Q-tip and then an appropriately-sized hex screw to attempt to clear any flakes and bits out of the holes. Then I heated the loose hotend up to 230C, lifting one end to prevent backflow, and did a "hanging atomic". Without the extruder gears in the way, this one did indeed make that satisfying "plop" and showed dirt on the end:

The second one was nicer, didn't show any signs of dirt:

After that, I used the metal wire to try to push stuck dirt out, again at 230C and did one more atomic. There's a little bit of metal visible in there, so more cleaning is needed:

At the next one, I could see something black coming out with the filament I pressed through.

I rather like the sheer photographic look of these. They're very odd.

I noticed the jump up in temperature just before getting down to 90C, so that's apparently a thing the firmware does, not a result of me jiggling the wires.

Probably sticking the wire in from the tip was counter-productive, coming from the top and eventually pulling it out through the tip would prevent dirt from being pushed back into the tube.

After this showed nothing, I put everything together again and did a test cube - now on shiny new Kapton tape. Which didn't stick at all. I should have checked beforehand, Kapton is apparently not that useful for PLA.

It occurs to me that if, as Tim Hatch commented, the hobbed bolt was really poor quality, then maybe the hotend is as well. In which case, attempts at cleaning it are probably rather futile.

Monday, 1 February 2016

New bolt, new problems.

With my new pretty hobbed bolt mounted, I attempted a little extrusion. Unfortunately, all that happened was that the gear end started unscrewing itself! Nylock isn't enough to hold it, do I need to have the bolt with the fastening screw in the gear end? But then the hobbing doesn't go far enough in.

Found the docs, and indeed I was right the first time around. I just didn't have the nyloc far enough in, but then there is not a lot of spare room. I've adjusted it by taking the idler off and aiming for the teeth to align with the hole for the filament, but I'm concerned that the nyloc just won't have enough grip that far out. I'll try it this way, but if it starts unwinding itself, I will instead place a regular nut at the appropriate space, glued on with epoxy.

Curiously: I homed all axes while heating was ongoing, and there were no temperature readings in the meanwhile. Such single-threaded. Very modal. Much block. Wow.

And I was right. Just a little bit of extrusion and the bolt holds still while the gear merrily unwinds. The old bolt was born with the end nut, so there was no way it could come off. To the epoxy!

Epoxy takes about 24 hours to harden. Heating it reduces the hardening time and strengthens the result, according to the packaging, so I left it on the heated bed at 40 for the afternoon and evening.

In the morning, I tried to fit it, but due to some epoxy seeping out, the nut didn't go as far in as it should. See how the hobbing is off from the filament hole below it.

Filing down the epoxy (carefully disposing of the dust) got me back to a good, solid bolt with an appropriate spacing:

The test extrusions are very different from with the previous bolt. Where before it would build up a string that would then fall over, now it folds down like when laying down a rope. Oddly satisfying.

I did a 10cm extrusion with a mark, and it fell 7.6 mm short. I guess I should re-adjust my e_steps_per_mm multiplier. While checking for whether this should go on top of my previous multiplier, I ran across Triffid Hunter's calibration guide, which actually gives a formula - and it's different from what I had. My Wade's is a 9/47 according to the receipt, while the formula in the Marlin code uses 11/39 - that's quite a difference, no wonder I had a big multiplier. I expect the hob diameter is the same, roughly. (39/11) / (47/9) = 0.6789.

Note to self: The correct Marlin firmware is the one in hardware/Marlin, not one of the 2+ other Marlin instances I have floating around.

The 100mm extrusion test was off by 17mm, probably attributable to variances in effective hob diameter. New version:

#define E_STEPS_PER_MM ((3200 * 47.0)/(9.0 * 6.75 * 3.142) * (100 / (100-17)))

Now who can tell me why this doesn't change the extrusion length at all? Anyone? Yes, you in the back? Correct! The adjustment factor is calculated as integers, and so get automatically rounded off to 1.

Writing it as

#define E_STEPS_PER_MM ((3200 * 47.0)/(9.0 * 6.75 * 3.142) * (100.0 / (100.0-17.0)))

should have more of an effect. And it does, but it's still 5mm off. Two test cubes show increasing lack of extrusion, and another extrusion test misses the mark by 34mm! If the epoxied nut is slowly coming off, I'm going to be annoyed. There's no sound of skipping or anything.

Triffid Hunter's guide suggests tightening the extruder idlers as much as possible. I won't quite go to the "my fingers hurt from tightening" stage, but close. Even with that, the amount of extrusion is way off. The shape of the test extrusion has also changed, from the "coiled rope" back to the "toppling wire". Either the gear is coming off or the nozzle is getting clogged again. The gear looks good, and the way this is slowing increasing speaks more to clogging. Time to go atomic? Let's give it a shot.

Now there's a strange thing. In preparation for the Atomic, I untightened the extruder idler screws. Just then, at 10C above the goal of 90, the hotend temperature increased by about 5C before falling some more. Coincidence? Maybe. There's some logic that prevents overshooting the temperature, but I haven't seen it do this before.

The atomic didn't work, only a short piece came out. I'm mystified.

I'm concluding that the nozzle is getting clogged again. I'm concerned that it's just happening, without any obvious reason.

Also, after unscrewing the hotend, it doesn't come out easily. Once out, I ran wire through it at high and low temperatures, but I don't feel confident that that's enough. Taking off the extruder idle to check on the alignment (which is still good) I see evidence of severe stripping:

Now is it stripping because it got clogged and had too much back-pressure, or did it get clogged because it was stripping and dust came down into the critical area? Or did some of the previous dust start the clogging, which then turned into stripping and thus more clogging?