Saturday, 18 February 2017

Printing woes with my self-printed extruder mount

Of course Slic3r had put config files elsewhere. Merging them together made everything make sense, and I was able to print again!

...with severe under-extrusion (and poor adhesion due to no hair spray). Changing the speed settings back to what they used to be didn't change anything (so once this is sorted out, I should change again to the more modern settings).

Symptoms are those of total stripping. Probably there is enough error in the width of the filament hole to push back and cause stripping. Alternatively there is more resistance in the gears., but that should cause gear skipping if it was too much for the motor.

G0 Z80 is appropriate for taking off the gears.

After opening: No sign of stripping, but the extruder idler was really hard to get off. Switched it out for the one I'd printed.

If there's no skipping and no stripping, we should be getting an even amount of filament out, but the first print was good in the beginning and then pretty crappy afterwards.

Let me calibrate extrusion - yes, way too little filament gets taken in. Something is wrong with either my E_STEPS_PER_MM calculation or the way it's used. It extruded 1.5 mm where it should have extruded 5. Wut??? I just copied over my old calculation. Just to see if it reacts properly to changes, I changed my correction factor by a factor 3. That got it pretty close. Weird.

Printing a test cube with this caused actual, confirmed stripping. Sigh.

Nice print suddenly stopped due to stripping.

I have to admit, the Pronterface UI works a lot better under Linux, the Mac version has weird UI issues.

I don't know what possessed me to think that, with all the screw holes in the extruder mount being too small, the filament hole would be the right size. I drilled it out with a 4mm bit, and now it seems to have the same amount of space as the old one. Just need to get the drilled-out bits out of there. First a couple of cold pulls, then hopefully I won't actually have to remove the whole thing again - though there could be a rim at the bottom that will need drilling from the other side.

After three cold pulls and checking that the hobbed bolt wasn't too full of red filament, I made this (double-height) test cube:

The clogger/stripping is not in evidence, but the amount extruded is not perfect - it is severely and systematically underextruded. Now that could either be because the extrusion multiplier is wrong, or because there's enough pushback to prevent full extrusion. Giving the consistency of the piece, I'm thinking the former. I thought I used to have an extrusion multiplier of 1.1, but it was showing up as 0.9. Increasing to 1.1 to see what happens. And what happens is ... stripping. Ok, time to take this bugger apart again and make it as smooth as possible on the inside.

As I feared, the nut traps holding the other end of the idler screws are not holding the screws fixed, when I mount the idler the screws turn back into the motor, which is probably not good. A nut trap with room for a nylock nut would have worked better. There is almost but not quite room for a nut on the motor side.

The mount is a lot easier to take off and on than the previous one, and the hotend mount part is pretty damn solid and easy to get aligned, if a little problematic if the nuts can't go far enough into the nut traps.

I'm concerned at how easily it strips. I was trying to calibrate the extrusion rate, and it pretty much stripped immediately, possibly due to too little idler pressure. If I can't get that to stop, I'll probably order a professionally printed mount off Thingiverse, to be sure my print quality isn't getting in the way of being able to print.

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