joris.m
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Improving filament loading

Fri Nov 10, 2017 4:20 pm

Has anyone tried modifying the extruder holders so the filament gets loaded more easily? I sometimes have a problem that because of the bent filament I am feeding it (from the spool) and the very low tolerance of the hole above the extruder that the filament can't be pushed inside the plastic of the housing that goes to the tube. It has nothing to do with idler tension as changing that to no matter what doesn't change a thing. I think the problem is that because of the bend in the filament as soon as it passes the 2 "wheels" to go in the hole it goes slightly off-center thereby hitting the hole on the side and not sliding in. I would think making the hole a bit bigger and tapered might help a lot with this, especially for filaments that aren't very flexible.

Any suggestions?

joris.m
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Re: Improving filament loading

Sun Nov 12, 2017 12:03 am

Found another issue with this system. Well, actually 2.

First, if you load filament and it stays in your machine for a while, the filament gets bent because of the tubing it goes through. If you unload the filament the part that comes out of the tube is no longer straight as it was before loading, it is bent to the side. Trying to load that filament again resulted in my case (and yes I always cut off a small part to make the top pointy) that the filament was pushed outside to the side of the extruder, through the hole in the idler (because it missed the small hole at the top, hit the plastic next to it and the extruder just kept pushing the filament in). The only solution I see here is throw away the part of the filament that was loaded through the tubing. Can be quite wasteful if you switch filaments regularly.

Next problem was solving this situation. So you need to open the idler as to clean up the mess. But as soon as you untighten those 2 screws completely, the square nuts that hold them in place fall out, because they are at the bottom. The only way of placing them back is either by a lot of fiddling and using three hands, or by removing the extruder from the top of the frame so you can turn it around and drop the nuts back in. Not very serviceable either I would say ...

There needs to be a more precise way of loading the filament imo. You should be able to get into the small hole before the motor starts pushing it further through, or make sure the motor doesn't miss the hole. And in any case you should be able to retry a filament load without having to heat the nozzle and do an unload first.

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PJR
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Re: Improving filament loading

Sun Nov 12, 2017 10:15 am

Having been using the MMU for 12 months now, I can honestly say that I have not encountered any of your issues on either of my printers.

It makes things kind of difficult to suggest a solution to a problem which for me does not exist.

Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.

rafal.d
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Re: Improving filament loading

Sun Nov 12, 2017 8:11 pm

I hit myself with quite a severe facepalm just now when I realized the source of all my Extruder problems was that the bowden tube connectors on the multiplexer where not tightly screwed in :shock:

At this point I cannot say if they became lose or if I just skipped that step during the build but they were completely lose, as in unscrew-with-one-finger-lose. On every filament change it would clack-clack-clack and I was constantly fiddling around with the spring screws when the reason for all this was on the other end of the tube. Now I've tightened them with the 8 wrench and no more clacking, how awesome.

I think most problems originate from mistakes made during build, I mean 7 sections with 20-30 steps, each containing 3-5 instructions - there's a lot of room for error :D But this printer is so widely spread and most people are reporting what Peter said, it runs like a charm when it's properly set up.

So now I hope I can print the Chimera at last. Btw, this is how the Chimera looks with lose bowden connectors:
IMG_20171112_191203.jpg
IMG_20171112_191203.jpg (277.42 KiB) Viewed 244 times

tgunr
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Re: Improving filament loading

Sun Nov 19, 2017 1:08 pm

Two things I discovered:
1. The idler wheel with bearings has TWO bearings not one. i didnt realize this for a while as I had broken two idler housings trying to get the gear in and didn't notice how many 'extra' bearings there were. I was planning on printing two new housings when I discovered the the problem. Without both bearings the idler was a bit cockeyed when feeding in the filament. The instructions should probably have that in bold print.

2. I placed some small bits of foam into the square nut holes to prevent them from falling out.

After playing with this thing for a while I have some observations on filament loading. As I used to do embedded firmware at Apple I would make some adjustments in the code.

[*] Use phase one until you can see the filament appear in the tubing. The length you see should be less than the length of a fitting. You will see why below.

[*] Since there is no way for the firmware to know how far or long phase 1 lasted the phase 2 is set to fast feed slightly more than the length of the tubing thus jamming the filament into the multiplexer. IMHO, the phase two setting should be adjustable. Permit use of the knob to feed filament until it just enters the fitting on the multiplexor. I do this by hitting the reset button after phase one, then use the settings to manually feed the filament.

[*] Likewise for unloading, there should be two phases also, one for if filament is in the hotted and needs heating before extracting and one for when your just wanting to unload up to the fitting on the multiplexor. Again, the knob could be used for this function.

[*] The lead in line on a print should be in the firmware. Print a line across the X and ask if extrusion is happening. If not, rinse and repeat until extrusion takes place. If the firmware knows the filament is somewhere in the fitting on the multiplexor it can fast feed the distance between the bottom of the fitting and the hot end, then begin slow feed into hot end until extrusion is seen. Once extrusion is known to happen the current code should be good to go as there is now a baseline.

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PJR
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Re: Improving filament loading

Sun Nov 19, 2017 7:48 pm

tgunr wrote:
Sun Nov 19, 2017 1:08 pm
[*] The lead in line on a print should be in the firmware.
NO, NO, NO, NO definitely not. We already don't have enough control and you want to take more control away? Should we be forced to use Slic3r?

The loading method works and it would be difficult to improve (except for a double purge line at the start (which I use within KISS).

The purging is sufficient to make up any loading differences - there really is not a problem here; there's not much point improving something that just works.

Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.

joris.m
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Re: Improving filament loading

Mon Nov 20, 2017 11:15 am

When swapping filament myself I now heat up the nozzle and manually extrude until I see it coming out before launching the print. That way I am sure the purge line does what it's supposed to do and I don't have to wait half a first layer before actually seeing filament comeout.

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PJR
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Re: Improving filament loading

Mon Nov 20, 2017 12:52 pm

joris.m wrote:
Mon Nov 20, 2017 11:15 am
When swapping filament myself I now heat up the nozzle and manually extrude until I see it coming out before launching the print. That way I am sure the purge line does what it's supposed to do and I don't have to wait half a first layer before actually seeing filament comeout.
Joris - if you have to do that then there must be an issue with your start G-code and/or profile.

Can you slice a simple model, zip up the G-code file and attach it to a post. I will have a look to see what is happening.

Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.

tgunr
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Re: Improving filament loading

Tue Nov 21, 2017 1:54 am

If I attempt to use the firmware menu load filament command the print always fails because the filament has not reached the nozzle. If I fiddle and adjust it manually so that it is extruding,, then I can print. Looking at the gcode from Slic3r I don't see anything special.

The gcode just does what it did before MM, start the heaters, wait for temps, home, lays down a line, then starts printing. If I hit reset, and start print again, rinse and repeat then eventually I get a line to lay down.

Here is the head of the gcode I just used:

Code: Select all

; generated by Slic3r 1.37.1-prusa3d on 2017-11-20 at 14:55:16 ; ; external perimeters extrusion width = 0.45mm ; perimeters extrusion width = 0.45mm ; infill extrusion width = 0.45mm ; solid infill extrusion width = 0.45mm ; top infill extrusion width = 0.45mm ; first layer extrusion width = 0.42mm M107 M190 S60 ; set bed temperature and wait for it to be reached M115 U3.0.12-RC1 ; tell printer latest fw version ; Start G-Code sequence START T99 M109 S190 G21 ; set units to millimeters G90 ; use absolute coordinates M83 ; use relative distances for extrusion G28 W G80 G92 E0.0 M203 E100 M92 E140 G1 Z0.250 F7200.000 G1 X50.0 E80.0 F1000.0 G1 X160.0 E20.0 F1000.0 G1 Z0.200 F7200.000 G1 X220.0 E13 F1000.0 G1 X240.0 E0 F1000.0 G1 E-4 F1000.0 G92 E0.0 ; Filament gcode ; Filament gcode ; Filament gcode ; Filament gcode G21 ; set units to millimeters G90 ; use absolute coordinates M83 ; use relative distances for extrusion ;BEFORE_LAYER_CHANGE ;0.2 G1 Z0.200 F7200.000 ;AFTER_LAYER_CHANGE ;0.2 G1 E-6.00000 F3000.00000 G1 Z1.200 F7200.000 G1 X109.592 Y79.240 F7200.000 G1 Z0.200 F7200.000 G1 E6.00000 F3000.00000 M204 S1000 G1 F2100 G1 X110.357 Y79.034 E0.02435 G1 X139.074 Y79.023 E0.88239

joris.m
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Re: Improving filament loading

Tue Nov 21, 2017 3:33 pm

Same here. I just load and manually extrude until I see filament. Then I start my print.

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