Not printing correctly for the first 10 seconds

I've been having problems with the beginning of prints for the last few days. For awhile it just didn't extrude anything at first. Sometimes for a few seconds and sometimes for a full minute. Sometimes setting it to "load filament" forced it to shove some out and printing immediately afterwards was successful. Sometimes now.

Right not it's behaving differently. It does start extruding right from the start, but the first bit that comes out doesn't stick to the plate. It all bunches up on the side of the nozzle. Once there's a nice little blob, it comes off and everything is fine after that. Of course, this ruins the print because that little blob messes up what comes after it.

Any ideas? Could it be a nozzle problem?

First, a minute is far too long to get plastic flowing. Are you seeing filament being fed steadily from the reel during that time, or is the extruder running but not feeding? If it is not feeding, first make sure that the print is not starting before your hotend is up to temperature (you should have a "wait for temperature" command near the end of your custom start code e.g. M116). If that's not the issue it is likely that the extruder is slipping. First check that your filament is not under or over-sized. If the filament is the correct size, a common reason for slipping is that the hobbed part in the extruder that grips the filament has become clogged with plastic dust and so not gripping well. You will need to clean the hobbed feeder (which may require partial disassembly of the extruder, depending on its design).

If the filament is feeding but not extruding for as long as a minute it means that the last print must have retracted the filament a long way after it finished (watch for this behaviour after your next print). This could be due to an erroneous command in your End G code, such as an extrusion command that is relative when your printer is set for absolute extrusion lengths. Maybe try putting the command "G92 E0" at the start of your end custom code, which will fix that issue if it exists but have no detrimental effects if not.

It is normal behaviour for a FFF printer to miss the first few cm of a new print (that is exactly the reason a skirt is printed), though nothing like as much as you are seeing.

Slic3r has a couple of settings to help. Look under "Print settings">"Skirt and brim". Here you can set the number of loops to print the skirt and also the minimum extrusion length. Set the number of loops to 2 or more, and the minimum length to something fairly high - maybe 30mm. This ensures that no matter how small the part, the skirt will always print enough loops to feed at least 30mm of filament, which should be enough to get a flow going. It is also normal for the first few mm of extrusion to fail to adhere to the bed. Make the skirt distance setting far enough away from the part so that the ball or loose thread of plastic that can result will not interfere with the print. Sometimes the nozzle will pick up a short thread or ball and drag it around for a long time, and it can eventually stick to the part somewhere and mess up the print. I try to knock off the dragging plastic if I see that happen, or just hope it comes off somewhere where it will not matter. Cleaning the outside of the nozzle will make it less likely - DO NOT use any abrasive to clean - an abrasive will make it worse! I wipe it well with a paper towel soaked in acetone.

Dave

Edited 1 time(s). Last edit at 02/07/2015 09:02AM by dmould.

For the problem of not extruding, I'm not sure what's going on. According to the heat reading on the front, it is reaching the target temp. Usually when the extruder is slipping there is a clicking noise, but I wasn't hearing that. I've actually detached the feeding tube and put my fingers on the filament, only to find that it wasn't moving at all.

Last time I had a filament jam I cleared out the gripper gears, just to make sure there wasn't a buildup of stripped off filament impeding the grip. I'm not sure if that helped or not.

As I said, it isn't doing that now. It seems to be extruding right from the start, it's just all getting stuck on the side of the nozzle instead of laying down on the masking tape.

There is one other detail I didn't mention. My start gcode has a bit that makes the printer extrude a line across the front of the platform. That's working fine. It lays down the line of filament, moves across the platform, then starts forming the blob on the side of the nozzle. If the blob isn't too bad and I let it go, then this doesn't happen again for the rest of the print, not even if there's a large gap on that first layer. I'm not sure why that first pause causes a problem.

I'll try printing with the skirt. That's a good suggestion. Thanks.

If the filament is not laying down on the masking tape, that may mean that the nozzle is too high above the bed at that point. Is the bed level enough?

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

If your start G code extrudes a line, it is possible that the long wait until extrusion (that now appears to be cured) was caused by that extrusion. My thinking is that if the printer and Slic3r is set for absolute extrusion moves, then Slic3r will not know that you have extruded filament prior to the print, so unless you added a G92 E0 command to re-zero the extruder, nothing would extrude until the total amount extruded at the start of the print was equal to what you extruded in your start code (the filament would in fact retract on the first print move).

Dave

dc42, I've done everything I can to level the bed and rechecked it. That's usually what has gone wrong, but I think I've got it this time.

Dave, there is a G92 E0 after that line is extruded.

Here are the last few lines of my start code before the actual printing. Resetting the progress is one of the last steps.

G92 E0; set E to 0
G90; use absolute coordinates
M320; acceleration enabled for all commands that follow
G1 Z0.2 F6000.000; move to first layer height
G1 X100 Y-73 F14000.000; move to front right corner of bed
G1 X-90 Y-73 E24 F2000.000; extrude a line of filament across the front edge of the bed
G4 P2000; wait for ooze to slow
G1 Z0 F6000.000; lower nozzle height to 0
G1 X-95; wipe nozzle
G1 Z0.2 F6000.000; set nozzle to first layer height
G1 F12000; ensure fast travel to first print move
G92 E0; set E to 0 again
M73 P0; reset build progress to 0
G90 ; use absolute coordinates

The first print with a skirt was a success. Next step will be trying to clean the nozzle.

Thanks for the help. Making progress.

The problem has gotten much worse. For awhile I could get the filament moving by putting a little pressure on it from above. Now even that doesn't work.

I tried taking off my nozzel and cleaning out the teflon tube. That didn't help. I also tried raising the temperature on the first layer, thinking that since it's fine once it gets started, it just needed a little more. That didn't help either.

So now when I try to print, I hear the motor slipping, and the filament doesn't move.

Any ideas?

If nobody has an idea on what is wrong, can anyone tell me how to make slic3r print with the left nozzle instead of the right? I've tried a few things, but they didn't work.

Thanks.

Sounds like a partially blocked nozzle. Try the cleaning process (retract filament when it is cool enough to be not quite solid). To use the other nozzle I would have thought you would simply specify the other tool in your start code - i.e. T1 or T2 and print as for a single nozzle.

Dave

I don't have any acetone, so I swapped the left and right nozzles. Now it works like new. Clearly that was the probably. I'll try to get some acetone and clean the dirty one, hopefully that will be enough.

Thanks for all your help, everyone.

Quote
JasonMBryant
I don't have any acetone, so I swapped the left and right nozzles. Now it works like new. Clearly that was the probably. I'll try to get some acetone and clean the dirty one, hopefully that will be enough.

Thanks for all your help, everyone.

Coincidentally I had a nozzle blockage just yesterday.

There are various methods of cleaning a nozzle, such as heating the nozzle and feeding filament into it as much as possible, then switching off the heater and retracting as the nozzle cools to the point when the filament is just barely molten. This will hopefully pull out a plug of plastic from the nozzle with whatever caused the blockage stuck to it. Leaving it to soak in acetone for a day or two, then removing the PTFE liner and rinsing or soaking again might do the trick.

A new nozzle is not all that expensive and it may be easier to simply replace it.

Dave

Edited 1 time(s). Last edit at 02/23/2015 08:24AM by dmould.

Well, I spoke too soon.

The nozzle was definitely part of the problem, but not all of the problem. The first couple of prints seemed fine, then I started seeing air printing again.

Most times that I print, I have to unload the filament, cut off the end, then reload. If I don't, usually nothing comes out or it doesn't come out for a long time. Then when I unload it the end of the filament is messed up.

I think something is causing the filament to significantly over-retract at the end of every print job.

Edited 1 time(s). Last edit at 02/24/2015 01:58AM by JasonMBryant.

Well, I've found out that getting the printer to use the second extruder is not as simple as using a T2 command.

That is all the progress I've made.

Quote
JasonMBryant
Well, I've found out that getting the printer to use the second extruder is not as simple as using a T2 command.

That is all the progress I've made.

You will probably be better off asking in the forum for your printer model. It does not appear to be a Slic3r issue.

Dave

You're right, I'm pretty sure it isn't. However, the temporary fix seems to be getting slic3r to print using the other extruder. So if anyone knows how to do that, I'd appreciate it.

I tried again to print with the second extruder, but it had several problems.

I set up my g-code for dual extruders. I used the example gcode from this page:

[groups.google.com]

Then I went under Print Settings/Multiple Extruders and set everything to '2'.

After I exported the gcode, converted it to .s3g, and took it to my printer, I started it. Unlike my past attempts, it shows both nozzles heating up. That's an improvement. That's still not quite right, since I only need the left extruder to heat up, but that's understandable, since I set it up for dual extruders.

The problem is that only the right extruder is heating to the 240 that I set for my first layer. The left extruder is only set to heat to 200. Why isn't it heating up to the right temp?

I changed the temp on the printer to override that. I'm printing in ABS, so I figured it would have problems if I left it at 200.

When it got hot enough to print there were more problems. The first thing it did was try to ram the extruders against the left side of the machine. After a moment of horrifying stuttering, it moved back to the bed and tried to print. Nothing came out. Given the position of the nozzles, I think it was still trying to print using the right extruder and not the left.

I think that important line in my custom start gcode is this one "T0; set primary extruder". Is that supposed to set it to the "2" that I put on the Print Settings/Multiple Extruders tab?

When you have multiple extruders, each extruder has two temperature settings, one for printing and one "standby" temperature. The non-printing nozzle is set to the "standby" temperature, which is hot enough so that it will not take too long to heat to print temperature, but cool enough to stop plastic dribbling out over the print while printing with the active nozzle or cooking in the nozzle (keeping plastic fully molten for too long can cause chemical changes that alter its properties).

Dave

I don't think that's what's happening.

The left extruder was 40 degrees less than than the left extruder. That's a big difference.

Plus, that's the extruder that was supposed to be doing all of the work. I set everything to the second extruder in the Print Settings tab. So if anything, the right extruder should have been the one at a lower temp.

Finally, there's the problem that it didn't print correctly. It started off by trying to ram the extruders into the wall, then it printed in a pattern that looked like it was trying to use the right extruder, not the left. Either way, nothing came out.

So I definitely don't have it set up properly to use the second extruder.

Status update: it's printing again.

I'm not sure why cleaning out the nozzle worked better this time than last time, but it seems to be working. Of course, I'm only 5 minutes into a 16 and a half hour print, so I'm still quite nervous.

Next up, I'll see if it goes back to jamming a little after every print. If that behavior continues, then I'll look for help in the right place instead of on the slic3r board. This board *has* been very valuable because it helped me sort through the various leads and weed out the wrong answers.

I'd still like to figure out why I couldn't get the right extruder to work, but that's a problem for another day.

Quote
JasonMBryant
Status update: it's printing again.

I'm not sure why cleaning out the nozzle worked better this time than last time, but it seems to be working. Of course, I'm only 5 minutes into a 16 and a half hour print, so I'm still quite nervous.

Pleased to hear you got it working. Nozzle-cleaning seems to be a pretty random affair - you can clean 10 times without success, and then the blockage clears on the 11th attempt (a bit like inkjet printers!). As said, I keep spares and just change the nozzle if it blocks (they are not very expensive), which (touch wood) has only happened twice over the past year. I suspect both cases were due to keeping the hotend hot for a long time (>15 minutes) without printing, or maybe suffering a brief overheat. I think the plastic cooks when in the nozzle for that length of time and/or overheated and changes its property, probably generating solid bits that cause a blockage.

Dave