Extruder flow not consistent

Hello all, new Robo owner here. I've been able to make a few things so far, (with much searching on the forums for research!) but I've hit a snag.

I was running an indicator mount, left it to go eat then heard a crunch. Oops? Everything seemed fine, but the head was off to the side of the part, looked like one corner had built up, head hit it, and the X axis belt skipped a few teeth.

Scrapped that part and started again, here is where the snag comes in.

The first layer seemed okay (you can see the skirt in the pictures, whole first layers looked like that).
Second layer the problems started, gaps and globs in the print. Also noticed that the extruder temp had fallen 5 degrees (down to 175), without my input (measured temp, setting was still correct at 180). I raised it 5 deg (setting at 185), and after a few moments everything heated back up (measured temp at 185). Globs and spaces still present. I'm not sure if the nozzle is clogged, flow rate too low, temp wrong, etc. Any ideas would be greatly appreciated.

Specs:
Printing PLA
190 deg first layer, 180 other
Heat bed off
Glass (Borosilicate?) bed
All layers .2mm
Speed 50 mm/s for perimeters, infill
Extrusion multiplier set at 1

I should also note that this is the first time I've used .2mm, other prints have been at .1mm. Maybe I need to change something when I increase the layer height?

Let me know if you folks need any more info.
Thanks for any help!

 

Adjust your z-height VERY SLIGHTLY. You want to go up a little higher but you are very close.

I can tell because of your outer most perimeter. Using that is a GREAT way to get your prints setup well. Notice how in your picture it looks like a flat ribbon? It should have some more height so that it looks more rounded. If you get a good first outer perimeter chances are your print will be good to go.

 

@Michael

But the first layer works, the others get problems, and they should have the right height above the first one...
That's bit strange...
Maybe the Temperature needs to be another 5°C higher, it depends sometimes on the material..
But I don't know really what causes this...

 

I know it doesn't seem like it makes much sense but trust me. The first layer should not be that flat it needs some height (it will be more rounded when it is correct) so that the next layer can adhere properly. What is happening is because the z-height is too low and the first layer is getting so squished down there are tiny little spots where filament is bunching up once it is extruded, multiply that by say 5 layers and by layer 6 the height of what has printed isn't consistent anywhere and thus this is the result.

You can see this in the outer most perimeter in the tip right corner, see those globs of material?

Temperature has a big roll to play in a lot of things, if the filament seems like it isn't flowing correctly up by 5 degrees. You only have to really worry about going TOO HOT if its oozing too much or you can actually see some discoloration.

Now PLA can be a little more "squished" to the bed then ABS for example but I've found that if I use my heated bed and some hairspray I can usually use the same z-height for PLA and ABS. Now nylon is another story, nylon you want to squish down as much as you can before the extruder jams in order to get the best adhesion as possible and minimize warpage.

It all comes with time, the longer you keep going and the more frustrated you get the more you will learn and understand. I've had my printer since June and it took probably 3-4 weeks of a lot of use to get really comfortable knowing what I can do and how to do it. In just the last few days I've gotten even more control thanks to replacing a very badly warped original wooden bed.

 

@Michael

Thanks for the information. very interesting!

 

No problem here to help.

 

Michael,
I tried raising up a bit (first .05 mm then .1 mm). Seemed to help, but the problem is still present. On a hunch, I pulled the filament out and looked at the hobbed bolt. It was full of ground up PLA. Going to try cleaning it out and see where I get with that.

Also, good to know about the temperature, I was afraid to raise it too much. On a possibly unrelated not, though, I am also having a heck of a problem with oozing, so I am hesitant to raise the temperature too much if that will make things worse.

I'll check back in in a day or two once I've had a chance to clean out that bolt. In the meantime, any other tips, tricks and comments are appreciated!

Thanks!

 

Do you have a z-height adjustment screw? If so it may get to a point where it is literally an 1/8th of a turn, or a 1/4 of a turn adjustment that you need to make. If you do not have the z-height adjustment screw I highly suggest you do the mod (just search the forums for it and you'll find it). Do you have retraction turned on under the printer settings tab of slic3r? That will help with oozing.

The ground PLA on the hobbed bolt is due to the pla getting jammed up (a side effect of the low z-height). Blow it out and you'll be better off. You mention you are printing on the glass bed, are you using any adhesion (hairspray, glue ect)? I personally like to heat up the bed even with PLA, it just works for me. Make sure your bed is also as clean as possible, scrapping off any print remnants with a knife blade and wiping down with some acetone is good practice.

Another thing you can try to help with the oozing is adjusting your filament diameter setting. If you have a measuring caliper measure 3 different spots on the filament (try to measure within like a 5 foot section) and average those numbers together for your filament diameter. That may help as well. For example if default is 1.75mm the average diameter may be closer to 1.70 by changing that setting the extruder will adjust the amount of filament to create a better print.

 

Michael,

I do have the Z-height adjustment screw, I've been using that and a feeler gauge to set my initial Z height. Once I've got it set, I've been using the Z offset to bring the head further up. I will try getting rid of the offset and working just with the adjustment screw. My switch was installed backwards (according to some pics I've seen on the forums). I flipped the switch around, but the setting is still pretty finicky. I'll set the height, move Z up, zero Z, and the head will not return to the same height that I had initially set, as measured by a feeler gauge. I'm assuming this is normal, but I was expecting a bit more repeatability.

I'm printing directly on the glass (no heat, no hairspray, etc.), I scrape it off and clean with isopropyl alcohol between prints. I'll also give it a try with the heat on. I got as much of the ground up PLA out of the bolt as I can with it in the machine, but there is still more in there (also, still doing the same thing when printing). I've got to get the hobbed bolt out to really get it clean, at this point.

As for the oozing, I do have retraction set, I'm using 1mm retraction. I've tried speeds from 10mm/s to 100mm/s, nothing seems to help the stringing/oozing issues that I'm having so far.

The tip on measuring the filament is great! I will do that before my next print.

I'm going to try to get that bolt out and clean it properly tonight, I'll implement some more of your suggestions and give it another shot as soon as I can. Once I get this part done, I can install the bed levelers and finally get everyhting level (and find out if there is any warping in the bed)

Thanks for the help!

 

So the set screw isn't always hitting the z-stop switch OR it is but the head doesn't return to the same place? If it is the second of the two make sure that the mount for the switch is TIGHT, and that it isn't moving around. If it is the first one something is getting hung up OR its set too low and the extruder is getting stuck on the bed. If its stopping too high then I am a bit stumped unless something like a cable or filament is holding it up and suspending the carriage.

 

Michael,
It is the second case, Z hits the switch every time, but does not always end up at the same height. Found that the mount for the switch was broken from being over tightened, super glued it back up. I will tighten it some more, hopefully not too much or it will end up as it was originally!

Mark,
The drive rods feel tight, but I have not checked tightness with an allen wrench; I will also have a look at that when I get a chance.

I'm glad to hear that the Z is consistent, I just need to do some tinkering and find out what is loose on my machine.

 

is the z switch backwards on yours?