Z axis slips down by a layer or two, digs into print

Filament type: PLA
Extruding Temp: 200 first layer, 190 after that
Bed Temp: 30
Bed makeup: sprayed with AquaNet

Hey folks, first time poster. I'm a teacher and we got the printer with a grant. We've had it for about 2 weeks now and we have been successful in making numerous attempts but no success in printing a full object yet. We thought we had all the parameters figured out as far as speed, temperature, etc but now it seems we have something new and can't seem to figure out what parameter addresses it -

So about 20 layers into the print (maybe 1/4 inch or so), the extruder head dips down into the top couple of layers and begins to make grooves into the print. It of course rips it off the bed at that time. It did that twice at the same height. I checked the grooves on the tall bolts that drive the z axis. There was a bit of fuzz on a groove and I cleared it off and thought that was it. The next print it did the same thing but now 15 layers into the print. Everything else seems fine - no curling, no strings, no clogs. I don't think it's the G-code. I'm pretty sure it's a mechanical thing. What should I be checking??

Thanks in advance!

 

Hi Enrique. Couple of questions.

1) Are the nuts on the threaded rod fully inside of their pockets in the X Carriage? You should NOT be able to see the nuts when you look underneath the X carriage.

2) Have you flashed the Robo to the latest firmware?

You can read the Robo 3D User's FAQ here http://melodybliss.org/robo3d/

 

Sounds like they need to lube their rods with grease or synthetic lube

 

Thanks for the quick responses guys! Mike I can certainly try to lubricate the rods. Would WD40 be fine or does it require some special lubricant?

Melody the nuts are in there - that was one of the early issues that I resolved. By that I mean they are flush or just below the opening for them. They don't stick out. However I haven't done anything with the firmware. I just got the printer so I assumed it was up to date. I will also do that. I will be trying the same build again after I have applied your very gracious suggestions and report back. If I can actually get something built before the weekend that would be amazing!

 

Also check the length of the wires to your z axis end stop. They can get caught up under the case and then it would limit the carriage's ability to go higher. WD 40 is not a good lubricant.

 

I can move the extractor to over 100mm height manually. It seems tbere are no issues reaching that height. It's just that as it is printing, it will all of the sudden slip down by a couple of layers, and dig grooves into the print destroying it. Very much like it's slipping the threads. i tried changing the layer height to account for the metric rods ( layer height 0.2046mm and 0.3034 for the first layer). Should I be making more modifications to the settings to account for the Imperial Rods?

 

WD-40 is used for removing grease and grime to remove stuck bolts and some cleaning applications. It's not ideal for lubrication as it gums up causing more issues.

I went to my local ace or any other auto store and got some super lube. You could also use grease or motor oil but those smell bad in my opinion.

You really want something like synthetic lube since it doesn't smell and lubricates well.

 

white lithium or black grease works perfectly fine.

Stock settings should get you printing, it really doesn't need changes till you print something and decide what it needs from there. Its something stuck and coming free that's doing it im sure. I would guess either of the two nuts, or the extruder is loose in some way.

 

*begin WD40 rant*

Please please PLEASE do not use WD40 as a lubricant. It's not. It's really horrible as one.

*end WD40 rant*

white lithium, black grease, light machine oil, any of those will work. I'm personally partial to Boeshield T9. They make a version for bicycles which allow you to apply individual drops of the lubricant to where it's needed.

 

Thanks again guys. I am trying again as we speak. Too late for the WD40 warning, it's what I had at hand. Hopefully it won't gum things up too bad since I just did a light coat and I'll try to get some of the recommended lubricants in the meantime. So far the most success I've had is a third of a supporting bracket and about 14 or so failed attempts beside it. BUT hey, maybe today it will work. I sprayed the bed twice with hairspray, re-checked my settings, the nuts seem to be in place and not sticking out, using pretty much the regular PLA settings with the exception of slightly heating the bed up to 30 because it's so cold here and it seems to help the base stick, and the temperature of the filament to 200/190 because it seemed to get better results than the 190/180. If this try fails I'll cut the temperature back by 5 degrees. I returned the layers heights to .2 and .3 since I had good results with those to begin with. I'm using the blue PLA plastic from Robo3D also, not sure if that makes a difference. Anyways, keeping my fingers crossed. If it doesn't work I'll give it a few days until I can regain my patience and try again maybe next week. The students here and the administration keep coming and asking to see what I built...not helping =/

 

That didn't take long. The base came loose from the bed. OK, readjusting the height of the extruder, making sure it's close enough to the bed to release a nice squishy firsts layer. There are posts saying that 70C is recommended for PLA while others say not to heat it at all. Not sure which is best but since this isn't working, I think I'll up the temp to 50C. Leaving everything else the same and trying again.

 

I have been using Molykote 44. Works great for both the threaded rods and all of the bearings.

 

Thanks again guys! Ok, here's the update - no lubricant yet but 205/195 temp with 50 deg initial bed temp PLA and I got 90% of the print done! I was as close as I've gotten! This is what I'm printing http://www.thingiverse.com/thing:126873

So the issue was that when it got to the top of the build the entire piece started to rock back and forth with every pass and eventually came off the bed. After some reading I decided to up my bed temp to 70 and keep it that way to make the base more "sticky". However, near the beginning of the print process, the bed temperature cut off. I've read about some of the issues with the bed not being able to keep it's temperature. I am trying now to see if 50 degrees is a temperature it can hold.