Bed height/leveling when heated

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wermy
Posts: 28
Joined: Fri Jan 20, 2017 1:49 am

Bed height/leveling when heated

Postby wermy » Thu Jan 26, 2017 4:12 am

Hey guys,
I just discovered a pretty significant issue with my N2... I noticed that my first layer kept having issues extruding as if it was too low, even though I had it set pretty high(like 0.3mm was what started finally working). It also looked like the bed wasn't level: one corner of the part would manage to extrude some, but the opposite corner would get progressively thinner until it stopped extruding.

Several times I'd carefully make sure the bed was level and adjust the z-stop so it was right at 0.2mm - it was about as exact as I could get it. Checked at several different points on the bed and it was pretty level as best I could tell. But every single time it would start almost dragging on the bed, and wasn't able to get any plastic out due to how close it was (and would be worse in some corners than others).

On a hunch I heated up the bed first, then checked the nozzle height and bed leveling. Sure enough, when heated up my nozzle is not nearly 0.2mm - I can't even get the spacer under it. What's worse, it doesn't appear as level as with the bed cool either.

Anyone else run into this? I noticed several bubbles under the buildtak - is that perhaps the issue? Or is there something more serious wrong design-wise with this printer?

I have to say my experience hasn't been great so far. Something wrong with the driver board fan (they are shipping me a new one), my x-axis is slightly misaligned and now this. :(

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walshlg
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Joined: Wed Mar 23, 2016 12:01 pm

Re: Bed height/leveling when heated

Postby walshlg » Fri Jan 27, 2017 5:40 pm

this is real, its not just you , its everyone. Once you get it close to good then printing with a raft takes up most of the un-levelness problems. BUT I hate rafts. There are several threads about the bed leveling mod. You also must level with the bed and nozzles hot and stable for a good 15 minutes, but then if you level with glue on the heated bed it gets sticky and grabs the paper so tough to get z-stop height perfect. Best is clean off all glue (if you use), heat it all up and let it sit. Then adjust Z (always increase distance before you start to prevent bed damage). I set height for about 200um without glue, then I spray on hairspray, and let it dry and its about 100um thick so 100um offset. BUT you always get some globs.

OK to tell you the truth what I really do is: level a clean and cold bed with no glue. Heat it all up and let it sit with the lid on for a good hour, then re-level. That leveling holds for a good month with the mod. In regular use, I leave the glue on, level hot but keep the paper moving constantly (a sheet of copy paper is 100 um thick) and adjust Z as best I can. Some filaments are better with 200 um Z distance, others stick best with 100um Z heighth.

wermy
Posts: 28
Joined: Fri Jan 20, 2017 1:49 am

Re: Bed height/leveling when heated

Postby wermy » Fri Jan 27, 2017 6:16 pm

walshlg wrote:this is real, its not just you , its everyone. Once you get it close to good then printing with a raft takes up most of the un-levelness problems. BUT I hate rafts. There are several threads about the bed leveling mod. You also must level with the bed and nozzles hot and stable for a good 15 minutes, but then if you level with glue on the heated bed it gets sticky and grabs the paper so tough to get z-stop height perfect. Best is clean off all glue (if you use), heat it all up and let it sit. Then adjust Z (always increase distance before you start to prevent bed damage). I set height for about 200um without glue, then I spray on hairspray, and let it dry and its about 100um thick so 100um offset. BUT you always get some globs.

OK to tell you the truth what I really do is: level a clean and cold bed with no glue. Heat it all up and let it sit with the lid on for a good hour, then re-level. That leveling holds for a good month with the mod. In regular use, I leave the glue on, level hot but keep the paper moving constantly (a sheet of copy paper is 100 um thick) and adjust Z as best I can. Some filaments are better with 200 um Z distance, others stick best with 100um Z heighth.


Thanks for the advice! Yeah, I suspected the whole "factory leveled so you never have to!" thing was too good to be true. I'm going to get parts today for the bed leveling mod. Sigh. Really hoped this printer would be as plug-n-play as my lulzbot mini.

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walshlg
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Joined: Wed Mar 23, 2016 12:01 pm

Re: Bed height/leveling when heated

Postby walshlg » Sat Jan 28, 2017 7:25 pm

ADVICE ON MOD: the one thing I wish I had done differently - use a spring with 2x the spring constant for the center screw, say 10lb/in in center and 4-5 for outer screws. Also don't forget to get LONG screws - I forgot and had to put 20 lb of bricks on the print bed to compress all the springs enough to line them all up with the holes!

wermy
Posts: 28
Joined: Fri Jan 20, 2017 1:49 am

Re: Bed height/leveling when heated

Postby wermy » Sat Jan 28, 2017 7:49 pm

walshlg wrote:ADVICE ON MOD: the one thing I wish I had done differently - use a spring with 2x the spring constant for the center screw, say 10lb/in in center and 4-5 for outer screws. Also don't forget to get LONG screws - I forgot and had to put 20 lb of bricks on the print bed to compress all the springs enough to line them all up with the holes!


Ah, thanks for the tips... I just finished the mod though - printing a test cube now. :) Felt good to actually get this thing leveled!

NewbPilot
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Re: Bed height/leveling when heated

Postby NewbPilot » Sat Apr 08, 2017 1:38 pm

walshlg wrote:ADVICE ON MOD: the one thing I wish I had done differently - use a spring with 2x the spring constant for the center screw, say 10lb/in in center and 4-5 for outer screws. Also don't forget to get LONG screws - I forgot and had to put 20 lb of bricks on the print bed to compress all the springs enough to line them all up with the holes!


*sigh* i cant believe I have to put bricks on my brand new, 1 day old N2 :(

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walshlg
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Joined: Wed Mar 23, 2016 12:01 pm

Re: Bed height/leveling when heated

Postby walshlg » Mon Apr 10, 2017 2:58 pm

LOL yeh done it too, but you don't need the print bed on, although then you need something to push down. Personally I just put a piece of paper on the bed and the brick on that and it worked - another thing is get some long neck pliers or something to push the screws around until they line up in the holes


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