3dbenchy detaches from bed while printing

Hi everyone,
after building my kossel mini and printing the qbert-like cubes successfully, i tried with the 3dbenchy boat.
After printing 5mm the boat detaches from the bed and is dragged by the extruder around.
I thought it was because of warping of the tip on teh front of the boat, but i added a fan, no warping of the tip, but it happened again..
I used the same slicer settings as the cubes. It seems the heated bed temp drops to room temp after the first layers, but i haven't found a way to tweak that, cound that be the issue?
What am i missing?

Hi,
So could be a number of things:
1) what material are you printing with? What are you printing onto? On the whole your heated bed should stay on but can be slightly cooler by 5-10 deg C after layer 1.
2) over extrusion will eventually build up and result in the object being taller than the nozzle z height, at that point or shortly after, the nozzle will hit the object and knock it off.
3) you mentioned the fan, most materials will curl upwards when printing an overhang especially with thin layers 0.2 or less, a fan helps but abs for example curls depending on the direction the air flow comes from, hence twin fan setups, ring shaped fan cowls etc... With a model like 3dbenchy correct cooling is very important, with PLA use fan after layer 3 probably at full speed. ABS benefits from light cooling even though conventional wisdom is no fan. PETG same cooling as PLA.

See if that helps. 3dbenchy is designed to be very difficult to print well.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I forgot quite a few details...
1) PLA on a borosilicate glass plate with heated bed at 60°C. I didn't find a way to set the temperature after layer 1 with Kisslicer. The target temp just drops to 0 after the 1st layer...
2) that's what happens, but i think it's not because of overextrusion, the bow of the boat is soft (this is why i added the fans) and when it hardens upwards it acts as a hook on the nozzle and it will drag it around.
3) even though i am not printing with ABS, "abs for example curls depending on the direction the air flow comes from" is extremely useful, i didn't think such a possibility.
Thank you very much!

1) I don't use kisslicer but go on their forum and find out the setting to keep the bed on, or for the time being just use your lcd or host program to send a M140 S60 after the first layer, this will maintain the bed temp.

2) If you are sure you are not overextruding, either reduce your speed a lot (the folded up overhang hardens as the nozzle moves away but will soften when the nozzle comes near it again, do this slowly and it wont knock the part off), or, and I'm joking here a bit - print very fast so the edge doesn't have time to harden before the next layer (might work better in a heated chamber) but with a benchy your looking for maximum quality which won't be achieved printing fast.

Good luck - post pictures, try printing it in grey it shows up the issues better and is easier to photograph than black or white.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Thanks for the tips!

1) I just use the lcd setting. By host program to send a M140 S60 after the first layer you mean in case i use the PC to "drive" the printer? It just bothers me that i can't set it from software once and for all, so i won't forget to set it while writing this post, for example.

2) so far i am printing easier stuff almost succesfully (I just learnt that sometimes 45° slopes are a pain to print and from now on my prints will be full of ribs if not printing with the grid underneath), I will try 3Dbenchy again soon. In any case i think i will try a combination of different size fans and distance from the build plate and airflow orientation according to the print.

Actually I print in green, it makes plastic less boring than grey! Apart from jokes, in my opinion green highlights surface defects quite well, even though i saw grey plastic only in pictures.

Yes so if using LCD menu when the first layer has finished - you're going to watch it print to make sure its okay right? Use the LCD to set bed temp to whatever you want, assuming your slicer wont do it for you.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

yes, that's what I am doing