Hotend drag solution

Hi everyone.

I'm sure I am not the only one who has had their hotend nozzle drag along their print as a result of overhang curl or print surface lift during prints. Although the best remedy for nozzle drag is to eliminate the previous layers curling and lifting to cause a collision, it sometimes seems like an unavoidable occurance. This problem gets even worse on 3d printers that have very rigid extruder carriages because the collision between the hot end and the previous layer can cause the stepper motors to skip steps or detaching the print from the print bed, thus ruining what would be an otherwise successful print.

To fix this problem I have been considering springloading my hotend to allow it to raise up when it collides with any lifted surface. I am sure I'm not the first to think of this idea, so I was wondering if anyone else had tried to implement a setup such as this and if so, whether it resulted in improved print reliability.

I am considering trying this out on my 3Dlabtek Prusa i3 as I am planning on switching to their aluminum x-carriage and a new E3D nozzle because I am assuming that there will be very little "give" if the nozzle does drag, meaning I will almost certainly have my stepper motors skipping steps.

I have attached a cross section diagram of a CAD mockup I quickly did to illustrate what the setup would look like. Let me know what you think

Edited 1 time(s). Last edit at 03/18/2014 11:34AM by THE_SHRUB.

This isn't an exact comparison, but with my first setup I had a hotend that didn't completely fit into my extruder (a couple MM in diameter difference). I used O-rings to take up the space, packed in pretty tightly - but they did give enough that when the hotend ran into something it would give a bit. It was OK -- and for a while I thought it was a feature -- but it seemed to increase issues with ringing around corners at higher speeds… and it also seemed to create small offsets with homing after collisions or moving by hand.

Of course mine being a first prusa I2 build, it's quite likely that the issues i thought i were due to a slightly flexible hotend mounting were actually due to other issues in the frame / belts / etc. I think though that it would be worth trying some before / after prints, and if possible allow the adjustment of spring tension to dial things in a bit. Also probably useful to test at the different print speeds you'd be likely to use.

i do think that i've had more problems with the hotend dislodging prints from the bed since i went to a more rigid mount though.