Layers not sticking together properly

Hi every one, I have built my own design, wich use a buddaschnozzle hotend with a 0.5mm nozzle.
I have this problem, the first 3 or 4 layers are gorgeous, but then, the filament doesn't glue to the previous layer every where, conducting to a rough layer as you can well see on picture IMAG070, and it becomes naturally worst every next layers....
I tried changing every parameters but can't find how to solve this...
Maybe you will have better ideas than I do
Thanks a lot !!!!

what speed are you placing the material down at? it looks like your feed stock is skipping. how hard is it to push the feed stock thru by hand? it should slide like butter. if it starts off sliding easily and still extrudes difficult after a minute or two it could be heat creep.


what also may be happening is that the feed stock could have heat creep from components and become rubbery inside the cold zone when flow is not fast enough, such as layer change and retraction. you can alleviate this by adding a fan pointed at the cold end. Also if you insulate your hot end it will need to be on less, which means the cold end has more of an opportunity to reach equilibrium with the surrounding air temp.

after looking at pictures of your design i think you are using a fan correct? i don't think you should use retraction with this setup. it looks like the there is no thermal break between hot and cold end.in a good design heat block would be flush against nozzle and the m6 rod would have a 1/2 inch gap between hot end block and cold region, or the m6 rod would be turned to reduce thermal transfer of energy right above the heater block.


also if you are using a bowden design the bowden tube needs to be slightly oversized and needs flexibility to move freely. for example the way it appears to be taped defeats purpose of low friction. i cant tell if you are using bowden or not.

also temp of robot print is too high of a temp. what temp are you printing at? again think of heat creep.

Edited 3 time(s). Last edit at 04/30/2014 06:09AM by jamesdanielv.

Thanks for your detailed answer.
You have seen right, i got a fan on the cold end, and a bowden tube configuration, the fan is maybe a bit under sized, it'a 30x30mm
I gonna check how hard it is to push the filament when it's starting to mess up the print.
I am not really sure about your creep idea cause, I can start a print a long time after the hot end reached temperature, and first layers are good, and if i think that it should have already creep in the cold end if it was the reason of the problem.
But however i will check as I said the strength needed to push the filament when it's starting to print bad.
I am printing between 175 and 185 cause higher the extruder jam a lot, probably due to some verry soft pla in the cold end. Again, the cooling fan is probably to small.
I don't use retractation for the moment, cause with bowden tube it's not that easy, at least I have other problem before
I will aso try as you said to lower the heating block against the nozzle, so it will be as far as possible from the cold end!
Thanks a lot I hope I am wrong and you are wright about heat creeping in the cold end

Ok then, it seems that you was right, after a whil it become verry hard to push the filament.
I adjust the extruder to be as strong as possible...
I lowered the heater against the nozzle, i also check that the ptfe tube is well locked and do not leave a gap near the M10 barrel and itself.
then I also put a bigger fan a 40x40.
Wanna see how it works now!!!