Nozzle blocks at the exact same point in the print

Ive been printing a plate like part for a customer and every time at 40 minutes in, it blocks when it's doing a long line down the perimeter of the part but not at the start (might be a coincidence). When I take my j head apart, the blockage is always in the barrel above the nozzle. I've taken it apart about 10 times today to use a small Allen key to force the pla through the nozzle and try to clean it a bit. I also have a fan pointing at the cooling fins so that's not the problem. I'm printing pla at 210 and it's worked fine for a long time and so has my feed rate setting. Hopefully someone has experienced this in the past. Thank you in advance for any help.
Ben

What kind of hot end do you have? PLA has a known issue with some hot end designs - notably J heads - where the filament will jam inside the upper body of the hot end. The problem is that the body temperature gets hotter than it should. The solution is to put a small fan aimed at the extruder body - not at the print. Also, the fan should be always on - not controlled by G Code. I have a 25mm fan aimed at mine. I also have a switch on the circuit so that I can switch the fan off if I'm printing ABS.

Hi, thanks for the response but I have a 25mm fan that's always on pointing at my j head cooling fins. Unfortunately this was installed a long time ago so it's not the cause of the problem.
Thanks
Ben

You could design a similar part, that has the long print " long line down the perimeter of the part " right at the beginning of the print. That way, you´d find out if it´s a temperature problem occuring after 40mins. or a general feed-issue.

-Olaf

I've just done a test on a large perimeter as you say and it printed fine but it's on this print specifically at the same layer. I've resliced it and it hasn't helped. The 3d model has a section where two extruded objects intersect each other as it was the easiest way to design it so I was wondering if the fact there are overlaps in the stl make a difference?
Thanks for the help so far

The fan has to point to the top where the filament enters the extruder to cool the rising heat. Not sure what you guys using Bowdens do for this. Mine is open to the air. Haven't had a clog since installing fan.

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Ben.folkes
I've just done a test on a large perimeter as you say and it printed fine but it's on this print specifically at the same layer. I've resliced it and it hasn't helped. The 3d model has a section where two extruded objects intersect each other as it was the easiest way to design it so I was wondering if the fact there are overlaps in the stl make a difference?
Thanks for the help so far

I´m not an expert, but you might have nailed it! My printer is off duty ATM, otherwise I´d have made a testprint with overlapping structures.
What design-SW do you use?
-Olaf

A funny shaped model shouldn't, in itself, block your extruder.

I wonder if it is putting down lots of little blobs and doing a lot of retractions and pulling warm swollen goo into the cold end.

Can you slice it with no retraction set?

-a

What's the print speed? Do you have the fan starting later or is 40 in the object changing air flow?

Thanks for all the replies. Turns out that intersecting meshes were causing the gcode to extrude twice as much material which blocked the nozzle. Netfabb cloud repaired it and it printed fine.
Cheers
Ben