My extruder jammed and I was unable to reverse the filament or pull it out by hand. I had to take my j-head hot end off of the extruder and pull the PLA filament out with a pair of pliers while the unit was heated to 240C to remove it. I was running it at 185C the last time I used it. The filament appears to have softened along the length of the PTFE tube and melted in the extruder assembly. The only obvious deformation is the area that mushroomed and turned brown, but I measured the diameter of the filament on the reel and the part that entered the PTFE with a caliper. The filament in the PTFE was from 3.30mm to 3.40mm and the filament on the reel was between 2.95mm and 3.10mm. Does anyone have any suggestions to prevent this kind of jam? I've read that fans can be used, but I don't know of a good way to mount one to cool the PTFE without also cooling the brass. Click For Photo https://reprap.org/forum/read.php?262,139764,139764#msg-139764 Thu, 10 Sep 2026 06:57:06 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?262,139764,144101#msg-144101 https://reprap.org/forum/read.php?262,139764,144101#msg-144101 MaFraL Printing Sun, 22 Jul 2012 19:20:31 -0400 https://reprap.org/forum/read.php?262,139764,143781#msg-143781 https://reprap.org/forum/read.php?262,139764,143781#msg-143781 MaFraL Printing Fri, 20 Jul 2012 15:35:04 -0400 https://reprap.org/forum/read.php?262,139764,143440#msg-143440 https://reprap.org/forum/read.php?262,139764,143440#msg-143440 At the bottom of the carriage I have just put a piece of ducttape, which points the airflow (sort of) through the vents.

I have had similar problems with my j-head before I added the fan. After that I haven't had a single jam.]]> HansPeterHaastrup Printing Wed, 18 Jul 2012 08:26:11 -0400 https://reprap.org/forum/read.php?262,139764,141248#msg-141248 https://reprap.org/forum/read.php?262,139764,141248#msg-141248 MaFraL Printing Wed, 04 Jul 2012 11:34:26 -0400 https://reprap.org/forum/read.php?262,139764,140997#msg-140997 https://reprap.org/forum/read.php?262,139764,140997#msg-140997 aplavins Printing Tue, 03 Jul 2012 00:47:08 -0400 https://reprap.org/forum/read.php?262,139764,140555#msg-140555 https://reprap.org/forum/read.php?262,139764,140555#msg-140555 In my experience of extrudes, you do need active cooling on the insulator (including the J-head) to remove the risk of jamming. I don't think this is emphasised enough to people. It doesn't have to be a strong fan, just a gentle breeze across it will prevent heat creep upwards. The fan may cool the heater block as you suspect, and you do have to take some action to prevent this. You can insulate the block, fit a ducting to the fan, and so on. I have both. I use some Teflon sheet (oven liner) and some kapton to wrap the heater block. I use some teflon sheet simply taped below the fan/above the heater block to keep the airflow away from the print and heater block.

Have you a blog or photos of your extruder? Do you need any more advice on reattaching the j-head to the extruder?

I agree with Nophead. The j-head slot doesn't quite align with the holes provided to pin it in, and can be a challenge if you are trying to drill it through. I pinned it with some coat-hanger wire! I may move to a grove mount once I can find some aluminium of the matching thickness, or get a friend to mill a slot!
Regards,
NumberSix]]> NumberSix Printing Fri, 29 Jun 2012 13:08:08 -0400 https://reprap.org/forum/read.php?262,139764,139812#msg-139812 https://reprap.org/forum/read.php?262,139764,139812#msg-139812 MaFraL Printing Mon, 25 Jun 2012 14:52:13 -0400 https://reprap.org/forum/read.php?262,139764,139792#msg-139792 https://reprap.org/forum/read.php?262,139764,139792#msg-139792 -------------------------------------------------------
> I have yet to try groove mount. It seems to need a
> precisely machined metal plate because the
> thickness of most sheet materials would not be
> accurate enough, or am I missing something? I
> would love a better mounting method.

Tantillus uses a groove mount but it does not rely on the groove as much as the lip above the groove. This is also how the Gregs groove mount works, you are simply trapping the lip above the groove between the extruder body and the two bolts.]]> Sublime Printing Mon, 25 Jun 2012 14:02:21 -0400 https://reprap.org/forum/read.php?262,139764,139783#msg-139783 https://reprap.org/forum/read.php?262,139764,139783#msg-139783
The J-head is tricky because it usually comes with a groove that doesn't quite line up with the holes. That tends to make the drill wander and can snap the tap. It is better to get one without the groove.

I have yet to try groove mount. It seems to need a precisely machined metal plate because the thickness of most sheet materials would not be accurate enough, or am I missing something? I would love a better mounting method.]]> nophead Printing Mon, 25 Jun 2012 13:03:21 -0400 https://reprap.org/forum/read.php?262,139764,139778#msg-139778 https://reprap.org/forum/read.php?262,139764,139778#msg-139778
Do you have a link to a page describing the method you used to mount the hot end?]]> MaFraL Printing Mon, 25 Jun 2012 12:40:44 -0400 https://reprap.org/forum/read.php?262,139764,139769#msg-139769 https://reprap.org/forum/read.php?262,139764,139769#msg-139769
The heat at the top is caused by convection, not conduction. The outside of the insulator gets too hot to touch where it meets the extruder base but it must be cooler inside or it would jam. If you run the extruder on its side you will find the top stays cool. That implies insulating the brass heater block would keep it cool, or a tiny fan to disrupt the convection.]]> nophead Printing Mon, 25 Jun 2012 12:02:37 -0400 https://reprap.org/forum/read.php?262,139764,139764#msg-139764 https://reprap.org/forum/read.php?262,139764,139764#msg-139764
Click For Photo]]> MaFraL Printing Mon, 25 Jun 2012 11:36:29 -0400