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Filament tightness through PTFE rod

Posted by Drangid 
Filament tightness through PTFE rod
March 21, 2013 04:33PM
My kit is one that uses a PTFE rod in the hot end. I'm using 1.75 filament, and it's a bit tight to pass through the tube, especially since the filament is a bit curved from coming off the spool. Should it be sliding through the tube very loose? I feel like the extruder would have to exert a lot of force to push it through. Is it safe to widen the 1.75mm hole, or should it be very snug?

Also, in testing out the filament, I'm feeding it into the extruder and over the hobbed bolt, but finding some difficulty in getting it to feed through the hole in the bottom of the extruder. I have to do a lot of wiggling to try to thread it through the hole, essentially blind. Am I missing something here? Like maybe the whole should start much wider but then taper down the desired size?
Re: Filament tightness through PTFE rod
March 21, 2013 05:51PM
You want tolerance to be tight but still for the most part slide in with little to no wiggle a little drag is OK but u don't want to have to useforce to get it through bend the filament some to get it straight should go through much easier also make sure your hot end lines up properly with the hole in the bottom of extruder. If you have hinged extruder you should be able to directly insert the filament into the hole at top and be able to see it. Also cut off the end of your filament if its got a flat spot that may be keeping the filament from sliding in other thing u can do is get 1.75 dremel bit and deburplastic in extruder but do not expand the hole that will cause play and make filament want to walk out of hobbed bolt
Re: Filament tightness through PTFE rod
March 21, 2013 09:47PM
Great question. I have a new kit I'm putting together and had exactly the same question. 1.75mm and a nice J-head. It takes more force than I expected to get the filament through the PTFE but I'm sure it's really not much compared to what happens when extruding. Hopefully it all just works. :-)
Re: Filament tightness through PTFE rod
March 22, 2013 09:23AM
Okay, so I've heeded your advice tattooedfish and I didn't drill through the hole in the PTFE rod. I found I could improve the grip from the hobbed bolt, and it has enough force to slide it through the tube no problem.

But I did go as far as expanding the whole just on one end, to make it easier to feed the filament through. I used a large drill bit and went it just a few milimeters, then drilled deeper using a smaller bit, and continued until I reached 1.75mm. Then smoothed and cleaned all that. Now I can load my filament through the extruder and it slides right into the PTFE like butter, but it is still held well as 90% of the hole is still 1.75mm wide.
Re: Filament tightness through PTFE rod
March 22, 2013 11:26AM
I just suffered through this problem with a buda-style nozzle. The kit was from Gadgets 3D and included a PTFE tube that had an internal diameter of 4 mm. This kit was for 3mm filament.

I measured my PLA to be 2.85mm, so the difference of 1.15mm is quite a bit of slop. This gap allowed melted plastic to flow up the tube, where it would cool, adhere to incoming filament, and jam.

I tried numerous things but eventually ordered a replacement tube from Lulzbot. It's ID is 3.0mm, and it works fine. I've actually tried to jam it, but even that attempt only made the filament sluggish, and after running a couple mm's through, the resistance was entirely gone.

So, yes you want a good fit between the tube and your filament, but loose enough that the filament can be pushed through easily. Your setup sounds perfect.
Re: Filament tightness through PTFE rod
March 22, 2013 01:57PM
Glad to see u got it working for . I wasn't meaning like drill out the hole large just simply with extruded parts they might not be within 100% of exact size depending on who printed the part and deburing with a 1.75 but would ensure appropriate size. Let us know if u have any other issues
Re: Filament tightness through PTFE rod
March 22, 2013 06:43PM
Ahhh BrentB! I have been having the identical issue with a G3D nozzle, i am in the process of trying to rectify it at the moment.
I will have to measure the PTFE and see if mine is that big as well. I am suspicious it will be because my blocking problems sound identical, runs allright for a while, then blocks, and when i pull it apart there is a heap of hardened fillament up the PTFE liner blocking it.
Thankyou for sharing, im sure it will come in very handy!
I have exactly the same problem with my G3D hotend: it clogs after printing for a while. The cause also seems to be a heap of hardened filament at the PTFE tube part.

However I've measured its inner diameter and it's exactly 3.0 mm, so I'm confused...
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