15 min fix for jam free QU-BD

[REdington]

Mike
I didn't see anything at Enco that would have a long enough LOC (length of cut) to do the barrel. The longest I saw for 5/32" was 7/16" and the 4mm was the same. I have found some, but they are special order. I like keos idea of grinding the end of a extra drill bit square and using it.

codepunk
The purpose of the stainless barrel is for heat dissipation at the cold end. When I had a jam on the stock barrel that I polished, the mushroom was close to the cold end. It was caused by heat creeping up the tube (the common problem with the QU-BD). It never jammed when it was extruding with very little stopping between extrudings. I think with the PFTE liner, the melt zone stays close to the same place and the cold end is doing what it is suppose to do. I think the problem with peek over the stainless for the barrel is that when you run ABS with the higher temps, the PEEK will soften on you. I have seen where the peek has soften enough that the threads strip and come apart on some hotends.

Rodney

[codepunk]

I had the PEEK rod and PTFE arrive today so I will give both mods a try and see how things go. Wish I could give it a try but unfortunately I have to travel the rest of this week. I suspect you may be correct about the PEEK rod but hey I have a chunk, might as well give it a spin.

[codepunk]

I did not try the PEEK as I don't thing there will be enough material to make it strong enough. However I did modify my stainless barrel as you suggest here and have not had a jam since.

[bloomingtonmike]

Who else has a QUBD MBE that is jamming?? We want all these extruders working on the ordbots for sure!! Let Rodney?Redington and I know and lets get you printing!

[bobt]

Rodney - Could you post a summary of the steps needed for this fix. I have read thru the thread several times and am not sure what you have changed and what others have changed. Please include a reference for the other items like Bdale's bearing change if they apply. I have 2 units that I want to put online but am unsure as to what pieces of the mods to do in what order. I have all the parts for all the mods that I think are needed for the QU-BD unit including the tubing. So could you put the instructions all in one complete post as to what is really needed to be done.

Thank You
Bob Teeter

[bloomingtonmike]

BobT - There have been no changes to the overall procedures in the first post.

Rodney has been offline a bit this week.

Assembly can vary. Here is mine after doing this a few times now.

Cut the barrel at the hobbed portion.
Drill long barrel section only with Type 22 drill
smooth/ file cut edges of short and long barrel
Slot the small barrel portion.
Teflon tube installed in long barrel portion - cut it flush and do not crush tube - use a razor blade and roll through the cut gently
Screw long portion into cold block bottom
Capture that with small piece - use screw driver in slot - I like to make small portion stick out enough and use nut on top of it too
Thread on plate mounting nut on bottom of long portion
(you can mount the plate now to the cold block if you want - I do)
(also now decide if you want to drill hotend for thermistor hole using type 50 bit or tape the thermistor on the normal way, I mount my thermistor now and also do my teflon and kapton taping now).
Screw nozzle to hot end, then loosen 1/2 turn
screw on hotend/nozzle to the coldend/plate/barrel assembly
Tighten nozzle to barrel
Install MK7 gear on nema17 if you want
Put it all together - Install Bart or minimalistic MK7 parts, cold block/hotend/plate assembly, heatsink, and fan to nema17

Assemble with

[Joe_E]

I have to say that I am now a believer in the ptfe tube mod. I had my printer working great before with Barts bearing quide modification and a mk7 gear. when I ran low on the Zen toolworks PLA that I had, I ordered some from kbellenterprises on ebay because the reviews looked good and for $28 per kg, it was cheap. The good printing days were done though, because I could not get the new PLA to print for longer than a few minutes. I tried many different temps. Different retracts. different speeds. I even put a screw in the bearing guide so that I could add pressure with no luck. So I decided, what the heck, lets try the ptfe tube mod.

I decided not to get as fancy with my approach though. I knew that the ptfe tube needed to be captured and that I wanted it as close to the nozzle as possible, so I decided to have it against the nozzle. rather than cut the barrel, I just drilled into it and captured the ptfe against the nozzle. before trying it, I first cranked the temp on the nozzle to 250 C and held the ptfe tube against it to make sure that it could take it and it was fine.

My steps:
1. I used my drill press to drill a hole 17 mm deep in the long end of the barrel using a normal 5/32 drill bit (my big drill bit set is all SAE). I used the barrel in the ckuck method to line it up before drilling.
2. I cut the end of the ptfe tube I had off flush with a razor blade.
3. I stuck the tube into the hole all the way and cut off the part sticking out with about .5 mm sticking out using the razor blade again. I wanted it to stick out a little so it could get compressed.
4. I used a 7/64 drill bit on the other end to round out the end of the hole a little so it would be easier to feed in.
5. I threaded it into the hot end so that the ptfe tube would be against the nozzle. and made it tight enough to be held well.
6. I tried feeding filament into it by hand and checked the length to make sure that it was feeding smoothly all the way to the tip.
7. I then re-assembled my extruder and started printing.

***One thing to be careful of is to not over-tighten your nuts on the modified barrel. The walls are very thin. My first attempt ended up breaking my barrel. Luckily I had a second barrel handy from the second qu bd extruder I got with my printer but never installed.

I have printed for about 10 hours with no issue since.
One other tip that I have with PLA is that with my old PLA, I got my best results at 210 C. With this set up and the PLA I am using now, I am running at 205 C. I always had bad luck at lower temps. I do have a good fan duct to cool my PLA though.

RIght now, I am giving the new setup a good test. I am printing a lithopane from thingiverse at .1 mm layer heights.


I hope this helps take away any fears people have about the effectiveness of this mod and that it is really easy. Honestly, if I didn't have a drill press, I think I could have done it with my hand drill. You do have a guide hole after all

[Alup]

Since it seems to be that the pipe is jamming because heat is creeping up the cold plate to the top of the cold end and that is causing jamming, Could't you just drill a few holes or a slot in the heat sink? This would do 2 things, it would cause the heatsink to get colder faster and it would also allow air to directly hit the cold end cooling even better than the cold plate does.

If i am wrong about this please let me know, I came up with this from my experimenting with overclocking computers.

[orcinus]

Stupid question...

Has anyone tried applying teflon coating to the barrel as a temporary solution?
As in - just spraying it in and pushing a filament through so it spreads the coating evenly?

Most PTFE aerosols are rated up to 260 deg C, so should be fine for PLA and ABS (until it wears out).

[rickmellor]

This mod should be incorporated by Qu-Bd into the units they sell. It has made my extruder 100% reliable and I'm getting some awesome prints from it.

I had one issue with this mod in that it shortens the filament barrel too much ... it made it hard for me to get the nuts tightened when mounting the thing. With that in mind I made one small deviation from this plan but otherwise kept everything else the same:

Instead of cutting the filament barrel at the narrow point, I didn't cut it at all. Instead I drilled it out from the inlet side to a depth of 17mm, using the #22 bit. I then used another #22 bit that I flattened the end on to act as a poor-man's endmill and used that to square up the bottom inside of the barrel so it won't compress the PTFE tube.

Next, I ordered a second filament barrel from Qu-Bd and cut this one 5mm from the inlet end. I then slotted it per the original build instructions.

The PTFE tube was squared on its end, pushed into the filament barrel and then cut flush with the end. The whole thing was then assembled as usual.

In addition to the filament barrel mod I also installed a Mk7 drive gear. Other than these two things my MBE is stock. I'm not using the idler arm mod... the set screw is working fine for me. So far I've managed multi-hour prints without a hitch.

Thanks for the help with this REdington. You totally saved this design.