Bowden tube fit with brass tube question

[mastory 44]

I started assembling my machine last night. Have a question about how the Bowden tube is to fit with the brass tube. The instructions explicitly say the tube should protrude from part 8B by 8mm exactly. I adhered to that, but when I got to bolting the extruder tip to the carriage, there is approximately a 3mm interference between the plastic tube and the hollow brass tube. In other words, there is about a 3mm gap between the aluminum plate and part 8B caused by the interference as mentioned. I have the tip and brass tube screwed together very tight by hand. I am suspecting perhaps a short depth of the tap in the tip or possibly an over length brass tube.

Beyond a blanket statement of adjusting the tube to 8mm exactly, what is the theory behind this fit condition? Is it intended to be a compression fit? i.e. is the tube supposed to be compressed 3mm? Some other lesser distance?

Without the benefit of further advice, I would re-adjust the 8mm to say 5.3mm and then allow the fit to be slightly compressed when bolted together. This should cause a sufficiently tight connection between the brass and plastic tube without causing the tip to deform and obstruct the filament. I would think that when heated up, the plastic tube will mold itself to fit as long as the interference isn't too great to start with. This given the end is cut square and the brass tube has the right form.

I noticed the end of the brass screw isn't particularly square or flat. More so, the shape of the end of the screw seems to the result of the thread run-out and how it relates to the thru bore. Should I square up the end of the screw?

Your thoughts?

Thanks,

Matt

[Daid 306]

There should be no gap between the bowden tube and the brass. Having a gap there will be a disaster as PLA will build up in there and you'll get the famous plug.

I have a 1mm gap between the aluminum plate and part 8B, because my tube sticked out a bit to far when I re-assembled my printer head. It prints great, without any problems. But 3mm sounds as a bit much. Just make sure the connection between the tube and the brass is perfect. But be careful with both the brass and the peek, it's easy to break both!

[mr_seeker 0]

Working on improving the Mechanical build wiki, but it takes at least 4-8 hours to get one part of the wiki done. Currently the guy who is helping me is gone for the rest of the week and I dont have too much time to spend on the wiki.

Currently we finished part 1 (frame) and 7 (electronics, which was a horrible mess btw) but all the other parts are still a mess and many of the pictures are outdated. It would help us a lot if people would look over the build instructions and edit where necessary.

[approx 0]

I received the ultimaker kit a couple of days ago. I am seeing the same observation as mastory. The instruction says that the tube should protrude from 8B exactly 8mm. This creates about a 3mm gap between 8B and the aluminum plate. Is it ok to have a 3mm gap - of any gap for that matter - between 8B and the aluminum plate? or should I shave off 2.5mm from the tube to reduce this gap?

[Daid 306]

A small gap between the plate and 8B is not a huge problem, but if the gap is too large, then your head can be tilted (due to the tube being off center) and I don't think that's a very good idea.

What I find odd is that you say 8mm is way too much. While for a few others it's been a bit too short.

(4-8 hours is quite long for each step... I took 8 hours to assemble my machine, and make the first sort of print)

[approx 0]

i really only get a chance to work on the kit for a couple of hours at a time after my kid goes to bed

Since mastory had the same issue, i wonder whether he made the tube smaller - 6mm or so..