Filament slips off hobbing

Hi Guys, I am impressed with myself that I have gotten this far, I have managed to configure the firmware correctly for my Sanguinololu, assembled the Prusa Mendel, aligned the bed, done several "dry runs", even managed to get repetier and sprinter to work (working on marlin atm).

My extruder..... I hate it! The hot-end I brought from the NL due to not wanting a cheap chinese one, and wanting to save a little money over the english ones, but I think it's chinese... it's the latest j-head.

I couldn't find a way to remove the brass hex bolt from the PEEK so I inserted the 1.75 sleeve down the 3mm sleeve which is a tight fit and seemed to work, opinions on this please let me know.

The hobbed bolt, I originally tried a dremmeled bolt I did myself, worked 'ok' so I ordered a hobbed bolt from a reputable eBay'r... and it seems to grip while it is on the hobbing, but it soon goes off the hobbing and free wheels on the non hobbed part, this happens when the X asis moves, or given enough time of extruding filament without the hot-end.

I don't know how I am supposed to keep it in alignment? I tried adjusting the tension on the free wheel to push it back and it always seems to go to the motor side of my accessible wade's or occasionally the other way.

My thought so far on the issue:

* Hobbing not deep enough to 'track'
* Spring tension incorrect (I have tried all the way and a little tension and a lot of spring, it either does exactly the same or doesn't get pushed)
* Plastic parts wonky

Yes, I have tried it without the hot-end, same results.

It hurts to be so close... yet so far away from printing.

I use ball bearings for the free wheel side.

They are easy to add a groove to, just by taking a dremel with a cutoff wheel and grind in a groove while holding between two fingers.
You can add a bit of friction so the bearing doesn't match the dremel speed.
Pay attention and it's very easy. I would foresee some blood if you are fiddly or hesitant in this.

After a minute or so of sparks and spinning, there is a nice groove in the outside of the bearing.

I also make sure the tube that guides the filament into the drive wheels is down close, even trimmed to a V shape.
And also, the tube that receives the driven filament is up close to the drive wheels, with a chamfer to lead in the filament.

it sounds like his extruder does not have a guidler thing, so the filament is moving, the grooved bearing will probably work for now, i would print yourself the wades reloaded extruder from thingiverse, ive been using it and its great.

That's great! Thanks for the advice guys, with careful tensioning I have managed to get it to stay 'OK' but not great, I think the extruder I got was one that came with the STL bundle for the Mendel Prusa v2 as that was how it was sold on ebay, the Z axis ends were shockingly crooked and cracked at a slight angle, it's entombed in epoxy and zip ties for now!... but that's another story, I see this RepRap as more a RepStrap till I re-print all the parts in my luscious Faberdashery PLA. I don't know what the rules are for talking up places, but out of everywhere I have ordered all my parts from they have had the best customer responses, and included a generous upgrade which I did not expect in the slightest, pure classy folks!

EDIT: Forgot to mention what I shall do! I shall take a fresh skate bearing, pop it in the vice, I think the engraving tool will be the best to get a groove on, and see how it goes from there! I brought some bolts and I may try hobbing a bit deeper on one of them if that fails.

Thanks again for the kind help!

Edited 1 time(s). Last edit at 04/30/2013 01:39PM by Joshorilla.