Sunday, 5 April 2009

Coach Bolt Hack

The M8 bolt in my BfB extruder hasn't been gripping the filament well. I've tried the standard tricks, sharpening the thread, increasing the force (until I cracked the acrylic), but I'm still able to pull the filament out by hand against the thread. While shopping around, I came across some coach bolts with much deeper, sharper threads. Simple replacement of the M8 bolt was difficult - there aren't nuts that fit and it was impossible to attach the existing gear or provide vertical support.
I needed a bolt with m8 at one end for the gear and bearings, and coach bolt screw at the other for the filament bite. So I made this:

From Coach Bolt drive


It's soldered together ( see pictures for more detail of how), but if I had an extruder I could easily have made a coupler, since the joint is in compression.

From Coach Bolt drive


It seems to fit OK into the BfB assembly, with a little modification of the bearings (one bearing, rearranged nuts to fit). It grips the filament lovely now, and hand-winding the gear drives the filament well.
I then attached my rebuilt extruder nozzle.

From Coach Bolt drive


I'll post later when I've tested the nozzle.

3 comments:

BodgeIt said...

I like it what a great hack thic could help others out with the BFB extruder, do you get any wobble from your solder join?

Renoir said...

The solder join is solid as anything. (standard electronics solder, just a bigger heat source to get the bolts to temp).
The main wobble tends to come from the fact that there's about a 2 degree misalignment (it moved slightly while cooling).

Seems to work so far...

1m93 said...

Brilliant hack! Despite the rough, not to say stone-age, looks :-)
I will try this or something similar to my dysfunctional BFb extruder as well.