My extruder kept stopping about every hour on a spool of new filament. I eventually discovered that this filament has periodic "flat spots" as if it has been slightly crushed at intervals several meters apart. The hobbed part won't grip the flattened sections and so slips & wears a groove. Instead of throwing away that spool, I decided to design and make a friction-feed extruder for my Ormerod, based on [www.thingiverse.com] I've re-worked the design in OpenScad, making a few changes and adding a hook to fit the X-arm and a fitting to take the standard Ormerod Bowden tube. I completed it yesterday and printed with it for about 2 hours with no problems. It also works fine with a very old spool of filament that has become brittle and so frequently breaks at the hobbed part in the standard extruder. While just unwinding the filament from the reel will cause it to break if you are not careful, it seems to go through the new friction extruder without breaking, and while I can see and hear it sometimes break inside the Bowden tube as it goes around the bend, that does not stop it feeding (only stops it retracting) so it still prints OK.
So the advantages are: (1) allows the use of damaged filament or filament with poor diameter consistency. (2) is less likely to cause brittle filament to break in the extruder. (3) a temporary blockage or too fast extrusion will not cause the hobbed part to wear a groove in the filament so the print is not ruined.
Disadvantages are: (1) It is physically bigger and slightly heavier. (2) the weight (motor) is further from the X-arm which may cause an acrylic arm to twist unless it is mounted on the position close to the Z support (no problem with my aluminium arm) (3) the gearing is lower so there are less steps per mm, resulting in slightly less force being available - the motor skips occasionally when infilling at 65mm/s print speed, whereas the original extruder can handle 70mm/s before starting to skip (4) It's a bit more fiddly to load the filament - the end of the filament must be tapered and the first 20mm or so straight when loading, otherwise it may not feed into the exit hole correctly, though it seems to load OK 9 times out of 10.
I should think the belt will wear faster than a hobbed part, though belts are readily available & cheap, and easy to replace.
If there is any interest I'll do a full write-up with assembly instructions etc. and put it on "Thingiverse" as a derivative. Meanwhile I've attached the Scads - [www.thingiverse.com] should provide enough information to figure out how it goes together - all additional parts are exactly as detailed there (using a 5mm hex head bolt as the drive axel and a nut (head) trap instead of grub screws).
Note the SCAD file "Chassis.scad" will make 4 different parts depending on the value set for the "Parts" variable (1, 2, 3 or 4). Other variables can be changed to make different variations as detailed in the comments. You can tweak values in the "Parameters" scad to get good fits on the bearing and hole clearances etc. The defaults work with my printer.
Edited 2 time(s). Last edit at 05/02/2017 09:37AM by dmould.
* Works with the *new* Quickset nozzles which really gave me pain with the hobbed belt extruder
* It has a belt tensioner with screw which lets you control friction in a very controlled manner.
* It is also made to directly fit on an Ormerod.
* Geared with enough force.
* Much more reliable
* Large Wheel to keep filament bending down.
Drawbacks of my design:
* TPU it bends out of the belt and does not work.
* Its heavier.
* More Complex build.
* Filament Change a tad more to fiddle.
Also it has a much steampunkier look ;-)
I have not seen any wear out on my belt for the last half year i have been printing with this extruder.
That was the post I was looking for! I remembered your post when I decided to make a belt extruder, but did not find your post.
As I didn't find it, I adapted the Thingiverse design I found instead. Your post would have saved me several days' work. My adaptation is a very similar design to yours, but yours appears to be a bit easier as it is open on one side so misfeeds are easier to spot & correct (although I have only had one misfeed after scores of filament changes, and that was due to a very mis-shaped end on the filament - easily corrected). The lever-cam tensioner on my design variation is also quick & easy, though the lever will hit the bed at low Z heights if it is in the down, "not tensioned" position (which it will never be while printing). The motor drive is by a belt rather than gear driven, which makes it pretty much silent in operation - quite uncanny when you have become used to the "zzz", "zzz" sounds during retracts. So far it has not failed during a print.
The design I posted here works, but needed a bit of tweaking to avoid fouling the X carriage runner, which I have now done. I have taken photos of all stages of construction of my final version, and plan to make up a instruction document and put it on Thingiverse over the weekend - though as you have stated, there appears to be surprisingly little interest in a belt friction extruder.
I think it is well worth while having because of the advantages listed in my OP. So far I have not found any downsides after using it for about 20 prints. I have not yet run out of filament during a print, so I don't know how easy feeding a new reel during a print will be. Usually I just push the new filament into the extruder just as the tail of the old filament is disappearing into the inlet, and keep pressure on it until it reaches the feed mechanism. If that doesn't work with the belt extruder (I see no reason why it shouldn't), I can always pause the print just before the filament runs out and load the new reel "offline".
@fotomas - Yes, I saw your extruder and was impressed by its simplicity. The downside was the lack of power due to it being direct drive. I felt that it would probably skip unless I slowed the print speed, so I based my design on one that has a reduction drive. I suppose you could fit a bigger stepper motor, but I wanted to re-use the original stepper.
I still have not got around to putting mine onto Thingiverse. I'll have to pull finger and do so this weekend. I got side-tracked helping someone set up a couple of Raspberry Pi's as a VPN tunnel to his office LAN.