Saturday, 10 January 2009

Feeding ABS with Worm Gears and Threaded Rod

Here's a method (inspired by all the other folk experimenting with alternative filament feeds) of feeding filament using Worm Gears and 3mm Studding.

Next job is to design the holder to mount it all to a RepRap extruder and a feed motor assembly.

The pitch of the M3 is 0.5mm per turn giving a feed rate of 0.5mm per turn of the drive shaft.

The tooth pattern cut into the gears is aprox 1mm deep so 0.33 of the diameter of a nominal 3mm plastic filament.

Whilst it all feels to grip prety well I will need to actually make an assembly and do some measurements to see how well it works really.


Bert said...

Nice work! Really love the gear cutting trick.

I'd be tempted to use plain rollers (or even ball bearings) on the outside of the filament, though, as this would make the grip depth more controllable on the driven side of the filament.

aka47 said...


I thought the same as you but gut feeling told me to go with the gear on both sides approach.

I really don't know why though as looking at it logically I would have to agree with you.

As they are idlers it should make no difference so why go to the effort of cutting gears for it.

I have found reasons later for many things, that justified going with the gut feeling, often enough, that I will stick with this for now.

Bert said...

The way I see this, it is likely that the thread won't cut all the way in when using hard materials like ABS, right?

Now, I have no idea of what you have in mind for the rest of the assembly. If you plan to use a spring-loading mechanism for the backing wheels, then I agree with you, this would make little difference, if any.

But if you are planning an (adjustable) fixed stop for the backing wheels, then having threads on them would make the filament "float". In other words, sometimes the driven wheels will cut deeper in the filament and all will be fine, but sometimes it will be the backing wheels that cut deeper, opening the door to slippage.

Having flat wheel on the back of the filament thus creates a more stable "reference plane", so to speak.

aka47 said...

Yup, spring loaded it is.