Extruder for Rostock Mini

Hi guys I'm trying to build a rostock mini, but a bit confused with the extruder design. From the RepRap wiki, the extruder uses a special kind of stepper motor ( the one with a big cylinder on top, not sure what it is called). This motor is a lot more expensive than Nema 17 and the shaft has a diameter of 8mm. What is the purpose of this extra piece? Also, I' not sure where to find a gear for this motor. Is there any other good bowden extruder design? Thanks.

I had a similar question. Check out the link: [forums.reprap.org]

Its a geared extruder. In my opinion, worth it.

You can also use a stepper without integrated gearbox with some of the geared extruders.
This option will be cheaper and you will be able to set your gear ratio yourself.
It is better to get stronger stepper and use low gear ratio (e.g. 2.5:1) so that your retract speeds can be around 10 cm/s.
This is the option I prefere since it allows me to keep higher retract speed (the ratio of integrated gearboxes is typically around 5:1; that is too high, i.e. your tratracst will be slow).

Thanks guys, any idea where to find the extruding gear?

You can get MK8 Drive Gear (from any seller) or if you are in US get the hobbed pulley from trinity labs.
If you can select prefere pulleys which can be mounted on M8 screw since most geared extruders use M8 screw.
But there are also some which use Φ5mm shaft or M5 screw (but I had a problem to buy M5 screw localy which would really have 5 mm diameter).
You will need to adjust OpenScad file of some extruder to set gear ratio you want.
You must pair extruder you like with the driving gear.
Some extruders do not need drive gear, they use M8 hobbed bolt. You can do your own hobbing with a dremler tool. The hobbing can be on the bolt body or on its head (M8 bolt with head for hex key). The second one is probably better because it has bigger diameter.

If you have some uncommon spare ball bearings (compared to the common 608 or 629) or driving gear and want to use them (instead of buying/making the right ones for the extruder of your selection), then I have a parametric geared extruder where about 40 parameters can be set. If you want it let me know and I'll post it.

That would be great hercek. I am still calibrating my Kossel,The extruder is a larger Nema 17 direct drive with what was sold as MK7 Drive Gear and a Delrin lever and what looks like a 608 bearing, but if I run into problems it would be nice to have a back up solution available.

The link to the OpenScad source file: [www.hck.sk]
General shape is always the same as on the pictures but the dimensions of the parts of the extruder depend on the parameters.
Currently there is 45 of them. The parameters were tested with these two options at least:

• three 608 bearings with M8 home made hobbed bolt;
• one 608 bearing, two 625 flanged bearings, Φ5mm shaft with of-the-shelf pulley (this is on the pictures).

Edit: extruder.scad file link changed.

Edited 1 time(s). Last edit at 03/05/2014 02:24AM by hercek.

Hercek Hello, I fail to compile the file, I get error OpenSCAD.
I need to generate the stl for the following items
1 608, 2 625, 5mm diameter (MK7), bowden connector 3/8 "x 4mm
Might you help me?

Probably OpenSCAD bug. Try to use only F6 (Compile and Render). Do not use F4 (Reload and Compile) or F5 (Compile). OpenSCAD has two paths for object rendering. The one used after F6 uses CGAL and is not that buggy.

Have you reason is a bug, F6 really works, thanks

You may want to try OpenSCAD version 2014.03.
It does not crash with the file (at least on my machine).
Although F4 (Compile) is incomplete.
So it is still better to just use F6 only.