Hi, I have just completed a mcwire style cartesian bot controled with reprap software running on an Arduino board.
I'm extremely impressed with the accuracy of the design and ease of use of the sofware!

I've got it running with a dremel mounted to the z axis and it engraves text and cuts out 5mm perspex beautifully! But now i want to build an extruder assembly for it in the hope of being able to print out parts for a Mendel.

My question is which extruder should I use? there seem to be quite a few different types on the reprap wiki. Which one is best for someone who has no access to printed parts (but does have a lathe).

Many thanks for your help

ro

I'd recommend a direct-drive stepper extruder. The best way to cut the thread if you have a lathe is detailed here:

[kirbyandco.blogspot.com]

Personally, I took apart my stepper, wrapped the rotor in tape to prevent swarf gnarling it up, then made a wooden jig to attach the bearings to the lathe toolrest. I used an M5 tap, M3-6 is probably best. My extruder is incredibly hackish:

[picasaweb.google.co.uk]

but works great, if you're designing it yourself you should make sure you push the filament against the motor shaft with springs to maximise grip. If you can find strongish gears, you might get better results gearing the stepper down first, but its more effort to build.
For the hot end, its pretty easy to turn a nozzle on a lathe, I'm using power resistors as heaters which seems to work well, but others have had good luck with nichrome+kapton.

Thank you very much for your advice. I think I'll steal your designs but use mdf for the stepper mounting.

I like the pinchwheel extruder better than the direct drive. [objects.reprap.org]

A variation that gives you more torque and a smaller step size is Wade's geared extruder.

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

The pinchwheel is practically the same, its just a bit of a pain to make the parts without a printer already. I've also had much better results using a sprung idler wheel, which the official mendel extruder doesn't have.

The geared extruder doesn't look like too much more work, especially as I have a load of gears from an old laser printer (which my steppers came from too).

Would I notice much difference in the end result between the geared pinchwheel design and the direct drive design?

I haven't had time to finish getting my extruder working yet so I can't speak from personal experience but FWIW, many people speak highly of Wade's geared extruder and its variants. I had torque problems with the stock non-geared extruder that I'm hoping Wade's design will solve.

Rob.

I'm using one of Wade's extruders, and so far it's been extremely reliable. I could never get my original direct-drive extruder to work, because of insufficient torque.

If anyone who has problems with the direct drive extruder is using "off the shelf" Steppers (eg: that are listed on Stepper Motors wiki page - even if you scavenged them), then please update the wiki or let me know which Stepper you're using so that we can document this.

If we can figure out approximately how much torque the direct driver extruder requires in the process, all the better.