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Part 07 - Extruder

The extruder mechanism is based on the Bowden design, the idea being that it uses a 'hobbed' bolt (basically a bolt with teeth cut into a groove in it's length) to draw the filament through it. Its useful in this design because it offers a number of benefits, such as not being mounted on the head (reducing weight), meaning faster prints and less vibration, and the ability to reverse the filament out of the machine. Lots of info can be found here on this design.

Assembly of the parts is pretty easy, although look out for the nyloc nuts...make sure you don't over-tighten these before you've mounted the motor on the block...like I did. Only then did I realise that the toothed gear needed to come off again to get the final two restraining screws in...and those nylocs are swines to get off again.


When you fit the toothed cog onto the motor shaft...make sure to give the inside a once over with a needle file before fitting - it's quite tight otherwise, and if it's like mine, which has a couple of slightly deformed teeth, and will require replacing, if you can't get it off again easily you may damage the stepper when pulling it off.

The idler assembly.

Once fitted, I wanted to make sure that filament would be fed properly, so I cut off a length, installed into the extruder and manually moved the larger cog to see it feeding back and forth without snagging. At first I had the idler set way too tight and couldn't even get the filament in, but after loosening it went in. 

The next issue was that I noticed that the idler bearing wasn't moving at all with the filament - I resolved this by removing some material from the back of the idler plate, where the bearing protrudes - I actually had to take a fair bit off in the end, but not the bearing runs smoothly with the filament.

Here you can see the pneumatic fitting installed, along with the Bowden tube itself - I've read a lot on the forums that this pops out of the fitting under pressure - I tried to get mine out, and even with the restrainer compressed it's still a very tight fit - there must be a heck of a lot of pressure building up here when in operation to make it pop out!

And finally, here is the extruder fitted to the printer frame, and the bowden tube connected to the hot end. It's starting to look like it means business now! I just hope my mediocre engineering skills have been up to the challenge...time will tell!