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Milled transparent extruder

Posted by Petrus 
Milled transparent extruder
September 17, 2011 07:39PM
This is the extruder I made for converting my DIY CNC mill [forums.reprap.org] into a repstrap (the mill was designed for this since the beginning).

The extruder is mostly made from polycarbonate, other parts are standard screws and bolts or parts salvaged from epson printers.

Milled parts :

The extruder is composed by 9 parts milled in polycarbonate and held together by M3 screws.

The ball bearing (13mm ext, 5mm int 4mm width) used as idler came from an old hard drive.
Instead of springs, I use small rubber tubes, they came from the rollers of the printer.

The axle and bushings came from the same model of stepper used to drive the extruder.
The pinch wheel is a timed pulley from an Epson D88 printer.

The grip looks good:

I'm working on the hot-end now.
open | download - extruder_1.jpg (39.5 KB)
Re: Milled transparent extruder
September 17, 2011 09:09PM
Nice smiling smiley I'd be interested to know if you ever get excessive gear wear on the plastic gear because of the metal driver. What hot end are you thinking of? I'd definitely recommend power resistors compared to nichrome, my insanely-bodged extruder made from ceramic resistors and offcuts of wire has printed for >50 hours with no problems, while I've gone through 3 nichrome designs that have just infuriated me:

Re: Milled transparent extruder
September 17, 2011 11:06PM
Built my most of my machine using polycarbonate - great material for building with if you have a milling machine.

See write up at - [www.reprap.org]

Just upgraded it with a Makebot MK6+ extruder that has stainless steel barrel lined with PTFE - had to use a fan to cool the PLA filament to stop it going soft and benting before it entered the extruder assembly.
Re: Milled transparent extruder
September 18, 2011 06:23AM
I am building an extruder like this one : [www.thingiverse.com]
With wire heater too.
What was the problem with your nichrome wire heater ? Did you found why it failed ?

I think we can improve the design by using a brass insert to increase the thermal mass and by winding some copper filament on top of the heating wire to improve the thermal conductivity.

RepRot, Nice design, very clean and it looks indestructible, but why a so big stepper for the extruder ?
Re: Milled transparent extruder
September 18, 2011 09:02AM
I had some problems with the nichrome getting too hot and damaging the kapton, the thermistor broke, so the arduino thought the extruder was too cold and kept increasing the temperature. I also found the resistors a lot less fiddly to use, and harder to break with repeated disassembly of the heater. It's a personal preference really though, either would work.
Re: Milled transparent extruder
September 19, 2011 03:51AM
I was using fibre glass insulated nichrome wire on a brass barrel with a thermal coupler temperature sensor. the assembly was wrapped with kapton tape. This assembly gave off a really bad smell. Dismantling the unit, both the fibre glass insulation as well as the kapton tape were very charred. The nichrome wire heater didn't fail. Another issue I had was the a delay when extruding and ooze after stopping even with reverse feed.
I played around with making some barrels out of brass. I believe that PLA has a problem with sticking on the inside of the brass barrel. Also the inside drill hole in the barrel has to be very smooth. I ended up deciding the designed using an PTFE insert was a good design and purchased one.

The reason for the large extruder stepper motor was it was free, I also like direct drive rather than gears. I still have more of the smaller stepper motors that I used for the X , X, Z but don't think they have enough horse power for direct drive. The minus side is there is more mass to move. I currently use acceleration.
Re: Milled transparent extruder
September 19, 2011 06:13PM
I would say you are getting excellent grip on the ABS. Just make sure the stress is not on ending up on any other critical parts. Keep an eye on the plate with the screws to make sure it is not bulging.
A very clean design overall...nice job!
Re: Milled transparent extruder
September 29, 2011 07:18PM
I made some progress on the hot end :

The first vertical lathe I made was too high to drill the barrel, so I made a new one much more flat with a brushless motor from a laser printer :

The stainless steel rod was very hard to drill, I had to reshape a cobalt drill-bit with a dremel :
I also had to sharpen the drillbit several times during the drilling.
With the original shape, even if the drill was new, it just slide on the surface without removing any material.

Now I need to wind the heater and drill the tip to complete the extruder.
Re: Milled transparent extruder
September 30, 2011 08:42AM
I have done some work on Printing using Polycarbonate filament, as you have used PC on this extruder, you may be interested, the post is here

And my blog on it is here


Re: Milled transparent extruder
September 30, 2011 04:11PM
Some temperature measurement :

The heating wire is a kapton insulated alumel wire from a K thermocouple.
The result are even better than I expected, with the heater at 7V (I=1,3A) the temperature of the tip rise up to 250°C, and the entrance of the hotend does not rise above 50°C with the fan turned off.
With the fan at 6V (low speed) the entrance fall below 30°C.
I pushed it to 400°C, the entrance was only 61°C with the fan turned off and 31°C with the fan at 6V.

I also extruded some ABS and PLA by hand without any issues.
Re: Milled transparent extruder
November 14, 2011 12:11PM
I improved the extruder, it is now more compact, and the most important: way more reliable, the previous design was constantly clogging up.

Re: Milled transparent extruder
December 07, 2011 05:17PM
Hi Petrus,
Nice work. I feel your pain in having to drill through stainless! smiling smiley I wouldn't have tackled a shaft as long as you manged to drill through though! I eventually found the best approach to drilling stainless was lots of pressure and low speed, no lubricant. Just get the drill to bite in and keep the pressure on as it peeled away.

What I wanted to mention was that my little experimenting with a stainless insulator concluded that the best tweak by far I made was actually narrowing the neck of the tube, just above the heater, removing the thread and part of the shaft, to reduce the cross-sectional area of the tube. You could do this with in a lathe, or just with a small grinding wheel in a Dremel. This have a termendous impact on how the flow rate of heat up the tube. It creates a bottleneck. It helps greatly keep the heat where you want it, rather than having to expend energy cooling it after it migrates up the tube.

Hope this helps. Best of luck with your design and printing.

Re: Milled transparent extruder
December 10, 2011 08:22AM
Thanks for the tip, I will do that the next time I take apart my extruder.
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