Monday, August 02, 2010
No more melting extruders: Removing PTFE from the hot end
Just a quick and very sleepy post before bed.
I have a confession. My extruder works far less often than it's in a melty state of not-workingness. And this makes me sad. And causes me to spend unneccessarily on PTFE barriers, which invariably melt due to being in contact with a 240°C heater barrel, causing the extruder to irreparably jam. This is just silly, and I decided that I needed a new hot-end extruder design if I was going to go more than a few weeks without a catastrophic extruder failure.
At first I had a look at the new design for the MK5 extruder, but it still uses PTFE (though I'm told not as a structural component), and it looks to contain far more custom machined parts and thus will likely be far more expensive. Being a graduate student, I decided to think cheap, and see what I could do with the parts I had. Recently, an all-steel hot end was put up on Thingiverse ( http://www.thingiverse.com/thing:3452 ) that looked very promising, but I didn't have much luck trying to drill a very accurate 3.2mm hole down the middle of an M6 steel bolt.
In the end, after some tinkering and chatting with my Dad, we settled on an all-metal hot end based on the parts that we had available. We used the existing MK4 hot end parts, and similar to lampmaker's all-steel hot end, we 1) reduced the nozzle to half height to reduce the length of the hot zone, and 2) added a thermal break in the brass heater barrel. We constructed some heat sink plates out of aluminum, and tapped these plates to M6 to encourage a good thermal contact between the barrel and the fins. A couple of small fans were also added, as in lampmaker's all-steel hot end design, to cool the fins.
Because the force of the fans was so great, and because this is new extruder was to be used on the simple and inexpensive acrylic makerbot-clone with a heated build table and chamber, we added in a small baffle to prevent the fans from cooling the print itself, and instead direct the air flow upwards.
We completed the design Saturday night, and so far after about 5 hours of printing, the hot end has performed virtually flawlessly. Because this design uses parts that people with already-clogged MK4 extruders will likely have on hand (except for the aluminum), and because you could conceivably make this with very simple tools, this design might be a great solution to either fix your currently broken hot end, or to experiment with an inexpensive, alternative hot-end design that you should be able to increase the temperature on to encourage a pretty good flow.
(click to enlarge)
happy tinkering! :) i hope this helps!