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Mendel Prusa Easy Hot End

Posted by jcabrer 
Mendel Prusa Easy Hot End
March 09, 2011 03:47AM
I'm really pleased with the Prusa design. By my estimate, there's about 75 fewer parts than Mendel. I've included pictures of the build so far, and of the experimental nozzle I'm working on, made from a brass air hose coupling and mig welder tip, which is copper.
open | download - IMG_0115.JPG (229.4 KB)
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Re: Mendel Prusa Easy Hot End
March 10, 2011 09:41AM
Looks really good. I like the wrappings. Give it the "Look".

Where did you get your printed parts?
Re: Mendel Prusa Easy Hot End
March 10, 2011 10:32AM
Hi jcabrer

Can you describe your hot end please?

I am particularly interested in the interface between your hot end and the thermal break.

Is there any special machining involved?

Re: Mendel Prusa Easy Hot End
March 14, 2011 12:47AM
I used four set screws coming in from the sides to lock the Teflon rod in place. I don't know how well this works, but without any instructions on assembling the Wade's Extruder, I just did what seemed logical when I noticed the four holes there. I suspect that if the hot end get too, well, hot, then the nozzle may wander a bit while printing, but I haven't seen this happen yet in testing it out.

The hot end consists of four parts (top to bottom order):

1. 40cm x 1/2" Teflon rod, drilled out 3mm, with bottom end turned down to 8mm diameter. I just stuck it in the drill press and used a rasp file to do the job,

2. The brass coupling is a standard 1/4" air hose variety, but I threaded the inside of the small end to accept the MIG welder tips.

3. The MIG welder tip is threaded into the brass coupling, along with the Teflon rod, and then I drill the whole thing out 3mm (again for the Teflon), to about 0.5mm of the end of the MIG tip. What can I say? I'm very good with the drill press!

4. The aluminum block is nothing special. Just drilled out to fit snug on the end of the coupling (not the MIG tip), and split on one side to allow for tightening up a bit more.

If I can find my good camera, I'll take some close ups for ya.

Edited 1 time(s). Last edit at 03/14/2011 12:54AM by jcabrer.
Re: Mendel Prusa Easy Hot End
March 14, 2011 12:59AM
The parts were purchased on eBay from a seller called elderfarrer2hy7. With one minor exception, all the parts looked great. I didn;t like the rod couplings included so I made my own to give a bit more flex to the Z-Axis steppers.
Re: Mendel Prusa Easy Hot End
March 14, 2011 05:55AM
The insulator is normally attached to a Wade's extruder by pushing it into the base and then drilling through the small holes in the side and inserting two M3 bolts all the way through the insulator and the extruder block.

Re: Mendel Prusa Easy Hot End
March 18, 2011 03:05AM
Love the concept of this i started sourcing parts for this early this morning, however i had a class this afternoon and we are building a makerbot cupcake with the mk5 extruder. We needed to fix a couple of things so we took apart the hot end to replace the resistors and i was surprised how small the melting pot was. (roughly 2.25mm^3) Insanely small.

Given that information i dont know how a larger melting pot will react (more strings possibly) moving across open areas.

All of the abs inside the PTFE tube was un-effected by the radiant heat of the extruder all the way to the tip.

Might be something to think about.
Let us know how it works.


Edited 4 time(s). Last edit at 03/18/2011 05:00AM by xjcrawler01.

Mike Wheeler
Re: Mendel Prusa Easy Hot End
March 18, 2011 11:01AM
All of the metal in both designs will be at basically the same temp. So the molten plastic on the makerbot tip will extend up into the insulator, just like on the lincon electric tip.

Oh, wait. nevermind. I see what you're saying. The makerbot tip has a PTFE tube inside the hot metal barrel, and you're saying that keeps the plastic from melting until it gets way down at the end. I wonder if that's true or not. You say it was unaffected, how did you determine that? What temperature did it get up to? If it got hot enough to soften (but not quite actually melt) you'd still get about the same problems as if it was molten. PTFE doesn't conduct heat as well as metals do, but even so I'd think it'd get hot enough to melt the plastic inside it unless it's actively cooled.

There's an idea for you. Replace the PTFE tube with a pair of nested tubes with water between them to conduct the heat away and keep the plastic cool until it gets all the way down to the end. Sealing them together properly at the bottom may be a problem, and you'd be relying on convection to take the heat away...

I'm building it with Baling Wire
Re: Mendel Prusa Easy Hot End
March 18, 2011 12:37PM
Yes - I think the plastic inside the PTFE tube must melt but it obviously does not deform since it is being held in shape by the tube. I would guess the inspection was only caried out once the hot end had cooled down, allowing the feedstock in the PTFE tube to harden in the shape it is being held in.

One way to determine this is to pull the feedstock out of the hot end and see whether it has deformed as a result of being pulled out. I would expect it to be somewhat streched.

It's not like the heat decides to remain in the melting pot. The PTFE tube is completely surrounded by hot metal so there is no place for the heat to go. I am sure the PTFE cannot act as an adequate insulator keeping the inside cool.
Re: Mendel Prusa Easy Hot End
March 18, 2011 04:00PM
Like an idiot i dident bring my camera or take any pictures. damn 20/20 hindsite

I would guess the inspection was only caried out once the hot end had cooled down, allowing the feedstock in the PTFE tube to harden in the shape it is being held in
Come to think of it you all might be right i remeber seeing the groves in the abs from the gear on the extruder and they started to melt into each other about 1" from the tip. that is just about where the heaterblock starts. so ignore that other post eye rolling smiley
I dident even consider that it being could and would be reformed exactly to the same size as the PTFE tube. Without measuring you would never know that it changed states a back.
Re: Mendel Prusa Easy Hot End
April 20, 2011 10:38AM
There is a manual for the wades extruder here: [garyhodgson.com]
Re: Mendel Prusa Easy Hot End
April 23, 2011 07:10PM
Yes. The melting pot need only be a big as you need for material to extrude out the end. Before that, it will be heated to varying degrees as it travels down the tube. The plastic coming out of the Wildseyed Simple Hot End is only about 165C when the aluminum block is at 200C.
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