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Whot end? Alternative extruder mount design

Posted by Wauter 
Whot end? Alternative extruder mount design
September 20, 2011 06:57AM
First of all, hi everyone. I'm pretty new here, have been reading a lot here and this is one of my first posts.

I have ordered/found almost all of the parts required to build a prusa mendel and am waiting for everything to arrive. The hot end I will be making myself.

I've been working on a different method to mount the heater & barrel to each other and to the extruder, by means of a aluminum cylinder and screws to clamp heater and barrel in the center of the cylinder. I've put the idea up on the wiki:
Whot end

I hope to test it soon, but in the meanwhile, What do you think of this idea?
What would be the caveats to this mounting method?

I mainly want to discuss the mechanical mount. I included some thoughts on barrel length and cooling on the wiki page, but that is just me thinking out loud, I'll read a bit more on that topic first (as I've seen some HEATED discussions on that here.. smiling smiley. I will start of building a pretty standard wire heater with standard length PTFE barrel first and start experimenting with different barrel configurations from there. I think this mount system should really facilitate that.

Anyway, tell me what you think

Re: Whot end? Alternative extruder mount design
September 20, 2011 07:22AM

Always nice to see new ideas bouncing around. smiling smiley

My first concern would be whether the screws/pins holding the heater barrel would be strong enough to handle the vertical force exerted by the extruder? I guess if the pins are quite deep in the barrel it should hold, but there will definitely be some force, both up and down from the extrusion and retraction.

Looking forward to seeing it in action when you get your build up and running.


garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net
Re: Whot end? Alternative extruder mount design
September 20, 2011 08:51AM
If "heated discussions" on another thread means what i am thinking about, then i would probably be responsible by at least a part of that, so have my apologies to you for that. I just felt insulted and i do know at least 2 others better than me in reprap felt the same, so i think that is what happened at least about me, if any explanations are required.

About mounting, i had 2 grooves on my thermal barrier pieces, one on top and one like 1,5cm from block.
First i was using a "axis safety ring" (dunno the right name), on the top groove, to stop the ptfe slide down. It was on the cold side of the ptfe so i didnt worried much about deforming. Only that when heating, the long ptfe had a big dilatation so the Z height had to be adjusted when coldhot.

Now i am trying a pretty brute force thingy like some sort of teeths gripping in the lower groove. Its somehow nice that i can unscrew and screw the block without ptfe rotating, because the teeths wont let it slip nor radial nor axial. I dont know about deforming in this case thought, will have to see, its more probable as that joint is typically slightly hotter than the cold end.

A third way i thought about but couldnt put in practice, would be fairly close to your method. To have 2 x M3 stainless steel threaded rods like ~7-8 cm long passing through block and being hold in place by thermal barriers mounted on the 2 vertical screws each side (the M4 ones that come down from the extruder plastic body mount). The SS should have both less temp coef and a fairly good resistance, its common for manufacturers to tamper with normal steel recipes but at SS there is nothing that can be changed, so SS is always as it should be - good.


In the picture you can see one of the M3 threads in the last block i made, i just didnt had the long ss screws to put in there yet. I had to reduce the width of block in the area only because i couldnt find an M3 tap that passes through completely, so that is the max thread depth my m3 tap can do. I am not worried too much about thermal issues (there will be flat thermal barriers at the end of screws), but more worried like if the two M3 screws that long will hold the block in place properly or not when extruding. If using M3 SS threads (or long screws) will prove to work, i think it just might be best way to do it, since the stress in the ptfe will be minimal - hence long life, and the differences in Z heigh wont depend on temperature so much. Which i believe would be advantages on your mount type.

About your mount with 3 screws "needlepoint" (is that correct word?), would be nice to see it in practice. I just cant think of how those 3 screws would fit to carriage afterwards. Also the block should expand at temperatures, which means it might just push the screws off a little, in extremis could make them unscrew. Also the block in the machine will be subject to vibrations from all the "giggling" around the machine does, and if the screw points are sharp, the block material might deform itself and make some ridges around the sharp points which will give it some play, sooner or later. This will be increased by the fact that probably the screw material will be SS probably and the block material will be softer, like alu or brass. Well this is my point of view and i can also see lots of downsizes like these in any other of my own approaches, so dont let these defuse you.

I would be also very much interested in a good reliable way to make support for block itself instead of ptfe, so if you do take things forward, pls post.

Cheers and good luck!

Edited 1 time(s). Last edit at 09/20/2011 10:29AM by NoobMan.
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