Geometry of nozzle

I have nearly got my Prusa up and running and am now making a hot end for the Wade's extruder, but I haven't seen anything on the geometry of the nozzle. Should the nozzle have a flat tip? If so, what diameter? Maybe it would be better convex - and here again, what raduis?

Thanks for any info you can give,

Mike

I think it should be flat from the hole out to a diameter a little bigger than the maximum filament width you want to extrude, and then should taper to roughly match the drill cone inside.

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I believe the tip should be close to flat, as a rounded tip decreases heat retention near the tip. You don't want the plastic to be cooling/changing temperature before it has completely extruded.

Thankyou Nophead and Marnargulus - I apologise for not replying sooner but my employers have been keeping me busy.

While I am waiting for a delivery of ABS and PLA filament, I have been trying to build a hot end with rapidly replacable nozzles; the present design has a silver steel nozzle clamped in a purpose made heatsink. this seems to work quite well and the cold end of the steel nozzle maintains about 36 degrees when the tip is at 300 degrees.I have managed to push 1.75mm ABS filament through this nozzle which has a 0.26mm hole 3.5mm deep



I have started on Mk2 of this design based on what I have found and the heater block will have a single support post and will be a push fit on the nozzle - the present nozzle is screwed into the hot block. I have found the a surprising ammount of heat is conveyed to the heatsink by convection so am insulator made of cuttlefish bone will be put between the hot block and the heatsink.

Mike

I also tried different nozzle tips. Once during a build of slightly taller objects, the nozzle started to drag around my objects untill they came off the bed (that is a heated bed which normally sticks very well). I guess it was because the nozzle tip was too flat, probably more width than the planned extrusion width, and started to hang in the adiacent depositions.
I find it hard to make a flat tip for two reasons: the width is hard to fit (especially that it may vary a little), and also the perpendicularity of the flat plane is hard to achieve - at least for me with simpler DIY tools. In the end, I find it best if the nozzle is just sharp, as it is easier to achieve and somewhat safer. I also find the flatness of top layer to be nice with sharp tip, in fact it never came to me that it might be an issue like that. I guess most of the filament width is still flattened by the tip during travel, and sides are just more tempted to stick to the others or fall to gravity, or something like that.

What i did found in a nozzle build similar to your, is that inside the block, the top thread and the nozzle lower thread have to match perfectly. If they dont, they leave a wider gap and it will create a pocket of air (i seen it while disasembling the block with the melted plastic inside and a big air bubble to one side). And that air doesnt like to go downwards, hence it will be something like an air pocket inside a water tank of plumbing - that is will try to equalize the pressure, hence it will give tones of more ooze and will also have problems if extruder needs to start extrude fast at top speed. Maybe it could give some bubbles also if at least some air parts get trapped.

So basically, i would advise to make sure that from the top entrance of the block, till exit, the plastic will basically travel inside a single cylinder which has the width as close match to filament width, not too big/wide at any point. For minimal ooze and proper response time, etc.

Good luck!

Edited 2 time(s). Last edit at 09/09/2011 07:14AM by NoobMan.