Monday, November 23, 2009

Quick Ideas: Extruder Innovation

Problems within current “RepRap” designs
IMHO, some of the current designs have lost "consistency"

Maybe because it’s an “open” project? or
Maybe its trying to do everything without any constraints?

ATM many users are using 3mm diameter feed stock filament. Many are outputting finished material via the nozzle out to the build material in the area of 2mm or less. Some of the advanced users from my reading are using various methods to achieve the 1mm finished product output.

One such method used is to stretch the output material to achieve
1mm finished product. IMHO, consistency is lost in the process.

If users are moving in the direction to process smaller, and smaller output via the nozzle hole pre treatment, or more detailed preparation of the filament before hand to make higher quality output is needed.

The consistency fix?
My thinking atm is that consistency of build quality is being achieved and processed, within the extruder (whatever type used). What would be much, much better is to achieve the consistency at the feedstock or filament level. Eliminate the variations at the nozzle output to build level. Thereby eliminate the pressure within the extruder design. Why try and squeeze 3mm feed filament in and try and out put “finished” at 1mm? Pre-process the 3mm and re-spool the filament into a standard 1mm feedstock to the extruder head. That’s a 3>1 reduction making a lighter less stressed and consistent quality extruder.

Other benefits:
Use up dead space within “RepRap” designs.
Make available different colors and kinds of material at a twist of a knob. (have a design to put yet to paper)
Recycle I love the idea of using plastics around the house and recycle them into something else that can be used. Saw somewhere a device to take strips of soda bottles and feed it into the extruder, great idea! Ok this is design is done, now take this concept and add my idea and you have trash to 1mm feedstock ready to be used when needed.

I have about a half a dozen other ideas building off this simple concept and am sure this will open up some new doors to innovation.


  1. not sure you'd be able to apply enough pressure to 1mm filament.. molten plastic has a viscosity similar to cold honey (as long as we keep it below discolouration temperature anyway), so it requires a significant amount of force to ram it through a ~0.5mm hole.

    If you want to go this route, construct your extruder so it only heats the outer layer of plastic for adhesion, and then you will need to work out a way to cut the filament when you stop extruding. The code is already available in the form of the blocker solenoid stuff - affix a blade instead

  2. Thanks for the input I will look at it.

  3. Most of the filiment outputs are 0.5mm range. Nophead is stretching this to 0.3mm You push 3mm rod in, but once it's melted (as is needed to get a good weld), it's just a viscous liquid. It's then _extruded_ out a 0.5mm or 0.3mm hole to get the output filiment. Going to something smaller than 3mm input rod, you run into mechanical problems as you need to keep the input rod stiff enough to apply pressure to the melt in the extruder head. If you go larger than 3mm, you begin to run into hydraulic amplification degrading your feed accuracy.

  4. Exactly as AdShea said.

    You need a given amount of pressure in your melt chamber. The force on the filament is proportional to the cross sectional area of the filament, ie: d^2.

    There's a force above which the filament buckles, and then jams. Stiffness goes up with d^4, and buckling force varies approximately with stiffness.

    So, max pressure is proportional to d^4/d^2 = d^2, assuming that your feed mechanism can supply enough force.

    If you drop the input to 1mm, you can only achieve 1/9th as much feed pressure, so your ultimate max extrusion rate is 1/9th as great.

  5. At the moment, extrusion pressure isn't limited by buckling, but with 1mm feedstock, I think it would be.

    Also, I can't see why 1mm feedstock would be more consistent that 3mm feedstock.