Thanks for posting it here @zapins, interesting process!
@cgoflyn: It’s for a wax extruder. I’d think wax will be less hard to deal with than plastic.
here are some horsepower per diameter recommendations. 38 mm = 12 Hp but hey still depends on length and screw type (mixing, no compression, breaker mesh grid size)
well, all i can tell you about the motor is :
– once you have plastic in the barrel, it creates huge friction, no matter what.
– we ship extruders with standard 750 W and a 1:20 reducer, 3 Phase (inverter), it is just enough for less stressful applications
– it also depends on the quality you can archive, consider straighten out the barrel as well. our best tolerances we’ve managed to machine were about 0.1 mm
– the v4 team recently reported that 2 Kw is not enough for beams and so they added a 3Kw but couldn’t see much difference
– industrial screws with your size are used with 4 Kw + motors, i’ve visited a few factories and those screws operate on a pretty precise spec you just can’t do in the garage.
– you are not extruding high quality pellets! those flakes coming from the shredder are way harder to deal with.
– at the end you want twice the power you need 
and yes, it’s 0.3 on each side, we tried 0.5 and also 0.4 but it turns more heavy to turn and create too much film along the barrel, obviously. I just saw some recommendations about (see docs soon) this but it didn’t really work out well. you can be luck to get the screw and the barrel with a 0.1mm tolerance. over time things seem to move so we went for 0.3 which was way more easy to deal with. going for less was even worst. i guess the specs/numbers for extrusions depend of course on the materials used.
about the documents, let me check, will post them here tomorrow.
about the breaker plate : it’s recommended yes, but also, depends on what you want to make though, it can work without too.
about welding: yeah, depends of course on your structure. we’ve opted for TIG, it’s way faster after all
see you in a bit! i am really eager to see this beast working
g
The 1/3 motor is connected to a 20:1 gear reducer to knock the speed down from 1700 to 110 rpm. That should make the motor effectively 20x stronger because of the gear reduction. So it is as if I am using a 6 & 2/3 hp motor to turn the screw. Hopefully enough power?
So 0.3 mm on each side for a total of 0.6 mm if you include both gaps? That’s quite interesting. Larger than I had thought. Does the gap size change with the size of the screw or material being extruded? Or is it pretty constant across different setups?
True about welding pulling the barrel out of spec. The cylinder I’m starting with has thick walls, at least 1/4″ thick steel. Maybe a bit thicker. I’ll try keep welding to a minimum and use a mig to reduce heat input when welding the hopper on. I’ll be adding a thrust bearing at the back between the motor and the gear box to reduce backward pressure on the gears. The type of box I bought isn’t designed for massive amounts of back pressure.
Any idea about the necessity of a breaker plate? The commercial units all have them, but hobby DIY ones don’t seem to.
Do you think you could point me in the direction of the technical document threads? I’m finding it difficult to navigate this forum compared with other ones. It is set up in a strange way.
To melt out the PLA I had it in my burnout kiln which I had running with the propane on. I do not have a thermocouple on it yet but I believe it was around 1700 F. Ideal temperature for burning out is 2 hours at 900F but I haven’t set up the PID solenoid and thermocouple for the burners yet. I have the parts but just haven’t plugged it all in yet.
Why bronze? Because it is a good bearing material on steel so the lifespan will be long, it is easily poured, machined, repaired, has a similar expansion coefficient as steel so as it heats up it won’t bind in the tube, my foundry is a bronze foundry, and I had some extra bronze on hand. But it could have been made out of aluminum or cast iron as well. I just don’t usually cast those metals.
I was trying to figure out the tolerance it should be machined to. Basically what is the ideal gap between the screw and the wall? 1 thousandth? 2? 3?
wow very impressive work! Looking forward to see how it runs, why did you end up casting it in bronze?
Wow, thanks for posting, loved the video. Great use of 3D printing to build up a robust part. What temperature do you melt out the 3D print (PLA?)?
Thanks again.
Here is the hydraulic cylinder with band heaters attached. The far right side of the cylinder has been cut and a 2″ black pipe welded on. The end caps are simple black pipe end caps from the hardware store that can be cut into different shapes and hopefully will act as dies.
And one more pic of the up close final bronze casting. There are some small pits and defects which I could tig weld and repair if I wanted to, but I don’t believe the holes extend very far from the surface and so I doubt if they will structurally weaken the screw. Basically I don’t think they will affect the function of the screw at all and will become plugged with wax over time.
Here is a video of the casting of the screw.
A few more pics of the process. I’m hoping to have it finished and running in the next 2 or 3 months.
More pics of the process
Here are up close pictures of the final bronze casting. There are some small pits and defects which I could tig weld and repair if I wanted to, but I don’t believe the holes extend very far from the surface and so I doubt if they will structurally weaken the screw. The walls of the casting are 1/2″ thick silicon bronze so I don’t think the defects will affect the function of the screw at all and will become plugged with wax over time.
