A deck screw extruder

deck

A lot of great ideas happen in the middle of the night, and for [Werner] it’s no different. One night he came up with an idea for a new 3D printer extruder, and after a very basic prototype, we’d have to say he might be on to something. It’s basically a deck screw acting as a worm gear to drive filament, but this simple idea has a lot of really cool advantages.

There are two really interesting features of this extruder, should [Werner] ever decide to flesh out his idea into a real prototype. First, the stepper motor for this extruder can be extremely small and mounted directly above the extruder. This opens up the doors to easily creating multi-extrusion printers that can handle more than one filament. Secondly, using a deck screw as a worm gear means there is a huge area of contact between the plastic filament and the driver gear.

Whereas the usual extruder setup only makes contact with the plastic filament along one or two splines of a hobbed bolt, [Werner]‘s design drives the filament along the entire length of the deck screw worm gear. This could easily translate into much more accurate extrusion without all the fiddling around with springs and hobbed bolts today’s extruders have.

In any event, it’s a very interesting idea, and we’d love to see [Werner] or someone else make a functioning extruder with this design.

Comments

  1. Screw-driven extruders are older than dirt. We all laugh at (what used to be) BFB because they still use them. The problem with them is that they’re no good for fast reversal to prevent ooze.

    • ge0griff says:

      What if you had two screw drives 180 degrees opposite each other? They both turn the same direction, but only one is applying force depending on direction.

      • Dax says:

        Screw drives work by biting into the filament. If both are biting and one isn’t turning, the filament isn’t going anywhere. If both are not biting, you need a mechanism to select which one is, which would make the system complex and failure prone.

        • ge0griff says:

          What I meant was that both screws are spinning the same direction. One pushing, the other pulling. When it reverses, they switch directions and roles.

          • SavannahLion says:

            Given that such an arrangement would cause both screws to “bite” into the filament in the same way, the whole pulling/pushing bit would be rendered moot. Might as well have both motors on the same side or even a geared system to do the work.

            From the suggestion, it sounds like you’re thinking of backlash which is caused by slight gaps between mating gears. Since the worm gear (the screw) creates its own mating channel in the filament, I would imagine backlash would be non-existent.

      • There’s no reason a regular screw drive can’t be reversed (though it does increase the potential for problems). It’s the *fast* reversal part that doesn’t work. Any reversal would be too slow to completely stop ooze, and the reversal step would take long enough to both noticeably slow down the print and cause artifacts due to the hot nozzle dwelling on the plastic. Pinch-wheel extruders using geared-down brushed DC motors instead of steppers have similar issues.

    • Brooks says:

      That doesn’t seem that hard to fix (I say, having never worked with an extruder) — how much reversal distance do you need?

      What you can do for a fast reversal is simply pull back on the screw. It should be reasonably simple to give the screw a half-inch or so of fore-and-aft travel, and put in a second motor (or even maybe use a solenoid?) to do that motion. … as I see t-bone has already suggested below.

      • @Brooks,

        Depending on hot end design, you need anywhere from a few tenths of a millimeter to a few millimeters. You could move the whole drive mechanism back, but that would require another actuator. It would have to be a pretty strong actuator too (I say, having spent the last four years designing, building, and operating 3d printers, and having a couple of extruder designs under my belt, including the one from which the extruders on the majority of the printers in MAKE’s upcoming 3d printer guide are derived), and would require enough support circuitry and enough weight on the toolhead to make all of the potential benefits to the size and cost of the extruder a wash (at best).

        I’ve come back to the possibility of using various types of worm drive (of which a screw extruder is one) several times, and always come to the conclusion that it’s relatively low efficiency is too high a price to pay for the advantages of the high torque gain in a small package as long as faster moves are still required for some functions.

        • Dax says:

          how about using a sparser thread?

          Less force, more speed.

          • Worm gears (this is essentially a rack-and-worm drive, whereas the pinch-wheel designs that replaced them are rack-and-pinion, the rack being the straight(ish) filament with teeth being cut into it by the drive mechanism) have a huge efficiency loss (torque output is less than the mathematical product of input torque and gear ratio) compared to achieving the same equivalent gear ratio using any type of unequal gear/pulley/wheel system, and this inefficiency increases when the worm has a longer lead. Combined with the lower effective gear ratio, what this means is that you end up needing a bigger, more torquey motor on the input to achieve sufficient torque than you would with a (more efficient) pinch-wheel design with appropriate gearing.

        • draeath says:

          How about you put springs on the thing and pull cables to pull the extruder against the springs? Then, to adjust the extruder location (pull forward or back) you just vary the tension on the cables. Kind of like bicycle brakes.

  2. Taylor says:

    This is brilliant. It has so much surface area to grab

  3. 0xfred says:

    Wouldn’t the contact between the screw and the filament cause the filament to get twisted up before the extruder? I didn’t see any evidence of this in the video, but it seems likely to happen.

  4. Salokcin says:

    Look at the comments on the YouTube link. Many people already have made a functioning extruder using this “design” (a screw, but not a deck screw). So he took someone else’s working design and replaced a nicely machined part with a $0.01 deck screw. Cool.

  5. ok boss says:

    Don’t you love with when already working design is being used by someone well known to claim. This lead screw design for extruding is atleast 2 years old. Seen it multiple times on reprap.org

  6. BiOzZ says:

    how thick is your drywall? XDD

  7. Mh sounds intereseting, i hope there will be a prototype!

  8. t-bone says:

    He probably got the idea while tightening a hose clamp, unless he’s already made an auger feeder for his cat.

    Now to make it into a little bendix motor somehow, where a solenoid pops the screw in and out.

  9. One other unmentioned problem on this old idea, it twists the filament in such a way that your filament holder has to rotate on 2 axes to keep the filament from breaking/twisting.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 92,295 other followers