jhertzberg

I like your idea, but make sure you either take retraction into account, or consider a needle valve or shutter to stop flow when necessary. I would love to see some friction feed ideas that don't rely on a hobbed bolt. Can you make your increments both small enough to avoid visible pulsing artifacts, and fast enough to print quickly?

Regarding using a rotating wire in a tube (bowden cable) to get mechanical energy to the head, chopmeister tried it and had no success. See http://umforum.ultimaker.com/index.php?/topic/2544-small-steppermotor-for-direct-extruder/?hl=hysteresis#entry18161. I have been playing around with the idea of constraining a loop of beaded chain under tension in a pair of PFTE bowden tubes with beaded chain pulleys wed to gears, within a housing, at either end. I previously built an articulated arm, attached to the head and the back of the frame, with a pair of pulleys bringing power to the head from a motor on the frame, but still don't have that working satisfactorily.

Glad we could help. The topic of bed adhesion is inexact and evolving. I just saw the following thread http://umforum.ultimaker.com/index.php?/topic/3016-while-waiting-for-the-heated-bed-printing-on-glass/

If your tape is lifting off, you may have to strip your old tape off, and clean the acrylic bed with isopropyl alcohol before putting fresh tape down. You do this in order to clean any old adhesive and bits of dust off the acrylic, to ensure maximum adhesion. Make sure that the isopropyl alcohol has evaporated off of the acrylic bed before putting down the new tape, and as gr5 said, use the widest tape you can find. I use 48mm wide 3M Scotch-Blue Painters Tape for Delicate Surfaces since it has a smoother surface for smooth bottoms. Make sure that the tape is down firmly. Eliminate all bubbles. I use an Exacto knife to lightly score the tape to let the air out of any remaining bubbles, because you don't want to give lifting a place to start. I mentioned UHU brand glue stick, but other polystyrene glue sticks would probably work as well. You can try a thin coat where the corners will be later printed. I have not used this for PLA prints, but have done so when printing Nylon directly on my acrylic bed (no tape). Other people have used a light brushing of cyanoacrylate glue (super glue) where the corners will print, but I am a little nervous about that. Regarding putting the UM in a heated chamber, I can't say for sure, but in addition to the control electronics underneath, in the long run you may also need to cool the motors, and the amplifier board at the hot end. You will also need to replace any PLA printed add-on parts such as belt tensioners and fancy fan cowls with versions printed in ABS or Nylon. If you are keen on doing this (and I would not be), then look into the kinds of water cooling kits that PC overclockers use.

A few things you could try first: Rotate your design to not be at 45 deg to the bed, to change the fill pattern orientation in relationship to the corners of your design. This will alter the direction of shrink forces. Turn on brim (in the Platform adhesion type dropdown). You can make the brim as wide as you need by increasing the Brim line amount in the expert settings. Brim trims away easily. Clean your blue tape with Isopropyl Alcohol. Rub a thin layer of glue stick onto the bed (UHU brand is frequently mentioned.)

Yes, I'm trying to get away from the plunger entirely. I don't want to drag around 60cc of material that may be as heavy as precious metal clay, and I want a more continuous printing process than syringes would allow. I do like the idea of using two bike bowden cable housings to constrain wire drive cables! I plan on feeding the paste to the head through tubing under pressure, but I want to finely control the feed rate with a small moineau pump on the head, and a wire drive would turn the rotor rather nicely. That's so much easier to provision, build and maintain than the Rube Goldberg contraption that I was coming up with. Thank you! I apologise for hijacking isphoarding90's thread, but it seems that your solution may serve him as well. Only one question: How would one best cleanly splice the wire (or synchromesh cable) into a closed loop after feeding it through the compressionless tubes?

Thanks, chopmeister, for confirming my worry regarding flexshafts. My reason for exploring direct extruders is to come up with a more elegant design for paste extrusion than all of those designs where filament is used to push a syringe plunger or whatnot. Another design that I have been mulling would be to: mount the extruder motor at the top-right-rear above the case, which drives a splined shaft running right-rear to right-front, which drives bevel gears mounted on the right y sliding block which drives a second splined shaft mounted onto and above the y sliding blocks, crossing above the head, which drives an extruder assembly mounted on the head. I figure that that even when well lubricated, this assembly adds enough carriage weight and friction that I wouldn't want to even try this without first switching to snowygrouch's direct drive mod. An alternative to splined shafts would be square rods with captured square linear bearings, except that square linear bearings are so expensive in comparison to splined shafts.

I meant the bowden tube specifically. I wouldn't want a bowden adding any friction to retraction if the drive motor was downsized severely, so something with at least a 4mm ID would be a minimum. For the electronics, a lightweight sleeve or coil that stays out of the way seems sufficient. If the extruder gearing is on the head, it may make filament swaps easier to separate the electronics from the filament, or just feed the filament naked to the head. What do you think of using a flexi-shaft to transmit mechanical energy from a motor mounted on the frame to the head? Do you think that given the torque and low speed that there would be much hysteresis or backlash? There was a RepRap forum thread on this, but it petered out inconclusively, and someone posted a rough design in Feb 2011 as http://www.thingiverse.com/thing:6653 Under the "so crazy it just might work" category, I wish I had the parts to try a sliding square shaft like here http://garyhodgson.com/reprap/2012/01/experimental-off-carriage-extruder-motor/ but with the extruder motor mounted behind a pivot at the right rear corner, the shaft cantilevered in front of the pivot, and the sliding shaft coupler on the head similarly able to pivot. The coupler could potentially bind, but the arc is less than 90 degrees, so perhaps not.

illuminarti, what does a tube do for you in this case? It seems that the primary problem with a head mounted extruder is the aggregate weight of the motor and the gearing, and of the two, the motor weight is the more difficult to reduce. I wonder about the possibility of using either a flexible drive shaft or a sliding square rod to connect a rear mounted stepper to extruder gearing on the head.

When I first assembled my Ultimaker, I got very noticeable banding at a 3mm interval from a lead screw imperfection pulling the platform back and forth to the limit that the smooth rods allowed. I reduced the banding somewhat by disassembling the nut box and sanding it to hold the nut more loosely. The banding is greatly reduced, but not always eliminated. I'm thinking of taking it all apart again, sanding a bit more, and putting some teflon tape on the rubbing surfaces to allow the nut to float more freely. Has anyone tried any lubrication to allow the nut to laterally move more freely?

I have installed a second extruder motor to push paste. For the stepper driver I went with a standard Pololu A4988, and added a heat sink to it. I had to cut away some of the origami cooling duct and loosen the screws a bit to get the electronics cover back on over the new stepper driver and heat sink. Now I assume I have to rebuild the Marlin firmware to make it aware of the second extruder. Are there any code changes aside from changing #define EXTRUDERS in Configuration.h to 2? Given that this is for a paste extruder, do I need to do anything to tell the firmware and the UltiController not to bother with checking for a hot end temp? I assume that illuminarti's write-up here (http://umforum.ultimaker.com/index.php?/topic/2026-how-to-build-your-own-marlin/) is the best and latest build instruction, right?

Regarding your bowden tube fix. I recommend Owen's bowden clamp (http://www.thingiverse.com/thing:11864). It cured slipping for me.

Thank you Owen. I just looked at the thread. (I've got to remember to keep checking the Google Groups threads, as well as here, for these tips.) I do think that the answer Taylor provided is not quite right, though. He links to JSX-XH 2S connectors, which are 3 pin. Jelle's comment set me on the right path. It looks like the 4 pin JSX-XH 3S connectors are the right ones.

Does anyone know the specification of the JST connector for the motors, and a supplier in North America? The motor I have has bare wires. Going on Ebay, I am finding a confusing plethora of 4-way JST connectors, none looking quite like the ones on the stock UM motors.

Hello Daid, Are there any special problems with adding a second extruder with an unheated extrusion head? I am building a paste extruder, similar to http://www.thingiverse.com/thing:25195 but with flexible tubing to transport the paste to a syringe tip on the extrusion head, like a bowden tube. I am picking up a Pololu A4988, Black Edition, and a SOYO SY42STH47-1504A motor, but I don't know if Cura and/or the Ulticontroller will need any tweaking to work without a heater or thermocouple associated with extruder #2 connected to the Ultimaker PCB (v1.5.6). Do you have any concerns with my choice of driver or motor? Thanks, Jeff

Not totally clear, but perhaps Taulman 645 nylon may be interesting to you.

Thanks illuminarti. I took another pass at the mechanical: I again pulled out the threaded rod and Resiliert coupling, and checked if there was any bend/wobble in the rod and the motor shaft. Though the rod is straight, there is either an imperceptible bend in the motor shaft, or the the coupling is not holding the rod true center, such that a wobble is amplified up the rod, detected by running the z screw up and down with my finger lightly against it. I further loosened the nut capture to reduce the rod wobble pull against the z axis rods. The right hand "after" print in the photo below is from after loosening the nut capture, in comparison the the "before" print. I printed the "before" single walled at 50mm/s and 0.15mm layer height. I printed the "after" single walled at 20mm/s and 0.08mm layer height. I'm pretty happy with the result, and I'll just keep in mind that if I get unacceptable striping I'll just slow it down and print in smaller layer heights. Thanks again for the info. -Jeff

I'm dealing with this too, and there are a few other discussion threads with the same issue. So far, I have torn down the z stage, and sanded the nut capture to stop it from binding the nut in place, re-lubricated threaded rod and the 12mm shafts, and checked that the Resiliert coupling is evenly tight to the motor and the rod. Now, the nut capture is no longer tightly bound in place, but it is not so loose that it floats freely. The two left items in the photo below were printed before the teardown, the three right hand items are from after. There is not much difference. The single walled cylinder on the far right was Jorised, and I see that the defect does not spiral upward, but stays at the same positions (every 3mm) as the un-Jorised cylinder next to it. How loose should the nut be in the capture? Is it conclusive that the problem is z axis wobble? Or, could this be from the z motor missing a step at the same point in each full rotation, causing the layer's material to be deposited in a relatively smaller vertical space? I ask because the cylinders in the photo below were 50mm, as designed in SketchUp, yet they measure 49.75mm on my digital calipers. A single step on a NEMA 17 motor attached to a threaded rod with a 3mm thread distance would lower the platform 0.015mm (200 steps per rotation) and a 50mm high print requires 16.6... rotations, and 0.015mm x 16.6... = 0.25mm, exactly the shortfall on my print! -Jeff

I'm dealing with the same issue. Take a look at the following thread for more info: http://umforum.ultimaker.com/index.php?/topic/198-lines-in-z-height/