Playing around with some hob cutting techniques, getting some very pretty results. @Joshua_Rowley
5mm inside bore?
Yup - for these prototypes at least.
I wonder if there will be some more cold end work coming from team e3d…
Why does a cold end and a hotend have to be two discrete separate items?
well you still need a hot zone and a cold zone eh
What kind of cutter are you using? A tap?
if i had to guess they use a cutting disk and increment the hob
@Sanjay_Mortimer Have you passed your eyes over any soon to be expiring stratasys patents lately by chance? I’m really keen to see someone use a much smaller stepper like a Nema 8 or Nema 11 with a worm drive to drive a hobbed pulley. This seems to be what the commercial fdm machines use.
@Tim_Rastall worms have been tried by community members, but all the ones I’m aware of have been abandoned due to the really low efficiency of worm gear torque transmission and the high step rates making rapid reversal difficult.
@Whosa_whatsis fair enough, any examples you can point to? Has the small motor idea been discounted then too? I recall the UP! uses a nema 11…
I believe it’s a Nema 14. It’s also a pretty small-diameter drive gear, which increases the force for a given torque.
I know at least one design using a printed worm and gear was lost when the designer decided to remove all of his stuff from thingiverse (for the usual reasons). Here are some others:
http://builders.reprap.org/2009/01/feeding-abs-with-worm-gears-and.html
@Whosa_whatsis
Ah, yep. Nema 14 it is on the UP!, Worth noting it’s direct drive.
I’d seen nopheads worm extruder in the past but I’m imagining something with a mK8 sized hobbed pulley or even smaller, being as you’re not limited by the nema drive shaft diameter. It also looks like he was on the inefficient end of the bell curve for worm drives in his tests.
Anyway, discounting worm drives , I hope you’ll humour me while I explain my thoughts in greater depth:
Big steppers like nema14s can rotate much faster than is necessary to feed filament (under normal circumstances) correct?Assuming this is correct, a smaller stepper with appropriate gearing should do the job. So, if you establish a maximum required feedrate (probably for retraction purposes) and a minimum torque value (for a predetermined material/temp/speed worst case scenario) you should be able to establish the optimum combination of motor and gearing ratio. What I’m suggesting is that if you have good quality metal gears and have done the maths, a smaller lighter stepper than usual might be achievable,
On my direct-drive extruders, I run the motors at the maximum step rate that Marlin can achieve for retraction. My (planetary) geared extruders skip if I try to move them at the same step rate (a lower speed in mm/s), even though they have much higher torque, due to efficiency losses in the gearbox, and that’s with planetary gearing. A worm gear would be much worse.
So, what sort of mm/s does that equate to? Does it need to be that fast? Or to put it another way, is their empirical evidence to support that maximum retract speed? Im just trying to understand the edges of what’s known btw.
When you retract, you always want to do so as fast as possible to remove pressure before plastic can escape (though as it turns out, the same is not true of recovering from reversal). This is particularly true for bowden extruders.
Marlin’s maximum step frequency is 40000 steps/second. For the steps/mm on direct-drive extruder, that comes out to about 170mm/s or 10200mm/min. Significantly slower retraction results in slight blobbing plastic where the retraction occurs due to pressure continuing to push plastic out of the nozzle before it can be zeroed by retraction, and a worse (and more noticeable, in my empirical experience) is an insufficient amount of plastic on restart because that extra extruded plastic is missing. It is possible to compensate for this with extra length on restart, but that results in too much plastic being extruded, and can lead to more blobs, especially on prints with a lot of small gaps to fill (particularly with Slic3r’s poor path planning, which results in more starts and stops than necessary).
@Whosa_whatsis i thought you might say that 
Although, from my own (less comprehensive) experience I’ve not seen a great difference between 120mm/s retracts and 160mm/s from a blobbing and re-prime perspective and I’ve been printing a lot of nylon recently with a long bowden tube… I assume there’s a point where there’s no benefit in retracting any faster…; retraction relieves back pressure, therefore minimizing ooze right? But the rate at which the plastic oozes isn’t just defined by the back pressure but by gravity and viscosity and nozzle diameter (I assume) so even with infinitely fast retracts, you’re still going to get ooze due to gravity and outgassing (?). So, on this basis I’m guessing increases in retract speed become increasingly less useful past a certain point.
I posted some pictures of the inside of my Stratasys print head a while back. https://plus.google.com/112079438186671979082/posts/foX4MfwYD64
We use a worm gear on our cartesio, with the smallest nema17 motor and the larger Mk7 drivegear.
We use the nema17 because it also holds our electronics.
steps/mm: 2533
Max retract speed is 10mm/sec.
With a 0,5mm nozzle the max print speed is 250mm/sec
For more info see:
http://mauk.cc/mediawiki/index.php/Dual_extruder
@Jos_Scheepers You may have your slicer set for printing at 250mm/s, but with that many steps/mm, you’d have to print extremely thin layers to keep your printing speed from being reduced by the maximum speed of the extruder. If you tell the printer to move any of the axes faster than its max feedrate (or at more than the firmware’s maximum step frequency), it silently reduces the speed. I ran into this problem running a 14:1 geared extruder at 1/32 microsteps, and we’re now running them at 1/8 to avoid this.