#MakiBox A6 Weekend Update - Smooth Extrusion, Check!

2021-10-27 17:10 by Jonathan Buford (comments: 0)


Finally! Yes, finally, we have very smooth and strong output from the pellet extruder and can start the final integration into the Alpha units.We spent the last few weeks taking the last extruder design that had a reasonable output and tuning that up so that there is no binding up and that the output force is sufficient to extrude at a low enough temperature.


The output you see in these pictures is running at 220C according to our thermistor. It is nearly solidified at the time it leaves the extruder, so with a little longer extrusion barrel, we will have nice smooth and solid filament coming straight out. There are no air bubbles. Dimensionally, it is measuring at around 0.02mm tolerance, and it would be expected that will still improve if it is fully solidified before leaving the extruder. For reference, the tolerance on commercial grade printing filament is typically 0.10mm. However, we need this kind of tolerance to run 1mm filament through the system, since it is more sensitive to the diameter tolerance and less senstive to the output length tolerance.

The next step with this part of the system will be to design a final production extruder and then attach that to the feed tube. We then will hook up a hot end based on the same heater technology and should be ready to do test prints.

This was the significant gating problem for proceeding with wrapping up the rest of the MakiBox development, so now we will just be working our way through the final list of things that need to be wrapped up and are on the count down to shipping soon.

Thanks and have a good weekend.


maximpulse responded:
Congrats on all the progress coming together!

It IS amazing to see your solution in such a small package. Commercial extruders are the size of small locomotives.

And then to even imagine the possibility of the print head and the extruder as one part could someday shrink it all down again. Perhaps that isn't desirable, but the possibility is nice to be able to consider.

Thanks again for corresponding here on your blog.

maximpulse responded:
Is the clacking noise the gears slipping? 
And if so, is that on purpose so the gears won't jam and either burn out the motor or grind each other into dust?
And then, is it correct that the idea is that the feedback you are incorporating would come into play before such slippage occurred?
Jonathan Buford responded:

The clicking is the stepper missing steps when the torque is too low. It was running at about 1/4 speed, so if we double or triple the gear ratio we will have a slip free movement and still fast output. Since we are using a stepper, the upside is you can't burn it out the same way that a typical motor would if it is stalled. We will also try less microstepping, since that can have some impact on the performance.

Jonathan Buford responded:

Oh, just to confirm, the gears are not slipping.

maximpulse responded:
Thanks for the explanation. No slipping gears!
The clacking sounded so "wrong" it drew my attention.
Jonathan Buford responded:

Yep, I tried to minimize it for the demo, but we just need to increase the torque and that will fix it.

ipeerbhai responded:
Congrats! Getting pellet extrusion working is a hard problem, and solving it integrated into an affordable printer is quite the feat!

Question -- one of the problems in 3d printing is a soluable support. PVA is used, but it "melts" in air over time, making the filament hard to use in wet places ( like a garage in Seattle... ) Pellet may solve that, as storing pellets in a few sandwich bags with cat litter as dessicant is much easier than storing filament the same way. Could the system handle PVA extrusion as support material? A small enclosed space like the MakiBox would be good to control the cooling rate of plastic -- add in supported prints, and this would be killer.


Jonathan Buford responded:

Potentially, yes. I've not played with PVA yet, but that is the intended use case. Pellets are going to be easier to store to prevent moisture getting to it. Add a second extruder, and you would have an interesting combination.

Evan responded:
That's beautiful. Good to see the different colours too.

Regarding PVA extrusion - I'm guessing that any unused plastic (including the stuff that's been extruded but not printed) would have to be removed from the printer if it was going to be left idle for any reasonable length of time. Perhaps an alternative would be to just leave the printer hot permanently? With a well insulated shell, something the size of the Makibox would probably stay hot with very little power input.

Jonathan Buford responded:

The heater takes somewhere around 5-10W to maintain temp for the hot end. There isn't too much heat loss. It only takes 1-2 min to get things back to print molten, so probably not necessary to keep it on. The bed takes less than 10 min to reach temperature for ABS.

I would guess that it should store reasonably well, since everything will be contained in the feed tube and drive system. Probably just stick desiccant into the pellet hopper and you are good.

googlyhead responded:
Regarding the comment(s) on soluable pva support; does this mean a second extruder option is planned? what about a multiple extruder head? (not so good for soluable / different materials, but better in different ways)
Jonathan Buford responded:

We would like to develop this as an extension for the current box, but don't have a specific plan or schedule.

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