#MakiBox A6 Pellet Drive - Hot End Plastic Action

2021-09-04 20:35 by Jonathan Buford (comments: 0)

#MakiBox A6 Pellet Drive - Hot End Plastic Action

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Now that we have a final direction on the pellet drive, we are systematically starting with the final design process for it. Instead of starting with the drive itself, we are working with a proposed hot end design that would accomodate a single pellet stream to test our existing heater layout compatibility.

 

We manually pressed the pellets into the hot end to get the output, and you can see the resulting filament (1.0mm diameter) is very smooth and consistent. In fact, it is so consistent that the measured tolerance is +/- 0.01mm deviation. For reference, commercially available filament has a typical tolerance of +/-0.05mm typically, but can wander beyond that.

 

The temperature during extrusion did not dip, but we will need to adjust the settings for the feedback for controlling the temperature to be more in line with our system for best performace.

So, heating works, extrusion works, next we will build a drive and a hot end output. 

Stay tuned til next update.

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Comment

 

tecdroid responded:
 
yeaaaaaah!!! that's really hot :) how much of the box is missing now to finish the kit?
 
Guyren Howe responded:
 
It occurs to me to mention something that will need testing.

My understanding is that the device above will be connected to a teflon-lined tube that goes to the print head.

I think you'll want to test that you don't get any jams when the extruder is allowed to cool and then restarted. I'm worried that when restarted, the filament might develop a break in it, and the two sides of the break might overlap and jam.

Jonathan Buford responded:

The filament will be running through a cool metal tube prior to the Teflon tube that will act as a die for final sizing and would prevent this from being an issue.
 
Evan responded:
 
It's beautiful! And much smaller than the old design. Should have nice, quick warm-up/cool-down times.
 
Jonathan Buford responded:
 
Yep, around 1 min for ABS temp.
 
mziol (Twitter) responded:
 
Awesome to see! That is a nice consistent output, and 0.01mm is just excellent.

As far as the drive goes, have you attempted larger blades on the auger? I noticed in the earlier updates, you guys were using something with very small blades.

Jonathan Buford responded:
 
For this, we've tried larger and smaller screw sizes and have a couple 
of different options. We will be trying out some different methods for 
this new barrel and see what works best, since it is a pretty 
different problem to solve. Part of it is getting the material into a 
small column and the other is putting enough force behind it to keep 
it moving.
 
mziol (Twitter) responded:
 
Right. Have you tried making the steel portion a female coupling rather than a male one? It sounded like you were getting some jamming there as well from the reduction in shaft diameter.
 
topot responded:
 
How about this method?
Shatter the pellet as very small and supply to the head's hot nozzle.
in Addtional for the shatter method also may needed melt the pellet can be shattered as easily.

It may will be a good way and easy to supply to head as more smoothly without a zam.

1. Melt the pellet such can be easy to crumble and Shatter the pellet as more very small.
2. Push the sand of pellet to the head.
3. Melt the sand of pellet at the hot end to printing.

Sorry for my bad english jon. just it's my idea. ^__^ Hope you may found more good way. Cheer up! jon.

topot responded:
 
sorry missed typing.... not a zam... jam. ^__^;;
here is no way to modify my comment... T__T sad....
 
Jonathan Buford responded:
 
At that point, we are better off turning the pellets into a filament of consistent size. Any sort of transformation would require both energy and potentially change the plastic in some way. Plastic, especially ABS doesn't crumble when heated, it gets soft and moldable. To get small bits, we would either need to mill, grind it, or freeze it very, very cold. The filament extrusion process is something we have experience with, so safer to start with a more similar process and then look into others for next generation processes.
 
topot responded:
 
yes sure it will be soft but it can also easy to make pressure to make a shape of fine pellet. yes but it also needed cool time. 
I hope it getting cold when it being pressured.
actually grind make a loud noise. anyone would be do not want it.
so any guys knowing that plastic can't be crumble when it heated. ^__^; 
just It a way to make a weakness can be crumble.
Yes... it may getting more difficult a way to solve... sorry ignore me.
brainlessboy responded:
 
this is veryvery cool :-) here some feedback from a printrbot user:
I have been using printrbot for 3 weeks now. just to let you in on some details. printrbot is very well done but has allot of pitfalls, so before you get any good results allot of testing and tuninig is required. it prints ABS at 0.1mm but:

- lots of x y z speed tuning required
- the printerbed needs to be prepared with special tape (that is the most anoying aspect)
- very cumbersome filament handling (the role of filament is large)
- external power source (big pc powersource block extra on the table with open cables...very ugly)

can a print that is not used any more be transformed back to pellets and recycled for other prints? (this is simply cool if this works)

also did you concider the printer bed to be ready and no tape or any preparation is requried prior to printing?

any way :-) looking at our design is very refreshing looks so professional, i can't wait to get one :-)

 
Jonathan Buford responded:
 
@brainlessboy - Thanks for the feedback, that is useful and also interesting to see what the typical experience is.

For our unicorn plot, there was no calibration done to the machine. We did have to configure it properly to get the scale correct and we tested various speeds, but those will be known quantities for our end users. Actually, it will be just load and print, from what it looks like, with just the table calibration and leveling being the only calibration needed.

We do have an external power supply, basically similar to an XBox 360 or large laptop supply. But, this plugs into the side of the case using a nice looking socket, and the supply itself is just one wire to the wall and one to the printer.

Yes, bad prints could potentially be recycled by turning them into small pieces that are the right size for the pellet drive. This is something we will work on or someone will come up with a good solution in the community.

Print bed and tape, etc. We will need users to apply Kapton tape to print on. This lasts for many prints and currently gives the best output. We will look at other potential print bed materials in the future, but this is currently the best solution.

brainlessboy responded:
 
hey jonathan thanks for you response, i love the idea of the pellets! i think this is one of the factors which will produce consistant result ... but the printer bed is equally important. could you try to avoid end user heaving to use Kapton tape, I had the best results with ABS by sanding the printer bed with a 600 resolution sanding paper e.v. the metalic printer bed can be roughen up ... the more factors you can fix the more us endusers will get consistent results :-)
 
Jonathan Buford responded:
 
We will test printing without and see. It may be that with the heated build volume it may not matter so much.
 
Evan responded:
 
@brainlessboy - we've got a horribly expensive (ie $20,000+) Stratasys printer at uni, and it still require a substrate to print on. Like the Makibox, it does have a heated build volume.

Rather than tape, it uses plastic bases which can be removed from the printer and easily swapped over. This approach works well (and the bases can be bent to snap the printed part off) but obviously the bases require a significant amount of work to manufacture - they won't be cheap enough to use with a Makibox.

Perhaps one option would be to have a removable aluminium sheet that acts as the printing base. I would imagine that even if it can't be bent to remove the part, it could be dropped into the freezer and the different rates of thermal contraction would do the job nicely.

Jonathan Buford responded:
 
We will play with alternatives for the bases, I do like the idea of swappable platforms. I'm a little hesitant about using aluminum after seeing how easy it is to damage, at least for the grade we got from our laser cutter. We will keep looking at other grades and options over time and see if we can come up with perhaps an upgrade package for swappable beds.
 
Evan responded:
 
I just thought of aluminium because it's a good thermal conductor, but in the heated build volume it probably won't matter much. Maybe it'd be worth designing the Makibox with a couple of clips on the print bed; that way people can start with the tape and then if someone comes up with a good idea it'll be easy to clip it on later.

The key question is whether the base will be reusable, or just so cheap that you can discard it after a single print. For example, if you could clamp down a piece of paper then that might provide an adequate printing surface, and you'd just stick a new one in each time. Alternatively, if you had something like a flexible steel surface (eg. like a conveyor belt, so it can be flexed easily with no permanent damage) then that could be quite expensive to produce but reusable for hundreds of prints.

Anyway, I'm sure you'll come up with something. Starting with tape sounds like a fine option to me, and then alternatives can be offered as upgrade options as they're developed. No point trying to solve every single problem facing 3D printers in the very first Makibox design.

Jonathan Buford responded:
 
Especially at this point, we are making sure to just wrap things up quickly but well. It would be easy enough to clip onto the existing bed, so probably not necessary to do additional work at the moment. I do think we will try doing the Kapton in a stack that is pre-cut and has tabs on two sides to make handling it easy. This will also minimize the size and amount of material sent in the box, since the other option is a 120mm roll of the standard length.
 
brainlessboy responded:
 
yep i can live with the kapton for a start, but i think home printers should really go without any additional handling, makibox seems cool since the handling is very clean ... fill pellets, heat up, press print ... wait for the result ... focus on the task not on the printer :-)

 

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