#MakiBox Update - Piston Pellet Drive and Feed Tube

2021-09-14 17:33 by Jonathan Buford (comments: 0)

#MakiBox Update - Piston Pellet Drive and Feed Tube

This week has been one working on many small details for getting the whole extrusion system together. On one end we have the pellet drive mechanism, on the other is the hot end itself and the feed mechanism to connect them.


This video came out pretty long, clocking in at over 8 minutes. It has been a busy day meeting with different team members and getting a new engineering intern up and running, so my voice is a little tired.


The drive mechanism is looking promising, but we need to do some testing before knowing both the effectiveness and if using a recipricating drive will cause any issue with the output quality. 


We prototyped and successfully worked out how to attach the Teflon feed tube to the ends of the extrusion system.


The hot end itself is just a smaller version of the pellet nozzle, so it should be both stable and smooth.

The next week, we will continue to build the full extrusion system and will order another set of the revised chassis parts to test the updated design after we can confirm the pellet drive solution is working.


After that, we will test the output and decide what feedback sensors will be needed and most useful and then send out the initial beta testing units and wait for all the final production parts to be available so we could start production in mass. 

On the software and firmware side, we've gotten an additional developer and a UX designer involved on the initial core work for 5D Print, our host software. We initially thought that it would be a fork of the Pronterface project, but after evaluating our requirements and the work to implment those on the existing code base, we have decided to create a new, more simple and robust host program from the ground up. We will have some updates on that coming up as well as that project progresses. 

Thanks for everyone's support over the last few weeks. The team is really looking forward to seeing these final steps come together and see what amazing things everyone will do with their MakiBoxes.



David Contreni responded:
This was an especially interesting update. I'm really curious to see how these new parts work out. The last bits and pieces seem to be coming together.

I have a trivial question about the delrin-like plastic you're using to hold everything together. (Can't remember the name.) I notice you've used black and white. I'm guessing you've been using whatever was most available at the time you procured it. From the start, you've said that the Makibox will be available in a choice of colors. Do you have any idea what will color you'll use in the production models? Would black or white be another option?

kevinpfromnm responded:
Hmm, I'd probably rotate the motor 90 degrees, use a piston drive shaft (think steam railroad engine) perhaps with a spring so that if the pellet shaft is full, it doesn't bind. then also drive a wheel, or tractor tread, similar to your first design for filament mover (way back) that actually does the work of pushing pellets into the melt zone. Then the reciprocating part just does the work of keeping the other part fed.
Jonathan Buford responded:
Not so sure about a pivoting piston arrangement. Agree, other options are there to pursue, will probably try a couple of different ones.
topot responded:
I just hope you make a caption in the youtube whenever. hehe. 
I can't understand what did you saying play on it. haha
Have a good weekend jon and hope you take a rest as much.
And Thanks jon for your effort to make my makibox. I will love it.
topot responded:
yes all of said wrote on this post. I knew it.
cdurst responded:
I guess you've given up on just tossing in shredded recyclable plastic bottles and printing with that.

Your new designs seem to require the plastic pellets to be a particular size and shape. Won't they be harder to source worldwide than the plain old filament would have been?

Of course from a business perspective it's a great idea to be the sole source of compatible pellets...

GR0B (Twitter) responded:
Why not add more pistons, this would help with keeping the feed rate more consistent. Something like a steam engine (or car engine).

You could mount them from a single drive gear. If you wanted to keep the motor pointing that way use worm gears. This way you will not have to reverse the motor direction.

Jonathan Buford responded:
@cdurst - It was never a stated design goal of this machine to recycle whole bottles or other waste plastic on board, that is a job better suited to a separate machine that can process waste plastic to a form usable by other machines. The move to the standard pellets used in industrial injection molding and similar processes means that everyone can easily find local suppliers of cheap plastic, if they choose. There are significantly more suppliers for this form of plastic than filament. Also, the machine is able to process a wider range of both tolerances and types of materials than is possible with the filament form. For our sales, we will be able to offer pellets of good quality and in many colors for USD $10/kg. This is in comparison to the $20-40+ you currently find on the market today.
Guyren Howe responded:
What about a shredding stage that cuts the plastic into powder? That would remove the uncertainty about whether a pellet made it in or not, and also more easily support recycled feed.
Jonathan Buford responded:
It is possible, but tends to be both power intensive and the equipment is not free. There isn't much reason to pre-process pelletized plastic, it is pretty regular on its own. It makes more sense to handle readily available material with the least amount of processing and then create other processes and machines to handle other materials.
topot responded:
I have mentioned about the make a fine pellet too. but I think....
this feeding tube also cool idea. and hope it work. 
but there is no only one way to feeding into the hot end.
All of depend upon on hand of jon. but I was worried about a issue for clogged tube when the plastic was cool after finished print.
so to shattering would be good way to use a recycling plastic later.
but it can will be by our makibox later. we can make a adopter for that.
I think I hope make a shatter adopter into my makibox. 
The adopter is looks like a plug-in. ^__^; to make a fine pellet by using a recycle plastic.
I just hope makibox would be can be flexible to modify to more expandable.
topot responded:
sorry always about my mess english...
Evan responded:
I'm having some trouble seeing how this would be able to reverse direction to pull the filament back when lifting the extruder from the part. A very tight connection between the piston and the cylinder might work (and would tend to reduce gaps too), but then there's a risk of jamming and higher torque requirements.

On the other hand, it's certainly nice to be able to apply pressure directly onto the pellets, rather than using the earlier screw drive.

Evan responded:
I'm having some trouble seeing how this would be able to reverse direction to pull the filament back when lifting the extruder from the part. A very tight connection between the piston and the cylinder might work (and would tend to reduce gaps too), but then there's a risk of jamming and higher torque requirements.

On the other hand, it's certainly nice to be able to apply pressure directly onto the pellets, rather than using the earlier screw drive.

Evan responded:
I'm having some trouble seeing how this would be able to reverse direction to pull the filament back when lifting the extruder from the part. A very tight connection between the piston and the cylinder might work (and would tend to reduce gaps too), but then there's a risk of jamming and higher torque requirements.

On the other hand, it's certainly nice to be able to apply pressure directly onto the pellets, rather than using the earlier screw drive.

cdurst responded:
@jonbuford - OK cool, I didn't realize the pellet sizes were that standardized.
kaelaussie responded:
Will it be easy for users to pull the piston and extruder apart for cleaning?
Will you be making a separate machine (given your ingenuity and quality control) that can shred larger pieces of plastic into pellets at a later time?
I have done some research on pellets in Australia but most seems to be 2.5mm. Will these work with the makibox?
Please forward my thanks to your whole team for their ongoing quality efforts.
kaelaussie responded:
Will an end user be able to pull apart the pellet drive and extruder for cleaning and removing of blockage?
Will the teflon tube be cleanable in case the plastic solidifies in it?
I have researched pellets available in Australia and most are 4.5x3.6mm on average. Would these be useable within pellet drive?
Please pass on my thanks to your whole team for their hard work and ethics of placing quality for the end user first.
Jonathan Buford responded:
@kaelaussie - Yep, the end user will be assembling the big parts of the extruder. We will most likely pre-assemble and test the hot ends themselves, but at least the big chunks will be left as part of the assembly process. The assembly for the pellet drive will be one separate piece, so it will be possible to test it apart from the rest of the printer and the nozzle will be able to be separated for cleaning both the barrel and the actual hot end.

The plastic is already solid once it reaches the feed tube, so that should not have any maintenance other than possibly replacing it periodically due to wear.

Those sound like the same size we are using, but would just need to test to see.

Thanks, will pass your message along, although most everyone reads these comments, even if they don't actively take part in the conversation, so it is likely they will see it for themselves.

andybox responded:
It seems there are new ideas being generated faster than the solutions to existing problems.

I, personally, am not very happy with this reciprocating fork in the road your team are threatening to take. Material consistency/density will be determined by pressure - a pulsing pressure wave should result in varying density of material as the piston moves forward and back. For those of us requiring consistent material density, this is not a good idea at all, IMO.

The other concern I have with a recip mechanism is the RATIO of the amount of mechanism travel for amount of the linear travel of filament. In other words, you are, for example, moving the recip mechanism 40mm (say 8000 steps) per 1mm of filament push, whereas the archimedes pump steps only the amount needed to keep the pressure up in the teflon line, maybe 10 or 20 steps per mm of filament movement.

Again, the archimedes maintains density by more or less constant pressure in the extrusion process. All that motion in the recip leads to massive amounts of wear in the extruder mechanism. And then there's the cycling load fatigue of all the moving components, not to mention the moving component count, and, especially, thee wear of the nut on the threaded shaft, which did not exist in the archimedes. I'll put it out there and say the recip approach compromises the extruder life by 400x - 1000x.

What you are showing may be a solution, it may seem to work, but every bone in my engineering instinct (and the eyes that have seen failed reciprocating automotive windshield washer pumps) thinks this is a long term disaster for machine longevity and reliability. Sorry.

One other issue you guys need to think about is cleaning the material path as PM. If we're to use a solvent, you can't have soluble materials in the machine mechanism.I think any plastic in the material path (excluding the hopper) is going to be a problem.

-Mr Negative Vibes (aka aturudic).

Jonathan Buford responded:
@aturudic - I appreciate your viewpoint. The driven sleeve is 
something that could be easily replaced over the lifetime, same as the 
other high wear parts. For $300 for a kit, there will be some 
compromises that need to be made. Although, that being said, we are 
designing for the average user to not need to replace parts 
frequently, and I think this design would only have problems for 
individuals with very high use case. 

I think you are discounting the amount of wear in the gears that went 
with the screw drive, as they are more likely, from my experience, to 
wear out since they are driven hard, not continuously, as you outline, 
but reversed frequently as well during the normal printing process. 
The screw for the drive is the same four flute, 8mm pitch that is used 
for the machine drive itself. 

In that same vein based on our experience in testing the screw drives 
previously there are a few limitations that come with them that are 
not trivial. 1. They inherently use a larger barrel and nozzle, so 
there is much more material to clear out when changing colors or 
materials. 2. There is significantly higher losses due to side 
friction within the barrel in comparison to a direct drive. 

Cleaning material path, I'm not understanding what issues you are 
perceiving. The nozzle can be disassembled easily, and material 
cleaned out similar to others on the market. The feed tube should only 
be passing hardened filament, so there is no cleaning there, and the 
general hopper will be clearable by a dump hatch, just similar to the 
original hopper design we showed. 

As far as it seeming like we are opening up more questions than 
answers. Currently we have a nozzle that works, that is no longer a 
question, we have immensely reduced the design space by nailing this 
down and so now it is a matter of testing one or more designs for how 
to get material to that nozzle. We are in parallel considering all of 
your solutions as well as the plunger design, and have the manpower to 
do so quickly so you don't need to worry about serial work holding up 
the progress. 

I hope that sends some good vibes your way. 


Jon a.k.a. Mr. Sunshine
Evan responded:
I wonder whether you could actually use filament with the piston design, sort of like how a hot glue gun works. It'd require modifications, but that might be a fun thing to try once the Makibox is shipping (or end users might try it once their Makiboxes arrive).

Andybox - it'll wear faster than the screw in the old system, but is wear of the steel parts likely to be an issue? I strongly suspect that it'll have much the same life cycle as dot matrix printers had; it'll become obsolete years before any of the steel parts need to be replaced.

With the consistency, that most likely depends on how large a volume is heated compared to the volume that the piston pushes in. It'd be easy to modify the software to reduce the piston's throw, giving a smoother output at the cost of lower speed.

Sebastian Herp responded:
My month after month question remains. Jon, when will we likely see something printed with the makibox? Early october? ;-)

Just asking, because I really really hope to play with my own Makibox before christmas *g*

Jonathan Buford responded:
@Evan - Hmm, that could be an interesting filament drive. A cam based system with feedback.
kaelaussie responded:
Will it be possible to print with a resolution of 0.1mm.
kaelaussie responded:
Sorry I meant 0.01 mm
andybox responded:
resolution or accuracy?
Jonathan Buford responded:

I think the effective resolution will be lower than that, regardless of the positional accuracy. The output head is 0.3mm, so the smallest feature size would be that size or larger. To get that kind of accuracy, you would want to look at a low viscosity fluid and related nozzle or a lithographic technology.

kaelaussie responded:
Any chance the output can be increased to 15cm x 15 cm x 15cm so prints can be placed in any orientation to minimise support material and print times?
Jonathan Buford responded:
@kaelaussie - Not with the A6, but we will look at larger ones next. 
The mechanism will need to be slightly modified to make it stable for 
the larger size. For this one, we were focused on price and 

I'm not sure that cubic is necessarily more efficient, possibly easier 
to comprehend for doing the layout, but for larger ones, we were 
looking at keeping similar ratio of length to width of the bed. 

Is there a specific use case that the cubic layout is that much more 
effective? I'm looking at a lot of objects that would benefit from a 
longer axis, but would not necessarily use up the total volume of a 
larger cubic layout. For the A6, we made it large enough for things 
like phone cases, which need a longer length, but if we made the 
machine to fit 150mm on each side, it would add around 50mm on the X 
and Z directions, so, making the machine about 30% larger in volume in 
total, which would be not quite as portable, and would increase the 
cost of the case and other bits proportionally.
Evan responded:
I can imagine cases where you might want a lot of vertical height. For example, printing round rods or tubes (for use as spacers) only works well when they're vertical. For smaller things, printing them vertically means you can get more of them printed in one job.

Obviously there are other cases where horizontal length matters - many things cannot be stood up vertically. However, I can't think of a scenario where two large horizontal axes are necessary, apart from the obvious "printing big objects".

In any case, I think that the current size (15x10x10cm) will be fine for now. I'll look at getting a bigger one ("Makibox A0" has a nice ring to it...) if/when they're developed.

Jonathan Buford responded:
@Evan - Yeah, definitely will look into potentially doing a taller 
version, but an A0 would have a print area of 1189mm x 841 mm x 841mm 
of some orientation. :) The size is based on ISO page sizes: 
http://www.papersizes.org/a-paper-sizes.htm We could pretty easily do 
something like a tall A6 or A5, it was just with this one that we 
wanted to keep it a little more compact and portable, but can 
certainly see the use cases of larger machines in general.
Evan responded:
@Jon - I think an A0 would be great. The Makibox line would include both the most compact and least compact 3D printers ever to enter high-volume production!

Anyway, the A6 seems like a perfect size for 'home' use. It's big enough for 'small' objects, and 'big' objects can be done with multiple print jobs and a bit of CA glue. The small size should also help with the printing speed.

Presumably once people start to receive them, there'll be a whole lot of forum posts saying "I tried to print <some> but the Makibox just isn't big enough". That'll give a good indication of what a good size would be for a future model.

Jonathan Buford responded:
@Evan - Yep, agree. The new development we have slated will enable 
control systems of up to 0.5km using the same hardware (or at least 
minor variations of them), so larger machines will be possible without 
having to re-architect the controller. 

Those are my thoughts exactly, gotta start somewhere and then see how things go.
andybox responded:
It'd be nice if we could reuse pretty much everything except the rails and frame in going to a larger size machine.... as an "upgrade" and nod to your initial supporters, not to mention increasing the volume ordering/build of those components

Sent from my iPhone
kaelaussie responded:
I was looking at ReplicatorG but couldn't find a Model/Split.
I was going to do custom games pieces making up my own borad game with a puzzle nature to give to kids that would otherwise miss out for Christmas.
Could anyone please point me in the right direction for a model splitter?
Jonathan Buford responded:
@Andybox - Unfortunately, that would likely be only the motors, which would need the press-fit couplings properly removed and replaced with the longer shafts. More than likely larger models will be a next generation step in the other parts. But, that being said, it would be possible to design an upgrade kit for the existing hardware to expand one or more of the dimensions. One obvious one would be a tall version mod. But, that could also come from the community when we release the design files.

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