#MakiBox A6 - Pellet Drive Update

2021-09-03 20:59 by Jonathan Buford (comments: 0)

#MakiBox A6 - Pellet Drive Update

This is going to be a pretty detailed post, hang in there. For the short version, just watch the video.


We've been going all out for the last week on getting the pellet drive finalized and spitting molten plastic. For this design, we are trying to find a solution that will fit within the MakiBox, not consume much additional power, and be simple enough for the users to assemble.

The first design change we made from the last major version was to introduce a stainless coupling and a smaller nozzle that joins to a longer barrel.

This worked from a standpoint of isolating the hot end from the barrel effectively, but we found that the transition was too short and ended up binding up in the stainless coupling.

We tested two different nozzle designs by Friday, and found both to have the same end problem of getting stuck in the stainless. The first design was longer and resembled a smaller version of the last iteration. 

The second one was considerably shorter and resulted in a nicely melted volume immediately behind the nozzle, but it looks like the main brass nozzle pulled too much heat away from the stainless to where it always ended up as too cold and caused binding.

You can see the result of all three, the plastic plugs resulting from each test. The first one that is mangled we heated the longer nozzle up prior to running the pellets into it. That resulted in the pellets not even getting to the nozzle. The second had some pellets down the nozzle, but not full. The third was full, but still created a jam in the stainless area.

At that point, we had the open house, and we had to set all of this aside for the night. 

On Saturday, a previous approach that was considered started to make more sense to avoid the specific trouble we have had with these designs. On Sunday, I came in and did some preliminary testing of a revised drive mechanism that results in a single line of pellets being pushed into the barrel, making the thermal characteristics much closer to the printing hot end than the filiament extruders like the Filabot. 

The result of the initial testing was good, and today we iterated through many different variations and found what seems to be a workable direction. Tomorrow we will continue to build a full prototype that can be fitted into the printer and work towards having a hot test with this new design very quickly.

This should be a very active week of development, so stay tuned.
Guyren Howe responded:
I wonder if you could just connect the line of pellets through to the hot end and not bother with melting the plastic twice.
SolanGu (Twitter) responded:
Yes, do not bother to heat up the plastic twice. Let a fine line of pellets drop into your print head.

Somebody might have suggested this already, at a early stage of your development - however Muhammad Ali said it best, when he said

- I told ya!

Evan responded:
I've been thinking along similar lines. The big issue that I can see is that there's no easy way to reverse the drive (as you need to do when the printer is moving to a new location, to stop it dribbling out plastic along the way). However, that might not work even when the pellets are being turned into filament, unless there's a separate filament drive.
majikthise responded:
Hi. I'm sure I'm not the only one who's wondering how this project managed to get hung up on the whole pellet drive idea? The original concept was to use ready extruded filament and that sounds fine to me.

Of course a printer that extrudes its own filament would be a fantastic idea and really strong as a unique selling point but there must be thousands of people out there who are following this project but holding off ordering until they see a decent test print using whatever technology. I know at least half a dozen such people personally.

So why not park the pellet drive and concentrate on getting some test prints out? When the technical problems with the pellet system are sorted it could be sold as an upgrade, meaning more revenue for you guys and less frustration for the rest of us.

Jonathan Buford responded:
As much as it would be cool to send pellets directly to the output head, it is necessary for consistency as we need to have a sensor to know how much filament is extruded. In the future, it may be possible to combine these steps using a different method of feedback, but for now that is how it needs to work. Also, for a box this small, a tube of pellets will end up having to stick up and out of the box, which would eliminate the heated build area, so would have a lot of tradeoff.

For reference, this material is heated once already when you purchase pre-made filament, so it is basically doing the same in terms of heating as existing material, just you get to see it happen instead of it happening before you receive the material.

@majikthise - There are a few different considerations for why it is worth developing the pellet drive and for not shipping a filament system. Actually, these have been discussed at length in the forum, so you might peruse there as well. 
1) Once we ship a filament based system, we are stuck with 1-2 month lead times as well as large MOQs for the filament material. We would not be able to easily offer new colors as we will be able to in the future, and we could face potential production delays during ramp up or excess inventory. 
2) You can find pellets at many local suppliers if you want a very cheap option.
3) The same machine will be able to use many different materials, you are free to experiment with new things that other people can't consider printing with since the options are constrained to what is available in precision filament on the market. 
4) Things made with locally recycled plastic is just amazing and is an option with this mechanism.

ludzinc responded:

Love the idea of the pellet drive. Love the idea of being able to grind up old bottle lids and print from these. I'm kinda partial to coca-cola red.

But now that the pellet drive is going down the path of single pellet feed, doesn't this now limit you to pellets only (making your point 4 mute)? Ground up coke bottle lids as feedstock would be excellent....

But I'm with majikthise - now way can I justtify upfront investing in the Makibox (wife and children make for a hard budget committee) but funding a fished filament system can be approved.

I manage projects for a living - and you need to know when to prioritise, and when to cut something lose. IMHO the pellet drive is both an excellent idea, and a project killer.

ludzinc responded:

Go back