As you can see the basic design is very similar to the one Demented Chihuahua made. However, there are a few main differences. First, the filament guide must extend almost to the heater to prevent buckling in the filament. Also, the heater is insulated with drywall, or fire cement or some other insulating board. I choose drywall because it is dirt cheap and easy to work. Also in my machine I'm going to be using cartridge heater driven at mains voltage, switched by a SSR (time proportioning control).There has been some question as to whether or not the filament can be pushed directly into the heater body without the molten plastic squirting back up the filament entrance in the heater. I did some experiments back a year ago, but never got around to documenting any of it. I repeated the experiment last night and had no troubles. I used a 0.095" filament pushed through a 0.103" hole. If a generous chamfer is added to the heater entrance, then filaments slightly larger than the hole in the heater could be used. This would prevent ANY mushrooming of plastic and the heater entrance. However, this still needs to be tested. I really am confident that this is how the Dimension FDM machines work.
Let me know what you all think :) Please let me see the holes in my logic and ideas.
A very nice design. Would really like to see a prototype. I hadn't thought of the drywall as insulation but it would work very well. I once built a curing oven for cooking carbon fiber trusses and we used drywall for that...the whole contraption had to get up to like 400 F. I also figure that the problem is the tolerancing between the filament and the bore of the heater. However, I don't think larger filaments will work as the excess would just be scrapped off and left outside the heater barrel...resulting in something like mushrooming.
ReplyDeleteGood work though.
Demented
Hi.
ReplyDeleteFor my lashup ( http://cncfdm.blogspot.com) I used drywall ( and later concrete backer board, which was stiffer and thinner ) as an insulator.
It worked great-- as an insulator. But, as a mechanical material it was not very good-- it tends to crumble around fasteners and such.
I have gotten a lot of prototyping done with a version using cement board, which was then coated with a thin later of fireplace cement. But, it crumbles over time, which was disappointing.