Tuesday, January 02, 2007

 

Scrape and Fill

OK, this is just a bizarre idea off the top of my head. No real thought or research. Figured I'd throw it out here on the off chance that it sparks some inspiration.

The general idea is to use a semi-solid material as a combination support / mold. Something about the consisency of modeling clay might do. The process would go somthing like this:
1. Lay down a thin layer of material (trowel, squeegee, something)
2. Scrape away the areas where the part will be
3. Fill the empty space with plastic
4. Repeat

What got me thinking along these lines was the extrusion speed. It seems like scraping away a negative image might be faster than drawing a positive image. This would be especially true if you could use multiple tools to scrape the area. Wide ones for larger areas, for example.

I really need to get off my butt and put together a test rig to try out a few things.

Comments:
I know it can be hard sometimes to just get the ball rolling on a complicated project like this one.

Taking lessons from my current project, I got a design in the works similar to it, made from almost exclusively 1x4 lumber and drawer slides. Should be quite simple, compared to the alignment horrors that have been had using only rod sliders.
 
Right now the number of skills you have to master to make a RepRap is, not to put too fine a point on it, formidible.

Mind, Adriaan's creation of the Universal PCB for the mainstream RepRap is going to take a LOT of the pain out of getting the electronics right.

Cat has been running into the teething problems with getting the Java control programme working that I rather suspected was going to be the case. That will sort out in the fullness of time, though.

The really finicky bit, imo, is the Mk II. That thing, groundbreaking as it is, needs another design iteration or two with the notion of making it easy to fabricate kept in mind. Right now, getting the threaded polymer pump working right and the extruder head fabricated are far too intimidating for newcomers.
 
Hi i am kinda new at posting here but i have been reading about the reprap for some time now and have decided to explore building one my self, my question is what do you guys think about using 80/20 T slot for a frame and also using it as a built in track for sliding the xyz axis along?
 
Hi i am kinda new at posting here but i have been reading about the reprap for some time now and have decided to explore building one my self, my question is what do you guys think about using 80/20 T slot for a frame and also using it as a built in track for sliding the xyz axis along?
 
I've had no experience with 80/20 T slot. Give it a shot and see how it works! :-)
 
Oddly enough I've been toying with the same basic idea in my head for a couple weeks now in an attempt to figure out a good rapid prototyper design for artistic works (thought I lack most of the technical knowhow to actually build it, hence why I'm lurking at the reprap blog). As I see it the big technical issue with this approach is scraping away enough of each thin support layer to add the actual part material (I was thinking of various combinations of plaster, wax, and plastics for those). Leaving the support layers embedded in the part would be bad, as would digging down too deep and damaging the part below. If it those issues could be worked out then this approach could lead to superior part productions though, so it's worth research imho. The other thing I tacked onto this design was I only planned on having the cutting/carving head on a x/y axis and it would either be at cutting depth or raised on the z axis (binary states, no in addressable in betweens). I planned to drop the entire work area down as the layers were deposited to keep the mechanics of the layer deposition system and carving head simpler (at least that's how it worked in my mind).
 
I suspect that you guy are having a conceptual problem with how molten plastic behaves that I had for years till I finally got to working with plastics.

Here's the problem. Molten plastic doesn't pour like molten wax. It is extremely stiff in the molten state and will take a LONG time settling into a mold in an oven.
 
Molten plastic would be a no go in this situation, but a 2 part resin mixed as it was poured would work (assuming the support material could stand up to the heat generated during curing). For the design I was toying with in my head head it would scaffold with wax, carve out the current layer of that, drop in plaster and then repeat at the next layer after the plaster had sufficiently set. After the part was completed and the wax melted off the plaster I figure it could be cast in the final medium via a silicon mold of the plaster prototype. Admittedly not workable for a reprap, but that wasn't my goal at the time.
 
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