Tuesday, September 20, 2005

 

First non-circular object printed

Last night I ran off the first non-cylindrical shape from the Meccano prototype RepRap in EVA. It's shaped a bit like a keyhole and tapers as it goes up. It was done by programming the PICs rather than sending commands from a PC, pending my fixing of the serial control software that I mucked up. Here it is:



This illustrates several useful things:

o We can produce non-circular artifacts!

o EVA Produces fine filliaments on some corners, which are easily brushed off.

o The indexing of the turntable by means of a magnet and reed switch is sufficiently consistent in operation.

o It is possible to produce tapered objects.

All the layers fused beautifully, but the initial base layer was a little patchy possibly due to me depositing on cardboard. The turntable initially located itself under the head automatically, and after checking the EVA feed I created a stable and well-bonded base by running the bottom layer repeatedly without adjusting the height. Then it was just a question of enabling automatic control of the vertical axis and the object formed before my eyes.

Vik :v)

Comments:
Huh... I put in a comment and it got erased. Weird...

Anyhow, congrats Vic!
 
Oh, now I see. I forgot to publish it. Silly me! :-(
 
That's amazing! Well done!
So how durable is it? How long did it take to complete it?
 
Durable? Heh, not very. It won't fall apart, but it squishes fairly easily - it's just EVA hot-melt glue. I can make them with thicker walls, but the accuracy diminishes with deposition width.

The whole thing took 5-10 minutes; I didn't time it. I was running with a very slow deposition rate to reduce the amount of goop dribbling out of undesired orifices. The Polymorph extruder should be faster.

Vik :v)
 
Can you make thicker walls by just doing two or more layers?

It would be interesting to see a raster-scanned solid.
 
Two walls should be quite practical. However, I am having some difficulty with the SDCC compiler and have only just got the serial comms going on one PIC again.

Rather than hard-code more functionality into the PICs, I'd like to try and get the PC controlling the RepRap's movement. Once that's done, creating scripted objects should be much simpler and I'll try depositing some solid, filled objects.

A Polymorph extruder is not too far away from my little lab now, so assembling and controlling that will have to be slotted in too. Then there's the documentation. Busy days ahead!

Vik :v)
 
It looks like a lot of fun though - I'm jealous.

One of these days I'd like to try to do this with Lego - that would make it instantly accessible to a lot of people because computers, software, mechanical parts and sensors are all off-the-shelf items that Lego enthusiasts have in large quantities...but alas I have too many other projects demanding my time right now.

:-(

Keep up the good work!
 
I once stumbled on a website where people had made a Lego RP machine that extruded chocolate under computer control (and what better working material could one imagine?). Like a fool, I failed to bookmark it. If anyone knows where it is, tell me and I'll blog the URL.
 
Slashdot had the story about the chocolade 3D printer.

http://hardware.slashdot.org/article.pl?sid=04/09/10/1221251&tid=194&tid=159&tid=1
 
This may be what you remembered. It's pretty kinky.

http://www.instructables.com/ex/i/961360D260131028A786001143E7E506/
 
Hmm - well, there isn't really enough information there to know whether this worked well or not. What precision did it achieve? What deposition rates worked?

Still - it does demonstrate that you can build an XYZ table out of Lego and control it...not that this was ever really in any doubt in my mind. I've built much more complex devices.

The main problem is the need to deal with hot extruders in close proximity to plastic parts.
 
I've been meaning to test plaster of paris reinforced with fibreglass insulation. Should insulate and be fairly heatproof, as well as being structural.

Vik :v)
 
Wow! Great pic! again congrats!
 
plaasjaapie's was the one. Thanks!

Vik - when plaster of paris sets it's a hydration of calcium sulphate hemihydrate to calcium sulphate dihydrate. I suspect you may find that, when it gets near 100 C, the water of crystalisation (which is effectively where the water went) starts to come out again and it turns back to a powder. But I could be wrong.
 
Something that has worked well for us with plaster pieces has been to soak them in poly-urathane. one part poly-urathanes are water activated so it will dehydrate the inside of the plaster at the same time as sealing any future mositure out.

Of course if the plaster of paris doesnt work you can always use portland cement.

To save weight you might try using resin soaked newspaper wrapped around the fiber glass. low gloss poly-urathane has excellent heat resistance (the flatteners are mainly silicates).

Mike
 
Oops forgot to mention something. Plaster of paris is stable at high tempatures, the waters of hydration do not leave unless there is something to draw them off. It doesnt ever return to a powder, in fact if you bake it hot enough to drive off the excess moisture you can use it to cast metal with. It will however start to give off mositure at about 100C so I dont know what effect that might have on the plastic.
 
Oops forgot to mention something. Plaster of paris is stable at high tempatures, the waters of hydration do not leave unless there is something to draw them off. It doesnt ever return to a powder, in fact if you bake it hot enough to drive off the excess moisture you can use it to cast metal with. It will however start to give off mositure at about 100C so I dont know what effect that might have on the plastic.
 
I use plaster of paris to cast lead in. Once it's had residual moisture cooked out of it, it retains its structure and strength. Even quite fine details are preserved - reproduction coins can be cast.

Vik :v)
 
How are things going ?

There has not been a new
story on the blog for some
time.

Has the project run into problems ?
 
Nope.
 
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