Creating molds of Darwin parts with Plaster Rapid Prototyper?

Hi Guys!

I'm starting to shift into first gear with my "Let's build a RepRap" Project....

It seems that i *may* have access to a rapid prototyping machine which prints out plaster parts.

The plaster is wayyyyy to brittle to use as Darwin parts, but I had the Idea of creating "Inverse" Cad models of the Darwin parts, basically creating single-use molds...

Creating molds for more than single use would be complicated due to all the through-holes....

What do you think? possible? good idea?

-Leav

Hi Leav,

the idea is good and we periodically have some talk about casting and moulding with other methods and different materials ...

Maybe you can test the output-accuracy and calculate the fabbing-costs?

Viktor

Hi Viktor,

Thanks for the input...

Hopefully I won't be asked to pay for this (i'll to get the university to sponsor it) but I can find out what the cost is (i'm sure they transfer funds inter-departmentally).

I have had a chance to look at the of the printer and it looks pretty good... it's very accurate but it has a rough finish.

It is very very brittle! I need to think of a reliable way to transfer the molds to a place where they can be used without harming them.

but i'm getting ahead of myself... I need to get permission to use the printer first...

I'll update you guys when there is something to update about...

In the meantime:
could someone please point me to:
-Information about plastics that can be poured into the molds
-Information about how to actually use molds... perhaps a tutorial which assists in avoiding common pitfalls...


I'll google it but perhaps you know of good resources stuck at the end of the google index file...

-Leav

Adrian wrote a good tutorial here: [reprap.org]

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[www.hydraraptor.blogspot.com]

Thanks!

I have good news: I talked to one of my proffesors at the Technion ( www.technion.ac.il ) and I got funding for a RepRap project.

This means I might even get access to a plastic RP machine

would you suggest molding or RPing?

If the price isn't too high I might go with the Plastic RP and have it make all the parts...

Is there an advantage to pouring plastic into molds? seems to me it might be stronger...

I'll keep you updated (despite your best efforts ;-)

It's about USD$1K to RP the parts, using a non-RepRap. (I think that's the right number.)

Using plastic in plaster molds is much cheaper.

Note that if you can get your hands on a cheap small mill or router, that may be the way to go. For example, here's an Israeli dealer of the Sherline brand tabletop mill:
[www.geocities.com]

Some points to note:

The original parts were designed for RP with a support material. Those that required support have been re-engineered by Vik Olliver and Steve DeGroof to not need it and can be found here :- [reprap.org]

Not all parts can be made by milling without further modification because they have internal detail. You can definitely make the extruder with a mill though and then attach that to the mill you made it with to make the rest of the parts.

Some parts have internal cavities for captive nuts which have to be inserted through holes and slots and the rotated and slid into place. I think if you are molding you have to make cores and pre-insert the nuts into the mold. Ian Adkins would be the expert there.

I haven't sampled any molded parts so I don't know how strong they are compared to RP. RP parts made in ABS are pretty strong but are weaker in vertical extension because the layer bonding is not as strong as solid plastic.

Edited 1 time(s). Last edit at 05/20/2008 08:14AM by nophead.

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[www.hydraraptor.blogspot.com]

We have just switched to a LASER cut design as the moulding option is very complex as Nophead says due to the many internal trapped nuts so you need to make moulds with removable cores (the corner block moulds have 7 removable parts!) this means a lot of time on the lathe before you even think about pouring some resin.

If you can directly print a mould then you might make it easier it all depends on how much your printed items cost.

We are now back up with complete mechanical kits.

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Ian
[www.bitsfrombytes.com]