Getting Started

G'day from Melbourne,

I have been poking around for a short time and very excited about the RepRap concept,but I am wondering who I would speak to about getting organising the parts for the build?

Secondly, are there any restrictions on size or is it user definable? I would be considering something in the order of 36"x36"x24".

Cheers

Shaun

Making something that large is opnly useful if you will be constructing objects which are that large. You have to remember that the larger your device becomes, the less accurate it could possiblly become as well.

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Jay

Welcome home Shaun!

If you check at the bottom of the forums page there is a section for RepRap Users Groups, if you find one in your area it will be your best resource, if you don't find one, start one, it will become your best resource.

Parts:
The RepRap parts lister: [parts.reprap.org] can get you started, most of the stuff comes from McMaster Carr and Mouser but you can get it from Radio Shack and your local hardware store if your local hardware store has a lot of metric stuff. The tricky bits are the Stepper motors, the plastic connector bits, the extruder, and the circuit boards. This stuff is best obtained from the RepRap Research Foundation: [store.rrrf.org]
or Bits from Bytes: [bitsfrombytes.com]
in either case parts are still in short supply, but most stuff can be made (pcb's, connector bits) or gotten on ebay (steppers).

Size:
This is definitely a homebrew effort so all sorts of sizes are in the works. The biggest problems you will face is that you will be designing your own, therefor facing and solving your own problems, so be realistic about your abilities as a mechanical engineer; and at 2x3x3 feet you would be building the biggest machine I am aware of on this site. In order to be successful, these machines have to have a positional accuracy of around .03 mm over the entire print surface. The bigger your machine the harder it is to keep it rigid and the harder it is to maintain accuracy.

Anyway, welcome to the family and Good Luck with all your projects!
Brian D

In theory, you should be able to scale the Darwin design up or down by changing the lengths of the belts and rods. I don't think anyone's tried it though.

It would take a very long time indeed to make anything close to the volume of the Darwin, let alone anything much bigger, with FDM. Plus warping due to shrinkage gets dispropotionately worse the bigger the object is.

One of the many things on my list of experiments to try is to make something approaching the build volume of my machine, which is only 150mm cube.

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[www.hydraraptor.blogspot.com]

... here: [forums.reprap.org] i started a discussion about 'mega-sized-repraps' and fabbing with construction-foam (or 2K-polyurethane-foam) which you can extrude in centimeter thick trays from pressurized bottles.

With the possibility to print with trays of some centimeters diameter it's very interesting to design real big robots - for example for building furniture or architectural components ...

Viktor

Hi

I wanted to go large because I had intended to prototype largish items. Given that it is an untried, unproven size and my lack of familiarity and experience I should stick to the current design and experiment from there.

I did see a users group located in Sydney and perhaps a Melbourne group would be a great idea.

Cheers

Shaun

Prototype largish items? Are they one-piece? If they're smaller, and you're going to have to put them together from components anyway, then the size you need is, potentially, slightly larger than the largest piece you're planning to make.

Consider the Darwin design. Part of the design criteria is it can make its own parts, or a good number of them. Granted, much of it, particularly the rods, isn't fabricatible.

...fabricatible...yet!

Demented

Hi,

A single part would be roughly 24" in length and 10" wide. It is still however a valid point that if the Darwin has not been proven in this early stage at such a large scale then I will go with generic setup and and experiment from there. I have seen great success with DIY CNC machines at a scale that large using similar technologies, so I believe that there should be absolutely no reason why it would not/could not be accurate on a larger scale.

Cheers

Shaun

Personally, I doubt the darwin design will ever be able to fabricate all the darwin parts. The goal, as I understand it, is for future versions to be able to handle more and more of the fabrication. Perhaps the Watson, Crick or Wilkins model will be able to fabricate guide rods, then again, perhaps that model won't need them.

One issue is rigidity. The Darwin design isn't, supposedly, stiff enough to handle it, (I've no personal experience, so I'm going on hearsay here.) I don't know about the seedling.
Another issue is speed. As I understand it, currently laying down a lot of material is a time consuming process. Imagine building a house out of identical 4x2x3 lego blocks with a pair of tweezers.
A third issue is warpage. If you're machining material off a block of metal, odds are you don't notice size changes unless you leave the grinding tool in the same area for too long, (thus heating it up.) In FDM the material IS going to cool, and as it cools, it'll shrink. What will shrink first? What direction will warps occur, and how are they to be countered? I believe someone said, the larger the item, the worse the warpage, and that certainly makes sense to me.

I believe that this style of fabrication is going to lend itself to guess and check methods of design. There is a whole shit-ton of things that occur when a thermoplastic cools down and this isn't the type of thing a non-plastics engineer (read: almost everybody) would want to deal with or would even be able too!

Demented

I hadn't even thought of the cooling/shrinking plastic factor. Makes perfect sense. I should have thought of that myself actually. You are quite right in that I would have absolutely no idea where to begin in the forces at play with thermoplastics.

Cheers

Shaun