500mm cube build area Reprap in planning

Hi guys, I've been reading for a while, but this is my first post, so be gentle!

I'm really enjoying reading about the huge variety of modified machines & the ingenuity that has gone into making them,.. so I thought I'd make an effort to contribute too. I'm sure I'll be making plenty of mistakes along the way, but that's just half of the fun.

My plan is for a completely custom Repstrap unit with a larger than normal build area of a 500mm cube. I have a specific project in mind where something near this size will be required, but i thought I'd revise it upwards for the sake of an even number.

I'm planning to use materials that can be sourced locally for the prototype,.. very few printed parts are planned with the exception of the extruder assembly.

For the sake of rigidity & stability in a larger design, I plan on over-sizing the rails & threaded bars. I have a supply of M12 threaded bar nearby, and 25mm smooth chrome rails (normally used for hanging rails in closets) are cheap, readily available & very rigid. As much as I prefer the "bare bones" look compared to the enclosed Makerbot/Sumpod designs, I can see how the case also adds rigidity, so I'm considering a semi-enclosed design. Just enough laser cut board to add weight & remove any flex from the structure, whilst still allowing easy access to the components.

I have a bit of experience with engineering,.. but I'm a complete newbie to the electronics, so a big thankyou to the guys who have posted so much great info about that side of it!

So my first questions:
1. What are the most common problems involved in bigger repraps, and how do I avoid them?
2. I've seen bigger machines with multi-motor systems driving each axis. Is this really necessary? I would assume that the extruder head is the same weight, the frame supporting it isn't much heavier etc??
3. The one moving item that will be significantly heavier is the build platform. I've thought about swapping this to the z axis as its the axis with the least movement. The X & Y axis assembly would be fixed at the top of the machine with the build table dropping as the build progresses. Is this a stupid newbie idea, or could it have merit?
4. Finally,.. I'm in Ireland,.. the last place anyone ever wants to post nice toys too. Can anyone recommend a good place near me to order up electronics & motors?

Possibly Mendel parts in Holland, eBay or even look on Deal extreme for motors

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Experimenting in 3D in New Zealand

Thanks Nelson.

Forrest Higgs is building a reprap that sounds similar to what you're after, including a dropping bed and the X and Y axes at the top like the original Darwin - read his blog here [technocraticanarchist.blogspot.com]
If you're using larger, heavier bars, the torque of the normally used NEMA17 motors may not be enough to rapidly change direction. I got my motors from Zapp Automation [www.zappautomation.co.uk] who I think can ship to you, and seem reliable and knowledgeable.

Would Nema 23 motors all round be a better choice?

I just got back a price for the laser cut sheets I was planning to use for a box,.... I think the prototype at least will be constructed using plan B!!

Plan B is a Kitchen cupboard base unit. Its strong, rigid, accurately cut & pre-assembled, and the 600x600 footprint should just about allow me to achieve my half meter build area (or very near it). I'll be routing out big holes in the sides for easy access and I won't be fitting a door to the front,... I doubt it'll be the perfect solution, buts a LOT cheaper!

Njones Wrote:
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> Would Nema 23 motors all round be a better choice?

Yes, I think that's what Forrest is using. Check you can get motors that the electronics can run if you're going to use the standard reprap electronics (RAMPS) - I think most reprap boards can only run motors of up to 2 amps at 12V.

Keep in mind that you are having a ~16 times larger build volume (in comparison to a 200mm cube) with this printer.
You would need a insanely fast built speed, again this depends on the objects you are planning to build but I suggest you look into making a ultimaker style gantry with a bowden extruder and mount the extruder on top to minimize the length of the cable.