Oversize Mendel Prusa

I am working on a second printer to get a bigger build area and have been designing and collecting improved parts from Thingiverse. I like the look of the Mendel pro and from what I can see it shares a lot of parts with the Prusa I currently have but is wider, so my plan is to use the rod lengths listed in the Mendel pro and build an oversize Prusa.
My standard Prusa struggles to print the full 200x200 envelope without hitting something and for only an inch or so more I should get the full build area.
Who else has built an oversize printer? and what snags am I overlooking. I think the increase is so small that it should all work but I have been wrong before...

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Richmond, New Zealand
Thingiverse ~ YouTube

I have yet to build one but I'm assuming standard belt length will be an issue..

Thanks Rob, I have finished the printer and that was the only thing I didn't think of
It works brilliantly. I used plain stainless rods for the axes and stainless 8mm threaded rod for the z-lift and it is very smooth.
Build thread here: [forums.reprap.org]

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Richmond, New Zealand
Thingiverse ~ YouTube

I looked at the other thread that you meantioned, Wired1. What a Beaut! I'm a bit confused though. You say its an oversized Mendel Prusa but he smoth rods are the same size as my ABSPrusa that I bought in kit form from thereprapkitstore.co.uk.

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Using ABSPrusa Mendel Zaphod with Pronterface and slic3r 1.3.0. Printing well with 3mm PLA and ABS through 2 x J Head Mk IV b and Wade Geared Exruders. Controlled using RAMPS1.4 board running Marlin_v1.1.9

I mean oversize as in the X, Y and Z axes. My first Prusa supposedly prints 200x200x100 but in reality it is more like 190x190x90 so I wanted to stretch it out to the dimensions of the Mendel Pro. It worked out 230mm (X), 220mm (Y) and about 110 in the Z depending on the extruder.
I think 8mm rod works fine for the X and Y axes if you use good quality rods. My MMax will be 10mm Z and 8mm X and Y but I am using chromed hardened linear rods that are significantly more accurate and harder than stainless rod and for not much more cost.
The 10mm rods are a similar cost to the 8mm and same for the bearings so there probably is nothing to lose by going bigger.

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Richmond, New Zealand
Thingiverse ~ YouTube

I ended up using the list of slightly oversized (in length for even dimensions) imperial rods listed in the SAE_Prusa_Mendel wiki site (http://www.reprap.org/wiki/SAE_Prusa_Mendel) and just adjusting them to their max before selecting a jig size. Then I substituted 18" rods for the 15" rods for the verticals, because the holes in the prusa brackets were loose enough that they accomodated about a 16.6" rod length before the angle changed enough giving me about 1.5" more z height. The extra rod now extends down beyond the brackets. The way I figure it, as long as you select and jig to a single length on each of the width, length, verticals, and rail width respectively it should work fine as long as the smooth rails are long enough to accomodate. The extra dimensions will help expand your build volume.
I am also borrowing the configuration from droftarts moving the z-stepper brackets to the bottom to see if it will give more z travel to the top. I have not finished my build yet to verity that one.

Nice. The biggest problem with the Mendel-type printers is the width of the top rails as this limits z-axis travel, however it is still a very good design and works well for it's intended purpose. I am now building a Mendel Max which still has this problem but I'd like to see a derivative that has either only one top bar or wider spaced bars. Maybe next winter.

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Richmond, New Zealand
Thingiverse ~ YouTube

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I'd like to see a derivative that has either only one top bar or wider spaced bars.

[www.thingiverse.com]