Talk me out of or into building this

I was planning to rebuild my Makerfarm i3v frame to an aluminum extrusion frame from the wooden frame. Then I found this 18"x18" heated bed on ebay [www.ebay.com] and I decided to experiment and remake my i3v into a large build-size printer instead.

The Makerfarm is the only printer I've built so I thought I'd just make a bigger scale frame so the 18" heated bed would fit.
Below is the basic frame design using 2020 aluminum extrusions and V-slot extrusions for xyz just like the makerfarm. I made the y axis 35" long to fit for the heated bed. I'm still not sure about the z build area, maybe 16". I'm going to use some printed parts from the Haeckel design to hold it all together. [reprap.org]


Is this too ridiculous? Is the 35" yaxis too long and it will sag? Or the large bed+print is too heavy? Would a 27" x carriage made of 2 v-slot extrusions sag? Is there something completely horrible about my design that I can't see because I have no engineering/technical background? Do you think it would work/be worth it?

I would really appreciate any advice or thoughts. I want to experiment, but also be careful with my money because it will cost a few hundred dollars to make this change.

Ccmain,
I can't comment on the construction details as my printer is completely different, other than to say: take a look at this one, it looks similar and yours may have similar issues.

With a bed that size you will need to think about what kind of filament you will be extruding, and possible shrinkage issues if you do large parts.

Good luck.

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
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It's not too ridiculous.
I don't believe your extrusions would 'sag' at those lengths, a 40x20 would look more correct for the x axis.

You'd want some diagonal or corner bracing perhaps on that box structure.
As it looks it would not cope very well with being moved about.

You end up with a long structure by going the 'mendel style' ie the build plate on the y-axis, it makes it twice as long as the build length

The first big question to ask yourself is; "Where am I going to put it?

The i3v looks a lot stabler in the Y direction due to the bracing. I would add a brace each side from the front top of the machine to the back at the bottom.

Possibly in need of some well placed crossbeams?

I know that increases cost and complexity, but frame rigidity seems to be a (major?) factor in getting good print quality (I could be wrong). I would guess it becomes more important as you scale up a design.

Edited 1 time(s). Last edit at 12/10/2014 11:50AM by dclarkm.

Thanks for all of your thoughts and suggestions. I'm gonna make another basic sketch that includes the 45degree supports and corner brackets that you all mentioned. I'm also going to consider a 12"x12" inch version, because as Alan Richard commented, Where am I gonna put it? And enclosing it is a different story. Another reason for the 12" version, is that I'm strict with myself about not leaving the house or sleeping during prints, and prints on a 18" bed would make that difficult to do.

The bed is a large mass to move about on the Y axis, as is the X axis. You might want to consider upgrading to NEMA 23s.

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Hola,

So I've decided to build a frame for a 12"x12" heated bed, instead of the 18"x18" heated bed.
Here is the draft:
(the 2 bars going across the front is the x-carriage)
In addition to the corner supports, I'll put a corner bracket in each 90degree corner to keep it extra tight. This version has an 18" z build, but I think I'll lower it because I'll never print something 18" tall. Or will I?