@Johan_Jakobsson At a certain point it doesn’t make sense to use extrusion profiles, anylonger. That being said, don’t try to build a miniprinter with extrusions 
Wow, that actually looks a lot like the one I have designed but I opted to have the linear rails on the top. Not strange though since my design goals are in some ways a lot like yours. I wanted the smallest printer possible with a buildplate of 20*20cm using MGN rails (MGN12 in my case). So it’s bigger than yours.
Here’s a short video of it: https://www.youtube.com/watch?v=z_bQdnB1b4M
I’m still a little curious how you handle belt tension on your printer. Do you use springs or a setscrew to tension the idler weels or do you just tension the belts as much as possible when attaching them to the hotend holder? I’m still undecided on which way to go for mine.
Oh, sorry, I completely overlooked your question. There are two ways to go. One would be using some sort of tensioning mechanism on the ends of the belt, like I did on my big printer. I wrote about this in my old blog: http://goo.gl/p6ykmW
The other way would be as I did with the DICE. I glued the ends into the carriage and made the motors adjustable. You could see it in the videos: https://www.youtube.com/watch?v=vm0SUbOJzU4
Actually, I don’t have a good picture of it 
I think the pictured frame can still work better with some changes. You’ll need to place the spool somewhere anyway, moving the motors behind the frame shouldn’t make the machine’s operational volume any bigger if the spool is on the rear face. Cut a belt passage slot through the rear vertical extrusions and you can move the motors outside the frame and closer to the corners. That should get you 40 mm more X travel.
nah, more like 13mm more Y and no X. I tried it all 
And putting the motors on the outside is ugly as fuck 
I agree, it is tempting to simply move every thing outside the frame, hence increasing the build volume. But, in my opinion it is like building a house and putting all the appliances on the exterior of the home. Ugly.
My question to that is where are you putting the spool? If you’re going for pretty, you’re going to want a housing anyway, and you can house the motor and spool on the back of the frame.
Hey, @Jeff_DeMaagd , I upped this pic because of @Johan_Jakobsson did mention something about building a small printer with extrusions. This is just a digitally CAD-design to show that I already thought about this and it would not work.
With my DICE, the spool is sitting somewhere beneath/behind the table, nonvisible and out of reach. The room on my desk is valuable and not for spools
@Rene_Jurack you said you were looking for a smaller hotend for the dice, perhaps something like this? http://deltaprintr.com/shop/parts-and-accessories/hardware/mini-hotend/
There are 1010 extrusions… And small steppers… As an experiment, you can really go small
@Johan_Jakobsson thx, I have an eye on this one, already. But 4-6 weeks and than it is only available in the US, I am in europe
@Adrian_Ciubotariu Did you see my little printer, the DICE? That’s the way to go 
@Rene_Jurack if you really want one I’ve got a friend who travels to the us regularly. Thought i’d get one too, but it’s only 12V and i’m using 24V on my printer.
oh, I didn’t know, that it is only for 12V. I use 19V-24V in every printer, too. :-/
Me neither, saw it on their forums. Hopefully there will be a 24V in the future.