Okay, so you’ve got nice shiny Windows 8.1. You’ve installed 3D Builder and done some funky stuff with embossing and resized and now, it’s time, 
you want to print it.
There is nothing quite like the feeling of holding something in your hand that used to be an idea… So you go to the Print option and….. there’s no printer. You don’t understand, you have Slic3r and Repetier and you’ve printed a tree frog from Thingiverse, so you know it works, but why can’t you print your new, fantastic design?
Well Windows support isn’t available for every printer yet, Makerbot, Printrbot, they’re in there, but not a lot of the others. So what can we do? 3D Builder uses Microsoft’s own file format .3MF, which Slic3r can’t open but, and it’s quite a significant but, Microsoft use an online version of Netfabb to fix files that need fixing. So, this is what we do…
We’re going to start with our design. No, this isn’t one I prepared earlier, I just opened one of the pre existing designs that 3D Builder has. Then we need to save it.
We don’t really have a choice what file type to use as MS only have the 3MF extension, but we don’t care, because that’s why we’re reading this!
So we have our wonderful new design for a single floor dwelling, lets call it house, and we saved it to somewhere on our machine that we can get to. So then we go to Netfabb Basic. NetFabb is a fantastic bit of software. You can repair and scale and slice and I use it mainly to repair the bad designs I do…
You can actually find the free version here. So open it and then go to Part and then Add Part and, in the dialogue box, 
browse for your 3MF file and load it in. Once you have it in the box, you can go straight back to Part and then Export and then select STL.
Save the file back to your machine and now you have a file that you can load into Slic3r or directly into Repetier and slice and print to your hearts content.
It’s a slightly long winded way to get round Windows not recognising your printer, but the ease with which you can add embossing and other cool stuff in 3D Builder means its certainly worth a bit of time to have a play with.
There is also a cool video series by Microsoft all about 3D printing and using 3D builder that you can find here