Do you own a Printrbot Simple? Have you had x-axis slippage and have struggled to get the x-axis fishing line on there REALLY tight? Well, this simple belt tensioner can help in some cases.

Simply download, print and snake the fishing line through the gaps in the serpentine. This will add just enough tension to resolve the slippage when the bot moves from one extreme to the next when starting the next layer.

One picture shows the before tensioned part right next to the part AFTER the tensioner was installed. The other photo tries to illustrate where the tensioner is applied.

Simply searched around on Thingiverse and became inspired by the referenced things. I've also seen a similar belt tensioner on the TypeAMachines Series 1.

But to install it on your Printrbot Simple you:
1) Get your fishing line belt as tight as you can get it.
2) Then, print out this part (it will still print at slower speeds with decent results as there are not accelerations large enough to cause the x-axis to slip.
3) Weave the belt in between the gaps in the serpentine part; making sure you keep the belt inside the gaps and that the piece is as close to the nuts holding the fishing wire as possible (otherwise the piece will possibly get sucked into the motor axis--not good).
4) Start printing nice and clean parts!