This is my adaptation of a safety cutter. It uses an x-acto blade #11 embedded into the print. YOU MUST pause the print at the correct layer and place the blade before resuming. If you don't know how to set a pause look bellow for instructions, if you do then it should be set to pause at layer 9 if printed at .20 layer height. Insert the blade with the point slid all the way forward. The file is purposely made with a little bit of wiggle room.

To create the pause needed to insert the blade refer to the picture bellow…

You slice the file and go to the layer you want to pause at, and then you right click the + and select add pause. The pause will pause before printing the layer selected so you want to choose the layer that first starts bridging over the blade location as in the picture above. If sliced at a .20 layer height it will be layer 9 just as in the picture. After adding the pause you then reslice the file and you will see it has a pause set at the chosen layer. Then you just proceed as a normal print. The printer will automatically pause before printing layer 9. Then you will insert the x-acto blade into position, with the point of the blade slid all the way forward in the opening. (The opening is purposely just a little oversized, with a bit of wiggle room.) Then once in place you can hit resume on the printer. You may get a couple strings as it goes over the blade, this is normal and no cause to worry, just let the print finish, and then remove them.