There are several designs for cutting plastic bottles into strips to make free filament and if you have ever made one you have probably had to grind bearings down or used a huge amount of force to pull the strip with a razor blade. Both methods work but a cheap set of kids scissors actually cuts through the plastic like a hot knife through butter and it doesn't require a large amount of force to pull the strips. This cutter was made for less than 8 dollars and can most likely be made for free with things you already have.
A note about removing the labels from the bottles:
If you fill the bottle with hot water from the tap and then pull the label off while the hot water is running over the spot where the glue is, it will soften the glue and you can use the label to rub the remaining glue off. Sometimes the glue is stubborn but you can definitely remove all of it this way. The water doesn't need to be super hot just warm enough to soften the glue.
Do Not Use Boiling Water.
Here are some design details that will make the cutter work better:
1) When you space the washers to install the scissors make sure the outside edge of the bottle is where the two blades intersect.
2) Don't let the ends of the blades extend too far past the washers, if they touch the bottle it will distort it and make the cut uneven.
3) Make sure the scissors are oriented properly so the edge of the bottle rides on the lower blade and the top blade acts as a guide for the bottle.
4) Pull the strip at the same angle as the lower cutting blade, and sharper scissors cut better.
I used lock washers with the nuts to secure the scissors because they will come loose if they aren't tightened in really well and there are some smaller washers where the scissors sit to act as a stop and adjust the cut angle if needed but probably aren't necessary. The plate is a 5"x 8" stainless steel safety plate used to protect plumbing pipes in wood stud walls, they are readily available at most hardware stores for around 3 dollars.
I have tried several different pairs of cheap scissors all with the same results > they cut the plastic easily and are rigid enough to produce accurate strips. I haven't needed to use a weight on the bottle with this particular design but it would probably help make better strips.
In summary if you don't have any bearings handy and have had bad results with razor blades, give a cheap pair of kids scissors a try, they work great.