After looking to buy extra ptfe tubes for the Sunlu filament welder I was a bit disheartened. One, they aren't always readily available and, two they're expensive. I bought 16 ft of the tubing off Amazon for $11.50 and designed the jig you see here to cut it to length.

All you do is put the tubing in the hole and push till it's flush with the other side, then use an X-acto knife in the top slot to cut it off square. It becomes very easy after a minute or so.