Stepcraft vinyl cutter drag knife holder

thingiverse

This is a holder for a Roland type dragknife in a Stepcraft cnc. Two parts are printed, the 43mm cylindrical holder for the Roland dragknife and the screw down clamp that keeps the dragknife in the holder with some spring pressure. These dragknives are designed so that the face slides over the surface held there under pressure from the spring. The depth of cut is set by how much the blade protrudes from the knife holder, adjusting the screw section at the top of the knife to just cut the vinyl, not all the way through both the vinyl and backing. The spring applies constant pressure (and helps to protect the knife if you should crash into the bed), it allows the whole dragknife to recede into the holder a short way. To adjust the pressure use a different spring or compress the spring more or less by screwing the clamp down more or less. You still get access to the ejector pin but to adjust the length of the blade that protrudes you need to remove the knife completely because the locking nut is inside the clamp. This shouldn't be necessary if you use blades that are all the same length. Remember to smooth the end of the aluminium holder so that it doesn’t grab the vinyl as it glides over the surface, do this with the inner section removed to avoid getting grit in the bearing, remember to clean it out afterwards. My new dragknife was rough to assemble because it still had chips or grit from when it was made originally, some cleaning alcohol and new light oil improved it significantly. Thread matching:- The threads in the holder and clamping lid are designed using Fusions thread function and the fit may be too tight after printing. I scaled the clamping lid X and Y by 98.5% in the slicer to make it just a bit smaller to ease the fit. My spring has an OD of 14mm and the wire section is 1mm. The whole spring is 3 coils of uncompressed length 12mm. The spring just needs to be a close fit around the knife (1/2" ID). My model of the Roland-style knife is measured from one I bought online. I guessed at what was inside the screw in part and I didn't include the bearing. Yours may be different depending on the manufacturing "quality". An excellent informative tutorial on vinyl cutting with your CNC can be found [here](https://www.kronosrobotics.com/using-a-dragknife). A video about [setting up the drag knife.](https://youtube.com/watch?v=qBlrwkqlNfQ&feature=share) And [this one](https://youtube.com/watch?v=2fO41mmdXIM&feature=share) is very good, has a few important tips. And Lars Christensen has a very clear [video for Fusion users and Stepcraft’s own drag knife](https://youtube.com/watch?v=s1fs3ByL2Jg&feature=share) but all the information is valid You will see some designs are rigid or have a spring press on the ejector pin, those might be troublesome if the whole knife can't move.