TWEAKIE my CNC machine under construction.

CNC is only limited by our imagination.

Here are some very basic drawings of the Vinyl Cutting attachment that I have made for TWEAKIE. I know that It is not perfect and improvements to the design could easily be made, however it works surprisingly well and does exactly what it was intended to do. I have purposely not given full dimensions here as they are not important and can be chosen depending on the materials and parts available.

 

In order to keep the knife sharp and preserve the necessary angles to which it is cut a small jig was made for sharpening. The knife blade is removed from its holder and inserted into the jig. It is a sliding fit into the jig and only slight downward pressure is needed when rolling the jig back and forth with the knife edge touching the stone.

 

It is so easy to sharpen a knife blade this way. And remember sharp tools are the secret to success.

This knife carrier is fitted to the Z axis (see pic 36) it is again very basic but does its job.

 

It is necessary to apply a small downward force to the cutting knife, just enough to pierce the surface of the vinyl but not too much that the nose of the holder tears up the vinyl once cut. A small spring was used and compression adjustment provided. A back stop is also necessary so that the whole assembly is raised by 2mm movement of the Z axis without the knife dragging across the vinyls surface.

This type of Vinyl Cutting Knife (drag cutting) is the most basic where the shape of the cutting edge, is such that the knife rotates freely within the radial bearings and, always presents its cutting edge towards the direction of travel.

 

Although this system creates a certain amount of under or over cut at the corners it is hardly noticeable. However, for perfection, most vinyl cutting software incorporates corner steering routines to create perfect sharp corners when using this type of cutter.

 

Just for reference, my knife blade is 3mm diameter (not a standard size for professional knife blades) it is this size because I already had two 3mm I/D miniature radial bearings.

 

Making a simple vinyl cutter.

These are the dimensions I tried to achieve when grinding and sharpening my knife blade.

 

I ground, using a wheel (and taking care not to overheat and loose the temper of the steel) flats on either side until the 36 degree angle was achieved then ground away the back until the tip offset was about 1mm then finished off with the diamond stone and sharpening jig. Not perfect but pretty close to these dimensions.

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