First off, if the blade cuts too deep, you don't adjust pressure... you adjust the blade exposure. With vinyl, only the tippity tip of the blade should be exposed because vinyl is so thin and you don't want to cut into the backing sheet. My personal guideline when setting the blade exposure is that if I can see the blade tip, then I most likely have too much showing. I can feel it with my finger tip but not really see it.
The best thing to do is use a small shape, such as the ring shape in SCAL's library, to do a test cut. The ring makes it easy because if you get a clean cut, you can lift ou the ring shape from your vinyl and easily see of the blade cut into the backing sheet based on the inner circle of the ring. If it did, then you need to reduce the blade exposure... but leave the pressure alone for now. If the ring cut in some parts but not others, then you know the exposure is fine and you only need to increase the pressure. If the ring didn't cut at all, then I would increase pressure AND increase the exposure just a TINY bit and test again.
Once you get a clean cut ring and no cut lines in the top of the backing sheet, then maybe try something a little more detailed... like a small ABC just to make sure you still get a good cut.
Note that I don't own a US Cutter... this is just the testing philosphy that works on most drag-blade cutters and I've been using it with great success for years.
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Sandy McCauley
Manager of Customer Relations and Education for KNK USA
Owner of
http://www.iloveknk.com/