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Skipbreather · 12th April 2008, 13:48

Another tip: How you grind your tool bit can make a BIG difference. When I built my own BOV I learned the hard way (read: lots of reject parts in scrap pile) I needed clearances in the 0.0005” range. That requires a very smooth surface. I got it by a combination of fine cuts and a (relatively) rounded radius- call it several mm- on the tip of the tool bit instead of the usual tip profile that looks like a sharp point to the casual eye. The tool bit must be very sharp, too. Plastics dull HSS bits quickly so you need to study the grinding instructions which quite possibly came with your machine. If you don’t have any handy, the article below was copied from the Sherline website. Playing w/ turning speeds also greatly affects finish. Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed.

In the end, you’ll find that experimentation with YOUR machine with various materials- metals AND plastics- will teach you much more than you’d expect. If you are in uncharted territory- for you- ALWAYS cut a test piece first to get the basic parameters down before committing you precious I-only-have-one-of-them parts to the machine.

Ken