Adriatic posted:
Actually, if it is Bakelite or a hard plastic, the high rpm would likely be beneficial to the cut. There likely wont be enough cut heat to wipe out the cutting edge anyhow.... but coolant/oil seldom hurts.
Too slow a speed on brittle stuff and it is more likely to grab and chip out and/or crack either the work or bit. In fact with some compounds, grinding a hole vs cutting may be the way to go.
At my family's gauge making shop, I was taught to use a low feed, a high speed, and a dull, steep rake bit for avoiding grabbing at the cut on brittle plastics. A dull, deep cut rake at high speed will scrape vs cut too fast. Even do running in reverse to break out the bottom cleaner (or to cut by melting in reverse or fwd). On some plastics this will melt through less than clean, but still beats grabbing and cracking or cutting so fast you get an oblong or incomplete cut on breakthrough (a half punched hole with a spiral plug still there) I just clean & open those messy cuts with a file/grinder (yes I have hand broaches too (tiny, fine, file/reamer of sorts for tiny precision holes.))
A pilot hole always helps. Even at 3/16". Your cuts will usually be better with a pilot; and the bits, especially starting tips, will stay sharper longer on the bigger (more expensive) bits.
Thank you for the advice - my plan when the new bits arrive was to actually use hi speed, low feed. My concern is the type of bits https://www.amazon.com/gp/prod...00?ie=UTF8&psc=1 these look like wood boring bits, I'm quite afraid these will snag/chip on the bakelite-like material - hence the hi speed.
