After watching a Stuart Batty video on his 7 fundamentals, I started noodling on his comments about lathe speeds. As I understood him, you want to turn at a speed that perhaps makes you a little apprehensive, but definitely not scared, characterizing the difference as one that might result in a workpiece bouncing off a faceshield vs going right through the helmet. At one point he characterized that at about 40 miles per hour, surface speed, of course.
So, a quick spreadsheet later, I had surface feet per minute for 1" - 20" diameter pieces, 100 - 3600 RPM. I highlighted those in red that were over 40MPH ... which turns out is 3520 SFM! Now that's an interesting coincidence ... at least if you have a PM 3520 lathe. I'm not sure whether that's really a coincidence, but it's sure a handy mnemonic.
Anyone know the source of the PM model number itself?
(SFM = RPM x Diameter in Inches x PI / 12)
(SFM / 88 = MPH)
So, a quick spreadsheet later, I had surface feet per minute for 1" - 20" diameter pieces, 100 - 3600 RPM. I highlighted those in red that were over 40MPH ... which turns out is 3520 SFM! Now that's an interesting coincidence ... at least if you have a PM 3520 lathe. I'm not sure whether that's really a coincidence, but it's sure a handy mnemonic.
Anyone know the source of the PM model number itself?
(SFM = RPM x Diameter in Inches x PI / 12)
(SFM / 88 = MPH)
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