Flycutters and RPM

JR49

Active User
H-M Supporter Gold Member
Joined
Mar 20, 2014
Messages
440
Guys, please correct me if i'm wrong, but when figuring the RPM to use for a flycutter, I have always used: RPM = SFPM divided by the DIA X 3.82. (To find the diameter, I measure from the tip of cutting bit to center of flycutter body and multiply by 2) . This is the same formula you would use for drilling or turning on the lathe. How am I doing so far? I mostly machine steel so for say 80 to 100 max SFPM and a 2.5" flycutter, my RPMs are fairly slow. Whats making me question myself, is cause I just watched Joe Pie's latest u-tube video about setting a flycutter:
and at 8:00 mins. he starts cutting, and his 2.506" Dia.flycutter seems like it is FLYING!! I realize he is cutting aluminum, but thats a HSS bit in his flycutter, and I usually use a brazzed carbide bit in my flycutter. What am I missing here????? Thanks to all, JR49
 
To simplify the math, in high school machine shop we used the formula; RPM= cutting speed X4, divided by the diameter of the moving part; for cutting speed for steel, we used 100 for steel, perhaps 80 for cast iron etc. using four for the circumference is close enough to the actual figure and can be done without pencil and paper (in our heads) it just results in a somewhat slower cutting speed.
The best thing is to look an e bay and find/purchase a slide rule cutting speed and feed calculator; all the carbide tool companies gave them away to customers back in the day.
 
I don't think you're missing anything, JR. I use inserted carbide in my flycutter and for aluminum I am going at top speed (2500 rpm) even with the diameter at 3". With mild steel, I am somewhere in the 400 rpm range. If you're using brazed carbide, increase your sfm by 2-3 times and you should be okay.
 
Back
Top