# Macine Speed Formula / Ratio

• posted
I have seen posted here before a formula or ration for machining speed. I
didn't understand it at the time, and still don't but a metal working guy I
know rattled it off to me the other day, and I was finally realized that
this is something I probably need to know. That and where to look up the
machining speed for various metals. Until I have just been guessing.
Probably cost me more than a few cutters and certainly has cost me time when
I set something up to run slowly so as to be sure not to break cutters.
Can somebody please point me in the right direction? Not just the
ratio/formula, but some basic guidelines in how to apply it. Thank you.
• posted
(...)
Some feeds and speeds:
Have a look at chapter 8, pages 8-19 and 8-20 of:
--Winston
• posted
"Bob La Londe" wrote in news:grto37\$q1c\$ snipped-for-privacy@aioe.org:
(4xCS)/D = RPM is the formula. 4 = A constant (been too long for me to remember how it's derrived, but there is a formula for that also) CS = Cutting Speed (Surface Feet/Minute = SFM): You find this in tables for the material you want to machine. D = Diameter: Diameter of the workpiece at the tip of your cutting tool (not the OD of the material) in inches RPM = The RPM you should be turning the work (lathe) or cutter (mill).
So, say the CS for an aluminum alloy is 3000 SFM
You are turning it on a lathe to a diameter of 3.0", the material is 3.125" so:
4 x 3000 = 12,000
12,000/3 = 4000 RPM You should run the lathe at 4000 rpm If the lathe won't run 4000 RPM, then you just run it as fast as it will go. Note that this is IF you have the part clamped properly.
Note 2: SFM, surface feet per minute is the distance of material passing by the cutting tip in 1 minute. This has _absolutely nothing_ to do with feedrate so do not get the two mixed up.
• posted
Anthony:
I believe it comes from:
CS X 12 ------- = RPM 12/3.14 = 3.82 then rounded to 4 D X Pi
CS is in surface FEET per minute. Multiplying it by 12 changes it to surface INCHES per minute.
Diameter in inches X Pi of course gives the circumference in inches.
• posted
changes it to
How about meters/minute 3.28 X SurfaceFeet/Minute=3DMeters/Minute (3.28 feet per meter) FYI: dont get the 3.82 mixed up with the 3.28!
How do you keep the cardboard chip shields up behind the Bridgeport?
Holdzem=A9=AE of course!