Real Turning Speed per Diameter

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leehljp

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In another thread "Turning Speed", there is the discussion on turning speed for different kinds of blanks and other bits of information.

Quite often here, Bowl Turners who are used to turning from 50 RPM to 700 RPM max - have a strong hesitancy to turn at 2000 - 3000 rpm or more. There are a few bowl turners who become inquisitive and do the math. I spelled it out at close to the end of the thread mentioned above, but also realize most people will overlook it in an older thread. Therefore I am creating a new thread to make it easy for quick reference in the future.


12" bowl at 700 RPM:
12” x 3.14 = 37.68 inches
37.68” x 700 rpm = 26,376 inches per minute on the outer edge
26,376” / 12” = 2198 feet per minute
2198 FPM x 60 minutes = 131880 ft per hour
131880 ft per hour = 24.97 MPH or 40.18 KPH

24.97 MPH is the cutting speed of a 12 inch diameter bowl (on the outside diameter) at 700 rpm.


3/4" diameter blank at 3000 RPM, Notice the speed difference!

.75 x3.14 = 2.355 inches
2.355 x 3000 rpm = 7065 inches per minute on the outer edge
7065 / 12” = 588.75 ft per minute
588.75 FPM x 60 minutes = 35,325 ft per hour
35,325 ft per hour = 6.69 MPH or 10.76 KPH

6.69 MPH is the cutting speed of a 3/4” diameter rod at 3000 RPM

SPECIAL THANKS TO MAL (MagPens) For confirming my calculations.

3000 rpm on a 3/4" diameter blank is turning at 1/4 the speed of the outer diameter of a 12" bowl at 700 rpm.

CAVEAT: THIS DOES NOT MEAN THAT A TURNER NEEDS TO SPEED UP TO 12000 RPM FOR A PEN BLANK - TO EQUAL THE 12" DIAMETER SPEED OF A BOWL AT 700 RPM!!!!

Below is a bowl / lathe speed chart - for bowls only. This chart is fairly common on some bowl turning sites. But that only shows speed for bowls. Pens are a different animal due to their small diameter. So don't be afraid of the "need for speed" (higher RPM - around 2000 and up to 3000 rpm) to produce a smooth round pen.
 

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jttheclockman

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Definetly a huge difference between turning bowls, plates, and other items that are larger than our pen blanks. But there is also no set speed to turn pen blanks at other than mid range to fast. A little experimenting will give you an idea what an ideal speed is for your talents. I never turn my lathe to its fastest speed because it is a pain switching back and forth on pulleys. I just leave on center pulley and run the speed controller up or down and that has worked well for me. Could not even tell you what that speed is and really has no value to me. Sharp tools is the key. This works for me. Others milage may vary. But would not get all bothered by exact speeds. nice chart.
 
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leehljp

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John's mention of "Sharp Tools is the key" is right on. The slower cutting speeds of the pen blank work better and smoother with very sharp tools.
 
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