LumberJocks Woodworking Forum banner
  • Please post in our Community Feedback thread for help with the new forum software! If you are having trouble logging in, please Contact Us for assistance.
1 - 10 of 10 Posts

·
Registered
Joined
·
1,939 Posts
I was having a discussion the other day and the question of how fast the outside edge of a bowl blank is actually moving came up

I couldn't remember the math… been to long. Do any of you lj's or engineers remember the formula for that?

Lets say that the lathe is running at 500rpm and you have a 6" diameter blank mounted; how fast is the edge actually going?
 

·
Registered
Joined
·
248 Posts
Here is my guess somebody is welcome to correct…

Circumference = pi x diameter, so 3.14×6 = 18.84" circumference (distance around)

If that is spinning 500 times in a minute , that = 9420 inches a minute. That equals 785 feet per minute.

To have more fun… x 60 that equals 47,100 feet per hour…divided by 5280 = 8.92 miles per hour.
 

·
Registered
Joined
·
248 Posts
Now to have yet more fun…

If a 6" spinning bowl blank leaves chicago at 10:00 a.m heading for new york at 500 rpm, when will a 9" bowl blank leaving Chicago at noon heading toward New York spinning at 550 rpm pass the 6" bowl blank?

(my brain hurts just writing that question…)
 

·
Registered
Joined
·
1,939 Posts
Discussion Starter · #6 ·
I guess I could have worded that better…. The real question would have been regarding velocity….

Tip speed in Feet p/Sec i guess…. versus the rpm. You see the discussion was regarding the proper rpm vs the blank size which kind of morphed into this side question.
 

·
Registered
Joined
·
1,652 Posts
Do you mean, "for a specified tip speed and diameter, what should your RPM be"? Then it's just a matter of rearranging the equation (solving for RPM) and boiling down the constants. For tip speed in feet/sec and diameter in inches:

RPM = 229*tip speed/diameter
 

·
Registered
Joined
·
16,431 Posts
The next question this raises for me is: What is a good tip speed for shaping a bowl blank?

I did a little research and found several references to this simple formula: The diameter of the blank in inches multiplied by the lathe rpm should fall between 6,000 and 9,000. So, for example, you would want to turn a 10" blank somewhere between 600 and 900 rpm. A 5" blank should be turned at between 1,200 and 1,800 rpm, and so on.

This video explains it:

 
1 - 10 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top