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Determining the tip speed of a rotating disk

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Forum topic by Chris posted 1564 days ago 1766 views 0 times favorited 9 replies Add to Favorites Watch
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Chris

1866 posts in 2575 days


1564 days ago

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?

-- "Everything that is great and inspiring is created by the individual who labors in freedom" -- Albert Einstein


9 replies so far

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PaulfromVictor

220 posts in 1930 days


#1 posted 1564 days ago

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.

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CharlieM1958

15623 posts in 2803 days


#2 posted 1564 days ago

How fast is the edge going? 500rpm. :-)

But I guess you wanted miles per hour? Feet per second?

-- Charlie M. "Woodworking - patience = firewood"

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PaulfromVictor

220 posts in 1930 days


#3 posted 1564 days ago

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…)

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CharlieM1958

15623 posts in 2803 days


#4 posted 1564 days ago

In Pittsburgh?

-- Charlie M. "Woodworking - patience = firewood"

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Chris

1866 posts in 2575 days


#5 posted 1564 days ago

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.

-- "Everything that is great and inspiring is created by the individual who labors in freedom" -- Albert Einstein

View JJohnston's profile

JJohnston

1577 posts in 1876 days


#6 posted 1564 days ago

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

-- "Sorry I'm late. Somebody tampered with my brakes." "You should have been early, then."

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PaulfromVictor

220 posts in 1930 days


#7 posted 1564 days ago

13.08 feet per sec.

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CharlieM1958

15623 posts in 2803 days


#8 posted 1564 days ago

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:

http://www.youtube.com/watch?v=-3mqZjTgVc4

-- Charlie M. "Woodworking - patience = firewood"

View cosmicturner's profile

cosmicturner

403 posts in 1980 days


#9 posted 1563 days ago

I can answer the safest speed is 0.0
hard to say it depends on the cut your making and the type wood no real rule more of a feel but less viberation is better unless you want texture…chatter time
happy turning

-- Cosmicturner

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