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 Formula for converting FPM to RPM
 posted 20 September 2005 02:25 PM
Does anyone have the formula for converting FPM (foot per minute) to RPM?

 Posts: 55 | Location: Portland, OR | Registered: 02 March 2005 IP
 posted 20 September 2005 02:53 PM Hide Post
quote:
fr = (V/3.142D)Hz

Vib,

Why do you have "Hz" multiplied by rpm?

FPM divided by 3.1416*diameter equals rpm doesn't it. Then divide by 60 to get Hz?

Might be a little clearer if I said divide the FPM by 3.1416 and then divide the answer by the diameter(in feet) on the roll or felt length, depending on what speed you are looking for.

Thanks and Have a Great Day,
Ralph
Senior Analyst and Instructor @

 Posts: 2461 | Location: Mississippi | Registered: 01 March 2005 IP
 posted 20 September 2005 02:53 PM Hide Post
Rick,

I can send you the formula I use at the paper mill to get roll RPM from FPM if that is what you are asking for.

Let me know
Tommy

 Posts: 10 | Location: West Linn, Oregon | Registered: 17 March 2005 IP
 posted 20 September 2005 02:54 PM Hide Post
Oppps,
Where did you go?

Thanks and Have a Great Day,
Ralph
Senior Analyst and Instructor @

 Posts: 2461 | Location: Mississippi | Registered: 01 March 2005 IP
 posted 20 September 2005 03:02 PM Hide Post
If diameter is in inches;

RPM=(FPM x 12)/(D x pi)

 Posts: 72 | Location: Quebec, Canada | Registered: 24 February 2005 IP
 posted 20 September 2005 03:08 PM Hide Post
Rick,

FTPM = Feet Per Minute
C = Circumference of Roll in Feet or Length of Felt in Feet

RPM = (1/C)*FTPM

To get the Circumference of the roll take the roll diameter (usually in inches) multiply by Pi 3.142 and divide that answer by 12 to get the answer into feet.

D = Diameter in Inches

Circumference in Feet = (D*3.142)/12

If you are using SKF and the speed point setup, 1/C will give you the ratio you need in your point setup.

 Posts: 20 | Location: South Alabama | Registered: 16 April 2004 IP
 posted 20 September 2005 03:30 PM Hide Post
Thanks for all of the input. After playing with all of the formulas I found another one that works:

RPM=(FPM/pi)/(D*12)

 Posts: 55 | Location: Portland, OR | Registered: 02 March 2005 IP
 posted 20 September 2005 03:56 PM Hide Post
Simplified it comes to fpm=rpm x dia x .262

Danny

 Posts: 3545 | Location: Midlothian, VA, US | Registered: 22 February 2005 IP
 posted 20 September 2005 04:18 PM Hide Post
quote:
Originally posted by Rick Sheldon:
Thanks for all of the input. After playing with all of the formulas I found another one that works:

RPM=(FPM/pi)/(D*12)

Rick,

I can't get this formula to work.

Of course it is late in the day, and I'm tired and old.

 Posts: 20 | Location: South Alabama | Registered: 16 April 2004 IP
 posted 20 September 2005 05:43 PM Hide Post
I think that Rick got fpm and rpm switched.

The long formula is:

feet/minute=(revolutions/minute)* (Dia. (in.) * pi)/12)

The simplification factor that I used of .262 is pi/12 to convert diameter in inches to feet.

It is easier to understand the practicality if you think about it as this:

fpm=rpm x circumference

It's an old power transmission formula that was used all the time to chech on the maximum rim speed of v-belt sheaves and it was ground into my head from 15 years in that field. BTW it is 6500 fpm for standard off the shelf sheaves. Higher rim speeds require dynamic balancing and perhaps series 50 ductile iron as a meterial rather than series 30 grey iron.

Thanks for the trip down memory lane.

Danny

 Posts: 3545 | Location: Midlothian, VA, US | Registered: 22 February 2005 IP
 posted 20 September 2005 05:49 PM Hide Post
Hi Danny,

What I am doing is calculating roll rpm in a paper machine, where fpm is a known and roll rpm is unknown.

Thanks for all the input

 Posts: 55 | Location: Portland, OR | Registered: 02 March 2005 IP
 posted 20 September 2005 06:06 PM Hide Post
Rick,

Using the formula the way you put it with 1000 fpm and a 36" dia roll we would have:

rpm= ((1000 fpm)(3.14))/(36*12)=7.27 rpm

Using the other way:

1000 fpm=(rpm*.262*36)=106.0 rpm.

I'm pretty sure that you have fpm and rpm switched, but check me out again if you don't mind.

Danny

 Posts: 3545 | Location: Midlothian, VA, US | Registered: 22 February 2005 IP
 posted 20 September 2005 06:51 PM Hide Post
Some how I am missing something here? Would we say RPM= FPM/(pi*dia/12). Danny in your example:
1000 FPM/(3.14*36/12)= 106 RPM. Ya'll help me if I am wrong. I use to think this was easy but now I am confused.

Thanks,
Ronnie

 Posts: 431 | Location: Mobile, AL | Registered: 13 April 2004 IP
 posted 20 September 2005 07:39 PM Hide Post
I think the fog has lifted a little. A shower and something to eat helped. Alec's formula works, just looking at it different than I think about it. Danny's simplied version makes since when I substitute RPM and FPM. If
FPM=RPM*dia*.262 then RPM=FPM/dia/.262 Whew!! Eight hours sleep and I might get this.

Thanks,
Ronnie

 Posts: 431 | Location: Mobile, AL | Registered: 13 April 2004 IP
 posted 20 September 2005 10:40 PM Hide Post
It's all in the grouping and keeping the units straight. If you want an answer in feet per minute, make sure you're dealing with feet and minutes before you put it in the formula

fpm = rpm * circumference

I think that's the easiest one to remember. And like BamaVib mentioned, the 1/circumference factor is the same one used in CSI in the equipment setup (it's the same math).

Patrick

 Posts: 441 | Location: VA | Registered: 19 April 2004 IP
 posted 21 September 2005 07:14 AM Hide Post
Here I am Ralph.
I posted the formula, then realized that it wasn't very clear and there may be an error. I can do quick calculations on the floor in m/min with roll diameters converted to meters. I just didn't have time to clarify so I deleted it and went home. It's funny how I do this all the time but ask me to explain it and it gets all fuzzy I don't think I'm getting old yet............

ensing-dot-ron-at-irvingtissue-dot-ca

 Posts: 473 | Location: Great White North | Registered: 21 February 2005 IP
 posted 21 September 2005 09:28 AM Hide Post
OK Vibbase, We'll let you off this time.

Lot of ways to do the same thing here, so one should choose the easiest to remember.

All this brings up a good point, one who struggles with math is going to have a rougher road to travel in this field than normal.
Just my opinion and I could be wrong.

Thanks and Have a Great Day,
Ralph
Senior Analyst and Instructor @

 Posts: 2461 | Location: Mississippi | Registered: 01 March 2005 IP
 posted 21 September 2005 09:38 AM Hide Post
I hear you Ralph, I'm writing the CatIII exam this October and the math is unbelievable. When was the last time you used an oscilliscope to measure vibration and convert the volts to velocity?

So, I looked at the formula as written again;

Fr = V/(3.142D)

(divide by 60 to get Hz instead or cpm)I'm not sure why they added the Hz to the end of the formula without specifying division or multiplication, it's probably a typo on my sheet.

It's keeping the units the same that is important so if you're in feet per minute "D" must be in feet.

Would any of you like a copy of a formula page as it applies to vibration? It's the sheet supplied with the Vib Institute exams (CMVA is the affiliate here in Canada) I don't think there is any copyright problems. Let me know.

This message has been edited. Last edited by: vibbase,

ensing-dot-ron-at-irvingtissue-dot-ca

 Posts: 473 | Location: Great White North | Registered: 21 February 2005 IP
 posted 21 September 2005 12:15 PM Hide Post
quote:
Originally posted by Ronnie Lynn:
I think the fog has lifted a little. A shower and something to eat helped. Alec's formula works, just looking at it different than I think about it. Danny's simplied version makes since when I substitute RPM and FPM. If
FPM=RPM*dia*.262 then RPM=FPM/dia/.262 Whew!! Eight hours sleep and I might get this.

Thanks,
Ronnie

Ronnie,

I think you got it right, just typed it wrong.

RPM=FPM/(dia*.262)

Ralph,

You got that right. I would never have thought there would be this many post on this formula.
But like you said, "Lot of ways to do the same thing..".

Time to go back to work.

Let me see naught plus naught equals.......

Matt

 Posts: 20 | Location: South Alabama | Registered: 16 April 2004 IP
 posted 21 September 2005 01:51 PM Hide Post
Thanks Matt. 12 hours 7 days a week and I feel lucky I understood any of it. I only worked 8 hours today and I feel like I almost had the day off. I plugged the numbers into it the way you wrote it and the way I wrote it and I come up with the same answer? Not sure why that is but like what Ralph said,"so one should choose the one that's easiest to remember". I never really put it into a formula, just knew I needed circumference in feet and then divide into FPM. Works for me.

Thanks,
Ronnie

 Posts: 431 | Location: Mobile, AL | Registered: 13 April 2004 IP