Calculating SFM of your belts

Self Made Knives

Self Made Knives

Well-Known Member
Ken, opinion please? I didn't want to pollute Fred's post yesterday, so I started another. But you two got me to thinking about SFM on my grinder. I always hear everybody talking about it, but never new where I was at with mine.

So, to Google, then to Wikipedia and I found that SFM can be calculated using the following equation:
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Well, I'm using a 4" drive wheel on my direct drive grinder and when I plug that value in, I basically get RPM=SFM. Can it be that simple? 1800 rpm = 1884 sfm. Figure in a little natural slip with load and it really ends up RPM=SFM on a 4" drive wheel. My VFD/motor combo will run 3600 rpm max, so I'd say about 3600 SFM is my max.

Does this look/sound right to you guys?

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Yep, it's that simple.
circumference of the drive wheel = pi x diameter... on a 4" wheel, it's close enough to 12 that SFM is roughly equal to RPM.
 
Anthony, they've answered your question. In fact, I think it's 3.8" where RPM equals SFPM not factoring in any slip. So, for a ROT, yep, with a 4' drive wheel, RPM = SFPM is correct.

Even with 3 step pulley of the 2", 3", & 4" diameters, it's almost that easy. When using the 2X4 set with 4" drive pulley, it's 1/2 RPM of motor, so with an 1800 RPM motor that is about 900 SFPM (shaft RPM with drive pulley), and if 4X2, it's about 3600 SPFM, and with 3X3 then it's 1800 SFPM.

Ken H>
 
Harbor Freight has a tachometer that sells for about $20.00 that will measure SFPM or RPM. I have one and it works well.
 
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