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[Grayco]

I don't know how old my 12" saw blade is.  I have heard newer blades are designed to turn faster than old blades were.  Is that true?

Since I don't know for certain I am looking at spinning my blade at between 3000 and 3200 feet per minute at the edge of the blade.  Does that sound reasonable?

Thanks in advance for your inputs.

[Ranger_Dave]

I don't know about this feet per minute, but my 12 inch saw has a shaft speed of 1725 rpm and cuts most rocks pretty fast.

[Grayco]

I don't know about this feet per minute, but my 12 inch saw has a shaft speed of 1725 rpm and cuts most rocks pretty fast.

OK ... So your saw is moving about 5419 Feet per minute (FPM).  I've heard that between about 3200 and 6000 FPM is a normal range for modern blades, but I've heard that 3500 FPM is on the fast side for old blades.

Does anyone know if this is true?

[Ranger_Dave]

Can you show the math on that? Thanks.

Sorry, I don't know about old blades.

[kenny]

here ya go Dave (rpm x circumference of blade (inches))/ 12. Commonly called surface feet per minute, or spfm machinists use this approach for figureing feeds and speeds. 

[lapidaryrough]

Lapidary Blade Speed Recommendations

Approximate Arbor Shaft RPM Range
Blade Diameter    MK-301    MK-303
Surface Feet Per Minute    3000 - 4500    4500 - 6000
4" (102mm)    2860 - 4300    4300 - 5730
5" (127mm)    2290 - 3440    3440 - 4580
6" (152mm)    1910 - 2870    2870 - 3820
7" (178mm)    1640 - 2460    2460 - 3270
8" (203mm)    1430 - 2150    2150 - 2870
9" (229mm)    1270 - 1910    1910 - 2550
10" (254mm)    1150 - 1720    1720 - 2290
12" (305mm)    960 - 1430    1430 - 1910
14" (356mm)    820 - 1230    1230 - 1640
16" (406mm)    720 - 1070    1070 - 1430
18" (457mm)    640 - 960    960 - 1270
20" (508mm)    570 - 860    860 - 1150
24" (610mm)    480 - 720    720 - 960
30" (762mm)    380 - 570    570 - 760
36" (914mm)    320 - 480    480 - 640

[Grayco]

Can you show the math on that? Thanks.

Sorry, I don't know about old blades.

Sure... The math is easy. your blade is one foot in diameter. Times PI (3.14159) gives you the number of feet traveled in one revolution.  Times the number of revolutions per minute gives you the feet per minute.

1 x 3.14159 = 3.14159 feet per revolution x 1725 revolutions per minute = 5419.247 feet per minute

[Grayco]

Can you show the math on that? Thanks.

Sorry, I don't know about old blades.

Sure... The math is easy. your blade is one foot in diameter. Times PI (3.14159) gives you the number of feet traveled in one revolution.  Times the number of revolutions per minute gives you the feet per minute.

1 x 3.14159 = 3.14159 feet per revolution x 1725 revolutions per minute = 5419.247 feet per minute

If your blade was 18"

18/12=1.5 feet in diameter * 3.14159 = 4.712 feet per rev (FPR)  * 1725 = 8128.871 FPS

[Ranger_Dave]

Thanks. I get it now. I have a mild case of dyscalculia. I took bonehead math 3 times. Forgot 90% of it minutes after I finally passed. I think I've done pretty well for myself without ever using the quadratic equation.