Teeth per Inch in Blades

When it comes to blades, the number of teeth per inch (TPI) is important to obtain your desired finish and the proper feed rate. When it comes to machining, feed rate and cutting speed refer to two separate velocities in machine tool practice. These are used whenever machining with a mill, drill or lathe. Before one can make the feed rate setting in a machine tool, the feed rate in inches per tooth is converted to feed rate in inches per minute.

Generally, a coarse tooth blade, which is typically 2 to 3 TPI, should be used for re-sawing wood and cutting thicker stock of up to 8″ in thickness. The fine toothed blade which are 18 to 32 TPI, are generally used for thinner metals, including plastics under 1/4″ in thickness.

When Selecting TPI, you should remember the following standards:

1. The more TPI you have, the smoother finish you get but the slower the cut will be.

2. The fewer TPI will always allow a faster cut on appropriate thickness but leaves a slightly rougher finish.

3. It is advisable to have at least three teeth in the work piece. To help you decide which blade you need for a cutting application here are the standards.

A 32 TPI is suited for 3/32” minimum material thickness or MMT.
A 24 TPI is suited for 1/8” MMT.
An 18 TPI blade is suited for 5/32” MMT.
A 14 TPI blade is for 1/4” MMT.
A 10 TPI is for 5/16” MMT.
An 8 TPI blade is for 3/8” MMT.
A 6 TPI blade is for 1/2” MMT.
A 4 TPI is suited for ¾” MMT.
A 3 TPI blade is for 1” MMT.
A 2 TPI blade is for 1 1/2” MMT.

Band saws have various speed settings and it is very important to know their SFM or the surface speed of the blade. It is basic to select the proper speed you need for cutting wood or other types of materials. You can however check the operator’s manual of your band saw to determine the SFM. You can also use the following procedure to determine your machine tool’s SFM:

1. Determine the RPM: You can check the operator’s manual for recorded RPM or clock and measure time on the revolutions per minute of the wheels using a revolution counter or tachometer.

2. Next is to measure the diameter of the drive wheel in inches then multiply by .262 to obtain the wheel circumference. PM times the circumference would be equal to the surface speed of the blade. Thus use this formula; RPM x diameter or circumference in inches x .262 = SFM. With this calculation, you can now proceed in choosing the right blade for your cutting job.

A word of Precaution:
Remember that steel wood cutting band saw blades should never be operated at surface speeds above 3000 SFM.
The carbon hard edge flexible back band saw blades are more suitable for these jobs and can run up to 6000 SFM.

Basically, you have learned from this article what teeth per inch in blades are meant for, to get a rough or smoother finish. It also affects the cutting time and is now classified to teeth per inch according to use and thickness of cutting jobs.