Teeth per inch (TPI) is one of the first specifications you’ll see when looking at reciprocating saw blades. As you might guess, TPI is an indication of the number of teeth on the blade, typically ranging from 6 to 24.
Understanding tooth count will help you find the best reciprocating saw blade for different jobs. Why is TPI important?
Blade TPI is a factor in performance. Blades with a lower TPI cut faster and more aggressively than blades with a higher tooth count. Blades with a higher TPI create a smoother cut.
Blade TPI is also a factor in the material the blade will cut. Blades with a lower TPI are more suitable for wood. They work well for demolition projects where speed and the ability to cut through lumber and nails is more important than a smooth finish. Blades with a higher TPI measurement are perfect for cutting wood when clean edges are important. They can also be suitable for cutting metal.
A reciprocating blade set with different TPI specifications is an excellent choice for a do-it-yourselfer. A set gives you a range of options so you’ll be ready for a variety of cutting tasks.
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Along with TPI, reciprocating saw blade sizes — length, width and thickness — are other factors in finding the best blade for a project. Different materials and different uses require blades of different sizes, so it’s a good idea to have a variety.
Blade length determines the cut depth a reciprocating saw blade is capable of making. Longer blades make deeper cuts, so they can cut thicker material. The blade should be a couple of inches longer than the thickness of the material you need to cut. Standard lengths range from 4-inch blades to 12-inch blades, with 9-inch reciprocating saw blades being good, common choices for general DIY work.
Long blades can bend a bit and work well for flush cuts or cutting curves. A longer blade also cools better, which can give it a longer life. You’ll see longer blades used in pruning as well as heavy duty demolition work.
Shorter blades don’t flex as much as longer blades, so they cut more aggressively. You can usually control a shorter blade more easily and you’re more likely to get a straight cut. The rigidity of a short blade makes it work well on thicker metals and for starting cuts in material where you don’t have an edge or pilot hole (known as a plunge cut).
Like shorter blades, wider blades are more rigid and offer more stability than a comparable narrow blade. Manufacturers measure width across the face of the blade, from the teeth to the top of the blade, so wider blades have a higher profile. For demolition work, use a 3/4-inch-wide or wider blade. For cutting that requires a smoother finish or more careful work, choose a narrower, low-profile blade.
Manufacturers measure blade thickness across the edge of a blade. As with length and width, thickness is a factor in blade strength and rigidity. Blade thickness usually ranges from .035 inch to .050 inch or more.
Thinner blades are suited to general do-it-yourself work, detailed cutting and creating a smooth finish. Thicker, stronger blades let you do heavy-duty work and cut through tough, dense material. Thick blades create a wider cut (known as the kerf), removing more material than thin blades. Keep this in mind for work where measurements and cuts need to be exact.
Although fabricators often use abrasive wheels for cutoff, have you considered the benefits of reciprocating saw blades? “Recips” are excellent for cutting applications because of benefits such as safety through reduced vibration and noise, a drastic reduction in spark production and fire risk, ease of access to the work, large cut capacity and multi-purpose ability. With a push-pull motion, reciprocating blades can cut through metal quickly and cleanly. Bi-metal reciprocating blades will cut through everything from the thinnest sheet steel up to heavy duty steel sections.
There are a range of important benefits that recip blades offer. So, before you pick up your grinder and mount that abrasive wheel, consider the following:
Safety -
Due to the way reciprocating saw blades work in materials and the milling process, there are virtually no spark projectiles which can cause operator injury and property damage via fire or explosion. With recips, metal is machined away in chips from the material with each pass. The energy created from the recip cutting process is very limited, so in turn, heat is extremely reduced. The temperature is kept very low across the substrate and the cutting tool. This keeps high temperatures from building in the chips and reduces liabilities. Another advantage is that no “hot permit” is required when using recip blades, which saves on costs.
One the other hand, cutoff abrasive wheels rated to 80 m/s may spin up to 16,000 sfpm, and throw 1,800° sparks as far as 30' from the grinder. These actions put abrasive and metallic dust into the air, which can be inhaled. The liquid hot metallic sparks are not only dangerous to the operator, they can be a fire hazard. Also, depending on the substrate, the sparks can cause chemical reactions with the metals being worked, encouraging development of iron oxide (red rust) on various materials. Guards are required on a grinder, and if ignored and misused, users are subject to significant fines. For all these reasons, abrasives receive new safety regulations nearly every year.
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Particulate Size -
Recips produce larger chips and have virtually no wear. This means that the dust emissions are extremely limited, resulting in cleaner finished cuts and healthier air for breathing (another safety advantage). Cleanup is easier since the swarf is contained and distributed from the tooth gullets and deposited to the floor in one place, instead of becoming airborne dust that cutoff wheels produce.
With cutoff wheels, abrasives and metallic dust are generally very small, especially with fine grits. This results in a lower mass with particulates that can get hung up in the atmosphere more easily with a higher chance of being inhaled.
Cutting Tool Endurance -
Industrial grade recips, such as Starrett 3X Power Reciprocating Saw Blades, utilize premium quality materials that can endure a tremendous amount of torsion and still be used effectively with a very limited risk of breakage. This keeps the operator and those in the surrounding area much safer, reducing potential liabilities. In contrast, it is not uncommon for cutoff wheels that run at higher speeds to shatter, producing dangerous flying shrapnel.
Superior Reach -
If an application requires significant reach, recips are a good cutting solution. Since there are no guards on reciprocating saws, the blades can reach as far as a foot away from the end of the saw, getting into tight areas with precision and a remarkable degree of safety to the operator and those in the vicinity.
If using a cutoff wheel, it might be tempting to remove the guard in order to reach a particular area. However, it only takes a fraction of a second for a wheel to break and the results can be catastrophic putting the operator and those in the area at high risk, as well as putting the company at a high risk of liability.
Recips offer a versatile cutting solution that reduces changeover for substrate geometry differences, and offers better reach with a lighter tool. For example, a 9” grinder is required to cut a 3” pipe, but the recip saw size remains the same no matter the length of blade and the user can make the cut with a 6" blade.
Economics –
The right type of recip blade with an enhanced tooth design such as the Starrett 3X Power Bi-Metal Blade cut more efficiently, enabling users to make up to three times the number of cuts than conventional recip blades, and are engineered for use on corded and cordless saws.
In terms of wear, reciprocating saw blades hold a constant size and therefore, a constant sfpm so the cutting efficiency is very similar from the first and last cuts to be made with the saw.
A versatile solution which has the ability to cut aluminum, solid and non-solid profiles and stainless steel, 3X Recips blades will yield the best performance results in tube and pipe cutting applications as well as thin gage materials. This is where a user will find the greatest savings in cost per cut.
Note that an abrasive cutoff wheel benefits from high sfpm because the increased speed allows for faster impacting of the abrasive grains. However, the grinder does not increase in rpm as the abrasives’ diameter wears down, resulting in a constant decrease to the sfpm speeds of the wheel. So, there is a negative correlation between wheel diameter and seconds per cut. As one decreases from the start of use, so does the other.
See Chart 1 (below) - Performance cutting tests conducted at Starrett comparing 6" 3X Recip blades to 4.5" abrasive cutoff wheels yielded an average annual savings advantage of over $14,000 when making 74,750 cuts in schedule 40 steel pipe, as compared with using a variety of cutoff wheels for the same application. This example is based on what a small or mid-sized shop may see and assumes 3 operators at the national average labor rate* using 1 box of abrasives (25 wheels in each box) per week each for a total of 75 wheels weekly versus 6 recips per operator each week totaling 18 blades for the same weekly time period.
Operator Experience –
Importantly, for the operator experience, recip blades offer good ergonomics and convenience. For example, due to being able to cut faster, less time is spent operating the saw and experiencing vibratory forces. Particulate emissions are minimized and the recips have on average a 15dB quieter operation. In addition, fewer blade change-outs are required compared to wheels, which results in significant time savings.
Ease of Selection -
Reciprocating blades such as Starrett offer color coding on the universal shanks: for example, blue for metal cutting, red for multi-use, yellow for wood cutting, as well as black for heavy duty multi-use enable a fast, easy way to judge what blade to use for the application.
Typically, two different reciprocating blade shapes are offered:
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