Blade basics

Proper recip saw blade selection and timely replacement will make the most of your cutting time.

by Dan Anderson

I once spent a long, miserable summer working for a one-horse house-builder who was fanatical about “consumables.” He encouraged me to sharpen dull razor knife blades with a file and went ballistic if a reciprocating saw blade was discarded while it still had teeth visible anywhere on the blade.

I eventually came to view reciprocating saws as tools of the devil, designed to beat underweight college kids into a pulp while gouging ragged holes in framing, pipe and nearby objects.

A post-college job with a more progressive contractor quickly changed my opinion about reciprocating saws. We were an hour into a major remodeling job and some serious demolition work. I barely broke a sweat using a recip saw to slice through studs, nails and wallboard. When the blade inevitably dulled and the smell of burned wood drifted from my latest cut, the foreman shouted from across the room, “Get a new blade! You know, that’s why they’re called consumables.”

Yes, we went through a lot of blades on that job, but the cuts were clean, accurate and fast, matching the philosophy of the contractor. Encouraging the crew to use the right blade for the job, and to keep sharp blades in the saws, ultimately saved enough time to more than offset the cost of those consumables.

Spend cents to save dollars
“It all comes down to time and money,” says John Hedbor, Starrett marketing manager. “You really can save time by taking time to get the right blade for the job. Many contractors buy assortment packs of recip saw blades so they’ll have a blade for every sort of cutting job on a jobsite, but the result is that blades get used in the wrong situations because it’s easier to grab any blade from the pack than the right blade.”

Most recip saw users are well-aware of the general rule that you use coarse blades for wood and fine blades for metal and plastic. A few tips can further fine-tune blade selection to increase cutting capacity, improve quality of cuts, save time and reduce effort.

Blade selection
Number of teeth per inch (TPI) on recip saw blades varies from three up to 24. In general, the lower the TPI, the faster the blade cuts and the rougher the edges of the final cut. Coarse blades with 3 to 10 TPI  cut wood aggressively.

Recip blades with 10 to 14 TPI are recommended for cutting nail-embedded wood, composites, light-gauge metal and plastic. The goal is to have at least three teeth in contact with the material being cut at all times to prevent snagging. Ten- to 14-TPI blades work well for metal 1/4" and thicker. Thinner metals, including conduit and pipe hangers that range from 3/16" to 1/4" require 14 to 18 TPI blades; 18 to 24 TPI blades are designed for thin-gauge metal sheeting and metal from 1/8" to 3/16" thick.

Plastics and non-ferrous metals such as copper and aluminum are best cut at slow speeds with a 10 to 14 TPI blade.

“The issue with stainless steel and plastics isn’t the tooth count as much as it is the speed that the blade is operated,” says Tiny (Alan) Coffin, Starrett saw sales manager. “If the operator understands how to match speed with the material being cut, a variable-speed reciprocating saw can really extend the lives of blades.”

“High speed is for wood, slower speeds are for metal,” says Coffin. “Speed builds heat and heat is what destroys recip saw blades. As a rule of thumb, a blade should run warm, but never hot to the touch. If you’re cutting metal and the blade gets hot, you’re running the saw too fast.”

Heat is also the reason variable-speed recip saws should be run at slower speeds when cutting plastic. Run a recip saw through plastic at high speed, and heat eventually builds until the blade melts, rather than cuts, its way through the piece.

If it’s a big metal-cutting job, a trip to the grocery story can speed the work. “Spray a metal-cutting blade with Pam cooking spray after every few cuts,” suggests Coffin. “It will help keep it lubricated, which will reduce heat buildup and increase blade life. Starrett M-1 cutting oil, WD-40, or any other light spray lubricant will do the same thing, but it’s hard to spray and use two hands to guide the saw at the same time.”

Variable-pitch blades offer faster cuts with reduced vibration and chatter in metal. The blades have alternate tooth spacing between 8 and 12 TPI down the length of their cutting edges. Variable-pitch blades make good all-purpose blades where workers are switching between cutting metal and wood so often it’s hard to justify the time it takes to swap blades.

Select the saw and its setting
“It’s not only important to make sure you’ve got a blade with the right tooth count in the saw, but that the saw is the right type of saw for the cut you’re making,” says Tom Fogarty, Bosch’s manager of product training. “Recip saws come in different stroke lengths, generally either 3/4" or 1 1/4" stroke. Short-stroke saws are more precise and make smoother cuts, so they’re best for cutting pipe and PVC. Long-stroke saws are designed for aggressive cutting, but are more of a handful when making plunge cuts. Short-stroke saws really aren’t that expensive, around $99 to $109. It’s kind of handy to have both types of saws on a jobsite so you can do detail work or plunge cuts with the short-stroke saw, and fast or deep cuts with the long-stroke saw.”

Recip saws with optional orbital motion can destroy metal cutting blades in seconds if used incorrectly. Orbital motion lifts and resets the blade at the end of each stroke, which improves cleaning and speeds cuts in wood. But what’s good for wood cutting is bad for metal cutting.

“Orbital motion slams the teeth back into the metal on every stroke,” says Fogarty. “You’ll knock the teeth off in seconds. Metal cutting requires a straight back-and-forth motion, so make sure you have the orbital action turned off on saws with that option when cutting metal.”

Thick blades for big jobs
Another trend in recip saw blade design is thicker blades. Recip saw blades were typically 0.035" thick, but customer demand has produced blades of 0.040" to as much as 0.062".

“If you’re doing demolition, you probably need to use thicker blades and a deeper blade profile,” says Peggy Thomas, Milwaukee Electric Tool production manager. “A 0.062" blade with a 1" height profile will resist bending better than a thinner blade, and be less prone to wobble on the backside of cuts.”

The final key to maximizing worker and recip saw efficiency is to let the blade do the work. “In most cases, a sharp blade will pull itself into the work at about the right speed,” says Thomas.

“If you have to lean into a blade to get it to cut, it’s time for a new blade. In the end, you’ll make up for the time and cost of installing a new blade by making faster, cleaner cuts, with less effort and frustration.”

Published in the May 2004 issue of Contractor Tools and Supplies magazine.

back to top