Source: TOOLS OF THE TRADE Magazine
Publication date: August 13, 2012

By Michael Springer

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Oscillating multi-tools (OMTs) have been getting a lot of attention lately — new brands, more advertising, and a growing presence at supply centers and big-box stores. There are two main reasons for this surge in interest: First, the tools are genuinely useful on the job site. And second, Fein's patent on the technology expired a few years ago.

As the originator, Fein made oscillating cutting tools for decades before marketing them to contractors. The very first model was a plaster cast-cutting tool for physicians that hit the market about 45 years ago. It evolved into an automotive body-cutting and windshield-removal tool, and then into a triangle sander. Not until the introduction of cutting and scraping blades did the device became the OMT we're familiar with today.

For this article I tested full-size OMTs — corded models and cordless ones with 14.4- or 18-volt batteries. I chose not to include 10.8-volt (12-volt maximum) tools, because their lack of runtime would make comparisons to larger models unfair.

How OMTs Work

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The mechanism that gives these tools their oscillating action is quite simple. A bearing — slightly off-center with respect to the motor shaft — fits between a pair of arms that are connected to the blade-mounting spindle. With each turn of the motor, the bearing pushes the arms one way and then the other. It's a miniscule movement, but the high number of oscillations per minute (opm) allows the tool to work effectively. The opm matches the rpm of the motor, so at top speed the teeth on a cutting blade (which cut in both directions) could be taking 40,000 bites per minute.

The small angle of travel (between 2.8 and 4.0 degrees) accounts for the ease with which OMTs can be controlled as they cut, sand, and scrape. Because of the spindle's limited throw, the triangular sanding pad does not bounce out of corners. Scraping works in an unexpected way: The intense friction at the tip of the blade actually melts and softens old mastics and sealants — something you can't achieve with a putty knife.

Testing the Tools

To see what the tools could do, I spent several days using them for the kinds of tasks they'd be asked to perform on the job site. I cut baseboard in place over drywall, notched trim and framing, cut through drywall and floppy cabinet backs, and trimmed 1-by jamb material. When I wasn't cutting, I was sanding wood, removing grout, and scraping off old mastic. Click here to see my observations on the OMTs' performance.

I used Bosch blades for the comparative testing because their interface is the only one that fits or can be adapted to every tool tested. I did not set out to test accessories, but after using some from all of the makers who provided tools, it's my sense that the European-made Fein and Bosch/Makita blades are a cut above the rest. Their wood blades cut faster and truer without smoking, and their carbide-grit tools have a thicker and more even coating.

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The end of the motor shaft is milled slightly off-center so that the drive bearing moves side-to-side as the motor spins, pushing the spindle one way and then the other. Each rotation of the motor produces one oscillation.

Attaching Accessories

The traditional way to attach accessories is to bolt them to the spindle.

That's how it's done on the Ridgid, Makita, and Rockwell tools; the more-evolved machines have tool-free blade-mount systems. I prefer the tool-free approach because it makes it faster and easier to change or reposition blades.

Fein's blade clamp is controlled by a lever attached to the top of the housing; you pull up to release and push down to engage. A flanged holding pin comes free when the lever is released and clamps firmly over the accessory when the lever is engaged. The internal spring is very strong, so it takes a fair amount of force to retract the lever.

If you're not careful, the lever can "mousetrap" painfully onto your fingers when you push it back down. The spring is especially stiff on the corded SuperCut model.

Bosch's clamp lever is set into the side of the tool; it has smooth action and will not snap closed. The exposed positioning pins and spindle make it simple to attach and adjust accessories.

Porter-Cable's system is the easiest of all to operate. A spring-loaded lever clamps over the blade and positioning pins. Squeezing the lever frees the blade, and releasing the lever clamps the blade in place. The blades for the Porter-Cable tools are different from the others — they're open along the edge, so they can fit around (rather than over) the spindle.