Popular Woodworking 2001-10 № 124, страница 44

mortisers

Take great care when buying this machine; it's easy to get stuck with a tool that can't hack it.

It just makes sense that as Arts &

Crafts furniture has become a popular style again, mortisers have become a hot tool. In the last 12 months, five manufacturers have introduced new benchtop mortisers designed for the home woodworker.

And while that sounds like good news if you're thinking of buying a machine, it's not entirely. Some of these new machines have more features but aren't as gutsy as the ones that have been on the market for years. The bottom line is you've got to do your homework when you buy a mortiser, or you might end up with a machine that's frustrating to use in tough woods, such as oak and maple.

Motor Speed:The Big Difference

In the last few years, manufacturers have been introducing mortisers that spin at 1,720 rpm, which is half the speed of the older machines, which turn at 3,450 rpm. Slow-speed machines are supposed to keep the chisel and bit cooler, reduce smoking and run quieter. We've tested every benchtop machine on the market and what we found is surprising.

• Smoking: Slower-speed machines are supposed to smoke less as

the chisel and bit plunge into the wood. In tough woods especially the tremendous friction caused by the combination of the cutting and the chips passing up the flutes of the auger bit inside the hollow chisel causes the chips to scorch. We found that slow-speed machines reduce, but do not eliminate, smoking.

• Stalling: Here's the big difference: slow-speed machines were likely to stall in tough cuts. With the slow-speed machines, some performed better than others. We stalled the Jet only once during our test. But the Craftsman machine stalled more than a dozen times in each 1 H'-deep by 10"-long mortise we cut during testing. We couldn't stall a fast machine, even when we tried our darn-dest.

Slow-speed machines are more likely to stall for a variety of reasons. For one, slow machines cut bigger chips because they aren't turning as fast. Bigger chips are more likely to get caught between the chisel and bit. There also are other explanations that engineers could give you.

One important note: not all slow-speed motors are weak. The burly 1 hp motor on the Powermatic floor model mortiser 719A turns at a slow speed. But because the motor is so

SHOPPING GUIDELINES

for mortisers

• We know we're in the minority, but we recommend fast-speed machines. Just be careful and use a ¹/8" clearance between the chisel and bit.

• If you work with big parts, check the maximum depth under the holddown.

• You can spend a lot of money on chisels. Learn on the cheap ones and move up if you must. Many pros use inexpensive chisels that are properly sharpened.

• Make sure the chisel is at 90° to your table. Shim the underside of the table with tape to square everything up.

much bigger, it does not stall. It was some of the ¹/2 hp motors on the benchtop machines that gave us trouble.

• Temperature: Slow-speed machines are supposed to reduce the amount of heat in the chisels compared to fast-speed machines, so your tooling will stay sharp longer. Fast-speed mortisers heated up the chisel to an average of 237° after one 10"-long mortise. The slow-speed machines' chisels averaged 209° after the same amount of work. Heat is the enemy of a sharp edge, so you probably will be caring more for your chisels or replacing them if you own a fast-speed machine.

• Working time: Fast-speed machines will speed your work. It took us about a minute and 15 seconds to cut a 10"-long mortise using a fast-speed machine. When using the slow-speed Jet, the beefiest slow-speed machine, that same mortise took 2 minutes and 9 seconds. Other slow speed-machines that would occasionally stall in a cut took more than 3 minutes to complete the cut.

It should be obvious that we prefer the fast machines. The slow machines run cooler and generally have more features than the fast-speed mortisers. But the fast-speed machines are simply less frustrating to use.

Check the Holddown

One of the big gripes with benchtop mortisers is the holddown. After you plunge the bit into your board, the holddown is supposed to keep the work in place as you pull the chisel and bit out of the work. It doesn't always work this way. The holddown on the Multico PM 12 is the best, hands down. It rides on the same

10 Popular Woodworking October 2001