For $250 and half an hour's worth of simple improvements, you can cut precise mortises all day.
Mortising machines first answered the prayers of mortise-cutting
woodworkers over 120 years ago. Today you can buy a miniaturized
descendant of those old-timers. Though they're not the only powered
option you have for mortising these days, their square mortises are the
perfect match for tablesawn tenons. We tested eight benchtop machines
designed to cut mortises up to 1/2-in. wide. They're similar in size
and capacity, and all but one sell for less than $250. They all use the
same specialized chisels and drill bits. The machines are easy to set
up and ready to cut mortises within 20 minutes. After our own testing,
we invited a group of professional and amateur woodworkers to try out
the machines as well. All together, we cut hundreds of mortises with
each machine, using 1/4-in. to 1/2-in. chisel sets, in mahogany, red
oak and maple.
It's Okay to buy Cheap Bits
For testing, each machine was outfitted with new chisel sets from the
same manufacturer. We tried sets from British, American, Austrian and
Japanese manufacturers before deciding to use the cheapest ones, which
are made in Taiwan. You can spend a lot of money on chisel sets, but we
think these inexpensive ones (usually less than $20), are a good buy.
Out of the box, they needed the least amount of sharpening. They cut
clean mortises and we found them easy to resharpen. Besides, accidents
happen, bits get ruined and it's less traumatic to replace a cheap set.
Taiwanese sets are usually available from suppliers who sell benchtop
mortisers.
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A HOLLOW CHISEL with an auger bit inside is the secret to machines
that cut aquare mortises. First the auger roughs out the mortise by
drilling a hole and clearing the chips. To square the corners, you have
to force the chisel through the wood. This can take a lot of force-a
square 1/2-in. mortise chisel has a 2-in. cutting edge. That's why
mortising machines take muscle to operate.
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The Major Difference Between Machines Is Motor Speed
Traditionally, mortisers used fast-speed, 3,450 rpm motors, but now
slow-speed machines are also on the market. Three of the machines we
tested have 1,725-rpm motors. Why the change? Manufacturers we talked
to say slower speeds increase the life of the chisel sets. We think
that's one reason slow-speed machines are less stressful to use. You
don't have to worry about overheating the tooling. They're also quieter
and rarely cause smoke. However, they don't cut mortises as easily as
fast-speed machines. At a comfortable feed rate, we found cutting
1/2-in. mortises takes 5 to 10 foot/pounds more effort. Fast or slow
speed? You have a choice between cutting ease and ease of mind.
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Tune UP THE AUGER before you use it. With a small file, remove leftover
machining burrs from the inside adge of it's scoring spur and the
angled top edge of its cutting lip. When these bits get dull they can
wasil be re-sharpened. |
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Ingredients for Successful Mortising
Mortisers aren't foolproof machines. First of all, the chisel sets have
to be installed correctly, with clearance between the chisel and auger.
Tightening the auger securely in the chuck is critical. If the auger
slips during a cut, it gets pressed up against the chisel and both can
be ruined in an instant. Second, mortising requires technique, a
combination of force and finesse. After all, the motor powers the auger
bit, but it does nothing to square the round hole. Mortises are cut
manually, using the hand lever to force the chisel through the
workpiece. This can take a lot of effort. However, brute force isn't
everything. It's important to match the chisel's advance into the
mortise with the cutting rate of the auger. A feed rate that's too slow
causes burning; one that's too fast jams the chisel.
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MOTISING MACHINES are lever-operated and require some arm strength to
chop mortises. The lever, via a rack and pinion, controls the head's
movement up and down the column. A gas-filled shock holds th e head
stationary in any position. The motor powers the auger bit, which
extends through the hollow chisel. An adjustable fence positions the
workpiece and a U-shaped hold-down keeps it in position. Mortises are
made by advancing the workpiece along the fence while cutting
successive squared holes. |
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Hold-Downs: The Achilles' Heel of Mortise of Mortisers
Our tests revealed an unfortunate similarity between machines: The
hold-down systems don't work, especially when large chisel sets are
used. It's hard to withdraw the chisel after cutting a single
four-sided mortise, especially in a hard wood like maple. If the
hold-down allows the workpiece to twist, the chisel gets wedged in the
mortise and is impossible to get out. Easy withdrawal requires a level
of accurate machining and rigidity the hold-down systems on these
mortisers don't possess. The Multico machine is the only one that
separates the hold-down from the adjustable fence, which is a good
idea. Instead, it mounts independently on the column. Unfortunately,
this hold-down fails just as often because of its lock-down device,
which is a real pain to tighten. A chain is only as strong as its
weakest link. The inadequate hold-downs are frustrating because, for
the most part, these machines are well built. Fortunately, we found
simple solutions that eliminated the problems.
Hold Do you prefer smoking or non-smoking? Motor speed is an important consideration when you choose a mortiser.
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 SMOKING
AND BURNING are normal, according to the owner's manuals of fast-speed
mortisers. These machines are hard on chisel sets because they generate
a lot of heat while mortising. When they get too hot, the chisel and
auger turn blue and lose their temper (inset). Slow-speed machines are
much less likely to ruin chisel sets. Fast-speed machines are noisy and
nerve-wracking to operate, but they cut mortises with less effort than
slow-speed versions.
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LONGER HANDLE makes mortising easier. The extra leverage gained by
slipping a 20-in. length of pipe over the hand lever helps most when
cutting 1/2-in. mortises with slow-speed machines because they require
more effort than their fast-speed counterparts. Slow-speed machines are
also more likely to stall while cutting, so high motor amperage (min. 5
amps.) is important, especially when you lengthen the handle.
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At less than $250, benchtop mortisers are a bargin. Even so, you can
spend a lot less for machine mortising, or you can spend a lot more.
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 CONSIDER
AN ATTACHMENT for your drill press. It's inexpensive (less than $40)
and works well enough if you only need to mortise occasionally.
However, your drill press wasn't designed for mortising. The head isn't
rigid enough and the short handles don't give you much leverage. In
hard use the tables flex considerably.
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INDUSTRIAL-QUALITY mortising machines have large capacity and
adjustable tables. Instead of cheaply made hold-downs held by a
setscrew, they use a massive plate, threaded like a vise, to wedge the
workpiece firmly in place. Although it costs $650, our testers loved
this Powermatic model #719, which weighs in at 188 lbs.
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At first glance, the machines appear quite different. But we found
that few of the differences directly affect performance. It doesn't
matter whether the fence is cast iron or angle steel. What matters is
that the fence is square to the table. Two machines came with fences
that weren't square and needed replacing. It doesn't matter how the
head is mounted to the column. What matters is whether the head can be
adjusted so it can move up and down the column without racking. Only
one machine lacks this adjustability. It doesn't matter whether the
hold-down device is fastened to a post on the fence or mounted directly
to the column. What matters is that it does its job. At best, the
hold-downs on these machines are barely adequate. It doesn't even
matter which motor speed you choose. Although we liked working with
slow-speed machines better, fast-speed machines cut mortises just as
well.
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USE TWO SCRAPS OF WOOD when you install the chisel and bit. One acts as
a spacer between the chisel and its bushing to assure proper clearance
between the auger and the hollow chisel. Its thickness depends on the
size of the chisel. Check the owner's manual. The other scrap protects
your finger while you hold the auger in position for tightening.
Tighten the chuck in all three holes so the auger won't come loose
during a cut. Then remove the spacer and snug up the chisel against the
bushing. Square it to the fence (inset) and tighten the setscrew.
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Remember three things when you install chisel sets:
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Allow proper clearance between the chisel and the auger. |
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Tighten the auger so it won't slip. |
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Square the chisel to the fence. |
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The hold-down systems on these machines stink!
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THIS HOLD-DOWN doesn't sit flat, so the workpiece it's supposed to
hold is free to twist, or "rack," underneath it. Poor-fitting
hold-downs are common and they're the weak link in these machines.
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A POOR-FITTING HOLD-DOWN caused the chisel to bind in this mortise
because it allowed the workpiece to rack. Once a chisel is stuck, it's
a real pain to get loose. Some of our testers were so frustrated by
hold-down failures they decided they wouldn't buy any benchtop mortiser.
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CLAMP THE FENCE to the mortiser's table, using spacers if necessary, so it stays put when the chisel is withdrawn. |
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CLAMP A BOARD in front of the workpiece so it can't rack. Sand or file
the bottom of the hold-down so it sits flat. Then use cyanoacrylate
(CA) glue to attach a piece of styrene to its bottom. (Both CA glue and
sheets of styrene are available at hobby stores.) Styrene helps the
workpiece slide back and forth more easily under the hold-down.
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The hold-downs on these machines are a disappointment. The problems
were so obvious and our fixes were so simple, it's puzzling that no
manufacturer has bothered to come up with a better system. At the very
least, the manufacturers should include a section in their owner's
manuals titled something like "Getting the Most Out of Your Mortiser"
that would show how to make these improvements. We bet most woodworkers
would be willing to pay more for a machine that they didn't have to
mess with. Because none of the machines was able to consistently cut
1/2-in. mortises without additional clamps and fences, we've decided
not to give an Editors' Choice award. We'll wait for a basic machine
with a hold-down system that's effective through the range of its
capacity.
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Best Buys
With improvements to their hold-down systems, six of the machines we
tested consistently cut mortises effectively. Five of these mortisers
are competitively priced and received our Best Buy award. The sixth,
the Multico PM 12, costs $300 more. The Delta and Jet machines run at
1,725 rpm. Mortisers from Bridgewood, Grizzly and Woodtek, which have
similar castings and are virtually identical, have fast-speed motors.
These machines are a definite improvement over mortising on the drill
press. There are better ones on the market, but they cost a lot more.
At less than $250, all five of these mortisers are a bargain, and are
winners of our Best Buy award.