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.
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.
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.
Hold-Downs: The Achilles' Heel 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.
A HOLLOW CHISEL with an auger bit inside is the secret to machines
that cut square 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.
TUNE UP THE AUGER before you use it. With a small file, remove leftover
machining burrs from the inside edge of its scoring spur and the
angled top edge of its cutting lip. When these bits get dull they
can easily be re-sharpened.
MORTISING 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
the 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.
