Popular Woodworking 2003-10 № 136, страница 28
Endurance Test Jet's JBM-5 Mortiser With a few small tune-ups, this benchtop machine can handle just about any 'boring' task. With a couple of exceptions, I've used almost every benchtop mortiser on the market. After cutting hundreds of joints in a wide variety of hardwoods, I concluded that with the benchtop machines, the fast-speed mortisers are less likely to stall in use. (For a full report, check out "Mortiser Slug-fest" in the August 2001 issue of Popular Woodworking, available at popwood.com.) When I began that test of mortisers, I had Jet's JBM-5 slow-speed benchtop machine in my shop at home. After concluding the test, I had the option of buying one of the fast-speed machines. But I didn't. Here's why: The Jet has yet to fail me and it is hands-down my favorite slow-speed mor-tiser. The Jet has proven itself accurate, reliable and gutsy enough for demanding jobs, such as cutting 64 deep mortises in a Morris chair. And while it does stall on occasion, sharp tooling, a proper setup and some slick wax have reduced my downtime significantly. Out of the box, the Jet is a good machine. But with a few tune-ups you can make the Jet (or any other mortiser) perform better. Grind a notch in the hold-down's post, and your hold-down is less likely to go flying. The first order of business with the Jet is to square the table and fence to the chisel. Of the three JBM-5s I've used, all needed this minor tweak. The table should be a perfect 90° to the chisel, and the fence should be parallel to the chisel. To square the table, shim beneath it using masking tape at the front, rear or sides until everything is perfect. Then check the relationship between the chisel and the fence. If it's not perfect, add a thin wooden facing to the fence and shim that. Only one of the three JBM-5s required this adjustment. Next you should modify the Jet's hold-down. This is the weakest part of all bench-top mortisers. The hold-downs slip, so when you pull the chisel out of the work, the hold-down forks or the post that holds the forks flies off and your work is lifted off the table. There are two modifications. The easy one is to secure the post in the fence. It's held in with a set screw, which is not good enough. Mark on the post where the set screw hits it and grind a V-shaped notch in the post at that location. That will ensure the post never leaves the fence unless you want it to. The more involved modification replaces the entire post with a metric (usually 14mm) bolt that has threads on one end. Hacksaw the head off. Grind a notch in the unthreaded part of the bolt's shaft, as described above. Then use a nut to secure the hold-down forks at the top. This works brilliantly. Finally, learn to sharpen your tooling. An auger bit file ($10 from Highland Hardware: 800-872-4466 or tools-for-woodworking.com) will keep the auger bit in shape. And a cone-shaped sharpening stone will surely keep the inside flutes of the chisel honed. When setting up the tooling, be mindful of the gap between the auger and the chisel. It's like the mouth of a handplane. A large gap allows bigger chips (which can stall the motor). For the Jet JBM-5, I like a 1/l6" gap. SPECIFICATIONS JET Tools JBM-5 Benchtop Mortiser Street price: $200 to $250 Motor: Vi horsepower, 1,725 rpm Max chisel width: Vi" Max space under holddown: 35/s" Chisels included: V4", 3/s", Vi" Bushings included: 5/s", 3/4" Nice features: You can change most of the settings without tools.The machine is durable, accurate and powerful enough. Recommended modifications: Alter the hold-down post, shim the table to square. For more information: Contact JET Tools at 800-274-6848 or jettools.com. With these basic modifications, you'll find there's little that the JBM-5 cannot handle. Just about everything I build needs mor-tise-and-tenon work: chairs, face frames and raised-panel doors to name a few. And I can't envision ever replacing it, no matter what comes down the pike next. PW — Christopher Schwarz ABOUT OUR ENDURANCE TESTS Every tool featured in this column has survived at least two years of heavy use by the Popular Woodworking staff. 28 Popular Woodworking October 2003 |
