Popular Woodworking 2008-06 № 169, страница 51

#10 x 1" pan

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ELEVATION

HOLDING JIG

Cut a dozen such pieces and place them in the fluxjar where they are ready for use along with the flux. Note: Flux contains zinc chloride and needs to be used with caution.

Use a scrap of wood to pick out the pre-measured silver alloy square along with a dab of flux. This is a more convenient and accurate way than using wire solder common in plumbing work. The refill kits differ in this regard. Woodcraft sells its joint kit for $34.99 with a 10" length of wire silver solder and the refill kit for $9.99 with the same length of wire. Lee Valley Tool's splice kit sells for $32.40 and has a 7'/2" length of 'A" ribbon solder, while the refill kit at $18.90 gives you a larger jar of flux and 38" of ribbon silver solder. This will do 150 splices. I rate this a good buy.

The holder for the band joint is easily made from V2"-thick hardwood. It will hold the two ends for brazing and gives you the opportunity to accurately align the blade by sighting along the top. This wood jig is intended for small blades and torches as shown in the article. A metal holder is used with larger torches and heavier blades requiring more heat.

Jointing the Blade; Playing with Fire

After cutting the bandstock to length (plus 'A" for the scarf lap), the ends need to be ground to a bevel angle back about ³Ae" to 'A". Rather than do this at a grinder, I touch them on the belt sander. Visual inspection will guide you to making them even on both ends. Hold the blade so that the bevels are on opposite sides and mate when aligned in the jig.

The beauty of the ribbon solder will be appreciated as soon as you line up the band joint and have the ends touching each other. The wafer of solder and the small dab of flux

Supplies

For silver brazing kit and refill: Lee Valley Tools

leevalley.com or 800-871-8158 Woodcraft Supply Corp. woodcraft.com or 800-225-1153

For band saw blade stock by the coil: Olson Saw Co.

olsonsaw.com or 203-792-8622

■ blade stock in 100'coils

MSC Industial Supply Co.

mscdirect.com or 800-645-7270

■ Starrett and Morse blades in 100' coils

are held in place by the blade ends.

It is now time to turn on your torch. Silver alloy flows at about 1,200°F, and the joint will be heated cherry red in the 1,600°F range.

When it is fully hot the joint appears to have a molten shimmer to it. It lakes less than a minute to heat. The joint is now brazed, bui an important step remains: annealing. Heat makes the blade brittle. Ifyou skip the annealing step, your blade will soon break near the joint where the brittle joint area meets the non-heated steel.

In annealing, ihe torch is used to accomplish a series of heatings to restore the needed toughness to the blade. Back the torch away from the blade an inch and apply a few seconds of heat across the joint area. Allow it to cool for about 10 seconds, and repeat four or five limes more, backing away a bit more each time you swipe the joint. You want to heat the blade into the 400°F to 600°F range to temper out the hard brittle steel.

How do you know you have it right? Look carefully at the blade the next time it breaks. If the joint fails, then you have missed with the flux or given insufficient heat to the joint. If it breaks just beyond thejoint, you have not properly annealed the blade. If it breakselse-where, then you have a stress fracture from the blade repeatedly flexing over the wheels ofthe saw.

Annealing in the Literature

If the instructions with the two splice kits are what people follow, it is not surprising that the technical support people at band saw blade companies report poor results from woodworkers making their own blades. Nowhere is there any mention of annealing thejoint in either kit.

So I turned to the standard reference, Mark Duginske's "Band Saw Handbook" (Sterling). Both methods of making up a band are discussed. Here is what he says about resistance welding: "Before it can be used, you must

anneal it to restore the weld joint to the same metallurgical hardness and strength as the rest of the band. This is done by reheating it to an annealing temperature and then cooling it slowly." When discussingsilverbrazing, however, there is no mention of annealing after healing thejoint with the torch to (low the solder.

One band saw blade manufacturer spent $60,000 on the annealing machine for its blades. They guarantee the results. What you can do is the finesse ofthe blacksmith. It starts with knowing what needs to be done and how to do it. Then look at your failures and try it again.

The final step is to file thejoint smooth. Surplus flux forms a glass-like bead on the metal that scratches off with the end of your file. You will appreciate the premeasured flake of ribbon silver solder at this step, because there will be very little surplus metal lo be filed away as a result.

You can achieve consistently good results doingyour own silver brazing. Moreover, you can make up a new band the moment you have a need for it in a matter of 10 minutes. In my book, quality and convenience rank every bit as high as the savings in cost.

Finally, you will come to appreciate that silver brazing is not just for repairing a broken blade. Don't believe the catalog descriptions. In fact, you may find that by the time your blades break there is little or no useful life left in them, which is testimony to your newfound skill. PW

Author's note: Thanks to Dave Hout/or showing me this practical method for making up band saw blades. As shown, it works best on ^J/2" and smaller blades rather than larger resaw and band mill blades.

lohn runs The Home Shop in Charlotte, Mich., which supplies wood, copper tacks and other critical supplies tor the Shaker oval boxmaker. He also offers classes on a wide variety of woodworking topics. Contact him at shakerovalbox.com or 517-543-5325.

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