Saw Filing 101: Mig welding saw steel
Sept. 28, 2018 - In the old days, gas welding was the choice of most sawfilers, and for many it still is. In modern times, however, the mig welder has become more popular. Unfortunately, there is a learning curve when you switch over, and re-cracks are a common curse on new users. As with anything in saw filing, there are many ways to do the job and so, at the risk of offending filers who swear by their own methods, this is what works for me.
First you have to determine the proper settings for your machine. All welders are different so there is no universal setting, but take some scrap saw steel and practice until the burn sounds like frying bacon and it penetrates all the way through without making holes. If your weld looks like a cow patty and there are little balls of molten metal bouncing around, stop and turn on the gas. When everything looks good, write those settings down.
Now it’s time to weld and once again, you have some choices to make. Some people like to start on the inboard end of the crack and work their way out. Often a piece of steel is placed on the outside of the saw and the weld is started on the resulting tab to give a nice smooth transition. For myself, I start at the outside edge of the crack and hesitate just a bit to be sure the edge of my weld is full and even with the edge of the saw before working my way in to the end of the crack. None of these methods are wrong, just go with what feels comfortable.
Most filing rooms have welding clamps that hold the saw securely and in some cases provide a heated surface. A piece of copper or brass with a slot machined out to a depth of .030 is placed directly under the weld and everything is secured to prevent the saw from flexing and becoming misaligned. This method works very well and most filers use it. I prefer to do their welding on the bench. I place the brass heat-sink under the crack directly on top of the bench anvil. I have welded more saws than I care to admit and feel comfortable doing it that way. Your mileage may vary.
When you lay down your bead, be sure the tip of the welding wire is feeding directly into the crack. Do not weave the wire back and forth; it will lead to inconsistent penetration. Keep the nozzle about 3/8 of an inch from the weld, straight up and down and tilted slightly back from the direction of travel. When you are done, pick up your torch, which is already running with a neutral flame, and control the cooling of the weld. Cover it with a welding blanket or an old glove to help slow the process. You will know if you let it get cold too fast by the loud “ping” you hear as the saw cracks alongside your pretty new weld.
Do not move the saw at this point and when your weld is comfortable to touch with bare skin, anneal it by evenly heating the bead and its immediate area to approximately 700 degrees. This is best accomplished with the use of a heat crayon but once you are used to what the proper shade of blue looks like you can “chase the ghost” by watching for a shadow that will follow the torch around as you play the flame over the steel. Cover the weld again and wait for it to cool.
Dressing the weld requires subtlety. You want the saw to be as close to its original dimensions as possible. Grind too much and you might as well throw the saw away. I like to use a traditional grinding disc to bring the weld down close to the surrounding steel and finish it off with a sanding disc. When the top is done, go to the inside and do the bottom. Check to make sure you have good penetration; if you don’t, you will have to start over or weld it again from the inside. Both procedures are last resorts. It’s best to make sure you have your machine settings and welding speed perfected first.
When the weld is dressed to your liking, anneal it one more time. Not everybody does this extra step and some will argue against it but it works for me and I stand by it. You will find that once you have your own procedure nailed down you will become as much a slave to each step of your method as I am to mine. Good luck and remember, the goal is to never use the welder but just in case, you better practice with it until you can.
Trevor Shpeley is a former executive of the BC Saw Filers Association and works as a filer at Kalesnikoff Lumber in British Columbia.
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