Why do Oscillating Multi Tool blades wear out so quickly?
For the most part it comes down to heat and technique. Although the quality may vary greatly in the blades that are available, high temperature and poor technique are the culprits of premature failure in any blade. A normal power tool will either pull chips out of the cut like a drill, or it will throw chips out of the cut like a circular saw. An oscillating tool with its high speed and short stroke will actually pack the chips into the cut. This increases the already high level of friction. If you force the blade into a cut you will notice a little curl of smoke rising up as you begin to smell burning wood. With other power tools we have a tendency to give them a helpful push to speed up the work. This also increases the level of friction with an oscillating tool. The generated heat soon softens the teeth, and you end up with a black and blue blade with little rounded teeth.
We want to get the chips out of the cut. This means we are taking away heat with the sawdust and making more room for the blade to cut. If you are making a plunge cut you want to rock the blade with an in and out motion. Do this with light pressure. As you rock the blade you are widening the cut so that the blade doesn’t beat against the walls of the plunge. The in and out motion helps pull the chips out of the cut and lets the blade breath a little. You can apply some beeswax or even a bar of soap to the teeth. Any type of blade lubricant that cuts down on friction will help the blade last longer. Imperial has gone a step further and coated the cutting edge of some blades with titanium nitride. This serves a dual purpose of increasing the hardness, while it also greatly reduces friction.
When you are making a long cut move the blade along the cut line with long strokes. This will spread out the heat as well as remove the sawdust. Increase your depth of cut gradually. If it is possible, tilt the blade so that the leading edge will rise above the cut. This will facilitate the chip removal. Whatever the cut might be, try to keep the blade moving. Never stay in one place. Keep it moving like you would an iron on clothes, and rock the blade like you would a chainsaw to help clear the chips and get a better bite.
A few good techniques and an awareness of the heat being generated will help you get more life out of your blades. The type, length, and shape of the blade will also play a part in how hot things will get. The selection and use of blades will have to be another discussion.