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Setting Jointer Knives

Question

What is the easiest way to set jointer or planer knives? – Roger Bradley

Answer

Marty Milkovits replies: I use the magnetic jig that came with my Powermatic planer. For the jointer I use a height micrometer which will measure to 10,000, set in on the outfeed table and rotate the knife under the feeler, set to a tolerance of +/- 3/10,000.

Jon Siegel replies: The most accurate way is with a dial indicator. No woodworker should be without one because they have countless uses in the woodshop for setting up machines. Thanks to global trade, the price of dial indicators has gone down to a starting point of under $20 for an indicator and magnetic base combination. If you don’t have one, stop procrastinating!

Set your indicator base on the outfeed table of your jointer, and rotate the head until the edge is at the top. This gives the maximum reading on the indicator, and all knives must be measured in this orientation. Now set the first knife parallel to the outfeed table. Set the remaining knives so they have the same reading as the first knife. If you can get them to within 0.002 inches of the same reading, this is close enough. If not, then possibly only one knife will be doing all the cutting, depending of course on how fast you feed the wood. Anyway, minor adjustments of one or two thousandths can be made later by hand honing. This should be accomplished upon subsequent hand sharpenings: only sharpen the knives which measure high.

After you are satisfied with the placement of the knives, whether you have hand-honed or not, you now need to take some trial cuts, and set the height of the outfeed table correctly. If it snipes at the end, the table is too low, if the wood rides up, the table is too high. A few Craftsman and other small jointers do not have adjustable outfeed tables. On these machines, set the height of the knives about 0.003 inch above the height of the outfeed table.

Planer knives are set parallel to the head, that is, each knife projects the same amount. This is measured with a dial indicator in radial orientation, and the measurement should be written with black marker on the head itself. Each time you replace the blades, use this same measurement for the projection of the edge above the surface of the head.

This way you will not have to readjust any other part of the machine when you change blades.

If the head and the bed are parallel, then this gives good results. If not, then the work may have uneven thickness from left to right. It is usually recommended to correct this by adjusting the bed, but if this not possible, it can be corrected by installing the knives at an angle to compensate.

Fine tuning of this type can only be accomplished with a dial indicator.

Tags: Jointer, Tools