Setting and Adjusting Knives in an Old Planer

1920's-era iron is rock solid, but it can be finicky. Here are some detailed pro tips for aligning the knives in an old-school machine. January 28, 2014

I have accurately set knives in a number of jointers and know all the basic moves. This one, though, is something else again. The jointer is an L Power manufactured in the 1920s. Has a round, ball bearing head (original) that takes 3 knives of 16" width. Each knife is held in place by 4 gibs. The side facing the knife is machined on an angle, essentially creating a wedge which progressively tightens against the knife as the capscrews, which are inclined at right angles to the cutterhead, are tightened down and drive the wedge up. I am changing the knives one at a time and began by pulling the old one, cleaning the gibs in solvent and blowing dry and cleaning the area of the head that receives the knife.

After about 5 hours, I am still on knife number one and have observed a couple of things along the way. One is that the design of the gibs is such that the knife can jump up as much as 0.015" during tightening. I tried to allow for this in the basic height set up with the jackscrews, but the amount the knife is raised by tightening isn't consistent from one end to the other. In addition to that, the one time I was able to get the extreme ends of the knife within 0.001", the measurement in the center was 0.005" low. Originally I thought I might be measuring incorrectly (was indexing off the table) but got essentially the same result with a half moon type jig that indexes directly off the cutterhead. At this point I can't rule anything in or out. Knives were poorly set when I purchased the machine. Any insights appreciated. I'm about out.

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
Afraid I don't have much help for you. One thing is if the knives consistently jump upwards, could you use a block as a firm stop at the top?

If I'm understanding correctly it's similar to the Euro block shaper heads right? You tighten a screw downwards which pushes the wedge upwards? A good design for knives pinned into place, but I could see it being less than desirable for a floating jointer knife. I would also recommend checking in with the guys as OWWM.

From contributor D:
You've got more patience than I have. I'd just let them be proud slightly, .015" is good. Then raise the outfeed table and gradually lower it, jointing the knives down using a sharpening stone clamped to it. I've even just put successively higher grit sandpaper on plate glass clamped to the outfeed, and spun the cutterhead in reverse by hand whipping the drive belt around if your motor doesn't reverse. The cut quality you get after jointing the knives with crisp 2000 grit silicon carbide sandpaper is slick as glass.

From contributor R:

Piece of cake. I've changed knives on that type head. I repair and adjust machinery.

Put the knives in a bit high and put some tension on the gib screws. Take a piece of maple maybe 1" square and 5" long and a small hammer to tap the maple block on the edge of the knife to lower it down. I typically get it to .005 before the final tap down to 0". Use the end grain to the block. Don't put so much tension you can't tap the knife down without splitting the maple tap adjuster. You should then be able to tighten the knives with no movement. I can work off the outfeed table off the head with a straddle type indicator base and easily get the knives within .0005". I just did a 20" 4 knife jointer today in a leisurely 45 minutes.

From the original questioner:
Thanks for taking the interest. Contributor R's suggestion was golden. Spent about 30 min per knife and hit the 0.001" tolerance at the ends of each knife. Turns out I'm not done yet, though. I noticed earlier on that the knife height seemed to be low in the center and never assumed that a knife could be ground to a keen edge, yet still be concave overall. Such was the case and I'll have to replace them with a new set. Another thing I noticed was that the outfeed table was 0.010" higher on one side than the other and not coplanar with the infeed. This particular jointer has a design similar to the older Crescents with a four point type table support with small inclined planes on each. Anyone have any experience setting these up or can maybe point me in the right direction? This is sure looking like "get to know your jointer" week.

From contributor R:
With my technique you can compensate for curved knives. My sharpening service will straighten my knives if I ask them to. Steel can warp during sharpening. It won't warp every sharpening but it will every so often.

The inclined table adjusters found on Crescent jointers are better than parallelogram tables. Easy to adjust but you need a straight edge 2/3's the length of the overall jointer. Also an indicator to reference off the cutter. Every movement of an incline will make the opposite corner move the other way. When you think you are done, turn the height adjuster crank to run the table down all the way and run it up, then recheck. If it stays coplanar, you are done. If not you should be closer, then adjust some more.

I've had every issue you can imagine with jointers.

From contributor R:
The Crescent adjusters are easy. Keep a little tension on the locking bolt and tap the adjuster with a hammer and a block of wood. You use a feeler gauge under the straight edge to track your progress. I'll take Crescent over the old Oliver, which uses the same inclines with screw adjusters. The Crescent with its single pedestal base can be put on a mobile base. If you move the Oliver, the table must be re-leveled.

From the original questioner:
Thanks for the input. The configuration on the L Power is such that there are no adjusters per se. Four small ramps in the bed with complementary ramps in the table castings. Spline in matching grooves to keep everything straight and a cap to keep everything snug. After looking it over I think the best approach might be to loosen up at the point where the table support assembly bolts to the pedestal casting and then lift the table with machinist jacks and shim it. Fortunately I do have a 6 foot straight edge. Would love to get your opinion on this.

From contributor R:
Forget the machinery jacks. I clearly stated the simple procedure on adjusting the Crescent type inclines. Slight tension on the lock screw and tapping the inclines with the wood block and hammer is simple and fast.

From contributor R:
Each one of the inclines should have a locking bolt and there should be a slot to allow for adjustment. Using a jack and shims would be to make a simple thing more complicated.

Did you understand the knife info? The only reason to get new knives is for a spare set or if they have been sharpened too many times. A slight crown is minor and can be dealt with. Have you asked your sharpening service to straighten them out? I've seen guys struggle with this for years but no one asks the sharpening service this question.

From contributor A:
Some of the Pennsylvania Amish, who have round head planers and jointers use planer blades that are 1/8" higher than normal and drop the blades all the way into the bottom of the blade channel, press down and tighten. When they are removed for grinding and sharpening and are not tall enough, they lay a piece of shim stock under the blade for a 15 minute, three blade changeover. I bought higher blades for my planer, but have not gotten them in yet.

I had an earlier 1895 -1900s L. Powers 20" jointer with a square head and slot knives and sold it because of stories of the cutters coming loose. I know a guy who has all slot notched type blade machines and he uses new hardened bolts, nuts with spiny washers, some locktite and a torque wrench.

I kept the 20" slot blades because the buyer adapted a spiral head into it.