Why Does the Jointer Cause a Taper?

[Kevin Herber]

If I repeatedly joint a single edge with my jointer I end up with a tapered board. Why is that? I run the board completely across the knives with each pass. Shouldn't the board remain square since each pass removes the same amount of wood? I can't figure out what causes the taper :confused:

Any ideas?

-- Kevin

[Julio Navarro]

Are you putting the same amount of pressure uniformly?

[John Hulett]

While I'm no expert, I typically get the board going and once I've got enough wood past the knives, any and all pressure is applied on the outfeed side of the blades since that's the flat reference I'm cutting to. It's more of a pulling the wood through the cut than pushing.

- John

[Michael Gabbay]

I had the same problem. For me it was the outfeed table was slightly low. I reset the table and the taper is gone. Also, try doing one pass in one direction and then another pass in the opposite direction.

[Harley Lewis]

I am far from being an expert either -- but if the wood has any twist or cup or is bowed the jointer will take down the high side and level to the low side, making the top and bottom surfaces not parallel. That is why the thickness planer is the companion to the jointer -- it will make the top and bottom surfaces parallel once one side is flat.

[Scott Thornton]

Make sure your outfeed table is perfectly aligned with the highest point your knife makes. If it's not, you're either going to get a snipe or a taper...all the technique in the world won't overcome that!

Good Luck.

[Tom Hintz]

If the defect yo are trying to remove is not equal across the board, the jointer will be removing more material from one end than the other. The changes in pressure when starting the jointing process also induce a taper. How much of a taper depends on the amount of wood that has to be removed to true the surface.
Keep in mind that the joint simply flattens one face. It takes a planer to make the opposing face parallel to it.

[scott spencer]

Kevin - I'll assume the jointer is tuned well, and offer technique solutions. The two faces of a board are indendent of each other as far as a jointer is concerned. Assuming we face joint a board b/c of some uneveness (even minor), the surface points on the pre-jointed face will actually dictate the direction of the resulting plane of that face once jointed....that plane becomes your reference for all other surfaces of that board. The step of making the opposite face parallel to the jointed face is best done with a planer, which will make a face parallel to the reference face....a jointer won't.

Here's a fairly common method. Joint a face flat, put that face against the fence and edge joint 90 degrees adjacent to the flat surface. Put the unjointed face through the planer to make it parallel (use multiple pass to reduce thickness if needed), then rip to width on the TS. Assuming properly tuned machines, you should get a flat square board.

[Cody Colston]

Assuming the jointer is tuned correctly, when edge jointing, do as already suggested and swap ends with the board on consecutive passes. That will help to eliminate any tapering. You may need to orient the grain on the last pass for a super smooth edge.

[Mike Hill]

Kevin: Interesting that you posted this today. I am working on my first project a wall clock and had some 4/4 Cherry. I started to dimension it by putting an edge on it on my joiner. I came out with a board looking like a wave cresting at about 12' :) In the morning I am building a jig for my table saw that will put a straight edge on it, but will need to plane it to thickness first.

I went back through all the instructions on the jointer and checked Top Dead Center on the blades versus out table height etc. In addition I reviewed the method for feeding it. Neither helped. Like most crafts, I am assuming there is a lot of "feel" and "art" to woodworking and will keep trying. Not having a mentor or school is a deficit, but that can be overcome. Will read along with the answers to your question and see what I can learn.
Mike

[Shiraz Balolia]

If I repeatedly joint a single edge with my jointer I end up with a tapered board. Why is that? I run the board completely across the knives with each pass. Shouldn't the board remain square since each pass removes the same amount of wood? I can't figure out what causes the taper :confused:

Any ideas?

-- Kevin

As some of the others have mentioned, your outfeed table is out of alignment with relation to the cutterhead.
Here is a "quick and dirty" way to fix it:
1) Disconnect power to the machine.
2) Take a 12" or longer straight edge or very flat square and hold it on the outfeed table with part of it sticking over the cutterhead. I will assume that your cutterhead is a straight knife cutterhead.
3) Turn the cutterhead front to back by moving the pulley and adjust your outfeed table until the tip of the knife barely touches the bottom of the square, steel ruler or straight edge you are using.
4) Lock down your outfeed table.
Another assumption here is that all your blades have already been set to the same height before you begin, and that your table is not "drooping".
All things equal, should take less than 2 minutes. Hope it helps.

[Steve Roxberg]

I had this exact problem and as others have stated your outfeed table is low.

I also had the end of mine drooping and had to adjust the ways.

Excellent article on the Delta website on how to adjust it.

[Fred Woodward]

Drooping infeed or outfeed tables can contribute to the tapering or similar issues.
I had similar things happening on my jointer when I first tried to use it.
I used a long straight edge (I used a 36" straight edge) and leveled both tables to each other (length anf width of the tables...may need to shim the gibbs on the dovetails). Set the outfeed table height. Check for level on the outfeed table across the knives (each knife). Adjust knives accordingly. Square the fence to the tables.

[Dan Forman]

Here is an excellent tutorial on jointer setup. I had the same problem, this cured it. http://woodworking.homeip.net/wood/Tuning%20Tools/Jointers/Jointers.html

Dan