Why do I get tapered cuts with Jointer?

[Philip Florio]

Many times when I use my jointer on the sides I get a pronounced tapered cut.

I know my jointer is set up properly but this is something I guess from my technique.

I start with the face and then use that side against the fence. I know I'm in trouble right away because the cut stops toward the end of the the piece. My technique is to get the piece just over to the out feed table then hold firmly on the out feed table while keeping some pressure over the middle and end so it doesn't chatter or bounce over the knives.

Thanks in advance,
Phil

[Jim Becker]

From what you describe, your technique is not incorrect, so my suspicion is that the jointer actually is not setup/adjusted properly. Tapers are evidence of the infeed and outfeed tables not being co-planer. (parallel in all directions, but particularly lengthwise) The reason I mention this is that you say that the tool stops cutting consistently near the end of each pass...and that leaves more material on that end. Keep repeating that and you get a wedgie...

[Philip Florio]

Thanks,

I'll check again but this doesn't happen when I cut the face.

Phil

[Peter Quinn]

Do you start jointing the edge with the concave edge down? Starting with a convex edge down can cause you to simply follow the edge's geometry over multiple passes if pressure is quickly transfered to the out feed table or leading edge of the board. If jointing a convex edge down is desirable due to grain orientation or other considerations, put your hand pressure in the center of the boards convexity for several light passes until a straight edge is established over most of the boards length.

Also verify that your knives are parallel with your out feed table. Knives which are higher than the out feed table can result in tapered cuts like you describe, though I suspect this would present itself when face jointing as well which you indicate is not happening.

[Joe Fusco]

Philip,

A simple question might be how do you know the joiner is setup properly?

Since you say this only happens on the edges, one thing that comes to mind is that the knifes closer to the back of the joiner might be just a bit higher then the outfeed table.

You can easily check this by sliding the fence all the way to the back and placing a straight edge on the outfeed table at the back and slowly rotate the cutter head, if the straight edge moves up and down than that's one problem you can adjust.

[Philip Florio]

I use a dial indicator to check the jointer. I'll check again tomorrow.

I've attached a drawing to illustrate the set up and the resulting tapered board, of course I'm taking light cuts and this will be pronounced after many passes.

The out feed is in line to the knives and the knives are are in line across the 6" bed.

Phil

[Wilbur Pan]

Tapered boards are usually a sign that the outfeed table is too high relative to the level of the knives. The knives may be in line with the outfeed table, but they need to be high enough as well.

Here's an article that explains this with lovely diagrams.

The other thing that could be happening is that you are jointing a board that is pretty concave. In these cases, the jointer sometimes tends to remove more wood from the front of the arc than the back of the arc. I've learned to check out how concave my board is, and if it is pronounced, I'll take a few passes by running the front part of the board over the jointer knives, stopping, lifting up the board, and jointing the back part of the board. In this way, some material is removed from the front and back of the board, leaving the middle, before making full length passes on the jointer.

Of course, doing this maneuver is a lot easier with a hand plane.

[Frank Drew]

Tapered boards are usually a sign that the outfeed table is too high relative to the level of the knives.

That was my thought as well; the outfeed table needs to be exactly at the height of the knives' top dead center, and of course all the knives need to be parallel and exactly the same height. A jointer is relatively simple but the geometry is subtle and demanding.

Peter's point about which edge you are jointing is also very relevant; you'll never get a straight edge if you start jointing the convex edge from its very tip end -- you need to take the belly out first with a number of increasingly long passes. So it's usually easier to joint the concave edge, then rip the convex edge on your table saw.

[Joe Fusco]

Philip,

If what you've measured is accurate then an other answer might be that the back end of the out-feed table is high, or both the in-feed and out feed tables are high at their ends away from the cutter. This creates the butterfly effect and will also cause a tapered board. This is more likely then the table being higher then the knifes at the cutter head because you would have experienced a slight bit of a "bump" when passing the board over the cutter.

Zero the in-feed table and check across both tables with a straight edge to see if you have some daylight at or around the cutter head.

[Lee Schierer]

I used to have the same problem with my jointer and it turned out to b that the infeed table edge farthest from teh cuttter was a few thousandths lower than the part rirgt by the cutter. By raising up the infeed end of the table I was able to eliminate the problem.

You can also cause this by pressing down too hard as you feed the boards across the jointer. You can deflect the infeed table with the weigh tof ht e board and the added weight of you pressing down. Use just enough pressure to hold the board to the fence and table.

[Philip Florio]

Okay I checked the out feed table to the cutter, 2 knives are within 1/1000" and the third is off by 6/1000" to the out feed.

I have the Delta 6" x5, I've been dreading this but it's time to change the knives.

I'll also get a high quality 4 foot straight edge to make sure that both tables are dead on. I wonder if Home Depot has quality straight edges?

Thanks again,
Phil

[Wilbur Pan]

For a 48" straight edge, I've found that a four foot level works well enough for this purpose.

[Ralph Okonieski]

Philip,

I changed the blades on my jointer a few months back and encountered tapered boards AFTER installing the new set. After playing with the blades a few times, I finally read the instructions and setup accordingly. I do not remember what they suggested but it worked perfectly afterwards. Check the instructions and then the blades.

[Rod Sheridan]

Hi Phil, you didn't honestly mean to include Home Depot and "high quality" in the same sentence did you?

I use a "high quality" steel straight edge from Lee Valley, you should also be able to purchase them from machinery supply places.

regards, Rod.

[David Romano]

Hi Phil, you didn't honestly mean to include Home Depot and "high quality" in the same sentence did you?

I use a "high quality" steel straight edge from Lee Valley, you should also be able to purchase them from machinery supply places.

regards, Rod.

This thread could take a left turn in to how to buy a straightedge, but I'll give my suggestion. If you plan to buy one from a machinery house, mscdirect, macmaster-carr, etc, you will typically see specs such as width tolerance, thickness tolerance and flateness tolerance. These specs are not the one you are interested in. You want straightness, and unless the steel is described and sold (and priced) as a straightedge, this spec won't be listed. Without this spec, all the specs could be perfect but the long narrow edge you will be using as a reference could be bowed: concave one side, convex the other. This is the path I took. I then sanded one edge down on a large granite surface plate in our company's machine shop on a 4 foot 100 grit belt. This is the best way to flatten one. Using some additional jigs, I kept the edge at 90 degrees as well. It's not difficult, but it takes some time. The edge can be made straight to less than 1 mil.

Alternatively, and assuming they are flat enough, you could use the jointer beds in place of the granite plate. Swap ends often as you sand to counteract any biases.

Short of this, if your cuts are only tapered, you are still making one edge straight. Try using an edge jointed board as a starightedge and see if that helps you. Be sure to cut a few inches off the ends after jointing.

David