Jointer tapers

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Forum topic by RadOD posted 05-22-2019 11:05 PM 361 views 0 times favorited 6 replies Add to Favorites Watch
View RadOD's profile


2 posts in 272 days

05-22-2019 11:05 PM

I have a used Jet jet jj-6csx 6” jointer that I have been struggling with for months now. Every board I have ever jointed ends up with a taper – narrower at the leading edge.

I finally bought a 48” high-accuracy straight edge. I have adjusted the infeed as perfectly as I can – the smallest feeler gauge I have is 0.06mm. The front edge (furthest from blades) of the infeed sags where I can get the 0.06mm in but not the 0.07mm. Lowering the infeed 1/16” I have some plastic shims I put under the straight edge and I get the same results.

Being as careful as I possible can to put pressure on the outfeed but not put asymmetric pressure on the front of the board as compared to the back end, and after 3 passes, a 30” long piece of oak is a little more than 1/16” thinner at the front end than the back and the last 3-4” have not yet been touched by the blades.

I’ve been using the fact the the board is now flat and running it through the planer as a crutch. But I’m at my wits end. I can’t even decide if it is my technique or the machine. Can anyone give me advice?

6 replies so far

View CarlosInTheSticks's profile


289 posts in 767 days

#1 posted 05-23-2019 12:23 AM

I assume you are measuring the infeed droop with reference to the outfeed. I suspect the problem is with your outfeed. Even your tables out, put the straight edge on the infeed table and measure the droop in the outfeed table. If the outfeed table is drooping compared to the infeed table, you can repair that with brass shims under the ways. Once in place and leveled with the infeed table, lock it. Recheck your tables for parallelism, you should have removed the knives to level the tables. If they are now parallel, reinstall the knives.

PS. If you go ahead and level the outfeed table to the infeed. Your knives will be set to high, which is why they should be removed as mentioned above. If this is your first jointer, be careful setting the knives read an instruction manual, if you don’t have one, check out, many manuals there with instructions. With a straight edge on the outfeed table, the knives should just barely graze the straight edge when you rotate the cutter head.

View Aj2's profile


2280 posts in 2193 days

#2 posted 05-23-2019 01:03 AM

If you jointer isn’t taking a cut the full length. It usually means you outfeed table is too high in the cutting circle. Just lower it a few thousands. The wood runs into the edge of the outfeed and lifts out of the cut.
So do this testing on the edge of a board.
If you have nicks in the knives that will also make it difficult to get the out feed height right. So that why edge jointing is better.
If you tables are horribly out of wack you will not be able to get a nice tight joint on the edges of two boards held together with your hands.
But maybe still a good enough surface to run through the planer.
Good Luck

-- Aj

View MrRon's profile


5496 posts in 3638 days

#3 posted 05-23-2019 05:22 PM

I find that the more passes I make on a jointer, the more taper results. If the outfeed table is just 1 or 2 thousands off in respect to the knife, a minute taper will result and the more passes I make, the taper is compounded. The outfeed table must be perfectly level with the tip of the knives. My Powermatic jointer was doing that until I made certain the outfeed table and knives were perfectly in line.

View pintodeluxe's profile


5936 posts in 3208 days

#4 posted 05-23-2019 06:29 PM

I struggled when I had a 6” Jet as well. I would adjust the tables co-planar within .002” and everything would be fine for awile. I realized the tiny locking thumbscrews on the jointer would slip over time. So, needless to say I was constantly re-adjusting.

I switched to a Delta DJ-20 (parallelogram style jointer) and once set, it stays put.

Give it one more go comparing the infeed with the outfeed table. A straightedge held flat across both tables shouldn’t let more than a .002” feeler gauge underneath. Try laying the straightedge straight, as well as diagonally to check corner-to-corner.

I’ll bet you can get it to an acceptable level. Also, use a fresh test board after each adjustment. Once a board gets tapered and distorted by an out-of-tune jointer, it’s not worth salvaging the board.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View BobAnderton's profile


294 posts in 3185 days

#5 posted 05-23-2019 08:07 PM

The jointer is meant to give you a straight face and edge normal to each other, not necessarily one parallel to the opposing face. Running it through the planer with the jointed face down is how you get the opposing face parallel to the jointed face. That’s standard operating procedure. If the jointed face isn’t straight (flat) that would be a different issue and probably height of the knives relative to the outfeed, but that’s not the problem you described I think.

-- Bob Anderton - Austin, TX - Nova 3000 lathe, Alaskan Mark III mill, Husqavarna Saw

View RadOD's profile


2 posts in 272 days

#6 posted 05-23-2019 09:02 PM

I think I may have found the problem. I have a set of 1/8 think machinist triangles that are pretty accurate. I tried lowering the table 1/8 and seeing it it stayed accurate. It didn’t. The tables were much more out of alignment. This got me looking and there is a third screw to tighten on the indeed (compared to two on the outfeed) I hadn’t noticed. I aligned then properly tightened. Table stayed in alignment when lowered.

I only had time to do a couple passes but it looks good so far.

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