Is it me or is it the jointer

[algale]

I'm not really doing anything specific. I noticed this phenomenon when I was jointing one edge to be square with its adjacent surface. It took me 4 or 5 passes to get it square and when I was done, I noticed that the board, which had (nearly) parallel edges when I started, was tapered by a noticeable amount. So, to confirm what I thought I experienced, I took a scrap piece of 2x4 and made 15 or 20 passes cutting something less than 1/16" on each pass. What I found was that with each pass, the 2x4 became more and more tapered with more being cut from the leading edge than was cut from the trailing edge. Give it a try and let me know your results.

15 or 20 passes on a jointer set to 1/16 on a 2x4 is something you'd never do in the real world. But if you needed even 4 or 5 passes at 1/16 to joint that first edge then that suggest to me that your 2x4 had a heck of a bow in it to begin with and there is no way that the other edge was remotely parallel to begin with, regardless of what your eyes were telling you.

Assuming your jointer is properly set up (and I bet it is), I suspect two things are at work.

First whatever lack of parallelism existed between the top and bottom edges of that 2x4 at the start became a lot more obvious as the two edges got very much closer together because of the repeated 1/16th passes.

Second, if you didn't face joint the 2x4 before edge jointing it, then the face of the 2x4 riding against the fence was not flat. Accordingly, every time you shaved off a 1/16th from the edge, you are also shortening the face of the board and you are therefore are referencing off a face with a slightly new geometry with every pass. This will cause the edge you just jointed to be presented at a slightly different angle to the jointer blades the next time you run it through off the reference face, which in turn will result in further exaggerating the lack of parallelism and increase the taper of the board.

I dare say that anybody who starts with a 2x 4 and sets their jointer to take a 1/16th off and starts edge jointing a 2x4 in this manner will get a taper pretty fast.

[JPG]

When using a 'straight edge', the edge must be the narrow side against the jointer bed (not the wider flat side).

Another thing to check(again using the straight EDGE) is the straightness of the workpiece after 'jointing'(end to end). Pay close attention to the ends.

FWIW, once the workpiece is sufficiently onto the outfeed table, the downward pressure should be mostly to that end. The outfeed table becomes the surface that positions the workpiece relative to the blades for the remainder of the 'pass'.

If the leading end of the workpiece is raising above the outfeed table, the trailing end is prone to being over cut(creating a taper like difference).

One must consider the straightness of the workpiece prior to the pass so as to concentrate on removing the 'high' spots.

Keep in mind the blades are adjusted to the outfeed table, and the infeed table is adjusted to control cut depth. Once the workpiece is onto the outfeed table, it must be kept firmly in contact with it and the trailing end of the workpiece allowed to rise if needed. The opposite condition is when the trailing end is causing the workpiece to rise above the blades as it passes over them. If that is the case, the high trailing end must be trimmed first.

[JPG]

P.S. The purpose of the jointer is to create a flat, straight edge/face from a workpiece that is reasonably close to that to begin with.

Jointing to dimension by multiple passes with deep cuts makes no sense. The TS function does that far more efficiently. If the edge is 'crooked' to begin with, a bit of hand planing would be indicated.

A secondary function is the face/edge angularity(typically 90). That is where fence alignment and workpiece held against it becomes important.




Is this horse dead yet?:D

[dusty]

I'm not really doing anything specific. I noticed this phenomenon when I was jointing one edge to be square with its adjacent surface. It took me 4 or 5 passes to get it square and when I was done, I noticed that the board, which had (nearly) parallel edges when I started, was tapered by a noticeable amount. So, to confirm what I thought I experienced, I took a scrap piece of 2x4 and made 15 or 20 passes cutting something less than 1/16" on each pass. What I found was that with each pass, the 2x4 became more and more tapered with more being cut from the leading edge than was cut from the trailing edge. Give it a try and let me know your results.

To see whether or not you are cutting a taper, scribe a straight line along the edge of the board a specific distance from the edge. After making sure the line is parallel to the edge of the board, run that edge through the jointer two or three times.

If you are cutting a taper it will be obvious. The pencil line will no longer be parallel.

[pennview]

Mountainbreeze, your jointer when properly set up should NOT produce a tapered cut. If you set the depth of cut at 1/16", that's what you should be taking off the entire length of the board you're jointing if the jointer is set up properly and you're using proper technique.

Regarding set-up, both tables should be co-planer. Raise the infeed table to the height of the outfeed table and use a straight edge to ensure that the infeed table isn't lower at the infeed end or near the cutter head than the outfeed table. A decent level is probably adequate to check that the two tables are parallel. Check near the fence and also away from the fence. The outfeed table on the Shopsmith is fixed, so any shimming or adjusting will have to be done on the infeed table. If the tables are parallel, you need to check the height of the cutters next.

To check the cutters, use a piece of wood about 1 x 1 x 12". The size is not that important, but you don't want something too heavy. Lower the infeed table and place the wood so that most of it is on the outfeed table with a couple of inches over the cutter head and the infeed table. Now rotate the cutter head by hand in the direction it would turn when cutting wood. I set the cutters even with the outfeed table at the top of it's arc so the wood doesn't move, but some folks set them a few thousands of an inch higher than the outfeed table. Each cutter should just touch the piece of wood or perhaps move it ever so slightly toward the infeed table. Check all three cutters this way, and also check both ends of the cutter. You can mark the piece of wood when the cutter first touches it and place another mark where the piece stops after being moved by the cutter. Place the marks at the edge of the outfeed table near the cutter head so you can judge the movement. Each cutter should move the wood an equal amount, if at all. If not, you need to adjust the height of each cutter so that the wood moves an equal distance or the blade just touches it. All the cutters need to be at the same height.

If the cutters are too high or too low, or if the infeed table sags at the leading edge or tilts down toward the cutter head, you won't get a straight cut on the boards you're jointing. If you're set-up is correct, then the problem is with your technique.

[mountainbreeze]

OK, I'll have to do a more decisive test. I'll re-check the jointer as described. Then I'll start with a board that has been jointed and then planed. Then I'll return to the jointer and see what happens. Thanks again to all for the feedback.

[mountainbreeze]

15 or 20 passes on a jointer set to 1/16 on a 2x4 is something you'd never do in the real world. But if you needed even 4 or 5 passes at 1/16 to joint that first edge then that suggest to me that your 2x4 had a heck of a bow in it to begin with and there is no way that the other edge was remotely parallel to begin with, regardless of what your eyes were telling you.

As I said originally, I was cutting "something less than 1/16" on each pass". It may have been much less, I'm not sure because I didn't take note of the depth setting at the time.

[algale]

Mountainbreeze, your jointer when properly set up should NOT produce a tapered cut. If you set the depth of cut at 1/16", that's what you should be taking off the entire length of the board you're jointing if the jointer is set up properly and you're using proper technique.

This is not correct. I suppose if the edge being jointed has already been perfectly jointed and the face against the fence is already jointed and at exactly 90 degrees to the edge being jointed and the jointer is set up perfectly then maybe you will get exactly a 1/16 cut the length of the edge of the board and not end up changing the plane of the edge relative to the plane of the face or the other edge, i.e. create a taper. Otherwise you will be changing the plane of the jointed edge relative to the face and/or opposing edge (although the edge will be at 90% relative to the face against the fence.

Jointers simply don't cut parallel, not matter how well set up. Read the article I linked to in my first post which says in its first paragraph:
"The jointer is a very old, frequently used but mysterious woodworking machine. It looks so simple yet is highly technique dependent. The most common misconception about the jointer is that it is capable of intentionally cutting parallel surfaces. Lots of woodworkers are surprised when after taking a few passes on the joiner, they find that the board is getting thinner at one end than it is at the other. If you take one or two passes to true up a surface, the taper is not likely to be severe. Take several passes and tapering can be rather pronounced."
http://www.newwoodworker.com/jntrtaprs.html

[pennview]

Algale, I don't wish to get into an arguement regarding the jointer, but the jointer isn't supposed to cut tapers as a matter of course. Rather, it's supposed to true the surface of a board. Once you've trued the edge of a board, if you repeatedly joint the same edge of that board, it shouldn't take more wood off the leading edge of the board than the trailing edge, or vice versa. If it does, your machine is improperly set up or your technique is wrong. Moreover, if you rip a board to width, and want to clean up the sawn edge, the jointer should clean up that edge and not cut a taper. And, if you start with a board that has true, parallel surfaces, then you should get the same thing when you finish jointing a board, a true, parallel board, not a taper.

[Ed in Tampa]

I suspect the problem is two fold. I suspect the jointer setup.
But more importantly I suspect the operator.

If you are cutting say 1/16 your blade and outfeed table should 1/16 higher than the infeed table. Once you start the cut your downward hand pressure should be making sure the piece is flat to the infeed table. Once enough wood has cleared the blade you downward hand pressure should shift to the outfeed table. If you maintain too much downward pressure on the infeed the board can in fact tilt slightly and begin to tape.

Do this joint as deep a cut as you dare and half way into the board stop the machine. Now eyeball the board laying on the two tables. It should be sitting flat on the infeed, then the blade should be at the leading edge of the cut and rest of board sitting flat on the outfeed table. Use a light or feeler gauges to check it any gap will probably tell you instantly what the problem is.