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Thread: Jointer making convex cuts
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6th July 2021, 09:19 PM #1Senior Member
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Jointer making convex cuts
I just haven't been flatten boards that are sufficiently long and I'm about to give up and reach for the hand tools, but my workbench project uses a lot of ironbark, so that's not very feasible.
Firstly, to make sure I have the terminology correct when I joint 2 boards, the middles touch and the ends are apart.
My jointer is an old wartime Delta that I had quite some issues setting up, but I've gotten it to a point it's satisfactory. To get the tables parallel, I shimmed up the outfeed table, but the infeed table has one corner closest to the cutterhead slightly low, but only ~0.1mm. It's the best I could do, as I can't shim the infeed table.
To set the blades, the blades in the cutterhead will stay in place without tightening screws, so I stuck the blades in there with an engineer's square over the outfeed table, and rotated the cutterhead so the square pushes the blade down to the correct height by itself. I did this with a piece of masking tape under the square, so that after I removed it, rotating the cutterhead over the square gave me the slightest bit of audible and tactile feedback that the blades were touching.
I lowered the infeed table to set the cut depth to 1mm.
When I cut, I pressure the infeed until enough has gone through that I start pressuring the outfeed. The feedback I get is that it takes a deep cut at the start, but after I transfer pressure to the outfeed and start trying to pull the wood through, I don't get much of a cut and towards the end it's like the rest of the board has lifted off the infeed table.
This tends to happen with boards over 1.5m long
Any idea what I'm doing wrong?
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6th July 2021, 09:39 PM #2GOLD MEMBER
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Sounds like the tables are not parallel with each other
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6th July 2021, 10:06 PM #3
Do you joint the concave edge? The jointer can ride along the curve of a convex edge.
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6th July 2021, 10:27 PM #4Senior Member
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I feed the board in frowny face down, if that's what you mean.
Quite possible if what you say is true, that I create a convex with bad technique or the like and the jointer just keeps amplifying this effect
what would you expect to see, depending on which way they are out of alignment? Just trying to diagnose the issue.
How it's set up now, if you consider the 4 edges of the infeed and outfeed tables, the 2 edges on one side are perfectly colinear, and the other set of edges has the cutterhead corner of the infeed table ~0.16mm low
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6th July 2021, 11:54 PM #5
Frowny face down is the correct way. Its possible that it could be bad technique. You've got to make sure that you are applying sufficient down force on the outfeed table at the end of the pass. Check your outfeed rollers too to make sure that they aren't higher than the outfeed table.
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7th July 2021, 01:41 AM #6China
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Rollers??
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7th July 2021, 06:27 AM #7GOLD MEMBER
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7th July 2021, 06:35 AM #8GOLD MEMBER
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The board gets put on the table with the crowned edge facing up, so concave edge down, then just take a bit off each end until the whole edge is touching then generally I will take s bit bigger bite, i.e: lower the infeed table, and plane the whole edge. But my machine is pretty easy to get stuff straight because its 2.7 metres long. For really bent materials that are long, and if you only have a small jointer, maybe hit the ends down a bit first with an electric planer, then finish on the jointer.Sometimes it’s easier to take the tool to the job.
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7th July 2021, 08:21 AM #9
Perhaps its not your technique or the jointer. It could be the timber. Have you had the same issue with other boards in different species? Have you only jointed the one edge of each board?
Experienced wood workers have learned how wood moves, how it reacts to material being removed, how it releases internal stresses when it is machined.
The grain in the board; moisture content; how it was seasoned; whether it is plain, rift, or quarter sawn; how it was milled from the log; whether the board was milled from a straight bole, "reaction wood" or a crotch will all determine what internal stresses are "stored" in a board and then how the board will react when machined.
Try jointing both edges (if you haven't already done so), another species and / or other boards to see if it is your technique, the jointer or the wood. A process of elimination.Mobyturns
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7th July 2021, 09:43 AM #10Senior Member
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7th July 2021, 09:47 AM #11Senior Member
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If I can't get one edge parallel because the infeed table won't accept shims, is it possible to stick some shims to the bed? The concern is it has to be smooth so the board doesn't knock it off when pushed past
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7th July 2021, 11:16 AM #12
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7th July 2021, 12:09 PM #13Senior Member
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Yea, I have those. Not rollers, but just a plank of wood. I had to grind it down where it joins the tables, and it's only coplanar with the tables at the very end
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8th July 2021, 06:30 PM #14Senior Member
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So, I tried shimming all the ways I can, but there's only 2 spots where I could shim and it's impossible to get 4 edges colinear. So I resorted to sticking wooden shims to the infeed table, which eliminated the convex. Also, the knives were low, which couldn't played a part but the boards were not catching on the outfeed table. Pic related:
20210708_164800.jpg
Now I'm faced with another problem: I'm getting a convex (smiley face) across the width the board. The only way I can think of to cause this is if the knives aren't set flat, but I'm not seeing any obvious irregular marks on the surface of the board. I have tried setting the knives again. Same result. Any ideas?
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8th July 2021, 07:34 PM #15
I set my outfeed table a bee’s winky below the cutter knives; same idea as a hand plane. The knives are “scooping” a sliver of timber each pass so you end up with a scalloped finish; it’s the high spots that are lifting the timber up very slightly and introducing a slight curve.
Regarding technique; are you forcing the timber over the knives? I teach this method: introduce the timber as gently as you can long the infeed table; only pressing down hard enough to eliminate any tendency to chatter. Once you have a sufficient amount of timber over (and touching) the outfeed table transfer your hands so that you are now pulling the timber from the outfeed side and only applying pressure on that table.
In any case I always finish off by hand with a plane. I’m happy to have very slightly concave mating edges as it helps clamp the board ends. By “slight” I follow James Krenonv’s advice that the gap should be no wider than the thickness of a strip of paper.Nothing succeeds like a budgie without a beak.
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