Tuning jointer to eliminate convex cuts
Quickstep
| Posted in General Discussion on
My jointer cuts a slight concave shape in the boards I joint. In an effort to correct this, I lowered the outfeed table until I introduced a snipe, then raised it until the snipe was gone. With this adjustment, the apex of the cutters is just a couple thousandths above the outfeed table. If I joint two boards and hold them edge to edge, the ends don’t meet; they’re off by about 1/32″. Anybody know how to adjust to eliminate this problem? It’s a Delta DJ-20.
Replies
It sounds like the knives are not ground strait. I do not understand you’re set up method on the jointer? The cutter head and knives should be parallel to the out feed table and at 0 cut. The amount of cut is controlled by lowering the in feed table.
Let's look at your technique to verify that it's not the cause of the problem: You start with downward pressure on the leading edge of the board, as it sits on the infeed table just prior to reaching the cutterhead. As you feed the board into the cutters, as soon as there is enough of the board on the outfeed table (6" or so), you transfer downward pressure to the outfeed table, just past the cutterhead. From then on, you maintain downward pressure over approximately the same point--a few inches past the cutterhead--as the board moves by.
Does that sound like what you're doing? Assuming that the outfeed table is reasonably flat, the only way I know of to get a convex edge is to put too much downward pressure on the wood over the infeed table (thus lifting the leading edge of the board off the outfeed table). You should only be using the infeed table at the very start of the cut. From then on, all pressure should be over the outfeed table.
-Steve
Most likley you went too high with the outfeed table. You absolutely the knives are a few thousandths above the table! Could also technique. Worst possibility is the table is not coplaner. A machined straightedge about 2/3's the length of the entire jointer is required to verify and adjust. The paallogram table has four point adjustability.
the apex of the cutters is just a couple thousandths above the outfeed table
That's probably your problem. As you begin moving the board over the knives, the board is riding on the infeed table and leading edge will be ~.002" above the outfeed table.
As you continue the pass, your downward pressure is forcing the board into contact with the outfeed table. That contact (combined with the contact on the infeed table) forces the knives to cut ~.002" above the contact surfaces supporting the board - causing a concave cut.
Try this process.
Button everything up and make a few test cuts. For me, it's all about keeping even pressure on both sides of the kinves. Wood is flexible and trying to "help" the knives usually causes problems.
Edited 12/17/2007 9:37 am by Dave45
"That contact (combined with the contact on the infeed table) forces the knives to cut ~.002" above the contact surfaces supporting the board - causing a concave cut."
Except that he is reporting a convex cut. That's the puzzling part. A concave cut is easy to explain in terms of cutterhead/table geometry. A convex cut is not; I think the only ways you can get a convex cut are improper technique or a seriously bowed outfeed table.
-Steve
He is reporting a concave cut in the body of the post and a convex in the title ?. It could be setup or technique. But his description of the set up on the jointer doesn’t match any I know of so it sounds like he needs to start there.
Edited 12/17/2007 11:04 am ET by slo
Thanks, Slo. Saschafer's post threw me for a loop until I re-read the OP.
FWIW, if the OP is seeing a concave cut, I stick with my idea. (Been there, done that). If he's getting a convex cut, I'm clueless. (Been there, done that, too) - lol
Edited 12/17/2007 11:14 am by Dave45
"He is reporting a concave cut in the body of the post and a convex in the title ?"
Yes, but he also says this:
If I joint two boards and hold them edge to edge, the ends don't meet
That's definitely convex.
-Steve
Quickstep,
Technique causes a lot of problems.
If the blades are sharp, try feeding a bit of 6' stock or so onto the blades with pressure at the very end of the **infeed** table. When the end of the stock passes the end of the infeed table, keep the pressure on the end of the stock until it's unsafe to do so.
Rick's advice (post 4?) is sound - could be that the tables are not parallel, and the end of the outfeed table is lifting the stock off planar.
Let us know how you got along.
Cheers,
eddie
Edited 12/18/2007 2:55 am by eddiefromAustralia
I can't believe I screwed up writing my description. The cuts are definetly convex. Only by a tinch, the gap at either end is only around 1/32". For most of my jointing needs, this is insignificant, but for glue ups, it's a problem.
PS, it has a Byrd cutterhead.
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