How do I surface joint (6" Jointer) out a bow on a board's surface?

[Minh Tran]

I recently purchased a Grizzly G0452 and have been using it on Douglas Fir 2x4s. I've already prepared the jointer by making sure that the outfeed table is leveled with the tip of the blade when it is at its highest point. Afterwards, I made sure that the depth of cut is zero-ed and when a non-zero depth-of-cut is set, that the outfeed table and the infeed table are displaced in parallel by the set amount. I get mixed results in cut quality but I'm mostly having trouble fixing bows on surface joints and crooks on edge joints.
The Problem

The first milling operation that I perform on a piece of lumber is surface-jointing. The DF 2x4s I pick out are usually flat and straight. Those that are in good condition to begin with usually surface joint and edge joint easily to a square.
Occasionally, if I exert to much downward force at the beginning and end of a face joint and the cut depth is somewhat heavy (when cut depth is set between 2/32" and 3/32"), I end up with a bow.

What I've Tried

When trying to fix a bow, I noticed that I slowly worsen the bow if I support the board at the start of the joint, 3-4 inches from the board's edge. The error increases dramatically if I set the depth of the cut to 3/32". Which makes sense because I'm pushing the already shallow end of the board deeper into a cut.

I then tried to identify where the bow begins and ends and marked those region around the board (this reference helps me identify where my cuts are being made when I position my push block at a certain location). I decrease depth of cut to 1/32" and sometimes to as small as 1/64". I noticed that if I position my push block *after* and in between the bow as I feed the board through the cutterhead, the bowed region gets cut. This slowly fixes the bow.

Now ... the bow is about 1/16" proud, so if I set my cut-depth to 1/32", 2 passes should fix the problem. But after passing the board 4-8 times through, the board is still not flat! This confuses me.

I then increase depth-of-cut to 2/32" and push the board through on the bowed region but I over-cut and recreate the bow. @#$%@#$%!!!!! This meant the bow was <1/16" proud before depth-adjustment (but it was still noticeable).

What I'm Planning to Try

I'm thinking that I might get better results if I start from where the bow is less than 1/16" proud, plane it with a thickness planer, and then resume surface jointing. Maybe I should better stock than DF 2x4s. Do some species of wood surface joint/plane better than others?


Thoughts/tips?

[Andrew Hughes]

Minh it's sounds like it could be combination of your technique and the out feed table set too low.Im sure you have watched your fill of YouTube videos.
So try this. Set your out feed side lower till you get snipe.Then raise it a little bit after each pass with your test piece till the snipe is gone.Use the edge of a piece that's tall enough so it will not bend as you do your test.
Dougfir is easy to face.If your wood is fairly flat maybe one lite pass.

[Tom M King]

Once you get the jointer tuned, start the bowed board past the cutterhead to start taking the bow off. The easiest, and safest way to do this, if one doesn't understand how, is to get someone to show you in person. The important place for downward pressure is on the outfeed table. If you can hold the board down without flexing it on the outfeed table, and the jointer is tuned correctly, the board will come out straight.

I've seen more than a few people new to woodworking who think they have to make ever pass on the jointer a full pass. The only full pass you need is when the board is straight enough before the pass to make a full pass.

[lowell holmes]

I hand plane the convex bow out and then run it through the machines. Tom is doing the same thing on the jointer.

[Robert Engel]

What Tom ^ said.

On severely bowed wood I start with end of board closest to me, 1/3 - 1/2 of the board over cutter head and make several passes.

As you hear the jointer making contact with wood further and further, switch board around and repeat.

It will become obvious when its time to joint the full length of the board.

If you're producing a bowed board after several passes, something is wrong with the setup, most likely the outfeed.
I could either be set up wrong or it could be out of parallel. Check parallel with a straight edge use a space to lift off cutterhead.

If that check out, the way I check outfeed height is to lower the outfeed table. Rather than using a straight edge (hard to do if you have helical head anyway), with dead flat stock pass over cutterhead, stop machine and leave board in place. Then adjust outfeed table to just contact the jointed portion of board.

Fine tune

[Kevin Jenness]

Andrew and Tom have it right. The jointer is sensitive to very slight adjustments in outfeed table height and also to technique. I use a pair of boards as long as the outfeed table to dial in the height. When set up correctly the edges of the pair will fit together with no gap, belly or snipe. I usually use a straightedge to set the height initially just below the cutting circle so that when rotated the knives will carry the straightedge a millimeter or two, then use a dial indicator to monitor minor height adjustments until the two boards indicate a good result.

Boards longer than the outfeed table present more challenges to technique and often require less than full length passes to get the stock close to flat and straight. I have found that bowed stock often responds better to flattening on the convex face first, and to do that Tom's method is required. Set the end of the board over the outfeed table, drop the center of the board carefully onto the infeed table and push through. Repeat until the belly is gone and finish with a light full length pass. When dropping on your hands should always be over the outfeed table, behind the knives. A Euro guard makes this maneuver a little easier, with a porkchop you can push the guard aside with the leading edge of the board held above the table.

[Malcolm McLeod]

My 1st attempts with a jointer had same result - - I could have built a rocking chair. Adjust the outfeed table height.

[Mel Fulks]

Agree with Tom. I think perceived liability problems make all the TV and magazine guys work "bow up"

I've seen more than a few people new to woodworking who think they have to make ever pass on the jointer a full pass. The only full pass you need is when the board is straight enough before the pass to make a full pass.[/QUOTE]

[Rich Engelhardt]

I recently purchased a Grizzly G0452 and have been using it on Douglas Fir 2x4s
Forget the 2x4's and pick up some 2x6's.
Sticker them for a couple weeks.

You'll be amazed at how much better they do.