jointing before glue-up?

[mdhills]

Why would a pass over the jointer give a better surface than a table saw?
I've often seen this recommended, but still find it surprising -- I'd think a jointer would leave very minor scalloping that wouldn't be any better for a glue surface than a clean cut on a table saw.  (although a hand plane would be even better)

Matt

[Bill_de]

Why would a pass over the jointer give a better surface than a table saw?
I've often seen this recommended, but still find it surprising -- I'd think a jointer would leave very minor scalloping that wouldn't be any better for a glue surface than a clean cut on a table saw.  (although a hand plane would be even better)

Matt

My 4  steps are face joint. edge joint, rip to width on table saw, plane to desired thickness. 

During glue up, a jointed edged and a saw cut edge are treated the same. So far it has been working OK.

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[KC]

Why would a pass over the jointer give a better surface than a table saw?
I've often seen this recommended, but still find it surprising -- I'd think a jointer would leave very minor scalloping that wouldn't be any better for a glue surface than a clean cut on a table saw.  (although a hand plane would be even better)

Matt

I straighten one edge on the jointer and then rip to width on the tablesaw.  If everything looks good, on to glue.  If not, I'll do the other edge.

[WoodworkerTom]

I would think it depends on how well you keep the piece you are ripping consistently tight on the fence when feeding it.

I have done glueups both ways.  As long as there is no gap when boards are held together hand tight I glue up.  If there is a gap, I joint the edge.

I usually joint one edge with the jointer before ripping unless the edge looks pretty straight.  In those instances I shave a blade width off, flip the board and rip to width.

[Gary G™]

If you’re getting scallops off the jointed edge, you’re doing it wrong or poorly or your blades need sharpening.

[rwe2156]

If you’re getting scallops off the jointed edge, you’re doing it wrong or poorly or your blades need sharpening.

Yes, check your jointer.

I never glue up off the table saw, simply because the cuts are never perfect.

[mdhills]

If you’re getting scallops off the jointed edge, you’re doing it wrong or poorly or your blades need sharpening.

I try to have the tools dialed in so that the surfaces look good off the jointer or planer, and the edges of my table saw cuts are also clean.
But it depends on how closely you need to look -- the rotary cutting from a jointer or planer can sometimes be seen with a raking light, so for a truly finished surface, I'd either plane or sand afterwards.

I don't know that this irregularity would affect a glue joint.  But I don't think the edge off the table saw is any worse.
So I was wondering why I sometimes see advice to do a final pass on jointer before glue up.

Matt

[Hank Knight]

I don't trust the edges from my jointer or my tablesaw, although I think my jointer edges are probably better. I start with jointed edges and then make a couple of passes with a sharp hand plane, usually a long jointer plane. Then I check the joint by balancing one board on top of the other and passing a flashlight behind the mating surfaces to see how well they mate. If I can see light anywhere along the joint, the mating edges aren't good enough. I continue to work the edges with the jointer plane until they match perfectly and no light comes through. Then the joint is ready for glue. I don't believe in forcing a joint together with clamp pressure.

[mdhills]

I don't trust the edges from my jointer or my tablesaw...

Is there a specific area of concern?  straightness, squareness or smoothness?

[MichaelMouse]

Is there a specific area of concern?  straightness, squareness or smoothness?

Dull jointer knives can leave scalloped surfaces, or to extreme, heat hardened surfaces which don't allow max glue penetration. 

Tablesaws with a bit of heel can leave rough enough surfaces to show gaps and strings on surface.  

How picky are you?  Modern glues and good clamps can minimize both.

These slick an edge squarely when used properly Veritas Iron Edge-Trimming Planes - Lee Valley Tools  or, the old trick of simultaneously running a plane on mating edges, which doesn't care about perfectly 90.  Moxon vise is nice for this.