Flattening panel glue up problems

[Nick Mazzino]

Attempting to make my first table. I have been doing small projects recently to get experience woodworking. This is my first few months. I have a 15" spiral head grizzly planer.

I am having troubles flattening panel glue ups.
I joint and plane all my individual panels first. Glue them up. Then try to put them through my planer with an MDF planer sled as my jointer is only 6". I shim the panel up so it does not rock in the sled then run it through the planer. I have a stop on both sides of the panel on the sled so the panel does not pop up. My panels end up coming out not flat, either concave or convex. This has happened twice. Could the planer rollers be pushing the panel down in the middle causing this?

It is not an issue with my planer as when I do an individual board, it comes out great.

I have been using maple and walnut wood.

Any suggestions or tips for improvement?

[Cary Falk]

As long as most of the board is resting on the sled, I am not sure exactly where the issue is. How long are the glue ups? I think you need to do a little more work on the glue up and you wouldn't have to use the sled when you plane it. I hardly ever use a sled for the planer on a glue up.

[Nick Mazzino]

The boards have not been terribly long. Around 18" each. I suppose my glue up needs some work then. I am definitely having to plane after the glue ups.

[Steve Eure]

Personally I would mill my lumber before glue-up. Your boards should be the same thickness and have straight edges with no gaps before you glue the two together. If your boards are straight and true to begin with, you should not have to use excessive pressure in your clamps. Make sure that everything is flat and straight and you should not have to plane afterwards. If you do it should be minimal.

[Charles Lent]

Planning changes the board thickness. It doesn't do a good job of flattening wide surfaces because the drive rollers hold the board flat while cutting it, allowing it to return to it's warped shape, but thinner after planning. A drum sander is better for making surfaces flat.

If you are jointing your boards and each lies flat on a known flat surface before glue-up, then I suspect that your joiner fence is not set exactly at 90 degrees to the joiner knives (89 maybe). If you cannot get it perfect, jointing the edges of alternate boards in the opposite direction may help (so the edge of one board is 89 degrees and the other 91 degrees) . This would create a joint between two board edges that results in a flat panel, but the edges of the two adjacent boards (one a little more than 90 degrees and the other a little less than 90 by the same amount) end up making the surface of each board on the same plane with each other and the resulting panel is flat after glue-up. If you don't do this and the jointed edges are all 89 degrees or 91 degrees your panel will be warped by 2 degrees for every joint. I hope I'm being clear about this.

I do this whenever I'm joining boards for making a panel or table top and it works well for me. After I have laid all of the boards side by side and determined the top side based on the end grain of each ( alternating grain directions to minimize later warping), I mark the top side of each board with a Vee kind of arrow at the same end of each board. I also draw diagonal lines across each joint from board to board (one line for the first joint, 2 lines for the second joint, etc.) so I can keep the boards in the same sequence and orientation when gluing them together. I only place these marks on the top side of each board. Then it's easy for me to joint the edges of every other board (the odd numbered) in one direction and joint the edges of the even numbered boards in the opposite direction, thus negating the effect of a not perfectly set joiner fence. Even though I do this, I still frequently check and set my joiner fence as close to 90 degrees as possible, because I want other jointed edges to be very close to 90 degrees, even if they will not be glued to another board. I use my Wixey digital angle gauge for setting it.

Charley

[glenn bradley]

Charles hits on my typical response to this. Planers use an already flat reference surface to make the opposite side parallel. If you have an uneven side and are shimming it as you describe, you should be able to get a flat side IF your material is not moving between passes. That is, what is shimmed flat on run one has to be in the same place for run two. A dab or hot glue, double stick tape or coarse sandpaper can help assure each pass is using the same reference surface.

[Jim Andrew]

Have you tried using cauls? Mike Henderson posted about using cauls, and I tried his system and have had great results gluing up panels. Just search Mike Henderson cauls.

[Mike Cutler]

Nick

As others have stated, I suspect your real problem is in the individual board prep.
-Joint and mill all of the boards first to the same exact thickness prior to glue up.
- Make sure that you edges are jointed, or ripped 90 degrees to the face, or you will, as suggested, have to alternate the board edges through a jointer, or table saw to offset any deviation from 90 degrees.
- lay the individual boards out dry, prior to gluing, on a known flat surface. Any gaps in the seams have to be addressed. If it doesn't lay flat, with no gaps between the edges, it will never glue up properly.
- You shouldn't need to run the material back through the planer following a glue up. A light sanding maybe, but it should not need to be planned. I have done glue ups 30" wide, and 10' long, on a 6" jointer, and a 15" planer. It can definitely be done with what you have available.
- Cauls and a glue up frame/table are a must if you are going to be doing panel glue ups. You may even consider biscuits to help you align everything during the glue process. Google "glue up table" and you'll get an idea of what I am referring to.

Your planer can absolutely push down the center of the panel, which is what I believe is happening.

Once again, and I am not trying to be a jerk, if you need to run the material back through the planer following the glue up, something is wrong.

[Nick Mazzino]

Thank you everyone for the advice this is very helpful. I tried some cauls and have watched that video previously as well. My joint appears to be at 90 per my square.

I will double check the alignment of that and the jointer knives tonight as well as pay very close attention to my board prep and try another panel glue up this week.

Thanks again.