Shopsmith Forums

Gluing wood is a great subject all in itself. It was the subject of a whole quarter of 3 credits in forestry school. Chapter 9 of the "Wood Handbook" talks about it at length. I've tried to keep fairly current on the subject, especially since retiring.

Thought I'd pass this along for your consideration:

Yesterday I made a basic gluing mistake that caused me to pause and say to myself, "What a Dummie!:o !

Right after posting on the "Finishing Oak" thread that fresh wood should be exposed be for finishing and gluing, I went to the shop to try out the planer sled I glued up yesterday. What a blast! The front part of one of the side rails lifted up and the tip broke off. The stop block at the tail end of the sled broke off at the glue line. I knew, immediately what I had done! Too bad I wasn't thinking yesterday!

For the base of the sled, I used a 3/4" oak board that I had planed about 6 months ago. I was happy to find it in the wood rack, and was pleased it had two smooth faces. So when gluing the rails to the top face of the board, I just applied glue and clamps. Plenty of glue and adequate squeeze out.

The glue line didn't hold because of case hardening of the wood. Some would call this "glue starvation" and they would be partially correct. With glue penetration only into the freshly cut rails the starvation occurred because the oak carrier wasn't penetrated by the moisture in the glue.

Now I'm going back to re-make the sled. will probably use both glue and screws to hold the stop block.

Moral: It doesn't matter what you think you know if that knowledge is not applied.

The Project? - I am trying to plane inch and 1/4 oak strips to 1/16" thick for use in laminating counter edges in the Motorhome. They are now plastic, have hardened and chipping away.

Chuck
You know what would be an interesting experiment? Reglue the pieces without so much squeeze out and see what the results are. Sorry but old teachings die hard and I still believe very firmly in glue starvation (where too much glue is squeezed out).

My job teacher insisted on a uniform but consistant line of glue squeeze out but any more than a line and he either docked you for using too much glue or applying too much pressure.

Through the years I have always tried to abide by that rule and I'm certain of this that everytime I violated it I was dissapointed in the results.

I was also taught to lightly sand any edges that were ran through the jointer or planner that were to be glued and I now often to it on edges cut with these new saw blades that almost burnish the cut.

There was absolutely not too much squeeze out. There is/was glue marks remaining on the carrier board. Also there was a yellow glue color showing on the edging boards. Therefore the glue itself was the only thing holding the two pieces together. A mechanical and chemical bond between the two pieces of wood never took place.

Sanding before gluing would have been a better option than doing nothing, as I did, as long as the paper was 100 grit or finer. However knife cuts from a planer or jointer (re-planing) would have been best. (assuming the knives are sharp) Chapter 9 of the "Wood Handbook" (pages 2,3 & 4 clearly points out that a knife cut has better wetability than sanding, and also points out wetability of old surfaces can be improved by sanding with finer grits of sandpaper. Yes, I should have sanded!:o

The coarser grits and/or dull blades crush the surface cells and leads to a poorer joint.

Your shop teacher was a smart man and knew the blades in his shop could/would get dull enough to crush fibers.

One last comment about clamping. With the clamping systems available to us home woodworkers you can't apply too much pressure. The trick is to get the pressure uniform across the joint.