NewB Glue Up Question

[Mike Hollis]

So I bought some 8/4 poplar to laminate into 4x4 (nominal) posts for a bed I am building. After ripping the 9" wide board into two 3 1/2 " x 8/4 planks I put them together to see how they matched up. It was only then that I noticed that the board had a slight cup to it along its length, to the tune of 3/16" at the widest part over a 44" length. So to glue up I am thinking I want to put the concave faces together and pull the cup together at the center. I will be using 14mm domino's and glue.

My other choices are to have the convex faces together and have to pull each end together, or put them together like a couple of spoons and live with the slight cup. If it matters the bed will be painted so a slight gap could be filled with putty prior to painting.

What is the best way to glue these up?

Thanks,

Mike

[Doug Garson]

The best way is to joint the mating surfaces to eliminate the 3/16" gap. I assume you don't have a jointer but there are techniques to do this using a sled on a thickness planer or table saw. GOOGLE "jointing without a jointer" or "jointing on a table saw" and you will find some good descriptions on how to do it. You can also do it old school using a hand plane. Once you have the two surfaces flat you won't need the dominoes just glue and clamps.

[Mike Hollis]

I don't have a jointer, but I could make a jointing sled for the table saw.

Thanks.

[Mike Hollis]

Thinking about this, I don't imagine the table saw will work as I need to joint the 3 1/2" face. Can't picture how to do this. I suppose I could back to the shop where I bought the lumber and pay them for a few passes in the planer.

[Doug Garson]

You could try the jointing sled in the attached video.
http://www.youtube.com/watch?v=ryaL6buKmyo

[Pat Barry]

Lets say you were to clamp the two pieces together with the concave part in the middle, then you tighten it up. Would the result be straight? If so, I would glue them up like that and cal it good. The two bows (not cups) would balance out and there is no real need to joint the pieces.

[Mike Hollis]

You could try the jointing sled in the attached video.
http://www.youtube.com/watch?v=ryaL6buKmyo

Cool jigs, but that dudes saw needs a serious tune-up. Thanks for the link.

[Peter Quinn]

If I had to go for it, clamp the two concave faces together, so the gap is in the middle, and squeeze hard. Its your best bet. If the middle touches and the ends are gapped, thats far more likely to fail over time. But IME 8/4 poplar is not going to be as forgiving as that, you are better off jointing the faces to make them mate better, or having that done at a shop. I don't know any good way to do this with a TS, hand planes could do the job, but you real want a selection of planes (jack or scrub, #6 or #7, smother) that must be sharp and used correctly, not a push button operation. And once you have the faces flat and glued, you need the other face made parallel, preferably before glue up, or the next stages of joinery will be challenging. Making stock square is fundamental to working wood, lots of ways to skin the cat but no good way to avoid it.