Why are my frames twisted?

[Raymond Fries]

I have made four of these with two coming out perfect and two twisted. All four were square to within 1/32" when measuring the diagonals.
318829
I squared the stock. I glued it together with biscuits and used Jorgensen cabinet clamps. I used two clamps across the width at each end. The frame sat on the steel bars of the clamps. I was sure that the long boards touch the clamps at all four points of contact. The surface was level under the clamps.

What am I missing?

[glenn bradley]

Construction lumber is very wet, even when kiln-dried. I imagine if you lay a reliable straight edge along some of those edges you will find the culprit. I wouldn't stress over it too much. Your pair that came out fine may be teeter totters this afternoon. This sort of material only stay put once its fastened to something else. If these are going to act as a reference surface for something else to build off of I would pick a more stable material. If these will get squashed flat to the floor when a cabinet is set on them and then can be shimmed for square, I'd just move along without worry.

[John TenEyck]

If those are cabinet bases I would rethink using 2 x 4 material. I learned the hard way that 2 x 4's will shrink and all kinds of bad things can and will happen. I make all my cabinet bases out of 2 layers of 3/4" plywood now. No shrinkage and no problems down the road.

John

[Raymond Fries]

The frames are for a workstation for my lathe which will sit just to the left of the one in the picture. The twisted frames are just like the ones in this picture. I am in the process of redoing my shop to gain some storage space. Getting really messy right now. These workstations are the first two projects.

318830

Glenn - Had not thought about the moisture content. Just checked and it is 13 percent.
John - Good tip on the bases.

[Stew Hagerty]

I'm guessing you had a little too much clamping pressure on one side. It's very easy to do.

Here's what I've done before. I put the frames onto a dead flat surface, then I Inject a little fresh glue into each corner from the inside before loading each corner up with heavy weights on each corner. Make sure all four corners are really weighed down on the flat surface.

If that doesn't work, you probably have to open up the corners and do another full glue-up.

[David Ragan]

Anytime i use construction grade lumber for anything where stability really counts, I always buy 10, or 12" wide boards that are flat sawn straight across the center, then rip them, "hold the pith", and then have QS stock for whatever it is. It's more trouble.
(as has been said here, be sure to put all the lumber back after sorting through it @ BORG.)

[Raymond Fries]

I'm guessing you had a little too much clamping pressure on one side. It's very easy to do.

Here's what I've done before. I put the frames onto a dead flat surface, then I Inject a little fresh glue into each corner from the inside before loading each corner up with heavy weights on each corner. Make sure all four corners are really weighed down on the flat surface.

If that doesn't work, you probably have to open up the corners and do another full glue-up.

Thanks for the tip Stew. I finished the new frames yesterday and discovered that I could force a twist by just a little more pressure on the frame.

[pat warner]

Very easy to take precision joinery and screw it all up during assembly.
Just as easy to assemble crummy joinery in the right fixturing and square it up!
(Within limits that is.)
But given variable cuts, (saw, router or whatever), and the same gluing procedure (where some assemblies are true and others are not), I'd blame it on the cuts. Here's why:
As little as 6' (a tenth of a degree) can screw up squareness/parallelism at the rate of a 1/32"/ft. So if your gluing/assembly-fixturing and your cuts are variable, variation in squareness and parallelism is to be expected. Moreover, if your material prep does not include jointing, planing, precision rips & x cuts and QC is ignored (to prove you're on the mark): Anything can & will happen.

[Danny Hamsley]

Construction lumber is only dried to 19% moisture content. Oft times you will see a stamp that says "KD19" which means kiln dried to 19%.