Timber Framers Guild Forums Tools Timberframe Design When timber dimensions aren't right on . . .

Quick question, both specific and general.

What is close enough for all of you in terms of timber dimensions? As in, if your design calls for a 8x8 timber, how much shy of that 8" is still OK?

Specifically, in my application, the frame Im building calls for 4x6 braces, and today I made a mistake when milling, and instead of 6" have 5 11/16". I would never plan this and dont intend to mill more timbers like this, but is this still usable, or should I find another use for this timber (which I certainly can). This brace is oak, in a hemlock, oak, pine frame.

In my application, the frame uses housing that reduces the timbers an inch for their perfect timbers within. I don't know how much this would apply for a brace.

In general, do any of you have tolerances for how much the dimensions can vary before you call it too much?

If you're square ruling, your 8x8 post could be as small as 7.5".

Your braces can certainly be a bit more narrow in the width, that's no problem (although your structural bearing will change a little bit). Your brace thickness is important though--you'll want them exactly 4" so that you can frame the mortise 2/2 (2" from layout/2" wide). I usually saw my braces an 1/8 wide, let them dry a bit, and then plane them to final thickness.

I can't give a specific answer but I will say that the workmanship and materials are generally better historically on public buildings and bridges, less so on houses and barns and some smaller outbuildings are where the apprentice learned and made his and now her mistakes. In other words, the tolerances depend on the type of building.

4"x6" braces are big braces compared to historic New England framing. Without knowing the engineering, it seems you could cut off another 2" and still be O.K., especially with oak. It matters how long they are, too. 3" x 5" is a standard size brace.

Old frames sometimes have significant variation in the size of the timbers. One barn I worked on had a 12' girt sawn 7" tall on one end and 6" tall on the other...oops. Of course, rafters were often intended to be tapered.

I do not know of any written standards for tolerances.

Good luck;
Jim

I think a good approach might be:

Has it been engineered?
Check with the engineer.

Who designed it?
Check with the designer.

Who is paying for it?
Check with person writing the check(s).

Is it green oak?
You'll likely see another 1/8" or more in shrinkage!

But overall, yes, you can vary things when the chisel meets wood. Unless that 1/4" +/- is critical and will hold up the entire building, it is probably fine. On a brace, I'd let the error be on the up / top side so as to not mess with the bearing surface, which is what should be critical for pushing against another timber.

Danfink, braces are difficult but important to fit well. Due to the rigidity of the triangle they make, small differences in length are critical. Even a sixteenth-inch can matter.

It would certainly be possible and good to use the seat/housing depth to create a perfect dimension, from your reference face or centerline as appropriate.

Personally, I think a 3x5 brace is a more pleasing dimension than 4x6 - perhaps you can resaw all your braces to that size?

Pete