Question on brace width (Sobon Shed)

[SWdendro]

Dear Timberframers,

I'm new to timberframing and I have a question on brace width.  Specifically I'm looking at the plans in Will Beamer's Learn to Timberframe book for the Sobon "Garden Shed".

The timber list (pg. 88) calls for 3x5 braces (and 3x5 collars).  All other components in the design allow for housing/reductions given that the timbers could be slightly undersized (i.e., a nominal 3x5 brace might actually be 2 7/8 x 4 3/4 when received from the sawyer).

The brace mortises are specified as 1 1/2" off the reference faces and 1 1/2" wide (page 96-97).  This "inner" 1 1/2" corresponds the mortise width.  Thus, for the brace tenon to accurately fit this mortise (and not be undersized), it also needs to be 1 1/2 thick (pg. 110, see diagram in "step 6").

If I'm understanding everything correctly, if the brace width is actually less than 3", then the tenon itself would essentially be short the difference between the actual and nominal 3" (given how the reference face is specified on the braces, see page 108), and would be loose in the mortise.

Am I missing something here!?  Or is this an inconsistency in the plans?  Should the braces/collars have actually been specified as 3 1/2" nominal to ensure that they have sufficient width to accommodate both a 1 1/2" offset and a 1 1/2" tenon?

Thanks!

[Jim_Rogers]

When I cut my own brace stock, I cut it 1/8" over the actual width. So for 3x5 braces and 4x6 braces, I cut 3 1/8" thick and 4 1/8" thick stock.
The reason why is because of the timing between when the brace stock is milled and when the tenons are cut.
If you buy all your stock or mill it yourself, there could be a difference in thicknesses.
Milling your own would be easy to make it over sized. 
Some mills or lumber yards won't have 4 1/8 or 3 18" thick stock.
If you have your timbers on hand and you are cutting all your joints and you start with your sills, floor joists, and post. Then your tie beams, plates and nailers. And then finally getting to your brace stock, you may find that the brace stock has dried a bit. And it may have shrunk a little in thickness. If you brace stock has shrunk a little, then you won't have enough stock to make a full offset and a full tenon thickness. Both are important to maintain.
We layout and cut the offset first. Then roll the stock over and reduce the back side of the tenon down from the 1/8" oversize to the full tenon thickness. We do this by hand planning off the back side of the tenon. Using a caliper or a tenon checker to make the tenon the correct size.

Jim Rogers

[Brad_bb]

I do not understand what this quote means.


First, Green wood shrinks as it dries.  So getting your brace stock 1/8" thicker  will help account for the shrinkage.  You could even order your brace stock thicker than that and run it through your planer just before you cut your joinery.  Often times, enough time passes between receiving your green timber and actually cutting the joinery that it will actually shrink.  So you can play the game of accounting for that, so by the time you actually go to cut the joinery, they will be close to nominal size.  Harder to do that with larger timbers as they will take a bit longer to shrink.  I've milled bigger timbers and they've sat stacked and stickered in my pole barn(which gets enough air flow) for 1-5 years and after 1-2 years most of the movement and a decent amount of shrinkage has happened. 

I'm not specifically familiar with the plan you mention, but as to your questions, the tenon you cut on the brace should be 1.5" and your mortise should be 1.5 inch.  If the thickness of your brace is less than nominal, you'll just end up with a shoulder that is less than 1.5".  Not a problem.  
If the brace is supposed to be flush to the outside the timbers it goes into, then you may need to adjust the distance of your layout of the mortises from the edge.  If you do that, then you're "mapping" which means that brace is not dedicated to that location and no longer interchangeable with other locations.  You don't have to though.  it just means that there will be a small gap between the brace and the edge of those timbers.  Putting all the mortises 1.5" from the edge will mean that all the braces will be interchangeable.

[timberframe]

The only think I might add to Brads suggestion is that you could pick through your brace stock stash and choose ones that will be undersized a bit and have them go against the outside of the building where any "non-flush" faces will less visible.  Save the ones that ended up bigger for where you might want flush faces.

[SWdendro]

Thanks to everyone for sharing their thoughts!

Jim – This all makes total sense.  My timbers have been drying for about 8-9 months, so there may have been some shrinkage.  This combined with the fact that I specified 3" width to the sawmill has resulted in most of my brace stock being undersized.

I think the best advice, at least if someone wants to stick to the plans described in Will Beemer's Learn to Timber Frame is to order (or mill) brace stock sufficiently wide to account for shrinkage and variation from the mill.   I basically cut a practice mortise brace and brace tenon before I realized the issue.  Hopefully other beginners will catch this sooner than I did!  I was caught off guard as all of the other dimensions on the cut list seem to be spot on (and account for actual dimensions that are smaller than nominal), so I hadn't really critically thought about the braces prior to ordering my timbers from the local sawmill.

Brad – Nice idea.  I had been too dogmatic, thinking that the outside of the braces needed to be flush with the rest of the frame exterior envelope.  Keeping the tenon at 1 1/2" and reducing the shoulder width is a cool solution.  Since this is my first project, I'm hoping to mostly follow the plans and improvise only as necessary, so I may end up sourcing some new brace stock this time around, and knowing that the "mapping" solution could work moving forward.  Alternatively, I might cut all of the braces identically/interchangeably, and account for a 1 1/4 shoulder instead of a 1 1/2 shoulder. 

Dovetail Timberworks – Another good idea.  I just looked through my stock, and almost all are undersized in this case....circling back to the proposed solution above.

[Ljohnsaw]

In my cabin designing, I made my braces one of 5 lengths. Something like 218 braces. The two best things I did were, 1), made a very short test brace to make the all mortises identical, and 2), made plywood templates to layout the braces.

My test braces actually shrunk so my mortises were ever so slightly undersized. During fit up prior to razing each bent a little bit of shaving was required.

[mattgancz]

For a frame of that size, you are not going to need that many braces.  Presuming the outside is your reference face, make a mark to match brace to its mortise --- Search: TImber Framing Symbols for some light reading.  Use your combination square, or a mortise marking gauge, to get the depth of your brace.  Mark that depth on your post from the reference face.  It doesn't matter if it is 3" or 2.8734626" --- nobody experiences a timber frame through a Vernier caliper.  From there, measure back your 1.5" using your combination square.