Opinions on using 1.5" Tenon Thickness with Pine

landrand · March 29, 2007, 02:20:43 PM

I'm getting ready to build the Sobon shed and perhaps another similiar shed for wood storage. After getting some experience with these small sheds, I plan to build a small timberframe barn then a house in the next few years. All my timbers are white pine. Last year I bought a Mafell chain mortiser with the 1 1/2" chain and plan to use this tool for all the mortises. I selected the 1 1/2' chain because I figured I can always cut 2" mortises with it, while with the 2" chain, you can't cut 1 1/2" mortises.

From what I've read in several timberframe books, the 2" tenon thickness is prefered with softwoods while the 1 1/2" tenon thickness is better suited to hardwood timbers. Was wondering what you folks think about using a 1 1/2" thick tenon with white pine timbers? Although I could cut the mortises 2" by making 2 passes with the chainmortiser, it would be much easier just to standardize on the 1 1/2" thick tenon and only make one pass with the tool. Any thoughts or comments would be appreciated.

Raphael · March 30, 2007, 01:07:45 AM

I personally lean towards using 2" tennons w/ 2" shoulders for white pine, it's not very strong and better safe than sorry. Running two passes with the Mafell is pretty quick and easy, cut the shoulder (fence) side of the mortice first and you'll have no problems.

Griffon · March 30, 2007, 03:11:40 AM

On the other hand, your major joints could be implemented with splines exploiting the qualities of a hardwood. 1+1/2" would then be fine ;)

Jim_Rogers · March 30, 2007, 09:29:04 AM

The basic rule for tenon sizing is one quarter the beam thickness, so a 8" beam should have a 2" tenon, and a 6" timber should have a 1 1/2" tenon.
What sizes are your timbers?

Jim Rogers

landrand · March 30, 2007, 07:17:59 PM

My timbers will primarily consist of 8x8 and one 8x10 tie beam for the sobon shed. For the house project, I plan to primarily use 8x10's for posts and rafters. I've also cut a few larger timbers such as 8x12, 8x14, and even some larger 10x10, or 10x12's to use in areas where the strength would be needed. I did this project bass ackwards. I spent the last few years cutting timbers prior to having a detailed house design.

Griffon · March 31, 2007, 03:16:44 AM

Oh excuse me, splines don't register in Sobon designs.

In general though, shouldn't the question of proportion be secondary to the tension capability necessary in a joint?

Jim_Rogers · March 31, 2007, 07:46:07 AM

Griffon:
Splines have there place and are good to use when needed. And they require extra work to cut, as you have to now fit the spline to the mortise in the post as well as the mortise in the beam.
In a simple garden shed they may not be necessary.
If you choose to use splines in your shed design, that would be up to you.
I was just stating the standard tenon sizing rules....
He asked for thoughts and comments, I made mine and you made yours.....

Jim Rogers

landrand · March 31, 2007, 01:44:04 PM

My goal is to start building several small buildings before I tackle the house project. The Soban shed first using the book plan. This experience can then be applied to the next project such as a TF sauna and woodshed. Maybe a small barn and then the house. I envision learning from each project and applying the knowledge to the next. Maybe some of the joints used or even the design for the small buildings might be overkill, but my goal is to gain the knowledge and practice so it can be ultimately applied to the house project. Thanks for all your help.

Jayson · April 06, 2007, 08:16:23 AM

Go for it. Hands on is the way to go. Almost everyone I know can read a book. And many of those remember lots of what they read. But without grabbing a chisel and a mallet and tearing up a piece of wood or two I think retaining the finer points can be difficult. I've always follow the parameters Jim mentioned.
One thing I don't often see mentioned in books is common mistakes to watch out for. A common phrase may be measure twice cut once. That one is in all the books. How about : If you want to shine, stay on the right(versus wrong) side of the line. And : Take another look if you cut a foot. This is my personal favorite CHECK YOUR DEPTH, CHECK YOUR DEPTH, CHECK YOUR DEPTH...........This applies to most tools you will be using, circ saw, drill and mortiser. Oh this is a good one to think of when drawboring tenons: Moving to the end is a dead end. In other words after if you move your draw bore hole towards the end of the tenon that is a push bore. Another thing to remember is to take extra care cutting the last piece of a set of anything. You will not have any options as far as moving things around to fix them. And remember, if something looks strange like maybe you have taken to much wood out or you have too many notches. You probably do, consult another carpenter. I have seen guys spend days designing joinery and be very satisfied with the numbers only to cut and decide something just didn't jive. What I'm saying is be sure to trust that primative building instinct most of us have. Lots and Lots of Luck, Jayson

Griffon · April 06, 2007, 08:29:45 AM

QuoteSplines have there place and are good to use when needed. And they require extra work to cut,

I'm glad you said this Jim; I wouldn't think of using them without a use of a circular saw.

But wait a minute, is there a standard (or proportionate) depth reccomended for splines? I am using 8" beams, but my circ saw only cuts to 3½". A notion tells me they should sit at 50% depth ???

Jim_Rogers · April 06, 2007, 09:58:18 AM

I don't know of any published standards on spline depths.
Although cutting in a spline half way into a timber puts the joint in the neutral axis it could weaken the timber.
I would tend to follow a standard like shown in the Rules of thumb drawing:

But of course this means up from the bottom not down from the top....

In other words something like this:

Which states:

Splines Rules of Thumb
d is equal to or greater than 5/8 of D
h is at least 1 1/2 times or greater than H
Sd is 3/4 of D or larger

This drawing and these rules are my personal opinion on what looks right.
All spline joints sizes should be checked by an engineer for correct load bearing limits based on actual locations and loads.....

Jim Rogers

Jim_Rogers · April 06, 2007, 10:09:56 AM

Maybe "engineer" from VT can comment on the sizes and locations of his splines used on his frame.
Griffon, if you look in my gallery you'll see a album of photos of my visit to his raising where a lot of splines were used. The album name is "Raising in VT."
I've asked engineer to send me a photo with a ruler in it next to the exposed splines so that we could see how long they were, and some day I hope to get this info.
But again each spline size and depth should designed to be frame specific based on loads and sizes.

Jim Rogers