Recently a timber framer suggested I post these "General Rules" for joinery design, that I learned about recently at a Joinery Decisions workshop class.
Here they are:
There are 8 general rules to timber framing for joinery design.
The "Golden Rule": Design joints to do the same structural task assigned to the loaded timber without putting the capacity of the receiving timber at risk.
1). Cut the joints and arrange the fastenings so as to not weaken the pieces of the timber that they connect as little as possible.
2). Place each abutting surface in a joint as nearly perpendicular as possible to the pressure with it has to transmit.
3). Proportion the area of each surface to the pressure with it has to bear, so that the timber may be safe against injury under the heaviest load which occurs in practice and form and fit every pair of such surfaces accurately in order to distribute that stress uniformly.
4). Proportion the fastenings so that they are stronger than the loads that are anticipated in the pieces that they connect.
5). Place the fastenings in each piece of timber so that there shall be sufficient resistance to the giving way of the joint by the fastenings shearing or crushing their way through the timber.
6). Select the simplest forms of joints, and obtain the smallest number of abutments.
7). Both the tenon and the mortise should be shaped to be parallel with the grain of their respective members.
Most traditional layout was done with the layout tool at hand, which was the framing square. And as it has two parts, the body (the 2" wide part), and the tongue (the 1 1/2" wide part), most layout was one of these two dimensions.
Understanding and using layout faces or reference faces helps us to correctly layout, cut and join timbers so that every piece of the frame lines up to the others and it all goes together correctly.
Each timber has a reference/layout face and that face depends on what the "general frames rules" are, these rules were established by the master framer or frame designer.
But some standards usually always apply. For example, all gable end bents have to have joints flush with the outside of the building. All roof joints have to be flush with the top plane of the roof slope. All wall joints have to be flush with the outside of the walls, all floor joints have to be flush with the top surface of the timbers supporting the floor. These are general timber framing layout rules that apply to most if not all frames.
Some of the interior bents and other interior parts can have different layout faces and rules depending on the master framers plan and none of them are wrong, if it all goes together right.
Other standard rules for joinery decisions are that tenon size should be one quarter of the timber thickness. That means a 8x8 should have a 2" thick tenon and a 6x6 should have a 1 1/2" thick tenon.
Pegs should be one half the tenon thickness. So a 2" tenon should have a 1" peg, and a 1 1/2" tenon should have a 3/4" peg.
Now sometimes a 1" peg will take away too much wood and therefore a smaller peg may need to be used as long as it's strength is high enough as to not fail during it's load carrying capacity.
I hope this is helpful to you.
What is a bent? The link above this post, glossary, will not open on this computer, and my dictionary is no help.
Good Info Jim... thanks
Jim...
As usual, an informative post from you. Thank you!
Joel
The glossary, I believe, is in pdf format. This requires a pdf reader program. Most commonly used is acrobat reader. You can go to their website and download a free reader and then you'll be able to view the glossary. And you can print it for future reading and use when not "online".
I would suggest you get a reader program. I'm sure you can find one at www.adobe.com/acrobat (http://www.adobe.com/acrobat), but if not let me know and I'll find the correct website address.
A "bent" is an assembly of timbers. Like, for example, a gable wall (with or without rafters). It is usually assembled flat on the deck and then raised up to a standing position. The raising up can be by hands, crane, ropes and tackle, forklift, or other methods.
Jim Rogers
Thanks Jim.
Very good info.
It really does take a newbie a lot of study for this stuff to all come togher and sink in.. :P
Jim you are the bomb. Your info is always great. I hope to meet you someday. Please let me know if you are working on anything down south. I would love to help. Jayson
Yes, I must say, Thanks again.
Quote from: Jim_Rogers on September 06, 2005, 10:25:02 AM
Recently a timber framer suggested I post these "General Rules" for joinery design, that I learned about recently at a Joinery Decisions workshop class.
Here they are:
There are 8 general rules to timber framing for joinery design.
The "Golden Rule": Design joints to do the same structural task assigned to the loaded timber without putting the capacity of the receiving timber at risk.
1). Cut the joints and arrange the fastenings so as to weaken the pieces of the timber that they connect as little as possible.
2). Place each abutting surface in a joint as nearly perpendicular as possible to the pressure with it has to transmit.
3). Proportion the area of each surface to the pressure with it has to bear, so that the timber may be safe against injury under the heaviest load which occurs in practice and form and fit every pair of such surfaces accurately in order to distribute that stress uniformly.
4). Proportion the fastenings so that they are stronger than the loads that are anticipated in the pieces that they connect.
5). Place the fastenings in each piece of timber so that there shall be sufficient resistance to the giving way of the joint by the fastenings shearing or crushing their way through the timber.
6). Select the simplest forms of joints, and obtain the smallest number of abutments.
7). Both the tenon and the mortise should be shaped to be parallel with the grain of their respective members.
Most traditional layout was done with the layout tool at hand, which was the framing square. And as it has two parts, the body (the 2" wide part), and the tongue (the 1 1/2" wide part), most layout was one of these two dimensions.
Understanding and using layout faces or reference faces helps us to correctly layout, cut and join timbers so that every piece of the frame lines up to the others and it all goes together correctly.
Each timber has a reference/layout face and that face depends on what the "general frames rules" are, these rules were established by the master framer or frame designer.
But some standards usually always apply. For example, all gable end bents have to have joints flush with the outside of the building. All roof joints have to be flush with the top plane of the roof slope. All wall joints have to be flush with the outside of the walls, all floor joints have to be flush with the top surface of the timbers supporting the floor. These are general timber framing layout rules that apply to most if not all frames.
Some of the interior bents and other interior parts can have different layout faces and rules depending on the master framers plan and none of them are wrong, if it all goes together right.
Other standard rules for joinery decisions are that tenon size should be one quarter of the timber thickness. That means a 8x8 should have a 2" thick tenon and a 6x6 should have a 1 1/2" thick tenon.
Pegs should be one half the tenon thickness. So a 2" tenon should have a 1" peg, and a 1 1/2" tenon should have a 3/4" peg.
Now sometimes a 1" peg will take away too much wood and therefore a smaller peg may need to be used as long as it's strength is high enough as to not fail during it's load carrying capacity.
I hope this is helpful to you.
So Jim,
If you have a timber(s) that is 10X10, should a tennon be 2.5 wide or remain at 2"? What if it's hardwood?
Well the rule says it should be 2.5, and I've seen larger tenons and mortises in big stuff.
However, being hardwood you maybe able to make it just 2" but each frame design needs to be reviewed and understood before making a general statement like that......
Understood, I was just wondering how common it is to have larger than 2" in tennon in 10" stock, especially when it's hardwood. The stress and shear area needs to be calculated/sized for each joint for each frame.
As the name suggest, General Rules, there is always an exception, that is where I get into trouble or find myself ecstatic with a new solution.
As an example the tie beam pushed out from the gable plane to allow a boarding trench. Or a 3"x5" brace on a 9"x12" post using 1-1/2" mortice in soft wood.
Tim
Hi, one problem I ran into was a beam at the end of a deck which ran on a 45 degree back to the house. the post it was attached to was set square to the rest of the deck. with the beam and tenon entering the post at 45 degrees the tendency for the tenon to shear off along the grain and be ruined was discovered at fitting and we doubled the tenon thickness to 4". luckily we had 10x10 posts for the deck.
I'm wondering If there is a common rule for this. The engineer didn't pick up the potential problem on my drawings. By the way the project is done and looks great, but being my first traditional timber job it was stressful not knowing how it all would turn out, like driving in the fog.
I was wondering if I could get advice on theory and technique here. After falling out of love with construction after 20 years, I've been looking forward to doing alot more of this. What would i do if the post couldn't handle a wider tenon. The posts run through the deck and incorporate the railing.
................Blake
Quote from: Aikenback on December 11, 2009, 10:32:18 PM
a beam at the end of a deck which ran on a 45 degree back to the house.
You never stated what size this beam was. And in order to give you some advice, I'd need to see the whole joint.
Jim Rogers..
PS. As mentioned there are exceptions to every rule. Oh yea and welcome to the forum.
i'm sorry it took so long to reply, i dont know how to upload the picture. i also have a pdf of the joint in question. the beams are 8x16 with a 12'' high x 2.5'' thick tenon thru to the the center of a 10x10 (5'' incl. housing). The post runs thru to form the railing post above. 1-1/4" housings. A short beam runs into the last post and supports two short joists much like a hip rafter would in a roof except it's a deck and therefore like a floor. there's a trianglular section of the tenon that is susceptible to shear off with the grain. if I can become less of a caveman with the computer, I could show it.
Send anything you want to me and I'll post it for you.
(here is a picture that Blake sent me of his project) More of his work in my gallery under Blake Todd Album, some very nice work, indeed.
(https://forestryforum.com/gallery/albums/userpics/10095/2703/IMG00177-20091209-1026.jpg)
The mortises in one house I looked at had 2 3/4" layout on a post of about 9"x10" section. All of the posts on the Dutch barn I'm working on now are 2 1/4" layout. They range from about 6"x9" to about 9"x12 1/2". I wonder if the size of the framers square might have something to do with that sometimes. :D
I have a question regarding peg placement. I've read the "general rules" and have the "timber framer's workshop" book by Steve Chappell and run everything I want to do through an engineer, but the more I know, the better. (for me, anyway).
For a 1" peg in the through posts in the deck I did there seems to be little tolerance for placement. I believe I needed about 2-1/2" of relish and a minimum distance of 2" from loaded edge of post. The specs from the engineer required 2-1/2" from loaded edge. This means with the tenons butting into each other there was no ability in the joinery designed to increase the relish just for peace of mind. Unless I were to offset the tenons and lap them on either side of each other in order to run the tenon past the centre(Canadian spelling) of the 10" post. How common is this?
Also, what about the housing? If I were to set the pegs at 2-1/2" from face and then remove the housing, the face edge of the peg and the end of the housing only has 3/4" of "meat" between the post and the end of the beam. What would happen with an 8" post?
I had alot of confidence in this regard here because the posts were wider than the beams which gave me the full 2-1/2" from the face on each side of the beam.
Should one consider a spline joint instead?
Is this tiresome answering similar questions from different people over the years?
Am I cheating by asking questions here instead of taking a design course?
Should I just trust the Eng.?
Should I just stick to nails and 2x4s? (please no!!)
QuoteUnless I were to offset the tenons and lap them on either side of each other in order to run the tenon past the centre(Canadian spelling) of the 10" post. How common is this?
I'm not totally sure how common it is but when I questioned Jack Sobon about how to get the relish needed on tenon he suggested an over and under tenon set up:
(https://forestryforum.com/gallery/albums/userpics/10095/1232/Over_and_under_tenon_joint-1.JPG)
and to see through the joint:
(https://forestryforum.com/gallery/albums/userpics/10095/1232/Over_and_under_tenon_joint-2.JPG)
QuoteShould one consider a spline joint instead?
Each frame and each joint depends on a lot of factors. Each has to be evaluated based on size, location, load, type of wood are a few things on the list. So a general answer would be maybe.....
QuoteIs this tiresome answering similar questions from different people over the years?
No, over the years we have all learned more and more. Timber framing is a life long learning process, experiences add to your knowledge base.
QuoteAm I cheating by asking questions here instead of taking a design course?
A design course will help you understand more than you can learn by reading posts on forums. But keep asking questions.
QuoteShould I just trust the Eng.?
Yes, but you may want to help educate him in timber framing basics if he doesn't have a lot of experiences with timber framing.
QuoteShould I just stick to nails and 2x4s? (please no!!)
Every type of construction is something to learn......
Hi Jim, Thanks for all your help. This is great. After looking through some other pictures i saw the over/ under tennon. there is always a solution. I'm Gratefull. The engineer I use is listed in the TFG.
Blake.
P.S. I don't dislike stick framing that much It's just too much of the same old same old. It's a trade that is under appreciated by many.
I am about to start cutting the 3X5 oak knee braces for a TF project. After drying and lightly planing they measure 2.75X5. If I keep a 1.5" deep face for the brace surface what would be the implications of using a 1.75" tenon in a 1.5" mortise ?
Correction!!! --- The tenon would be 1.25" in a 1.5" mortise ---
Have the mortises been cut?
If they have then you're going to have very loose and sloppy tenons in the mortises.
If they haven't been cut then cut them to fit the tenons.
Jim Rogers
THANKS Jim--- The mortises have not been cut yet. You are very helpful and down right knowledgeable. !! Baryon
Why do timber framers work with big timbers?
They are bent that way. :D
Hello rjwoelk, and Welcome to the Forestry Forum.
Jim is there a general rule for depth of a given mortise or length of tendon?
Yes, but it is not a simple answer.
It all depends on the location of the tenon and mortise. Each joint has to be reviewed as to how much stress or load is on that joint.
Then the tenon has to be long enough to provide enough "relish" beyond the peg hole to have the strength to not "blow out" the tenon and split it along the grain.
The basis for this is something like at least 4 diameter's of the peg beyond the peg hole. But it could be more. I'd have to look up the standard rule, but I don't have time right now to do that.
Jim Rogers
Hi jim? I plan on building a saw mill building 24x30 10 x10 beams pine vertical post set on concrete pillars with strong ties in concrete 10 ft spaceing with rafters not sure on size probably 7/12 or should I have someone draw it up I need a 21 ft opening for logs near middle of 30 ft side of building
Quote from: Jim_Rogers on January 12, 2016, 09:36:39 AM
Yes, but it is not a simple answer.
It all depends on the location of the tenon and mortise. Each joint has to be reviewed as to how much stress or load is on that joint.
Then the tenon has to be long enough to provide enough "relish" beyond the peg hole to have the strength to not "blow out" the tenon and split it along the grain.
The basis for this is something like at least 4 diameter's of the peg beyond the peg hole. But it could be more. I'd have to look up the standard rule, but I don't have time right now to do that.
Jim Rogers
I am following along all these rules and based on this I have come to the following conclusion:
I have a 6" post, and a 4X6 knee brace with 3/4" pins.
This means:
1. the tenon should be 1" thick (1/4 the thickness of the knee brace)
2. the tenon needs to have 3" of relish (4x 'the pin')
3. the tenon need to be 1.5" from the edge (2X pin)
So in this case the tenon is 1" thick X 4.5" deep
Did I get it all right?
Some more notes:
- By the "peg rule" this peg actually should be 1/2 x tenon thickness or 1/2" and this would change all the numbers - 3" deep tenon???
-I have read that relish should be 3.5d - 7.5d for softwood
There are exceptions to every rule. Understanding when the apply does take some research and experience.
On a 4x6 knee brace we do 2" flush tenon and 1" peg.
(https://forestryforum.com/gallery/albums/userpics/10095/Brace_tenon_end_view_with_labels.jpg?easyrotate_cache=1230574680)
Also, we normally make the tenon length 3".
Recently in a discussion with another designer he felt that 3" brace tenons were too short. I believe he uses 4".
Braces are strong in compression and that's their job. Lack of pegs in braces have been found in many old barns and structures.
Some people say that the peg in a brace tenon is there to just hold the brace in place during raising.
Jim Rogers
Thanks Jim. One thing about the project I am working on is all the joints are under compression, so it should be a very forgiving project as far as pins go.
In general I don't see a use for pegs in tenons. The data I've read all talks a lot about peg failure under shear, and the pegs are weaker in shear than the wood in tension, so I understand.
(https://timberframehq.com/wp-content/uploads/2012/04/Exploded-joint.jpg)
I favor cutting tenons as half-dovetail, and using a wedge of a harder wood. The wedge is under compression and the tenon is under tension. For knee braces this has to be on the outside, which means your dovetail might be on the top edge and lifted by the wedge, which is unusual; and for a horizontal member with the wedge applied vertically, you'll want the wedge to be sufficiently tapered and to be driven in from above so it doesn't just fall out if it shrinks some.
If the wood shrinks a little, brace it, remove the wedge, cut a new hardwood wedge, and drive that in as a replacement. The building should be designed such that a load-bearing member won't just fall out if un-wedged, and such that the building won't just collapse if you pull a brace: it should be safe but not preferable to pull the wedge without first temporarily bracing everything up.
That said, I don't have a way to analyze all this except by dead reckoning. I'm aware that some folks who do this for a living also use wedges rather than pegs nowadays, so at least I'm not inventing some obvious advancement that everyone else somehow missed. That's a good sign.
What do you all think re wedges versus pegs?
Dude - That is a very handsome joint. Not sure I want to recreate it for knee braces but *DanG! It's great as shown as beam to post. Japanese? Tell me about the mortise cut angle trick bc I may have some slop with that joint if it's not through the post.
Thank you!
M Pratti
I've been around timber frames for years. I've only built one myself though, and it was done with scribe rule. I'm working on a deck/porch now with square rule layout. I have a question about Knee braces. I'm measuring from reference faces on one side of post timbers that have braces coming in from both sides. I'm thinking to inset the braces on the other side by measuring the same way, but from the non reference side. My perfect timber dimension is 7.5". Is there a problem with doing it that way? here is the front view timber layout plan.
(https://forestryforum.com/gallery/albums/userpics/61169/Andrus_2b.JPG?easyrotate_cache=1593025492)
Is there a rule for how long the tenon should be? What is the rule the distance along the tenon to place the peg?
Thanks
Clint
Quote from: cmiller on July 07, 2020, 11:59:17 AM
Is there a rule for how long the tenon should be? What is the rule the distance along the tenon to place the peg?
Thanks
Clint
I'm researching this, I will post back when I have an answer.
Jim Rogers
The timber framers guild engineering council has these two documents.
Sometimes that are easy to understand, sometimes not.
Maybe DonP can shed some light on this topic.
Jim Rogers
and
Hi Jim,
Is there a general rule of thumb for length of brace? For example if my span is 12' between posts should I use two opposing 48" braces or is 36" ok or is it mostly aesthetics? Also, if I'm putting a window or door centered in between 2 posts and the span is 8' do I still need to put braces in?
Thanks Jim
Quote from: rllintz on July 27, 2023, 03:05:05 PM
Hi Jim,
Is there a general rule of thumb for length of brace? For example if my span is 12' between posts should I use two opposing 48" braces or is 36" ok or is it mostly aesthetics? Also, if I'm putting a window or door centered in between 2 posts and the span is 8' do I still need to put braces in?
Thanks Jim
You can use braces that have 36" legs for that span.
If you have other braces at the ends of that wall you don't need to put braces in with the window or door. If you don't have any other braces in that line, then make the braces 2' or something that will fit. Good luck with your project.
Jim Rogers