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Author Topic: Newbie stuck on <simple> joinery  (Read 3451 times)

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Offline tburch

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Newbie stuck on <simple> joinery
« on: January 26, 2017, 03:43:40 am »
Hi All.   I saw this backyard fireplace structure on FB and want to model it as exercise in timber framing with mortise and tenon joinery, but I'm stuck.   



I chose to design it in two bents with a king post truss.  It has a pretty steep pitch to it. 

I've attached my SU V8 model. 



My questions, specifically, are

1) how do I attach the tie beams to my bents?  I thought I was going to use 8X8 posts and 8X4 trusses, and then set the 8X8 tie beam (not drawn yet) on the 4X8 shelf of the top of the posts, but that's probably not a good practice, seeing as the name of this beam is a "tie beam" and I've not really planned too well for tying it into anything.

After that, I have these questions

2) Where the king post meets the bottom chord and the two diagonal braces, how could that joinery be improved? 

3) I actually kinda like my 8" wide gusset going through the top of the king post and the two rafters, but would that be a good way to approach the joinery at the top?  …  I just considered that I might need a ridge board… 

I've started reading TF books, and I am actually enrolled to attend a school later this year.   Any advice you have is welcomed.   

Thanks, Todd
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'94 Ford 4830 Diesel 2WD & FEL.  Norse 450 skid winch.  Logrite fetching arch.  Fransgard Forestry Grapple.

Offline Heartwood

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Re: Newbie stuck on <simple> joinery
« Reply #1 on: January 26, 2017, 10:07:36 am »
Hi Todd,
Your tie beam IS drawn; it's tying the bottom of the rafters together. I think you meant the plate isn't drawn.
Bring the feet of the rafters in a bit and bevel the top of the plate, and tenon the peak of the rafters in to the king post. Forget the gusset (or spline) to join the rafters together.
Also, extend the king post bottom tenon to become a through tenon, and bring the bottom of the struts up on the king post so they aren't right down at the tie beam joint. Do an online search for timber truss joinery and you'll see lots of examples, or find the Guild's Historic American Roof Trusses series, (free download herehttps://www.ncptt.nps.gov/blog/category/architecture-engineering/). Here are some drawings from the Guild's Joinery and Design Workbook Vol.1. Note how the tenons are kept inboard to preserve relish at the end of the mortised timber.




Offline tburch

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Re: Newbie stuck on <simple> joinery
« Reply #2 on: January 27, 2017, 01:50:18 am »
Thanks so much Will!  I've made good progress… I think. 

Here's where I currently stand (all together and exploded some)

   

What I did:

1) I realized that I was trying to draw a frame with the top of the tie beam and top of the plate coplanar.  Once that sunk in, I scrounged around at the URL Will provided and found an article that specifically addressed what I was trying to do.  I went through the numerous options, and picked the simplest one.  The example used a plate and tie beam that were 8X12's oriented for more meat.  I kept mine as 8X8s.  Too chinchy?

2) I added a ridge beam, housed it into the trusses 1", and added a spline at its top to tie it to the trusses.  Ridge beam is 6X10 - seemed like a reasonable size, but I'm not looking forward to setting it.  Snow load here is 5 lbsf - if and when we ever get it here in Texas.  I'm planning on a metal roof, with full 1" decking all over it.  No purlins planned.

3) I thickened the trusses from 4X8s to 6X8s, so I could use the top spline and house the ridge beam.

What I didn't do:

1) I didn't bevel the top plate.  Since the tie beam and plate are coplanar, it didn't make sense (to me) to bevel it.  I needed the whole timbers to fit the mortises and tenons.

2) I didn't get rid of the spline at the top of the truss.  It seems like a reasonable approach to me, for two reasons: First, there is a steep pitch to the rafters, the tenons would have been pretty short and would have had a lot of long grain.  Second, since the king post is so narrow at the top, adding tenons to the rafters would have required twice the drilled holes for pegs in the narrow area.  With the spline I get half the holes in the king post.   (Now… I accept that I could be totally missing the understanding for the need for tenons and not using a spline here, but that's why I'm here asking.) 

I still need some guidance in the center of the structure.  Not sure what ought to be there to support the ridge.

a) another truss
b) one or two pairs of common rafters
c) none of the above

The reason I put the C choice is because I'm wondering if I could use diagonal braces that would extend from each corner post up to the center of the ridge.  This (I'm thinking) would provide end-to-end stability, but a fully decked roof would probably do that too.

Again, any feedback is welcomed.   Thanks, Todd
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'94 Ford 4830 Diesel 2WD & FEL.  Norse 450 skid winch.  Logrite fetching arch.  Fransgard Forestry Grapple.

Offline Den-Den

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Re: Newbie stuck on <simple> joinery
« Reply #3 on: January 27, 2017, 08:51:36 am »
I don't have any input on what you have drawn but do have a suggestion on what you have left out.  Neither the picture nor your sketch has any visible resistance to side load (wind mostly).  You will need some diagonal bracing to the posts if you expect it to remain standing.
You may think that you can or may think you can't; either way, you are right.

Offline tburch

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Re: Newbie stuck on <simple> joinery
« Reply #4 on: January 27, 2017, 09:03:53 am »
Yes, you are correct, it has no bracing, and I'm glad you brought that topic up. 

The picture at the top of this post also has no bracing.  And it also does not appear to use M&T joinery- probably just screws/lags.

At what point, in a structure like this, is bracing required?

In this structure, 12x16 w/ 9' posts, how would the braces be sized?
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Re: Newbie stuck on <simple> joinery
« Reply #5 on: January 27, 2017, 12:23:11 pm »
Just an idea - in regards to your ridge beam.  What if you tenon your king post into the ridge beam.  Then, just angle the rafters to the face of the ridge beam and use Timberlock screws to hold it?  Not traditional timber frame but no one will know you cheated!  It would not be necessary to angle the top of the beam.  The top roofing boards will support each other and cover the top.

As far as your bracing - are you attaching the back bent to the house?  If so, no bracing is needed on that bent but you might include some coming out from the house for aesthetic reasons.  On the front bent, I would put two braces on each post tying into both the tie beam and the other side beams.  I would make them at the same slope as the rafters, coming out horizontally  from the joint at least 2 feet and down whatever is necessary to make the slope right.  If you put them too close to the joint, they provide more leverage than support and can weaken the joint - IMO.

With 9 foot posts, no one should be hitting their heads on them.
John Sawicky

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Offline tburch

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Re: Newbie stuck on <simple> joinery
« Reply #6 on: January 27, 2017, 12:44:56 pm »
Thanks.   This evening, I will modify it again.  I think I'm going to lower the pitch some as well.   This particular iteration of the structure will be free standing, so I suppose braces are in order.   

I think Timberlock screws would be fine in certain situations.    Being new to this, I'm not a purist. 

I think if I set the ridge beam on top of the king posts, I could probably lighten it up too.   

 :P
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Offline Den-Den

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Re: Newbie stuck on <simple> joinery
« Reply #7 on: January 27, 2017, 01:16:11 pm »
Yes, you are correct, it has no bracing, and I'm glad you brought that topic up. 

The picture at the top of this post also has no bracing.  And it also does not appear to use M&T joinery- probably just screws/lags.

At what point, in a structure like this, is bracing required?

In this structure, 12x16 w/ 9' posts, how would the braces be sized?
If I was going to build something like this without braces to the legs; the posts would be steel tubing concreted into 4ft deep holes.  Would not be hard to wrap the steel with wood although it would be very hard to make it look like solid posts.
You may think that you can or may think you can't; either way, you are right.

Offline tburch

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Re: Newbie stuck on <simple> joinery
« Reply #8 on: January 27, 2017, 02:33:30 pm »
Yeah, I'm not into the look of boxed-up beams or posts.  I'm in it for the real deal of solid wood.   
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Offline Heartwood

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Re: Newbie stuck on <simple> joinery
« Reply #9 on: January 27, 2017, 05:45:48 pm »
Todd,
You don't have enough relish beyond the tenons on most pieces.
Move the bottom of the struts up about 6" on the king post; actually, just make them square to the rafter pitch and that should do it. And make the tenons full width; no need to trim them.
Sorry, but the spline at the peak still looks unnecessary. Put a triangular full-width cog on the bottom of the rafter into the king post (couldn't find a picture now), and widen the top of the post to make a diminished housing (see previous drawing).
You should move the feet of the rafters in on the tie beam, especially if you lower the pitch. I think you'll blow out the end of the tie beam if you get any spreading stress. You could also use a triangular full-width cog here to help resist thrust. If you can't visualize that, you should look at the Guild's Historic American Truss book referenced previously.
Also, no need to use two pegs on compression joints, it only weakens the timbers.
"I think Timberlock screws would be fine in certain situations. Being new to this, I'm not a purist." I think the old timers would have used screws if they had them, and it's usually the newbies that think timber framing uses no screws. The pegs can often compromise the structure.

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Re: Newbie stuck on <simple> joinery
« Reply #10 on: February 07, 2017, 01:51:11 pm »
Here's my current incarnation.  I've lowered the pitch to 14/12 and it looks better.   I've added braces.  I've worked out the inner trusses - maybe. 

As far as relish goes, what's the rule of thumb?   Generally, I've centered the tenons 1" hole, 1" from the base of the tenon. (There are a couple through tenons where I used a 2" spacing from the base of the tenon.)    Perhaps the term relish also encompasses the distance from the edge of the hole in the mortised piece to the edge?  If so, I agree that this distance is short.   

(Note - after I wrote this... I found in Will's book, page 80, the rule of thumb...  I should be using 3/4" pins in 1.5" non-thru tenons, and they should be drilled 1.5" from the shoulder... I'll make these changes later.) 

For my mortises and tenons, I've used a 1.5" spacing for setback from the reference faces and the mortise width/tenon thickness. 

I've allowed 1/4" to 1/2" gaps at the bottom of the mortises.   (Although, I just found a note in Will's book, page 80, I only need to allow a 1/8" gap.)

I used the same pitch for the braces, on the short ends as I used for the rafters.   For the braces on the long ends, they are a tad flatter.  I used 1.5" tenons on the 4" thick braces... I suppose I should 1" thick tenons?   

I'm getting happier with this as I go.   Comments?


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Offline witterbound

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Re: Newbie stuck on <simple> joinery
« Reply #11 on: February 13, 2017, 11:34:21 pm »
That is a lot of joinery for a small structure.  As a newbie you may be surprised how long it takes to do.  You may want to rethink whether it is all necessary after you get started.  Talking here from personal experience as a newbie.

Offline tburch

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Re: Newbie stuck on <simple> joinery
« Reply #12 on: February 14, 2017, 09:36:24 am »
That is a lot of joinery for a small structure.  As a newbie you may be surprised how long it takes to do.  You may want to rethink whether it is all necessary after you get started.  Talking here from personal experience as a newbie.

What would be your suggestion to reduce the joinery? 
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Offline Jim_Rogers

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Re: Newbie stuck on <simple> joinery
« Reply #13 on: February 14, 2017, 09:58:17 am »
I haven't downloaded the plan, so I don't know the answer; but how long is this frame from gable to gable?
I would make the center three sets of rafters just common rafters without collar beams and king posts.
And if one end is up against the chimney then that end could be just common rafters as well.
You have a three way joint where the plate and the post meet the tie. This could be a problem, there maybe not enough wood there to hold it all together. Normally we try to avoid three way joints by moving one timber up or down.

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Offline tburch

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Re: Newbie stuck on <simple> joinery
« Reply #14 on: February 14, 2017, 10:05:32 am »
Thanks Jim.   Would a three-way joint like this be OK? 



The structure is 12' x 16' as drawn.    Distance between each rafter tops is 42.5".
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Offline witterbound

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Re: Newbie stuck on <simple> joinery
« Reply #15 on: February 15, 2017, 07:56:36 am »
I like Jim's ideas.  The front king post framing needs to be the focus, and it has 8 joints in it.  The rest of the roofing structure seems like it could be simplified by using common rafters or a ridge beam.  In my first project, it took me an hour to layout and cut each joint ... And I had a chain mortiser and big circular saw.  If you want to spend the time to cut what you've designed for practice, you will surely get it.  But it seems like overkill.  Enjoy your journey. 

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Re: Newbie stuck on <simple> joinery
« Reply #16 on: February 15, 2017, 03:55:55 pm »
Thanks Jim.   Would a three-way joint like this be OK? 


The plate to the tie is the problem. You don't have enough relish (wood beyond) the peg hole in the tenon.
If you have any movement from gable to gable in the wind with an open pavilion type structure then the wood can blow out from the peg hole to the end of the tenon.
Usually we try and plan on 4 to 7 peg hole diameters from the peg hole to the end of the tenon.
Such as with a through tenon on a tie beam to post connection.
In your drawing the distance from the peg hole to the end of the plate tenon is very short.
Wind and uplift in an open pavilion is very important to plan on. I understand that you may not have any snow load in TX but you could have a high wind load.

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Offline tburch

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Re: Newbie stuck on <simple> joinery
« Reply #17 on: February 15, 2017, 10:46:13 pm »
Thank you Jim. 

I've expanded the post from an 8X8 to an 8X10.  The tenon on the end of the plate is now 5" long. 



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Re: Newbie stuck on <simple> joinery
« Reply #18 on: February 15, 2017, 11:17:59 pm »
I think there is another "rule of thumb" that Jim did not mention.  From the looks of your drawing (can't see the measurements), your peg holes in the timbers look pretty close to the edge of the timbers.  Personally, I would worry about the edge being split off.  However, I have been known to be wrong before...
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Re: Newbie stuck on <simple> joinery
« Reply #19 on: February 15, 2017, 11:32:37 pm »
Yes, I have adjusted them since I started.   Initially, I had 1" holes, 1" from the edge.    Now, I have 3/4" holes, 1.5" from the edge. 
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Re: Newbie stuck on <simple> joinery
« Reply #20 on: February 16, 2017, 12:08:46 am »
Yes, I have adjusted them since I started.   Initially, I had 1" holes, 1" from the edge.    Now, I have 3/4" holes, 1.5" from the edge.

I'll clarify.  Initially, I had 1" holes, centered 1" from the edge.  Now, I have 3/4" holes, centered 1.5" from the edge. 

I'm reading the maroon book.   Page 118.   Posts and sills.  8X8 timbers.  For the sills, there are 2" M&Ts, 2" from the edge.  On the mortised piece, that leaves 3" of wood.  The 1" peg hole in the mortised pieces appears is centered 1.5" from the edge.   

The tenon is 4 7/8" long, with the hole just shy (since it's offset) of 1.5" from the edge.  Let's call it 1/4" offset.  (Might be 1/8" offset).   That leaves about 3 1/8" inches from the edge of the peg hole to the end of the tenon.  This works out to be less than 4 pegs holes from the edge.   

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Re: Newbie stuck on <simple> joinery
« Reply #21 on: February 16, 2017, 12:31:55 am »
Rule of thumb for sizing. Tenon is 1/4 timber width, so for an 8x8 timber the tenon is 2". We normally offset it the same 2" and it is called a 2by2 layout. Pegs are normally 1/2 the tenon thickness. So for a 2" tenon you should/could be using a 1" peg.
For 6x6 timbers your tenon is 1 1/2" thick and peg is 3/4"
Normal peg hole location is 1 1/2" off the shoulder of the tenon timber and most of the time centered on the tenon, unless there are two pegs required by the engineer. Then they are spaced as the engineer says. But usually not in the same grain line of the mortise timber.

Hope that helps.

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Re: Newbie stuck on <simple> joinery
« Reply #22 on: February 16, 2017, 12:52:52 am »
Normal peg hole location is 1 1/2" off the shoulder of the tenon timber

Jim, is that 1½" measurement from the shoulder to the center or edge of the peg?  I'm thinking edge.
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Re: Newbie stuck on <simple> joinery
« Reply #23 on: February 16, 2017, 07:07:14 am »
Jim, with the square rule method, (as illustrated in the maroon book), the timbers are pared down from 8x8 to 7x7s at the joinery.  So, even though timbers are pared down to get to the perfect timber inside, the rule of thumb, therefore, always applies to the rough timber?
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Re: Newbie stuck on <simple> joinery
« Reply #24 on: February 16, 2017, 12:43:16 pm »
Normal peg hole location is 1 1/2" off the shoulder of the tenon timber

Jim, is that 1½" measurement from the shoulder to the center or edge of the peg?  I'm thinking edge.

I use 1 1/2" to center of hole. You see in the mortise timber the engineers don't consider the housing as a take away from the timber. So it adds the housing or 1/2" to the timber. They figure it's 2" off the long grain of the mortise timber when they do their calculations.

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Re: Newbie stuck on <simple> joinery
« Reply #25 on: February 16, 2017, 01:01:07 pm »
Jim, with the square rule method, (as illustrated in the maroon book), the timbers are pared down from 8x8 to 7x7s at the joinery.  So, even though timbers are pared down to get to the perfect timber inside, the rule of thumb, therefore, always applies to the rough timber?

Yes the rough timber is an 8x8 so the tenon is 2by2 layout.

You need to understand that when he wrote the maroon book he needed to cover his butt to make sure that every where the frame was built it would be safe.
When I told one of my timber framing teachers that I was going to cut that shed frame for a learning experience. And to use it to teach others timber framing he suggested several changes to make it easier. One was to not reduce it to 7" but to reduce it to 7 1/2". That saves a lot of housing work. The only place you may need the 1" housing would be at the tie beam to post joint. Especially if you're going to be storing something heavy above the tie beam in the loft area, like lumber for example.
If you're going to use two inch full dimension rough sawn planks for the roof decking you can space the rafters at 4' oc. (if you snow load is not real high). Everyone needs to verify snow loads for their area before making some joinery decisions.

Jim Rogers

 

 

The above frame was sold and erected in Halifax, VA:

 

 


Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension