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Author Topic: Question about timber joints  (Read 3948 times)

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Offline kristingreen

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Question about timber joints
« on: April 30, 2016, 05:52:37 PM »
Below, I've modified what I think is one of Jim's sketchup pics that shows a corner joint. The style of joint isn't really the issue but the areas that I've circled in red.

I've noticed these on some timber frames but not all. I don't even know what they're called so I don't even know what to search for on google. Are they just there for style or do they serve a practical purpose?

On the horizontal beam (I think that it's a 'cross beam'?) I can understand why you'd want it to extend into the long beam so that it can rest on top of the post's shoulder... but you can do that without taking any material off the cross beam.

It just seems like it makes all the other measurements overly complex.

On a completely unrelated topic, does anyone know where I can get that wood texture for my own sketchup drawings?



Offline Dave Shepard

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Re: Question about timber joints
« Reply #1 on: April 30, 2016, 07:10:11 PM »
Those are square rule reductions. Let's say those are 8x8 timbers. You would reduce them at the joint to the "ideal" timber size of 7". The angle is the transition from the ideal to the actual dimension.
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Offline ljohnsaw

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Re: Question about timber joints
« Reply #2 on: April 30, 2016, 08:35:36 PM »
...

I've noticed these on some timber frames but not all. I don't even know what they're called so I don't even know what to search for on google. Are they just there for style or do they serve a practical purpose?
...
It just seems like it makes all the other measurements overly complex.

(Image hidden from quote, click to view.)
As Dave stated, the ideal timber.  What is overly complex is the drawing.  From what I've been told when I was working up my cabin plans is that you DON'T draw that detail.  You make your frame with "perfect" timbers. 

What the drawing is showing (with the reductions) is how you would actually do it in the field.  For instance, when I mill my 10x15 timbers, I will probably make them 10 x 15 to allow for some shrinkage when drying.  But when I cut my joints (hopefully in the green wood), I will reduce at the joints to the "perfect" timber that is hiding inside what I milled.

Within reason, that reduction in the timber is not going to affect its strength.  Mid-span or where there are point loads is where the full depth is needed to resist deflection.
John Sawicky

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SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/32" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

Offline kristingreen

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Re: Question about timber joints
« Reply #3 on: April 30, 2016, 08:49:24 PM »
Now that I have a term to search on google, I found this... http://newheritagewoodworking.com/timber-frame-lesson-2-rules-learn

OK... hang on a minute... I feel like I just swallowed the red pill...

The timber inside? Of course! I get it! wow, never even considered what you might have to do if the timbers were not a standard size. I've been using 'Mill Rule' because all I have to work with is dimensional lumber but 'Square Rule' and reductions at joints will be necessary as I work with rough sawn lumber this spring.

Thanks!

Offline Jim_Rogers

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Re: Question about timber joints
« Reply #4 on: April 30, 2016, 09:06:07 PM »
When I took my second timber framing class, it was with Jack Sobon. He gave us a plan for the class project. There were two "rules" on the plan that each joint in the frame hopefully followed. One is the layout, such as 1 1/2" off the reference face and then 1 1/2" thick tenons and mortises.
The second rule was which end of the building all the interior bents were framed towards.
Then he told us two more "rules" that each joint had to follow. And with every rule, as usual, there are exceptions to those rules.
One of the rules that he told us was the "reduction" or size of the perfect timber. That is normally 1/2" under the "nominal" size. So if our frame was made out of 6x6's then the prefect timber inside is a 5 1/2 x 5 1/2" timber.

When I draw any frame design I tell my professional timber framing program what size the tenon has to be and what amount the "reduction" should be at the end of, lets say a post meeting a plate. And how long that reduction should be, like 1 1/2".
The reason why you have a reduction, is as mentioned to size the timber to a constant size that meets the "general" frame rule of the undersized timber.
Then the mortise in the plate is sized to meet that post's tenon and the plate is reduced to a 1/2" under the nominal size.
These reductions, which are on posts at tenons, for example, and the "housings" at mortises are the "resizing" of a timber to meet the rule. This makes the joints where the two timbers meet the correct size for a perfect joint to go together and not have any timbers interfere with each other.

What you have red circled are the reductions in the post and side plate. We normally do the end of the reduction in a 45 slope to give it some grace, or style if you wish.

Good question.
I hope my answer has helped you to understand why timbers are cut they way we do.

Jim Rogers

 

 

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Offline RuthStewart

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Re: Question about timber joints
« Reply #5 on: August 21, 2020, 01:25:57 PM »

On a completely unrelated topic, does anyone know where I can get that wood texture for my own sketchup drawings?
I know it's been long after this question was originally asked but just incase someone else is wondering the same thing, the wood pattern is simply a paint 'color' in SketchUp. There are options for wood, brick, grass, etc

Offline kikunak

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Re: Question about timber joints
« Reply #6 on: August 25, 2021, 07:21:38 PM »
I have two questions:
1. How "perfect timber" is marked on real timber, when it has varying dimensions along its lenth and twist at the same time?
2. How should I use power tools like saws, drill stand or chain mortiser on the twisted timber with marked "perfect timber"?
For example I have drawn two opposite parts of twisted timber. The inside is drawn "ideal timber" and the mortise is drawn with red line. Because the real surfaces are not coplanar, the mortises will not be parallel. When you put the base of power tool on the timber, it seems that is necessary to have large coplanar surfaces near tennon or mortise (below on the sketch) cutted to "perfect timber". In real photos of timber frames I don't see these surfaces. The plates on the photo above and startpost are small, not more than 2-3''.




Offline canopy

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Re: Question about timber joints
« Reply #7 on: August 25, 2021, 08:20:37 PM »
If a timber is out of square, you can't use square rule on it. One alternative layout method for this case is called snap line square rule where layout is done to chalk lines and levels. This method allows use of any timber no matter how much twist, wane, bow, out of square, or other anomalies exist. Using snap line square rule you choose the axis yourself rather than follow the faces of the timber. What you do is shim the timber to desired level on sawhorses, set the chalk lines, and then use a combination level to check mortises for square. To use power tools accurately like a chain mortiser, shim the tool to level on top of the shimmed to level timber. There are books that describe how to do snap line square rule as well as other layout methods.

Offline kikunak

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Re: Question about timber joints
« Reply #8 on: August 25, 2021, 08:30:49 PM »
canopy, thank you very much! Can you recommend the books?

Offline canopy

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Re: Question about timber joints
« Reply #9 on: August 27, 2021, 07:57:12 PM »
The books I have seen devote just a little space to the topic, describing the layout overall, but not in step by step detail. Just regular internet searches might also give you what you need.  A similar layout method to look for is JC Whitecloud's renaissance of what he calls "line rule".


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