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Author Topic: How off-square is off-square?  (Read 519 times)

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Offline TimFromNB

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How off-square is off-square?
« on: June 25, 2018, 09:30:50 AM »
Hello,

I will be starting my layout soon and was wondering what kind of tolerance (if any) I can have on the squareness of my 2 reference faces.

Most of my timbers have at least two square faces, but a few of them may be slightly off-square. I think the worst case would be 1/8" off square over 8", but the rest of the off-square ones might be off by only 1/16" over 8".

What is considered "reasonably square"?

Thanks!
Tim

Offline flyingparks

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Re: How off-square is off-square?
« Reply #1 on: June 25, 2018, 04:24:40 PM »
I'd call it good. But I can be lazy.

Offline D L Bahler

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Re: How off-square is off-square?
« Reply #2 on: June 25, 2018, 06:57:41 PM »
That all depends on what the project is, personal preferences, and many different factors. 

Most people will be fine with a tolerance within 1/16th of an inch. For residential construction that's usually fine. 

Some people like to keep tolerances to within 1/32nd of an inch. If you're building a bridge (which I'm sure you're not) you'll need to be that accurate or better. Or if you just want really nice looking joints, that amount of tolerance is going to get you there. 

I don't do much square rule layout, but when I have I have always used a line-rule layout instead of relying on 2 reference faces. That is, I'll make a perfectly square "+" shape on each end and snap layout lines down the middle of the timber. I do that partially as an extension of hewing layout, and because I never trust a face to be consistent. That's just how I do it though, you probably don't want to relearn layout at this stage in the game I imagine!

My layout method is essentially "Mathematical scribe rule" that is, by using snap lines you can cut location-specific joints without having to actually line up timbers in a scribe floor

Offline flyingparks

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Re: How off-square is off-square?
« Reply #3 on: June 25, 2018, 10:56:40 PM »
My layout method is essentially "Mathematical scribe rule" that is, by using snap lines you can cut location-specific joints without having to actually line up timbers in a scribe floor
I'll have to try that. That sounds like a great method. I'll try that sometime. A wise old man once told me, "We ain't building a rocket ship." I take that with a grain of salt. Sometimes it's good to build things like a rocket ship. Other times it's good to let tolerances increase a little for the sake of getting things done. I think 1/8" over 8" shouldn't affect your layout dramatically.

Offline D L Bahler

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Re: How off-square is off-square?
« Reply #4 on: June 25, 2018, 11:37:54 PM »
If you do try it, a key is that the timber faces are reasonably flat. Other than that, you also need to be thinking in 3 dimensions. 

Offline D L Bahler

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Re: How off-square is off-square?
« Reply #5 on: June 26, 2018, 06:06:11 PM »
Here's the cliff notes version of what I do...

First off, you make a vertical line down the center of each end of the timber with a plump line, or a horizontal line with a level (I use a level, because it's faster) Then you make a perpendicular line to these with a square. The intersections with the 4 long faces are then connected with a chalk line. 

Some people like to snap lines along the edge of mortises o save on layout. I don't like to do that though

When cutting joints into the timber, you use the layout line on that face to determine their locations. 

You can determine the length of adjoining timbers by measuring off the layout lines of perpendicular faces. It works like this: 

Assuming
1. the "theoretical" size of a timber is 8x8
2. The chalk line is in the "theoretical" center of a timber face: 
The ideal location of the layout face should be exactly 4 inches from the layout line. Whenever it is not, you can adjust the length of the adjoining timber accordingly. For example, if the actual measurement from layout line to face is 4-3/16", you will need to make the adjoining timber shorter by 3/16th of an inch. You have to measure both sides and several places, and might have to cut the adjoining timber slightly out of square. 

For cutting timbers to length, we also have to have a reference line marked some distance from the "ideal" end of the timber. All length measurements are taken off of this reference line, so we don't get confused when things don't come out perfectly. 

This system doesn't work, of course, with wildly curved or wonky timbers. It's meant as a shortcut for scribing reasonably straight timbers. 

It's not my own invention, I learned this method in Europe.  

Offline flyingparks

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Re: How off-square is off-square?
« Reply #6 on: June 28, 2018, 09:15:38 AM »
Looking forward to trying it out. Thanks for the explanation.


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