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Re: Arched Brace Trusses #5782 02/04/07 02:04 PM
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E.H.Carpentry Offline
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Timbo,

just what I was saying. If you lay it out on the floor you can double check measurements and there is little room for mistakes.
Trying to do the math on paper has to many risks involved for me and is way to complicated.

But everyone has their own ways.

Re: Arched Brace Trusses #5783 02/04/07 04:28 PM
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mo Offline OP
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I understand how to lay-out full scale on a floor. I do it quite often. That is easy (especially a bent (one plane)). Now suppose you did not have a floor that was 14'X 25' (centerline). Why not try to figure things out? What if you ever wanted to use curves in intersecting planes? In addition, (no pun intended), I think its nice to be able to find all neccessary information from a sheet of paper that you could fold in your pocket and show others. Plus, (again, no pun intended, its everywhere!), math allows you to convey information a lot easier.

When it comes time to actually build one of these (this was all brainstorming). I will most likely layout 1:1 but I would like to be able to proceed in more than one way. I think versatility is valuable. I like learning, too.

Anyone have some pictures of arch braces?

thanks, mo

Re: Arched Brace Trusses #5784 02/04/07 04:50 PM
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Tom Cundiff Offline
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I like to use natural curves. A bent like you are planing with natural arches would be one of a kind. Tom


Not all who wander are lost.
Re: Arched Brace Trusses #5785 02/04/07 05:45 PM
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Tom,

nice picture.
And what do I see there? A scarf/lap over a post. Somebody was thinking.

Re: Arched Brace Trusses #5786 02/04/07 07:29 PM
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I'm not knocking math, but I could could build it at scale quicker than I could ever figure it out mathmatically. No I would start with a scale drawing and maybe build it at small scale first. I love curvi-linier joinery , but the joinery can be very complex(to get right). Good luck to to the mathmaticians out there , wish I could wrap my mind around those calculations. Great project Tom , I agee about knowing how to do the math.


Timothy W Longmore
Re: Arched Brace Trusses #5787 02/05/07 01:43 AM
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E.H.Carpentry Offline
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I understand that one cannot layout the entire bend/curve on the floor if space is limited. But all you need is half a bend anyway. The other side is just a mirror image.

Doing the math is fun, too. But there are too many risks involved. Not to mention inaccuracy due to rounding.

Re: Arched Brace Trusses #5788 02/05/07 03:35 PM
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Joe Bartok Offline
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I'll try to get a hold of a picture of a truss with an arch. I also refined the theoretical elliptic arch and will try to post sketches and calcs tomorrow.
With modern calculators (especially the programmable graphing calculators) there's no inaccuracy due to rounding. And the risk of error is decreased.
Log Valley Roof : Off topic as this has nothing to do with arches, but it's a good example of why it's good to understand the math.
There was no time to test fit the parts and no room for error. As soon as the roof components were cut, the building was loaded and along with the crew and crane went on a journey by road and barge to the erection site.
The layout and cutting was done on horses sitting safely on the ground. The calcs were executed to five decimal places ... way more accuracy than needed. And the work was done quickly: the lengths and mortises on Valleys, jack rafters, header and ridge were done from a standing start in three days with a $15.00 Sharp scientific calculator.
I don't think this roof could have been done correctly and in only three days without trigonometry. Having said that, I am by no means knocking scale layout as an approach to solving joinery problems. The mortises on the irregular surfaces of logs defy calculation; they were done using jigs and projective geometry.
The same goes for this arch. I think that attempting a scale layout to "fit" an ellipse given the arch dimensions would involve a lot of time consuming hit-and-miss guesswork. The math allows us to find our working points accurately. Fitting the arch to timbers of a given width and length can also be done on paper but calculating the intersections can be onerous ... see my "Arch Layout Notes" link. This part of the job is best achieved with a full scale layout.

Re: Arched Brace Trusses #5789 02/06/07 04:00 PM
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Joe Bartok Offline
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Elliptic Arch Notes : the first image lists some formulas for working with segmented arches.
Just for fun I tried making the working point (WP2) such that the slope of the ellipse at this point equals the slope of the rafter. A set of iterative calculations were needed to home in on this point (–117.43, 87.87).

Found a couple websites with pics of trusses with arches:
http://www.pacificpostbeam.com/Trusses-Hybrids_a.html
http://www.rockportpostandbeam.com/timberframe.php

Re: Arched Brace Trusses #5790 03/05/07 04:59 AM
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Here's a photo from Carpenter Oak and Woodland's web site:


I don't usually rip off other people's web site photos but I work with two of these blokes and I don't think they'd mind.. :p

You can bet these were scribed; that's the way I'd recommend. The math makes my head hurt.
Chris


I think, therefore I am (I think)..
Chris Koehn
TimberGuides Design • Build
Re: Arched Brace Trusses #5791 03/14/07 02:21 PM
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Will Truax Offline
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I don’t mind the math, just like to get it all taken care of ahead of time, and then put the tape away for the rest of the job, or at least till the next type of layup.

I’m with Chris, arched brace trusses and most any curved work was historically, and IMO still is, scribe work. This is an efficiency thing as much as it is a right tool for the job thing.

To analogize, why would I pick up a Stratocastor to pick out a bluegrass tune



And am I the only one that would be reluctant to warranty a large sawn curve ? Not only is it gonna be unbalanced and bow when one side is whacked out of it, but I’d be concerned that it was gonna check or shear apart, never mind that every inch “curved” out of it would have to be discounted value wise, and intentionally introducing slope of grain, just kinda goes against the grain.

Besides wood grows crooked every day, the only real trick is convincing the loggers not to push it all into the chipper bound slash pile



"We build too many walls and not enough bridges" - Isaac Newton

http://bridgewright.wordpress.com/

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