# Laying out large arcs without a compass



## imaginegrove (Nov 19, 2016)

Here is a trick I use to layout large arcs without a compass


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## Lazyman (Aug 8, 2014)

A handy tip even for small arches.


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## jkeith (Feb 9, 2020)

A neat trick for sure. Thank you!


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## Nubsnstubs (Aug 30, 2013)

I could have used that info 3 months ago when making an arch for a doorway 81" wide… ........ Jerry (in Tucson)


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## 1thumb (Jun 30, 2012)

How do you arrive at the measurements needed for that layout?


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## SMP (Aug 29, 2018)

Interesting method. I usually just use a strip of bender board or 1/4" ply or whatever i have laying around. But that works too.


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## imaginegrove (Nov 19, 2016)

yes, 1/4" strip work but I've found that is isn't always an exact radius.


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## imaginegrove (Nov 19, 2016)

> How do you arrive at the measurements needed for that layout?
> 
> - 1thumb


Typically when designing, I'll know the width and height and not always the radius. a doorway for example, I know the width and how far the want the arch to go up. Hope this makes sense.
Subscribe to my youtube channel for more tips and tricks. https://www.youtube.com/channel/UCRSUIlle6P49snsndDOpdzw


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## Loren (May 30, 2008)

When I made my 15' and 25' dished forms for making guitars I used a wire pulled taut to draw an arc. It was a long time ago and I didn't know the geometry to lay it out any other way. These days you can look up a ton on google though I reckon the more obscure methods of woodworking will remain hard to learn from forums and blogs.


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## Tony_S (Dec 16, 2009)

> How do you arrive at the measurements needed for that layout?
> 
> - 1thumb


Use an Arc calculator online or download an app for your phone or tablet. I use 'ArcCalc'.
Enter the known and it spits out the unknown.
Works great for figuring out what an incapable framer has done when they lay out(screw up) a curved floor opening.


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## 1thumb (Jun 30, 2012)

> How do you arrive at the measurements needed for that layout?
> 
> - 1thumb
> 
> ...


Thanks. Good door explain. I get that part now


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## LeeRoyMan (Feb 23, 2019)

> Use an Arc calculator online or download an app for your phone or tablet. I use ArcCalc .
> 
> - Tony_S


I tried to download it to my flip phone but it didn't take….
Guess it's sketchup for me.


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## 1thumb (Jun 30, 2012)

> How do you arrive at the measurements needed for that layout?
> 
> - 1thumb
> 
> ...


Thanks. Cool stairs. At first glance I didn't realize it was a scale model and thought you had built stairs to nowhere. Thought you were crazy. But they looked so good I wondered why you didnt build another set to walk down.


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## Tony_S (Dec 16, 2009)

> Guess it s sketchup for me.
> - LeeRoyMan


Tried it twice now. It just pisses me off.



> Thought you were crazy.
> 
> - 1thumb


I am.


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## LeeRoyMan (Feb 23, 2019)

> Guess it s sketchup for me.
> - LeeRoyMan
> 
> Tried it twice now. It just pisses me off.
> ...


You just need help, 
and I'm not saying for what …..


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## CaptainKlutz (Apr 23, 2014)

rant mode on:

Another YouTube author posting a video link with vague description?
Thanks for nothing, AGAIN.

IMHO - Empty video troll posts using LumberJocks as advertising medium to gain more views and advertising $ should be banned.

If you genuinely want to share ideas with LumberJock community: 
Please post pictures and complete description of tip/technique/project with the video link. 
Watching the video should be a SUPPLEMENT to the post; not a REQUIREMENT to understand how you are helping other LumberJocks work wood better.

Rant mode off:


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## Dark_Lightning (Nov 20, 2009)

Yeah, this looks like click-my-youtube-video stuff. Not to say that it isn't a nice method, and maybe a lot of people here just don't want to follow the math.


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## mtnwalton (Aug 4, 2015)

Good tip; i've seen this somewhere before but forgot about it.


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## jkeith (Feb 9, 2020)

> rant mode on:
> 
> Another YouTube author posting a video link with vague description?
> Thanks for nothing, AGAIN.
> ...


You're right…every post *started by* this guy links to either his youtube channel or his business website. What are the rules on these sorts of posts?


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## PCDub (Sep 24, 2017)

Agreed. I don't click on links that are essentially unexplained. Not interested in potential for malware, no desire to add to ego boosting


> rant mode on:
> 
> Another YouTube author posting a video link with vague description?
> Thanks for nothing, AGAIN.
> ...


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## imaginegrove (Nov 19, 2016)

sorry guys about not describing this. didn't know that was a thing. Not really sure if I could describe it well and then suspect I get nailed for that too. I just though it was a good tip, I use it all the time.
thanks for the heads up.


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## Lazyman (Aug 8, 2014)

Man. You guys are rough. I thought the title was pretty spot on and it is actually a pretty handy tip, IMO. If this had been a new LJ account I would not have checked it out but since he's been around for over 4 years, I figured it wasn't a big risk. What is really odd to me is taking the time to complain when you are supposedly not interested. More fun to complain I guess.


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## Sylvain (Jul 23, 2011)

> Interesting method. I usually just use a strip of bender board or 1/4" ply or whatever i have laying around. But that works too.
> 
> - SMP


The method shown here produce an arc of a circle. The curvature is constant from one outer nail to the other.
The method with a bent strip gives a curve where the curvature varies continuously. It is maximum at the middle nail and nul at the two outer nails.
Both method are interesting but not equivalent.


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## SMP (Aug 29, 2018)

> The method shown here produce an arc of a circle. The curvature is constant from one outer nail to the other.
> The method with a bent strip gives a curve where the curvature varies continuously. It is maximum at the middle nail and nul at the two outer nails.
> Both method are interesting but not equivalent.
> 
> - Sylvain


You seem to have incorrect assumptions on how i use bender board.


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## Sylvain (Jul 23, 2011)

> You seem to have incorrect assumptions on how i use bender board.
> 
> - SMP


my comment is valid if one only uses 3 nails

If one uses multiple nails like for example in boat lofting my comment is indeed not valid.
see for example: 



from about 4'30" 
Except that the curvature is nevertheless null at the two outside nails whatever the number of nails one uses.


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## bigJohninvegas (May 25, 2014)

Scott, that is a great tip. Your the best, thanks.


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## waho6o9 (May 6, 2011)

Good to know Thank you


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