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Marking out an arc

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Marking out an arc

Postby Steve Maskery » 26 Jan 2022, 19:38

Nothing terribly exciting, but it might help someone, someday. How to lay out an arc when you know neither the radius nor the centre.



Enjoy.

Mod edit: url https://m.youtube.com/watch?v=EW6R-7dFu ... =emb_title
Last edited by Andyp on 26 Jan 2022, 20:38, edited 1 time in total.
Reason: Mod edit, added url
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Re: Marking out an arc

Postby Glynne » 26 Jan 2022, 20:27

There is obviously a link or a diagram but I can’t see anything other than text?
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Re: Marking out an arc

Postby Malc2098 » 26 Jan 2022, 20:30

Steve, could you post the URL of the video so us Safari members can view it.

Thanks.
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Re: Marking out an arc

Postby Andyp » 26 Jan 2022, 20:37

I do not think therefore I do not am.

cheers
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Re: Marking out an arc

Postby Malc2098 » 26 Jan 2022, 20:38

Cheers.
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Re: Marking out an arc

Postby Steve Maskery » 26 Jan 2022, 21:14

I didn't realise that that was a problem for Mac users. I'll try to remember that in the future.
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Re: Marking out an arc

Postby Trevanion » 26 Jan 2022, 21:47

The trick of using two sticks is quite clever, where'd you learn that one Steve? :eusa-think:
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Re: Marking out an arc

Postby Steve Maskery » 26 Jan 2022, 21:50

Trevanion wrote:The trick of using two sticks is quite clever, where'd you learn that one Steve? :eusa-think:


I have absolutely no idea. I expect it is as old as the hills, certainly I didn't invent it. But I feel as if I've known it for ever, so possibly it was a schoolboy lesson.
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Re: Marking out an arc

Postby Malc2098 » 26 Jan 2022, 23:06

I used to draw and elipse with two pins and a piece of string.

Using the same to bits of wood as Steve has with a piece of string tied to them creating a triangle with the top at the top of the arc, you can get an elliptical arc by using your pencil round against the string.
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Re: Marking out an arc

Postby Woodster » 26 Jan 2022, 23:36

That’s very clever Steve, thanks for posting. I had to do an Anse de Panier for an alcove in one of my old houses but I can’t for the life of me remember how I did it! I probably used a roll of old wallpaper. :lol:
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Re: Marking out an arc

Postby Steve Maskery » 27 Jan 2022, 00:00

Woodster wrote:I had to do an Anse de Panier for an alcove


Just Googled it. Ooh, that looks fun. I have seen it before (or something like it), a very long time ago, didn't know that that was what it was called.
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Re: Marking out an arc

Postby Andyp » 27 Jan 2022, 07:52

Steve Maskery wrote:I didn't realise that that was a problem for Mac users. I'll try to remember that in the future.
S


We can always add the URL to a post for you Steve, and anybody else

I forget the cause of the problem but my iMac, on Safari and Firefox works fine as does the iPad.
I do not think therefore I do not am.

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Re: Marking out an arc

Postby Steve Maskery » 27 Jan 2022, 09:37

Ah yes, thank you for doing so, Andy.
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Re: Marking out an arc

Postby MattS » 27 Jan 2022, 09:47

That stick trick is incredibly clever, thanks Steve!
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Re: Marking out an arc

Postby Rezi » 27 Jan 2022, 11:38

Thanks for that, very useful.
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Re: Marking out an arc

Postby Woodster » 27 Jan 2022, 11:53

Steve Maskery wrote:
Woodster wrote:I had to do an Anse de Panier for an alcove


Just Googled it. Ooh, that looks fun. I have seen it before (or something like it), a very long time ago, didn't know that that was what it was called.


We had an alcove that had a very unattractive arched top to it. After a few years I decided I really had to do something with it and found the Anse de Panier shape somewhere. After some measuring and marking I set to with some battens and steel mesh and replastered it. I included a spotlight in the design and it turned out really well. It’s a very elegant shape.
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Re: Marking out an arc

Postby Cabinetman » 27 Jan 2022, 11:56

Yes thanks Steve, I shall file that one away till it’s needed. Ian
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Re: Marking out an arc

Postby 9fingers » 27 Jan 2022, 12:49

For more circle related definitions and calculations such as those underlying the method Steve illustrated so well in the video see here http://www.1728.org/circsect.htm as mentioned in this thread over 7 years back.
viewtopic.php?f=20&t=387

The intersecting chord theorem at the root of the above is true even if the chords are not at right angles. An interesting more visual demonstration here https://www.mathsisfun.com/geometry/cir ... hords.html

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Re: Marking out an arc

Postby AndyT » 27 Jan 2022, 18:11

Nice one Steve. Video watched and added to my Liked Videos.

I too find it harder to remember where I read things, and sometimes it's easier to remember and find a video.

I knew I had seen something similar recently and after not too much head scratching I found it. It was in one of the many books Trevanion has been buying up and showing to us all (well, me at least :? ) over in this ever-lengthening thread:

viewtopic.php?f=19&t=4818&start=75#p97492

It's at Fig. 4 on Plate 4, alongside several related similar methods for this sort of thing, with the description at the top of page 14.

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Image


For anyone without a library the size of Dan's, a scan of the whole book is readable and downloadable here - note that this copy puts all the plates together after the text.

https://archive.org/details/encyclopaediaofp00tarb

I reckon your explanation is clearer and more memorable!
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Re: Marking out an arc

Postby Mike G » 27 Jan 2022, 21:05

I regularly have to set out 4 centred arches, which are classic late mediaeval/ Gothic shape for door heads and so on. I have a drawing set up which shows me how to do it, because it's not easy to remember....but in those days no doubt every carpenter could do it in their sleep.
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