# Measuring/placing/moving along arcs

**URL:** <https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546>\
**Category:** Modeling Questions\
**Created:** [April 4, 2022, 4:33pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546 "2022-04-04T16:33:10Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![Jason42](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Jason42](https://discourse.shapr3d.com/u/Jason42)\
**Post date:** [April 4, 2022, 4:33pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/1 "2022-04-04T16:33:10Z")

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I’ve been struggling recently with Shapr3d and arcs. There doesn’t seem to be any way to measure or move along an arc in distance units. This makes all sorts of operations into head-scratchers for me. I would love to hear your thoughts on how you would accomplish some basic operations involving arcs. Here are a couple of examples of things I just can’t figure out how to do.

1. Create an arc body that is a specific length along one of its curved surfaces.

2. Cut an existing arc body into equal-length pieces?

3. Create an arc (from a sketch or existing body) that has holes in it with centers that are specific distances from each other (for example, 2 inches).

Would love to hear your thoughts. Thanks.

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**Author:** ![SM1](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@SM1](https://discourse.shapr3d.com/u/SM1)\
**Post date:** [April 4, 2022, 7:53pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/2 "2022-04-04T19:53:39Z")

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As a general tip: Just click two points if you want to bring up the distance and set it.

1:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/2X/c/c07342fb3575a2b118da6025a823b82ca95b92a1.jpeg)

2: I don’t quite know what you mean other than using midpoint and drawing a line straight up. If you need a set arc, draw a new arc.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/2X/c/cb8dc18daa629255ada0ea5273186db203608db2.jpeg)  
 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/2X/f/f633070db2b556081e5a212779ee376bff193a26.jpeg)

3: Create the circles and constrain them to the arc, then you can set the distance between the centers by clicking both.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/2X/7/73f9511a494d4e674feee440e205d729f7e8c806.jpeg)

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**Author:** ![Jason42](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Jason42](https://discourse.shapr3d.com/u/Jason42)\
**Post date:** [April 4, 2022, 8:12pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/3 "2022-04-04T20:12:34Z")

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Thank you so much for your reply, but I think my questions still stand. Let me try to clarify a bit…

1. In your response to this one, you’re just measuring the straight-line distance between the two endpoints. I am looking for the distance along the arc. How can I create an arc with a specific arc length (in mm or inches, not degrees)

2. This is what I mean…  

3. Again, what you have done is measure the straight-line distance. I need the holes a specific distance apart along the curve of the arc. Look at your arc. What would you do if you wanted holes equally-spaced along the curve of that arc?

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**Author:** ![SM1](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@SM1](https://discourse.shapr3d.com/u/SM1)\
**Post date:** [April 4, 2022, 9:43pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/4 "2022-04-04T21:43:12Z")

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I see what you mean, my misunderstanding. For some reason I thought you wanted straight length.

Yeah there isn’t a way to sketch arc length yet (or not that I know of). You can see the length of lines (arc length) on the bottom of the screen if you click on the line.

I guess you will just have to calculate the arc length by converting the angle to radians and multiply by the arc radius. 🫤

For the latter two, you can copy and rotate the objects about the center of the arc. If this needs to be done based on arc length… you need to calculate the angle from the arc length.

(I have a feeling using revolve at some point might be easier)

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**Author:** ![PEC](https://avatars.discourse-cdn.com/v4/letter/p/67e7ee/32.png) [@PEC](https://discourse.shapr3d.com/u/PEC)\
**Post date:** [April 4, 2022, 10:16pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/5 "2022-04-04T22:16:43Z")

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Hi Jason,

There is no way to specify length on arc at present. So you have to use workaround solutions.  
Here are a few.

1/ @SM1 is right, to create an arc of a specific length, you must do the maths.  
L = 2 \* pi \* radius \* angle / 360  
angle = 360 \* L / ( 2 \* pi \* radius )

2/ Here are some workaround to cut arc bodies.

- If you want to cut in power of 2 (2, 4, 8, 16…) then you can use _add midplane_ and _split body_  

- if you need an arbitrary number of slices, you can use the following method  

3/ If you want equally spaced holes on an arc, you can do the following

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**Author:** ![Jason42](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Jason42](https://discourse.shapr3d.com/u/Jason42)\
**Post date:** [April 4, 2022, 10:43pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/6 "2022-04-04T22:43:41Z")

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PEC, those are some very nice workarounds - using midplane and constraints.

Although, these still don’t help you if you want hole centers at a specific distance of arc length from each other.

I’m a little bummed that such workarounds and hacks are necessary. The Shapr3D folks claim that it’s the “world‘s most intuitive 3D design app”. To make that claim, shouldn’t Shapr3D’s sketching and modeling tools make this sort of drawing operation much easier? I see no reason, for example, not to have an arc length dimension in distance units when sketching. Why force the user to do the math? It adds several minutes worth of (easily-avoidable) user friction and pain to what would otherwise be a trivial sketching operation.

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**Author:** ![PEC](https://avatars.discourse-cdn.com/v4/letter/p/67e7ee/32.png) [@PEC](https://discourse.shapr3d.com/u/PEC)\
**Post date:** [April 4, 2022, 11:04pm UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/7 "2022-04-04T23:04:14Z")

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Agree with you Jason, having arc length dimension in addition to absolute, horizontal and vertical distance would be great and would do the job for setting hole centers at specific distance on arc.

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**Author:** ![Wookiee](https://avatars.discourse-cdn.com/v4/letter/w/57b2e6/32.png) [@Wookiee](https://discourse.shapr3d.com/u/Wookiee)\
**Post date:** [September 19, 2023, 4:57am UTC](https://discourse.shapr3d.com/t/measuring-placing-moving-along-arcs/18546/8 "2023-09-19T04:57:21Z")

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Is there any update to this? Seems to me like a pretty high priority function.