Laying Out A Radius With An Obstruction At The Origin. - General Discussion - Contractor Talk

Laying Out A Radius With An Obstruction At The Origin.

 
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Old 07-05-2015, 05:44 PM   #1
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Laying Out A Radius With An Obstruction At The Origin.


Hey all.
I have been racking my brain for quite a while now and i still have not been able to figure out a way to layout this curve. As you can see the centre of the radius is behind a column that is already built so swinging it with a tape measure is sort of out of the question. I will use the total station if i have to but i was hoping to be able to learn the manual way of doing it (if there is one).
I experimented with shifting the point and reducing the radius but no go.
Plus the square return wall has no dimensions, it is all based on intersections..
Any advice is helpful.
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Old 07-05-2015, 07:27 PM   #2
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Re: Laying Out A Radius With An Obstruction At The Origin.


Nick:

Can you lay it out somewhere else and make a plywood template?

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Old 07-05-2015, 07:30 PM   #3
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Re: Laying Out A Radius With An Obstruction At The Origin.


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Nick:

Can you lay it out somewhere else and make a plywood template?
That's what I would do and then line it up with a few reference points that you can make on site.
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Old 07-05-2015, 08:46 PM   #4
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Re: Laying Out A Radius With An Obstruction At The Origin.


What i had planned to do was make my plywood plates to the specified radius, nailed down the one side that i could measure too (left side in picture) , and strike the arc as far as i could and twist the loose end of the template to that. My only concern is that being able to only measure a 1/4 of the way on the radius could mean that it could potentially go out... Then again it can't possibly go off that much in 10 or 12' plus, there is no dimension on the plan.. nobody will check

Im looking forward to forming this, it will not only be round but also sloped at the same pitch as the future garage ramp. The ramp on this job is going to require some very funky formwork..20' tall in some spots!
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Old 07-05-2015, 11:55 PM   #5
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Re: Laying Out A Radius With An Obstruction At The Origin.


There have been several great threads on this subject. Try a search for circle chord.

Here is a great excel spreadsheet to calculate out the coordinates that I linked in one of them:
http://home.comcast.net/~ronzu2/Wood...rc_layout.html

You will need to download the excel template calculator.
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Old 07-06-2015, 04:14 AM   #6
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Re: Laying Out A Radius With An Obstruction At The Origin.


Quote:
Originally Posted by Railman View Post
There have been several great threads on this subject. Try a search for circle chord.

Here is a great excel spreadsheet to calculate out the coordinates that I linked in one of them:
http://home.comcast.net/~ronzu2/Wood...rc_layout.html

You will need to download the excel template calculator.
I was thinking of that formula do to do it with coordinates, i am not sure it will work because i do not have the end point of the curve where it turns into the straight wall.. therefore i cannot figure out the length of the arc.
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Old 07-06-2015, 09:43 AM   #7
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Re: Laying Out A Radius With An Obstruction At The Origin.


Ok...I think I finally got what your trying to do!

Oops!... I had a bad solution!

Last edited by Railman; 07-06-2015 at 09:59 AM. Reason: wrongfull info!
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Old 07-06-2015, 11:37 AM   #8
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Re: Laying Out A Radius With An Obstruction At The Origin.


Quote:
Originally Posted by FramingPro View Post
Hey all.
I have been racking my brain for quite a while now and i still have not been able to figure out a way to layout this curve. As you can see the centre of the radius is behind a column that is already built so swinging it with a tape measure is sort of out of the question. I will use the total station if i have to but i was hoping to be able to learn the manual way of doing it (if there is one).
I experimented with shifting the point and reducing the radius but no go.
Plus the square return wall has no dimensions, it is all based on intersections..
Any advice is helpful.
If this is part of circle as viewed from above, on paper you can bisect a scaled down version of this curve in at least two places to find the circle center, then the radius length, then the whole circle.

Then you have to account for the ramp.

I recommend making a large three dimensional model of this thing from shoebox cardboard, to check your work. Use toothpicks, tape, paper clips, glue, etc.

Take it a step at a time.

Officially this is called Descriptive Geometry and the method for doing this was once a State Secret.

I'm sort of up on this lately because there is a way to extract cube roots by visualizing a cube within a cube, along with several rectangles.
I could not visualize this thing so I made a model from paper. So now all I have to do is recall what this three-dimensional thing looked like.

You can do it, we can help!

Last edited by GettingBy; 07-06-2015 at 12:12 PM.
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Old 07-06-2015, 04:20 PM   #9
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Re: Laying Out A Radius With An Obstruction At The Origin.


Scaling up from your drawing, the radius of the ramp viewed from above is 3.9 meters so the circumference is 12.3 m.

A protractor gives the angle as 50 deg so the length of the ramp viewed from above is 12.3 x 50/360 = 1.70 m.

Cut a piece of masonite 1.7 m long and draw a triangle on it with angles arctan 0.075 (= 4.29 deg), 90 and 90-4.29 deg. This is the ramp laid out flat.
Bend the masonite to a 3.9 radius. This is your ramp.

Placing the ramp relative to the shaded rectangle takes some more doing.
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Old 07-06-2015, 08:50 PM   #10
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Re: Laying Out A Radius With An Obstruction At The Origin.


Just demo that column out of there, layout the ramp, put column back.
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Old 07-08-2015, 07:37 AM   #11
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Re: Laying Out A Radius With An Obstruction At The Origin.


could you bend a pipe to an arc to fit just outside the column then lay out from the pipe?
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Old 07-08-2015, 08:51 AM   #12
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Re: Laying Out A Radius With An Obstruction At The Origin.


Here's one manual way - normally used when your framing square will do:

Place two nails (spikes, whatever) into the surface at two opposing points that will be on the circle. Place your square over the nails, and keep it in contact with the nails as you slide it around forming the arc of a circle that's traced out by the tip of the framing square.

For a big circle like you have, it's easiest to put a series of nails in along a (not quite complete) smaller circle that gets you out past the column (ideally same radius that gets you to the furthest point of the column, but that's getting picky), then use a loop of something that doesn't stretch too much and trace the final arc. Try string if you want, but it's imprecise.
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Old 07-11-2015, 10:46 PM   #13
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Re: Laying Out A Radius With An Obstruction At The Origin.


Make a template , cut it like a donut , then split it in 1/2 , then place it around the column .
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Old 07-11-2015, 11:19 PM   #14
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Re: Laying Out A Radius With An Obstruction At The Origin.


If you have access to a total station use it and be done with it. But there is a way to lay out circles with a theodolite sitting on the radius of the circle. I haven't used it in a while and would have trouble finding my notes just now, but if you want it, I'll try to find the formula.

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