# Another Complicated Arc Question

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Hi, can someone tell me please how to draw arcs with below conditions?

1. There are arcs with radius of 2700 tangent to the blue circle and tangent to the arc with radius of 2100 which its tangent point is lies anywhere at red line.

2. The center point of the R2700 arc is above the red line and the center point of the R2100 arc is below the red line.

Please show me the construction geometry.

See the attached image for more detail please.

Thank you

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#### Posted Images

There is no information about where to start either arc or where to end them.

Use the Tangent/Tangent/Radius option to draw construction circles.

Where are these exercises coming from??

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Draw an approximation of what it looks like using circles with correct radius and post.

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OK, this is the picture of the arcs looks like.

How do you draw the R2690 arc that tangent to R30 circle at point A, and tangent to R2100 arc at point B, and the R2100 arc is tangent to 3° line?

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I think you will have to use Parametric constraints.

You know, by offsetting the 30R circle, a circle on which the centre of the R2690 circle lies, and you know, by offsetting the 3° line, a line on which the centre of the R2100 lies. You know the distance between the two circles and you know the point of contraflexure (point B) is 90 from the base line.

Set up the constraints as needed and you will get the centres of the two circles.

I don't have parametric constraints on my version of AutoCAD, but as it came since AutoCAD 2010, you have all the tools to hand.

I have to do it by trial and error.

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56 minutes ago, eldon said:

I think you will have to use Parametric constraints.

You know, by offsetting the 30R circle, a circle on which the centre of the R2690 circle lies, and you know, by offsetting the 3° line, a line on which the centre of the R2100 lies. You know the distance between the two circles and you know the point of contraflexure (point B) is 90 from the base line.

Set up the constraints as needed and you will get the centres of the two circles.

I don't have parametric constraints on my version of AutoCAD, but as it came since AutoCAD 2010, you have all the tools to hand.

I have to do it by trial and error.

Sorry, I would like to ask, how do you offset a circle? I know only how to offset a line.

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Have you tried yet with the same technique?

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22 minutes ago, eldon said:

Have you tried yet with the same technique?

Do you mean using the parametric constraints?

22 minutes ago, eldon said:

I have basic foundation of AutoCAD as long as it uses classic commands. So parametric constraints would be my new experience in AutoCAD.

I will Google it of how to do the parametric constraints in AutoCAD 2014.

Edited by basty
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Here have you got with this? I think it would be easier for us to help in stages rather than walking you through the full solution - there is a lot in the second drawing you posted.

What have you drawn and what is the next step to do?

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There are several solutions to what you  ask.  For your construction keep in mnd the following:

1. To find the center of a circle of a given radius that is tangent to a line create a line parallel to the line on both sides at a distance equal to the cicle's radius.
2. To find the center of a circle of radius R1 that is tangent to a circle of radius R2 with a known location, create two circles concentric with R2.  The radii of these two circles are (R1 + R2) and (R1 - R2).
3. To find the center of a circle that is tangent to a line AND tangent to a circle use the intersections of the lines and circles from the previous two constructions.

For your task create the white 2100 circle first. The center of the 2700 circle is at the intersection of a line passing through the 2100 and blues circles with either the 2670 or 2730 circles.

Edited by lrm
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Why not post full image of task seen images like that before and they can be missing a vital clue.

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15 hours ago, BIGAL said:

Why not post full image of task seen images like that before and they can be missing a vital clue.

Because I rounded the number of the dimensions so that they are can be easy to read and remember/memorize.

Edited by basty
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You did not answer the request, that image appears to be one of those "exercise 23" draw this object and AGAIN often something is missing, post the full image.

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7 hours ago, BIGAL said:

You did not answer the request, that image appears to be one of those "exercise 23" draw this object and AGAIN often something is missing, post the full image.

Do you mean like this?

What is "exercise 23"?

Edited by basty
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Why is it constrained and no idea where to even start. Is this a real object for your company or a CAD Exercise out of a book etc.

Edited by BIGAL
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This is a real object.

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On 2/3/2024 at 5:34 AM, lrm said:

There are several solutions to what you  ask.  For your construction keep in mnd the following:

1. To find the center of a circle of a given radius that is tangent to a line create a line parallel to the line on both sides at a distance equal to the cicle's radius.
2. To find the center of a circle of radius R1 that is tangent to a circle of radius R2 with a known location, create two circles concentric with R2.  The radii of these two circles are (R1 + R2) and (R1 - R2).
3. To find the center of a circle that is tangent to a line AND tangent to a circle use the intersections of the lines and circles from the previous two constructions.

For your task create the white 2100 circle first. The center of the 2700 circle is at the intersection of a line passing through the 2100 and blues circles with either the 2670 or 2730 circles.

How do you obtain R2670, R2730, R2130, and R2070?

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50 minutes ago, basty said:

How do you obtain R2670, R2730, R2130, and R2070?

In your posted picture, I cannot see any circles that are of the size you have quoted.

@Irm's diagram does not show accurately your problem.

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What do you mean? You should see the image that posted by lrm.

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1 hour ago, basty said:

What do you mean? You should see the image that posted by lrm.

That is exactly what I did. @Irm 's diagram is not the same as your diagram.

So either you want to draw something like @Irm 's diagram, or you want to draw something like your diagram. If you want to draw something like your diagram, then solving @Irm 's diagram will not supply your answer.

For example, @Irm's diagram shows the r2100 arc tangential to the R30 arc. That simply does not happen in your diagram.

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