Taking a cut in a circle

[paul1391]

I need to know how do i take that cut inside those circles knowning only the annotations on the paper

[JD Mather]

Make centerline tangent to centerline arcs. Offset on either side by half distance.

 

The easiest way to get the solution is to use Geometry Constraints (I think these were first added in 2010 or 2011) and Parametric Dimensions.

 

Here is a picture in a next-generation MCAD program - notice that it tells me I am missing the radius dimension of this fillet and shows remaining degrees of freedom in the geometry with the missing dimension. (there is also a color change from purple to blue that isn't as evident from this zoom level)

Edited October 23, 2011 by JD Mather

[JD Mather]

Here is an image with the model fully constrained.

In modern MCAD programs most of the geometry constraints (like Tangent, parallel, horizontal) are added automatically - so I normally don't have the visibility of the constraints turned on as I know the software is taking care of this stuff for me. I turned on for illustration purposes only.

[JD Mather]

I realized I had the wrong dimension on the right side - no problem - with parametric dimensions the model is driven by the dimensions, change the dimension, and the model updates. (I have the fillets set to equal = their cooresponding dimensioned fillets.)

 

If you can't figure out how to do it in AutoCAD - post back and someone will walk you through each entity creation.

[eldon]

I would have thought that there is a dimension missing, because these two drawings are to the dimensions annotated. Am I missing something?

 

Perhaps there is a set angle or offset that is used

[JD Mather]

Attach your file here.

[paul1391]

it would be nice if someone could explain me how to do it in autocad

[eldon]

In fact, as long as the two end circles are 140 apart, one could draw any shape between these two.

 

I am just trying to prove that there is a dimension missing, so that to draw the shape, you have to assume some dimension, and cannot draw it only from the annotated ones

[paul1391]

ok i got it... but could you explain me what commands did you use in autocad?

[eldon]

This is how I drew it (there are probably other ways, but this gets it done)

 

First draw the end shapes with the jaws horizontal. Then put them at 140 apart. Then I rotated each -30 degrees about their cetre points A and C.

Next draw lines AB and CD which are parallel to the jaws. These are the points where the connecting shape comes out at right angles to the circle.

Then draw line BD and split it at the mid point E so there are two lines BE and ED.

Next draw the perpendicular bisector FG and also a line perpendicular to AB to G. This is the centre of the arc.

Similarly draw HJ and then DJ.

Using the Start, Centre, End option of Arc, draw the arc B to E, and D to E. Now offset these lines by 7.

To finish the arcs at the shoulders, I drew circles using the TTR option, and to tidy up, I trimmed and erased the construction lines.

[eldon]

Attach your file here.

 

I am not sure to whom you were addressing your peremptory order, but here is my file attached

[JD Mather]

I am just trying to prove that there is a dimension missing, so that to draw the shape, you have to assume some dimension, and cannot draw it only from the annotated ones

 

I used only the dimensions given and the only assumption was tangency (which appeared to be an obvious assumption). Did not need any other dimension.

Given the angle of the dimension and the centerline - I also made the assumption that these are parallel // and horizontal ___

Edited October 23, 2011 by JD Mather

[JD Mather]

I am not sure to whom you were addressing your peremptory order, but here is my file attached

 

I am not familiar with editing image files in a CAD program.

I was expecting your CAD file so that I could inspect the geometry constraints for your possible solution to the problem.

[eldon]

I was expecting your CAD file so that I could inspect the geometry constraints for your possible solution to the problem.

 

I am afraid that with my poor ancient version of AutoCAD, constraints are totally alien to me. I just drew it. I hope that my explanation of how I drew it suffices to satisfy you.

 

Which of my posted images do you think is not drawn to the dimensions given?

[JD Mather]

You don't need geometry constraints - I can add them myself to your "solutions" to determine if any of them are plausible.

[eldon]

I drew them all according to my stated method. The only variable is the angle of rotation at the beginning, which varies from 0 to a little bit less than 76 degrees.

 

You may have to draw it according to my method to check.

[paul1391]

thanks eldon it worked for me

also could you give me a tip on how to draw this thing?

[eldon]

It's getting a bit late for me, but I will have a go tomorrow.

 

Perhaps the Professor has an idea or two that he can put in writing

[paul1391]

my CAD professor tends to have a more communistic approach towards education... so everytime somebody asks her something she doesn't give much help at all

[JD Mather]

Which of my posted images do you think is not drawn to the dimensions given?

 

I gave it a second look and found a sequence that has infinite solutions - I will have to go back tomorrow and figure out what other assumption I made in my original solution that solved with the dimensions given. From my latest experiment it looks like you were correct - unless I can argue another valid assumption that most would agree as logical.