Object snap not working when creating TTR

[Anonymous]

My object snap disables itself when I'm selecting object points for ttr between two circles. Is this WAI? How can I get around it? I need specific points for where the tangent connects, not just somewhere I clicked on the circle.

https://gyazo.com/c8ddbc9807fb96032da91b756f89a118

[beyoungjr]

Hi,

This is normal behavior for TTR!

Your tangent position will be dictated by the selected objects and radius entered.  You cannot drive or override a tangency beyond the mathematical result determined.

\Maybe your workflow needs looked at?  Please post your example dwg and describe what you want connected.  This will reveal your full process and not just what I saw on your screencast.

Blaine

[Anonymous]

So I can't even enter a first position? I understand that for tangents, for one point on an object for a specified radius there will be another single point on the other object with which it aligns, but I can't figure out how to input that first point. I tried typing coordinates but it just ignores it.

Attached file: I'm trying to tangent the big circle (R3) to the two smaller circles under it, but I need it to touch the top quadrant reference snap of the small circle on the right, then whatever point that lands on the circle on the left.

[beyoungjr]

Hi,

I created a screencast for you to observe (sorry no audio).  At the beginning I show my running OSNAP settings so you are aware that they are useful but not interfering with my steps.

I tried to show several ways of connecting objects at points tangent.  Remember that lines to/from quadrants only work between objects where the X or Y quadrant points are co-linear, as in the 2 circles at lower-left in your drawing.  Also remember that those quadrant points will not continue as tangent points to the next object unless co-linear.

Fillet is always using tangent points so you will not see an indicator for OSNAP.  You will need to set your radius.

TTR doesn't care which running OSNAP you may have turned on because it is only looking for tangent connections.  If you enter a radius that is too small the command will fail.  There is no radius too large.

TTR and TTT positioning of the resulting circle often depends upon where you pick when selecting.  Of course you would finish by trimming these circles as necessary.

Typically you will not be entering coordinates for any of these because your cursor control easily identifies the connection points.

Hope this helps,

Blaine

[j.palmeL29YX]

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@Anonymous  schrieb:

Attached file: I'm trying to tangent the big circle (R3) to the two smaller circles under it, but I need it to touch the top quadrant reference snap of the small circle on the right, then whatever point that lands on the circle on the left.

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This is geometrical not possible. An R3 arc which begins at the upper Quadrant doesn't reach the left cicle. The radius must be 4.257... to reach the left circle. Or greater, but than you don't have tangencies between the arc and the circles.

cadder

[j.palmeL29YX]

In the drawing above I created the arc using parametric constraints.
If you are not familar with this you can also draw a correct circle with the basic commands.
In the video https://autode.sk/2y9qNBS  you can see why an R3 circle never can touch the one circle at the upper quadrant and touch the other circle tangent.
To solve the problem you must either rotate the big circle - then it doesn't touch the small circle at the quadrant or you scale the big circle to another radius. The correct radius you find with some construction (helping) geometrie as shown beginning at about 1:30.

cadder

[j.palmeL29YX]

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@j.palmeL29YX  schrieb:

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The radius must be 4.257...

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Oops, the drawing 181011-forum example.dwg which I posted above is wrong.

Here a corrected version - the radius of the circle/arc is 4.250, of course the same result as shown in the video.

Sorry for the confusion.

cadder

[RobDraw]

TTR is not going to work in this way. A circle that is tangent to another at a specific point (quadrant) and tangent to another circle has to have a calculated radius and can only be tangent to the 2nd circle at a resultant point. In other words, there is only one circle that can be tangent at the quadrant of a circle and tangent to another circle. The radius is a calculated value, you cannot assign a radius. This is a geometry problem. There are a couple guys over at CADTutor that really have their heads around these types of problems and will show you how to do this.

[j.palmeL29YX]

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@RobDraw  schrieb:

TTR is not going to work in this way.

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Therefore I didn't neither use nor suggest the TTR method, but draw the circle withhelp of some construction lines. The radius is the result of this construction.

cadder

[RobDraw]

@j.palmeL29YX, sorry, I wasn't really responding to your post. I clicked the wrong button.