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Drawing an arc tangent to arc and snap to non tangent point
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October 06, 2013, 05:30:15 PM
This has to be embarrassingly simple - but it is alluding me!

I am trying to draw an arc with a specified radius that is tangent to an arc and snaps to a non tangent point (intersection).
Help Please!
I am running TurboCad on windows 8


October 06, 2013, 06:01:56 PM
What you're trying to do may be geometrically impossible.

TC user since v3. MacMini 5.1. 2.3 GHz. 16 Gig RAM.
TC 19 Pro 64 bit. Windows 7.

* October 06, 2013, 06:43:28 PM
Sounds like you want the "Insert / Arc / Tangent to Entities" tool. Input the Radius value first, then Lock it (Ctrl+L). Click on the Arc to establish the tangent, then activate the "Through Point" option (Local Menu) and "I" snap to the intersection (if possible). Establish the start/end points of the arc.

You could also do this in reverse. Snap to the intersection with "Through Point" active, then turn "Through Point" off. "No Snap" to the arc to establish the tangent.
« Last Edit: October 06, 2013, 06:52:10 PM by John R »

John R.

V17—V21, 2015—2020
Designer, Deluxe, (Basic, Expert, Professional), Platinum
RedSDK enabled
Windows 10 Pro (1909), 64-bit

* October 07, 2013, 06:18:23 AM
Rotating the specified-radius arc about the centre of the first will keep the tangency, so draw them, then edit.  Select the specified-radius arc, relocate the yellow reference point to the centre of the first arc, rotate the specified-radius arc about the centre of the first, so that it meets its intersection point with the third feature, or can be trimmed to it.  Relocating the x axis rotation handle to the arc endpoint would probably help, too.  I'm assuming that the third feature isn't a second intersection with the first arc, in that case Mike is right.


October 07, 2013, 07:04:50 AM
When I wrote my reply I pictured the first arc with endpoints already established, which is why my first thought was that it might not be possible. If the first arc can be extended to form a complete circle then it is only impossible if (as Murray points out) the point is on the first arc or if the point is more than 2 of the fixed radii off the first.

TC user since v3. MacMini 5.1. 2.3 GHz. 16 Gig RAM.
TC 19 Pro 64 bit. Windows 7.

October 07, 2013, 07:14:50 AM
I was not aware of the "through point" command - that worked great!
Thanks everyone!