franksbedford wrote: ↑Tue Mar 26, 2024 4:08 am
After reviewing your drawing,
A) I drew the cord to connect the two points (...).
B) Then I drew an orthogonal line, and trimmed it to the height of the top of the slot (where the arc connects).
C) I drew another cord from the top of the slot to the center of the arc, and took that measurement, copy and pasted it into the two point and radius tool and drew an arc that seems to fit.
Agreed it fits, almost, part of C is bad practice, the values that you copy are rounded/truncated numbers.
That is if you want the arc to be tangent to vertical at the top of the slot of course ...
Wen you have the center position and two endings then simply draw an arc from Center, Point and Angles (
AR).
- Select CW in the Option Toolbar for this case.
- Indicate the center position by snapping to an end or to the intersection in my case.
(Or even to a manual intersection of 2 lines that don't actually cross)
- Indicate the radius by indicating a point on the expected circle/arc (point S or E)
- Indicate a start-angle by indicating a point in the required direction (point S)
- Indicate an end-angle by indicating a point in the required direction (point E)
Now it is as exact as can be, QCAD snapped to reference positions in full floating point notation.
Note that arcs do not have a start or end point, they have a center, a radius and start/end angles.
The conversion from Polar to Cartesian or reversed can never be exact, only as exact as possible.
franksbedford wrote: ↑Tue Mar 26, 2024 4:08 am
It's a repeatable technique for all four size domes that I can do.
Yes, the middle orthogonal of a chord always traverses the center.
An orthogonal to a tangent through the tangent point also traverses the center. (In this case the top horizontal of the slot)
The center is where both orthogonal lines intersect.
Basically the main technique exploited by several arc and circle tools.
But
CT1 fails for the vertical under the slot and point S and E for a circle, there is no similar arc tool, there are but two exploiting a tangent.
franksbedford wrote: ↑Tue Mar 26, 2024 4:11 am
Your notes on cardboard not stretching on the outer edge and compressing on the inner edge is very true. I need to think about that.
Not only 'think about', we need the specifics to estimate the required length of the side covers.
On the provided development marked as
17.8125276 + 0% for now.
How wide they should be to snugly fit at the interior is already defined, adapting is merely a linear transformation.
But you should transform the major Fit-Point splines, not the trimmed Control-Point splines nor those exploded to polylines.
BTW: Your last version has still the gap indicated by red remark circles in
d32_dome_arch (3).dxf
Sorry, but I had to diversify the different versions with a suffix as it seems you don't define revisions.
Regards,
CVH