How to array Isocircle ellipse on Isocircle ellipse

[harveyXRS9Z]

Hello,

Looking for help on how to array an ellipse around an ellipse in isometric view.

I've attached a drawing.  As you can see I've created isometric views of a 'flat' panel with a 'fluted' detail.  However I want to draw an isometric view of a curved panel of the same design.  These are cladding panels that go around a corner/radius.

I realise this is possible in full AutoCAD as it has 3D capabilities, but looking for help on how to achieve this in AutoCAD LT with the isometric function.

If I draw an ellipse to show an isometric view of the top of an individual 'flute', and then array around the bigger ellipse, which is the top of the curved panel itself, I can't seem to space the 'flutes' so they are meeting at a tangent with each other all the way round.  Obviously all the 'flute' ellipses need to be in the same orientation, as opposed to aligned with the bigger ellipse and this means the spacing between them changes as they go round.

I also started trying another way where I used a spline and converted to a polyline so I could manually drop on ellipse centres at each of the vertices, but I don't know how you would accurately work out the 'precision' of the polyline so that each of the vertices is one 'flute' apart.

In the drawing, the largest ellipse is the external diameter of my curved panel and the yellow line is the centre point of each flute.  The ellipse inside that is the internal diameter of my curved panel.  I have put one 'flute' at the bottom in the middle, but the start point of the yellow ellipse is on the right hand side.  the other ellipses are actually 'isocircles'.

Thanks

[boris6RGJZ]

I cannot think of a way to make it with one command. The only way I can find is to:

1. Draw the "isocircles" of the base - ellipses in isometric view with the appropriate radii

2. Draw the "flute" again as "isocircle" with center at the yellow circle (ellipse in isometric) and appropriate radius

3. Copy the "flute" ellipse with basepoint the center to the INTERSECTION of the "flute" with the yellow ellipse

4. Erase every second "flute"

5. Trim the inner part of the"flutes"

[harveyXRS9Z]

Thanks for that.  That is a good work-around, an in the event, would have been sufficient due to it being for a visual representation as opposed to a manufacturing drawing.

However, it doesn't work mathematically, and the 'flute' ellipses overlap the outside diameter of the curved panel, albeit by a small amount.

I guess the difficulty is that whilst the yellow ellipse and the outer ellipse are exactly 4mm different by radius, they aren't exactly 4mm apart all round.

Another way to do it would be if I could draw a 'flute' ellipse (or Isocircle) that is tangential to the previous 'flute' and also to the outer ellipse although I'm not sure if that's possible?

Would be glad of help on how to do this or any other suggestions.

Thanks

[boris6RGJZ]

When one draws in proper units and size (not like me in the previous posting ☹️ ), things match. And there is exactly one intersection of each small ellipse with the outer line.

Please see attached drawing, my bad!

It is important that the ellipses are all created with ISOCIRCLE in the proper ISOPLANE.

[harveyXRS9Z]

Hello,

Thanks for that.  I have tried again but still seem to get the small Isocircles overlapping the large one.  If you zoom into your latest drawing, yours appears to overlap as well, albeit by approximately 0.0009mm.

I've attached screen snippings from your drawing, showing the location of the overlap and then zoomed in to where you can see the two intersection points where the small ellipse crosses the larger one.

Maybe it's something I'm doing wrong?

[boris6RGJZ]

I believe that the software is making an ellipse that is approximation of the isometric projection of the circle, dunno. If you create the isometric as arch, things seem to match...

However, is this micron so important? 

[harveyXRS9Z]

To be fair, for the purposes of what I would need it for, a micron is not important.

Personally I would prefer something that is actually 'correct', but I realise AutoCAD LT has its limits.  I'd still be interested to know if there was a way to do it, if someone finds one.

Thanks for your help.

[boris6RGJZ]

I agree that geometry should be correct, but life gives lemons sometimes 🙂

Again - I constructed the iso projections with four arcs and it worked. Is it worth the effort? 

[Washingtonn]

The only way to use an array (polar) for your situation is with a circle then rotated in 3D OR as follows in 2D: 

Draw a line (blue) from the center of the large circle to the outside of the flute circle and then array your flute circles about the large circle (with a radius equal to the major axis of the ellipse).

The three points you want to be able to select - each side of the flute (red) and the outside point of the flute (green).  From these points you can project up to the ellipse and draw the flute ellipses manually as needed. It's a lot of work....