Construction Problem

[Laurel]

Hi

I've a problem with regards to the attached drawing. If anyone can help, I'd be very grateful.

The drawing represents a screen for a motor-boat. You can see an Isometric view, side elevation and plan (all white layer, 0). Each window in the screen is hinged, so that the window can be folded flat into the horizontal plane. (Shown as the yellow layer, FOLDED OUT). A2 represents A1 folded out, and B2 represents B1.

I'm struggling to draw an accurate representation of C1. How do I do it, please?

Thanks,

Paul.

[JD Mather]

You should have a book that covers developments.

Personally I would do it as 3D as there is miter concerns that don't show up in an infinately thin flat.

[Laurel]

Thanks for the suggestion JD.

I must admit, I'm not sure how you arrived at the drawing you have labelled C1, but I don't think it is correct.

Looking at your drawing, you have labelled the corners of my plan view of C1 as 1 to 4. I would expect the side you have labelled 2 to 3 to be the same length as the left most edge of the plan view labelled B2, but in your drawing of C1, it isn't.

Or am I missing something? :)

[Alex_AW]

Something like this.

[JD Mather]

I had Point 3 in the wrong location.


...be the same length as the left most edge of the plan...

I've never been able to follow a description like this - I have to refer to point labels to understand what we're talking about.

[Alex_AW]

Something like this.

I'm not absolutely sure about that variant.
This one (see attached file) looks more correct from theoretical point of view, but length of 3-4 line on the involute does not equal one on the top view. :?:
I think you'll have to make a 3D model or cut one from paper to be sure in a variant. If more sensible advises wouldn't come, of course.

[Laurel]

Thanks everyone for your sueggestions.

Alex - I can see where you are coming from with your first suggestion, but it looks a little too skewed to me. I'm not sure about how you have arrived at the 2nd option :)

JD - I don't know 3D (yet). You suggested a book on developments. Can you suggest one?

I've wracked my brain, trying to remember how I learnt how to do it years ago, and arrived at the drawing I have attached. I'm not sure of how accurate it is, but it looks right. Any comments?

Thanks again,

Paul.

[Alex_AW]

... I'm not sure about how you have arrived at the 2nd option :)


The key is here.

[Alex_AW]

... it looks right. Any comments?

...

About the results. Lines don't coincide a bit with each other.
About the way you've got it I'd say nothing . I didn't analyze it :wacko:- I'm afraid for my brain :).

[Laurel]

Yes, I see you are right - my solution doesn't fit either.

I'm struggling to resolve this, anybody else know how?

[scj]

Perhaps this could be a solution:
I've drawn 2 3D-Polylines in the top-view (so they should have correct lengthes). Than I moved the upper onre to the correct heigth (taken from the side-view). As all partial faces of the screen seem to be even you can rotate them down to the plane z=0.
Regards
Jochen

[Laurel]

Thanks for the help, SCJ. I've not yet mastered the art of 3D autocad, and so have not attempted the drawing in 3D myself, and can't say if I agree with your solution. :)

I've found the solution myself though, and have illustrated it in the attached drawing. I found an article in an old drawing book, which covered how to obtain the true shape of inclined triangles given an elevation and plan.

Yay for me!! :D

[Alex_AW]

Anyway your last solution looks the most correct beyond the rest 2D solutions. But there's something about it. You have started with point C, but if you were starting with point D you'd get a little different result. BTW - you can obtain it not such difficult way (look at the attached file).

PS. After all of this I think that learning 3D modeling not such a bad idea :D.

[Laurel]

I see what you mean. I really can't see where the 3mm discrepancy comes from. Everything else looks ok, and as I said, the solution was taken from a book. I thought the problem might lie with my original elevation and plan, but that looks ok too.

Your quick solution looks to work well in this instance. It is possible to do in this case as we know the lengths of sides (ie AC and BD are in the vertical plane).

There is another solution to our problem in the book I used, that is applicable for triangles that do NOT sit on the horizontal plane. I'll try that later to see if I can remove the discrepancy. For now tho, a 3mm tolerance in this case is perfectly acceptable, so I suppose I'd better get my drawing finished.

I'll post the other solution when I get the chance, (and would love to know if anyone can trace the discrepancy between triangles ABC and ABD) but for now, thanks for your help!!