Draw a rhombus with adjustable sides


#1

In SketchUp, I need to draw a rhombus with the following dimensions (of successive sides):

111.96mm x 108.63mm x 110.08mm x 109.02mm

My instinct tells me to draw a 110mm square, somehow tell Sketchup to unconstrain angles, and resize the sides per these dimensions. That matches the ultimate physical reality: as my project goes forward it is likely that I’ll need to adjust one or more of the dimensions.

Can’t figure out how to do that, or I’m going at this wrong.

A little help, please?

(Sorry if I’m being incredibly dense. I did do some searching…)

TIA


#2

The classic way is to create the first side and then draw circles at the endpoints that correspond to the second and fourth sides. The third side will always connect two points on the circles. Unfortunately, in SketchUp, circles are created as a chain of straight lines so your intersections will be close, but not necessarily accurate. The more points you use for the circles, the more accurate the result. To complete the rhombus, draw a line from one endpoint to a place on one circle, create another circle of radius 110.08 at that endpoint, and where the new circle intersects the other circle is where the third side connects.

Note that without specifying an angle, there are an infinite number of solutions.


#3

Thanks for the fast, carefully explained,and clearly illustrated solution.

The application is pretty rough, so “not necessarily accurate” will probably be good enough.

Thanks!


#4

Note that there are also several extensions, including TIG’s tangents one and my circle intersect one that will place guides at the exact intersection of the real circles not the SketchUp segmented approximation.


#5

Thanks for your suggestion to use an extension.

I’m a noob --and, because I don’t use SU often enough to retain more than a few of the fundamentals-- I’m reluctant to add more complexity by adding an extension.

OK, I’m willing to try. I spent a little time in Extension Warehouse, but I can’t identify what specific extensions to try from your description. Could you be a little more specific, please?


On this particular issue, it seems to me I’ve already moved from my original problem of drawing a rhombus to the apparently very different one of how SU draws/intersects circles.

Whew! All I set to do is to design a part to decently fit an out-of-square aperture made of wood. The first approximation would be a rectangle. Next better would seem to be a rhombus, but it seems that’s not so simple to accomplish.


#6

Why do you want to draw a wooden panel with these precise dimensions,in the first place? 0.02 MM ? my tape measurement tool display’s MM . On a rainy day my 2"4" are 51x100 , on a dry cold winter they could be 46x98. supposedly the panel was intended to be square, in practice I just would cut the largest dimensions , get a piece of sand- paper and adjust it by hand…


#7

Both of the ones I mentioned are available from the SketchUcation plugin store. Downloading requires a membership in SketchUcation, but both the membership and the download are free (there is an optional upgrade to a Premium level that does have cost, but it is not required).

TIG’s true tangents is here.

My circle intersect is here.

The ways we coded for selecting what you intersect are different, but either can do the job you want.
The name of TIG’s might not lead you to think it does intersections of circles, but it is in there along with other features that work with the real mathematical circles.


#8

Thanks for your reply. Good points.

OK, now I need to be more specific. I have a wood object with an aperture that’s nominally 110mm x 110mm. It isn’t square and –as you say–- the dimensions may vary with the weather.

My application: to 3D print an inside cap (in ABS) to close this aperture. I’ll do my best to approximate the actual dimensions of the aperture, shave a little for fit, and print. Depending on the results, I’ll adjust the design, and repeat as necessary to get a reasonable fit. At some point I’ll probably switch to sandpaper and/or a file.

No, the real precision required is not anything close to what is implied by the dimensions I gave. They are just one set of measurements I obtained from the aperture. I didn’t think it would matter to the original question I asked, since I was seeking a mathematical solution.


#9

Thanks!

Aha, yes, I already have a SketchUcation membership. I’ll give them a try. (Might take some time to get to it.) I’ll post back…


#10

If you can stand a goodly distance away from the aperture, you can take a photo and import it into SketchUp. Using the tape measure, you can scale the model to fit one of the sides. The result should give you a template to work from and allow you to construct the remaining sides along the angles involved. If it matches the photo and is dimensionally accurate, it should print and fit just fine.


#11

Though you could solve this in a mathematical way, [quote=“jimhami42, post:2, topic:42392”]
Note that without specifying an angle, there are an infinite number of solutions.
[/quote] so most ly we’ll wind up taking measurement of the diagonals.
But then you would still have to take in account the specific behaviors of the grain directions, humidity etc. etc.


The best SketchUp way is as @jimhami42 suggested : Take a good picture and import it into SketchUp ( You might want to enable ‘Use maximum texture size’ in the OpenGL-setting and draw some Arcs as the lines would probably not be straight lines after all. For more segmented Arcs, choose a higher number of segments at the beginning ( select Arc, then type the number of segments, enter, and start drawing on the image)
Traditionally, carpenters would gain some sort of ‘feeling’ of how the wooden parts would wind up over the years and they would take that into account. Of course it’s all Physics but I haven’t seen a computer program that would replace this ‘feeling’ and understandin. ( though the drawings off @DaveR pretty much captures this )


#12

Thanks for your suggestion – I never thought of using a photo.

I’m still getting used to SketchUps automatic constraints. Aha, I’ve finally managed to draw a sample rhombus using the pencil tool. Progress!

Thanks!


#13

Thanks for your help.

Whew, i’m a noob, so the arc and segment stuff is beyond me.

Fortunately, the item I’m capping is already broken (poor design, kludgy implementation) so I can’t possibly make it any worse. The cap I’m making will be out of sight, so there’s no worry about ugliness, e.g. poor fit, shims, whatever. And the life-span need not be long – a couple of years at most.

(A good part my motivation for even trying to do this crazy project is to learn-by-doing how to solve practical problems with SketchUp and 3D printing. I grew up in a subtractive fab environment with fairly tight tolerances and most everything square and symmetric. This is a whole different world… fortunately.)


#14

Thank you very much for your Circle Intersect extension!


#15

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