Best Of

Oh, I forgot to mention that the hint above about dimensioning/constraining to the origin is very useful. Thanks!

If you make changes upstream and your sketches downstream are not fully defined it might have issues. If you make no changes and only move forward nothing changes

Correct, the sketch itself won't move on its own, even if its not fully defined.

Usually what will happen is you may change a feature before that sketch, and it will then affect the sketch.

Oliver's comments are right on the mark. It is best practice to fully define sketches. Models can be made from under defined sketches, but you get into trouble when you make edits, or make configurations of that model. When you are starting out with simple parts, you don't notice this as a problem (although it's still there) - but as your parts become more complex, having under defined sketches will come back to bite you (and this is hard, and time consuming to correct later). My advice is to get into the habit of "fully defining" your sketches. There may be some extreme case where you wouldn't want to, but I can't think of one.

Hint - If you have a sketch that is difficult to fully define, don't forget to dimension/or constrain, to the origin

Your sketch entities have degrees of freedom. E.g., a circle has a center and a diameter. If you constrain those to known references or measurements, then you can be sure that it'll remain constrained to those. If it's not constrained, then future behavior is basically undefined. It may work most of the time, like an uninitialized variable, but upstream input may change in such a way that your sketch goes haywire.

Furthermore, if a sketch entity is underconstrained, then there's something you don't actually know about your design. Say, you can free-hand a rectangle and extrude it, but you didn't specify its dimensions, so those are not known quantities and therefore aren't meaningful nor reusable. It's like defining constants locally in code rather than keeping them in a central place where you know to look.

There’s no lofted bend in Onshape sheet metal. There are some ways to work around it.

https://forum.onshape.com/discussion/15807/sheet-metal-loft

It's like cutting up yarn into small lengths and laying the individual pieces on a piece of paper to form a picture with. It's all good, until a breeze comes by and blows all the pieces off.

If it's not defined, it's not controlled. That means it can change at any time if something else changes, or may not change correctly if another feature changes resulting in errors in your model.

Fully defining your sketches ensures that changes to your model have predictable and desirable results.

I had a half decent sleep. Thought I’d see if I could eliminate the part where I GUESSED at using 120mm instead of the original 114mm that I used in Sketch 1

So in PART STUDIO 1 —— I opened up Sketch 1 and RESET IT for what I originally had - which was 114mm (15mm x 3 + 12mm) x 2

Then I opened up Sketch 3 to see what the measurement was at the outermost part of the spiral and that was 14.25mm (.561 inches)

So then I divided the 15mm that I was looking for at this point, by the 14.25 that I had, and came up with 1.0526315789, which I used to multiply against my original 114mm in Sketch 1, and that gave me an amount of 120mm

So I went back to Sketch 1 and used 120mm for the diameter, and of course, that did the trick — without using guess work.

There is a part studio now called LESS FEATURES

https://cad.onshape.com/documents/8c572d2d91650b52eb553864/w/83050318ceb7545e5ddcfd62/e/86b7bb3599f1f9a9218049e1

But I have a feeling that the person that does the scoring is not going to be onboard with this method I used for making the spiral. Don’t ask me why. Just have a feeling. Maybe it’s because I didn’t get the score I thought I should have had on a test WAAAAAAAAY back in Junior College many decades ago. LOL

Oliver’s method is probably the better one to use

Here's how I suspect this would've been done originally, without geometric perfection:

https://cad.onshape.com/documents/4f8e24f45f65eaaf27f4c062/w/ab96230b0b9011db3364acc4/e/f7e0a6a549b5bb06b6e75f98?renderMode=0&uiState=670138fb08682a02aba05fcc