Linearly Variable Scale Transform

andrew_slovak

Hi all, I'm pretty new to CAD in general, and even newer to Onshape. I've realized that in one of my designs, I made one of the parts a bit too small, and want to scale it, rather than rolling everything back and re-designing much of the part studio, as there are many dependencies on the part in question. I know that simply scaling after the fact, isn't the best practice, but I'm not really going to feature efficiency, especially because the design of the entire part studio is finished, I just want to scale one part. For context, I'm designing an aircraft, and have found that the horizontal stabilizer is too thin at the trailing edge, but is satisfactorily thick at the leading edge, therefore, rather than scaling the whole part and making the whole thing thicker, I want to apply a variable scale factor that increases linearly as you travel down the chord length of the stabilizer/elevator, so that the leading edge doesn't scale at all, while the trailing edge scales by a factor of 2 or 3. Is this possible?

S1mon

The whole point of parametric CAD is to be able to make changes to parts easy to do. Much of the work of modeling in a parametric CAD system is anticipating and planning for how you might want to modify the part or assembly in the future. It’s much more like programming than it is pushing around clay.

Depending on how the part is modeled, a change like that could be modifying one number or it could be hours of work. It’s hard to say without seeing the model. Can you share a public model?

mahir

Ditto on @s1mon's comment. If making one little change is so difficult that you resort to direct editing, then I think it would be a worthwhile effort to go through the learning process of remodeling your design such that it is easily modified. Normally, direct editing tools like scaling bodies and offsetting surfaces are reserved for imported models that don't have any parametrics.

robert_scott_jr_

Hello Andrew

Could equations be what you are looking for? For example: dimension A = x, dimension B = x*.9, dimension C = x*.75, etc..

 - Scotty

andrew_slovak

S1mon said:

The whole point of parametric CAD is to be able to make changes to parts easy to do. Much of the work of modeling in a parametric CAD system is anticipating and planning for how you might want to modify the part or assembly in the future. It’s much more like programming than it is pushing around clay.

Depending on how the part is modeled, a change like that could be modifying one number or it could be hours of work. It’s hard to say without seeing the model. Can you share a public model?

Thanks for the reply. I've already kind of botched the flow of everything. I tried simply modifying the original sketch, but that caused a lot of things to break, and I was hoping to use this as a workaround, rather than going through and fixing everything that the sketch change broke. Since I'm new, I didn't do a great job anticipating and planning in the way that you described, which is why I'm in this position. I suppose I don't have much of a choice other than to simply go back, change the sketch, and then fix everything that breaks.

S1mon

It can be painful, but learning how to fix things when they break is a huge part of the process, especially if you're working with complex parts and/or other designers/engineers. 

One good trick - keep two windows open. One window is the current workspace that you're trying to fix, and the second is open to the last version that was working. You can step each of them through the feature tree and understand the references better especially when a change causes a reference to be missing.

eric_pesty

A couple more thoughts on this: I'm not sure how applicable this will be without seeing the model but when editing your "original" sketch be thoughtful about what you change. Specifically avoid deleting anything or if moving something too far breaks too many things you might better off adding a region to your sketch. For example if you have a rectangle and making it longer breaks a bunch of stuff, try adding a second rectangle at the end instead so that you can use that newly added part of the sketch exactly where you need it!

Also @S1mon 's tip about using two windows is a great one and you might find that it looks a lot worse than it actually is. It's quite common when you have a broken thing high up in your tree and a whole bunch of red downstream to find that fixing the first one makes a whole bunch of problems go away!

If it is really too much of a mess a "backup" option is to use some "delete face" at the end to remove your "wrong" part and re-draw a new part that is correct in its place. It's not "best practice" but if you really are in a bind it could help.