topic Re: Spline dimension woes in Fusion Design, Validate & Document Forum

Spline dimension woes

welbot — Wed, 16 May 2018 05:34:33 GMT

Hi,

No idea if this is possible or not yet, but I sure as heck can't figure it out 😕

I've sketched half a heart using a spline, which I then want to mirror and extrude etc. (That bit isn't a problem)

The problem is I've drawn the spline to the shape I want, but I need to make sure it is exact width and height.

I've tried using coincident construction lines with the outer most points of the top and side of the curve (to create a kind of bounding box) but when I then specify dimensions for the construction lines, it warps the spline instead of maintaining the overall shape. Is there a way to freeze the curvature of the spline to allow me to "scale" it by setting precise dimensions?
I have no idea what the dimensions between the fix points would be. I just know that from the bottom point of the heart to the upper most point of the top curve needs to be 4.25mm, and when mirrored, the width (from outermost point of side curve to the opposite side) needs to be 5.25mm.

i'm making a ring that has a heart shaped diamond, which needs to be set in what they call a bevel setting (basically a simple heart shaped vertical extrusion with a cavity, and lip around the top).

Another problem I'm having is, I have a model of a heart shaped diamond which was created in a different cad program (imported as stp), but the dimensions for that are also incorrect. Since it's imported geometry, I can't specify dimensions for it. I am able to see the bounding box dimensions in the properties of it, but obviously you can't just type values in to there. Is there a way to make some kind of bounding box geo that I can specify dimensions for? Trying to adjust it by scaling factor is a nightmare 😕

I tried doing a projection of the geo to a sketch, but it wouldn't let me dimension it, claiming it was over constrained.
I even tried doing a mesh intersection, but due to the gem's faceted profile edges, trying to set a dimension between the outermost points just caused the sketch to spaz out and throw lines every which way.
The gem itself isn't a HUGE issue, as I can just eyeball the scaling of it, but ONLY if I can get the precise dimensions set for the mount.
Any help would be greatly appreciated 🙂

Re: Spline dimension woes

etfrench — Wed, 16 May 2018 07:55:02 GMT

"Exact" is rather meaningless in manufacturing You need to specify a tolerance.

This rather crude technique will get you within a few microns:

Re: Spline dimension woes

davebYYPCU — Wed, 16 May 2018 08:08:17 GMT

No mystery to scaling by scale factor,

Desired size divided by Actual size, (DS / AS)

Smaller is a number less than 1, larger is a number bigger than 1.

Sketch scale is uniform (both) directions,

If you extrude the heart sketch you can scale the body by non uniform factors, either direction (3)

but you may find the result not as pleasing as the shape before scaling.

You can lock the shape of the spline with the Fix/Unfix constraint, the spline will mirror in a fixed state, but don't know if you can scale it when fixed.

Create the dimensioned box in a sketch, move / scale / your current shape, to fit the box, or you will be chasing your tail. Small number of fit points works best, constrain the top with a horizontal constraint on the tangent handle, and it wont be able to cross the line, side handle with a vertical constraint and it will stay in the box.

Sliding the handle points or the fit point to make the shape, when happy with the shape Fix constraint will change it to a green line.

Oversized to show proportions.

Might help.....

Re: Spline dimension woes

welbot — Thu, 17 May 2018 00:19:34 GMT

Thanks for replies.

I am aware of the need for tolerances, and this has been taken in to account already 🙂

I'm not sure yet if either of the methods will work for me yet, as I've tried something similar already using construction lines. I know less is is best when it comes to splines, but having to match the contours of the gem makes that a bit tricky. I haven't been able to get it to match with only 4 points, but perhaps I can use a method similar to the offset, fix the points, and then add more and tweak.

I think I'll try the scaling factor calculation first. I wasn't sure if that would work or not. I've used Fusion a bit in the past months, but mostly worked in 3ds max in the past, and used to being able to just type in values.

Also, i did indeed try fixing the points and then scaling, hoping that would maintain the shape, but you are correct in that scaling doesn't work. Once they're fixed, they're stuck in place, not just relative to one another. Would be great if there was a separate option to fix points relative to one another, rather than completely lock their position.

I will experiment a bit today and update 🙂 Thanks!

Re: Spline dimension woes

welbot — Thu, 17 May 2018 05:15:46 GMT

Not exactly the solution I was after, but have accepted the answer as thanks to this:

Desired size divided by Actual size, (DS / AS)
Smaller is a number less than 1, larger is a number bigger than 1.

I was able to scale the diamond correctly, so I can now just use that as a reference for the splines. I've yet to do the splines, but at least having one thing scaled correctly is a good enough start.

Thanks!