Trying to constrain this sketch while also being able to change some dimensions

[david7890]

Hello,

Can someone help me with setting constraints on this sketch for a 7 segment digital display?

I want to make everything a bit smaller, but I'd rather not simply scale it as then I would loose the existing dimensions and certain constraints.

I have set a parameter for the segment width (4mm) as well as overall width and height. I would like to change the width to 3mm, but when I do that the corner radii are not all the same (they are 4mm when width is 4mm, after changing width they are like 4.0x or 3.9x).

Also, if I try changing the overall width or height then I either get a constraint error or it messes up everything.

Basically I just want to scale the whole thing down but in a more precise way.

[rohit.bapat]

Hello @david7890 

I checked the file, can you please try adding the dimensions to the fillet arcs with a dimension referring to a desired parameter?

That way you can get expected results with the radii.

Thank you,

Best Regards

Rohit Bapat

[david7890]

Hi,

I can add dimensions to the top left and bottom right curve, but for the other two it says it would be over-constrained.

I should also note that I removed the perpendicular constraints on the middle bits (see "sketch" attachment) as I realised I didn't need them, same with the 4 degree slope on one of the sides. With those removed it was a bit better, but I still for some reason can't do those two curves I mentioned.

If I change the height then it gets all messed up as you can see from the "sketch 2" attachment.

[TheCADWhisperer]

@david7890 

If this were my design I would start with symmetry about the Origin and dramatically simplify the sketch (we can pattern features rather than in the sketch).

I would fully define all geometry as I proceed rather than wait until I have a complex sketch to try to control the geometry.

The sketch can be controlled with 5 dimensions.

[david7890]

Thanks, I'll try that.

The reason why it is so complex now is because I traced it from an existing sketch then tried to adjust to my liking (changing the skew angle and distance between things).

[david7890]

There is one problem with your sketch, though.

When I make the width and height smaller as well as the "segmentWidth" parameter, these lines do not connect (see attachment).

[davebYYPCU]

Make the end points the didn’t move - coincident to the part it should have been attached to.

Might help….

[david7890]

One other question,

I'm trying to set the distance of the top segment as shown in the attached image, but it's doing the dimension aligned to an axis rather than to the skewed line. The example on the right side is how I want it.

In my original file it was wrong as well, and in TheCADWhisperer's example it also appears to be the width of the line perpendicular to the horizontal line.

[davebYYPCU]

When setting dimensions you can find the correct version by moving the mouse around - depending on where the mouse goes the type of dimension switches, between aligned, vertical and horizontal.

If that is not working then before setting position, right click and select the one you want, selecting this way locks the choice in, and stops the mouse options.

either way - most want the width of the item, not (your request) the length of the angle cut.  Some would benefit from a driven dimension there.

Might help….

[david7890]

Thanks, that worked.

And yes, now that you mention it, I do actually want the vertical distance between the two lines. Because no matter what the skew angle is, the width of the top/bottom segments should remain the same. It's the width of the left/right segments that should be aligned, but I already do that by using a perpendicular construction line.

[david7890]

I'm still stuck with trying to adjust the parameters after I have everything sketched out the way I want it. Please see these new attached files.

I also found another problem with TheCADWhisperer's sketch, the bottom segment width/thickness is only 3.4mm instead of 4, and I get constraint errors if I try to change it.

[TheCADWhisperer]

---

@david7890 wrote:

I also found another problem with TheCADWhisperer's sketch, the bottom segment width/thickness is only 3.4mm instead of 4, and I get constraint errors if I try to change it.

---

@david7890 

Yikes!

That is an easy correction, but I still have to correct the corners.  Check back. I would like to simplify this more.

[david7890]

Thanks for the help

[david7890]

I finally got something that I am happy with, managing to get all the dimensions and constraints that I want.

I still don't understand why some constrains were not possible, or caused the whole thing to blow up, but I guess it is a rather complex geometry.

[davebYYPCU]

Not so complex, you just made it more complicated than need be.

you have 3 duplicates, that didn’t need being drawn or constrained. 

you will need to explain what is still not working.

Hint: Blue, orange and white articles are not fully defined.  Changing parameters with them involved will produce unpredictable/unexpected results. (Even if partially constrained)

Might help….

[TheCADWhisperer]

@david7890 

I was able to simplify the sketch.

Edit: After more thought - I should have made the corner cut lines Midpoint to the arc centerpoint in case the arc is set to a smaller radius.  The same as I made the other cut lines.

[davebYYPCU]

Slightly different version.

Change the parameters back to your sizes.

Might help...

[david7890]

Thanks for your help davebYYPCU and TheCADWhisperer.

I'm not sure I can use either of your designs, as I want to project the sketch onto a PCB as well as using it as a 3D object, which means I need the whole thing as a sketch rather than completing it with operations on the extruded 3D object. But what I ended up with is fine for now (as long as I don't touch it!).

[davebYYPCU]

As long as I don't touch it?

Updating parameter changes was the first question.

So - after changing the design, Sketch 3 will be there waiting for you.

Doing it the hard way is ....

Might help...

[david7890]

Ah ok, so you created another sketch referencing the edges and points from the 3D object? I didn't think of that.