Extrusion constraints

[makeable]

Disclaimer: total noob. Ive been tinkering for a few days, and have even sent off a design for laser cutting!

At the moment I am trying to model a bracket. Ideally, i will be parameterizing it as much as possible. It is a u-bracket. I have set some constraints on the inner dimensions, and I have used offset to define the thickness.

I extrude the sketch, to a ROUGH approximation of what i want:

 Then, on one of the faces, I start a sketch to define some holes which will be cut from both sides of the bracket. They are to be mirrored around the centre, and a fixed distance from the edges. I WANT to define the spacing between the holes, which would adjust the depth of the extrusion accordingly, but it seems I cannot do that - it turns the constraint into a "driven" one. No doubt there is an implicit constraint being set on the extrusion to the approximation I set earlier:

 

I have no doubt that this is likely caused by me doing this in a potential ass-backwards manner. What is the correct workflow to do something like this? I know I can do something similar in sheet metal with bendlines, but how would i do this otherwise?

 

[wersy]

If the holes are mirrored in the center, you can only measure the hole spacing OR the edge spacing. Otherwise it is overconstrained.

You have to choose one of the two.

[TheCADWhisperer]

See Attached for one method...

Whenever possible and practical - model with symmetry about the Origin.

Whenever possible and practical - use Origin Planes for sketches rather than part faces.

Create Named Parameters for future editing...

[makeable]

You can set both on a sketch, its only overconstrained because (i think) the extrusion is setting an implicit constraint.

[laughingcreek · Accepted solution]

define the important bits first.  in this case the distance between the holes.  then drive features off that (ie don't do the extrude first).

see attached file and screen casts for some ides.-

a handle 

[makeable]

Many thanks. From the screenshot this looks like exactly what im trying to achieve. I will have a look at the file you supplied a bit later and will get back to you. Thanks for the general tips as well - these sorts of things are missing from ALL the general tutorials.

[makeable]

Many thanks. This certainly works for this specific item, but it does seem to make the workflow more convoluted given my current understanding of things. i.e. instead of creating a U shape and then cutting holes, i am now creating an end piece, extruding it, using rectangular pattern to copy it, then creating a flat back piece constraining to the height of the edge and extruding that. Its very possible i'm being a complete idiot here 😄

[laughingcreek]

given your workflow description I'll assume you haven't looked at my file.  nearly identical to CW's.

[makeable]

Many thanks for providing the example - unfortunately, this seems to be a bit different to what I am looking for. Im looking for the extrusion height to be driven by the spacing, rather than vice versa. i.e. i want to specify the spacing, and then extrude based on the constraints. Following your calculated params idea, I can certainly do this by modifying the extrusion to be a calculated value based on the spacing, but ideally I was hoping to drive it off the other constraints rather than having to put in a calculation (i.e. have it auto-calculated based on its contained constraints).

[makeable]

Apologies, i didnt even notice there was an attachment. I will have a look!

[makeable]

Oh my! I did not realise you could use the points on a sketch as extents for an extrusion! That will make things a lot less complicated! Many thanks 🙂