slop-cad

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A parametric edit ​

Continuing from rounding a body. This is short, and it is the point of everything before it.

1. Change the width ​

Click the first sketch row in the Timeline to make the plate active. Press Sketch.

Find the 60.00 row in the docket. Type 90 and press Enter.

Watch what happens in order:

  1. The sketch re-solves. The rectangle widens.
  2. Both holes move outward, staying symmetric and staying 12 from their respective ends.
  3. The activity row in the status foot shows a rebuild starting.
  4. The solid rebuilds: the plate is longer, the boss is still centred on it, the recess is still in the boss, the slot is still there, and every blend is still on the right edges.

Nothing was redrawn. One number.

2. Why each piece followed ​

The holes stayed put relative to the ends because you dimensioned them with Distance to line against the edges rather than in absolute coordinates. An absolute position would have left them where they were while the plate grew past them.

The second hole stayed mirrored because it is Symmetric about the centreline rather than dimensioned separately. Independent dimensions would have looked right at 60 and nowhere else.

The boss stayed centred because its sketch sits on the top face of the plate, with its centre at the face's own origin. The face reference resolved to the top face again after the rebuild.

The blends stayed put because each names its edges by the faces meeting there, not by a number.

Each of those was a decision taken earlier, and this edit works because of all of them.

3. Change the thickness ​

Click the plate's Extrude row in the Timeline and change 8 to 15.

The plate thickens. The boss rides up to sit on the new top face. The holes stay through. The blends follow.

The extrude field is live, so this is one keystroke and a rebuild.

4. Change something further down ​

Click the boss's sketch and change its diameter from 20 to 28.

The boss widens. The recess, which sits on the boss's top face, stays centred in it and keeps its own 12 mm diameter, because it too was placed at its face's origin.

Features rebuild in order, so a change to feature 2 flows into features 3 and 4.

5. Watch the cost ​

Look at the activity row while you edit. Two numbers: solve and build.

The solve stays well under a millisecond. The constraint solver is not what costs you time.

The build is tens of milliseconds here. If you had cut round holes instead of a rectangular slot it would be substantially more, because curved cuts are roughly a hundred times the cost of straight ones.

It is a thing to weigh before designing a part with many round features. See rebuilds and speed.

6. What would not have worked ​

Some things you cannot change after the fact:

  • Add to cut. Delete the feature and make it again.
  • The order of features. There is no reordering.
  • Where a blend sits in the build. Blends are always last.
  • Which face a sketch is on. If its face is gone, there is no re-pointing it.

See what it will not do.

What this was for ​

The work in tutorial 1 was not bureaucracy. Every constraint was a statement about what should stay true, and this is where you collect on them.

A sketch that was drawn accurately looks identical to a constrained one until the day you change a number. Then one of them reshapes correctly and the other falls apart.

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