How to precisely position an un-constrained sketch
Sometimes a user does not wish to apply constaints and dimensions needed to fully shape and size a sketch. This could be because the data is imported from another CAD system, or it may be free-form, stylistic data (splines and such). However, it can be hard to align and locate the sketch precisely on the model, because each new constraint tugs the sketch out of shape instead of moving it. There are three good ways to accomplish this, depending on user taste, and also upon how much parametrization of the sketch you plan to eventually apply.
First, the easiest (read: lazy) way is to group-select all the lines, and choose TOOLS – BLOCKS – MAKE BLOCK. The lines are now all ‘frozen’ relative to each other, and can now only translate or rotate as a group. You may now apply sketch relations to the entire block to position it, and when finished, you may then EXPLODE the block to restore individual control to each line.
The second approach also requires that you first pre-select all the lines in the sketch. Then use the icon found under TOOLS – SKETCH TOOLS – MOVE, (you will also see the related tools ROTATE, SCALE, and COPY). These commands will allow you to position the selected lines very precisely, relative to a FROM and TO selection points, or by inputting jog distances or angles, and they result in no new parametric relations.
A third slick solution is to use Derived Sketch. A derived sketch is an associative copy of an existing sketch. It can only be positioned -- it’s size and shape is always exactly the same as the original. This behavior is ideal for problems where you want to reference the original sketch several times, or where you prefer to leave the original data as a master sketch in its original location. One disadvantage of this approach is that it is all-or-nothing, you can only DERIVE a sketch that includes every line in the entire sketch, and the other two methods listed above will also work on a few selected lines.
To DERIVE a sketch, first you must exit the sketch you were working on. Now use Ctrl-select or Shift-select to choose the sketch you just exited, and also select the plane that the new sketch should be built on. With these two items pre-selected, you will be able to Insert - Derived Sketch. You will now be editing a second sketch, an associative copy of the first. You may align and position this sketch, without causing any deformation. You can now Hide the original sketch. To make any shape changes later, edit the original sketch, an the derived one will update with those changes.
Optional: You may wish to sever the link between the two sketches, and delete the first sketch. To do this, right-click the derived sketch in the FeatureManager, and select Underive. Then you can delete the earlier sketch.
