16 Replies Latest reply on Aug 13, 2012 4:26 PM by John Burrill

# The point of sketching in an assembly?

Good day everyone!

I'm just curious what the point is of sketching in an assembly if you cannot cut/extrude or boss/extrude? Seems useless to me if you cannot do anything with the sketch. What do you guys use it for? Just curious.

Thanks

~Corey

• ###### Re: The point of sketching in an assembly?

I use them extensively for mating.  If I want to mate two parts using the center of their faces I can draw a line (use 3D sketch for this) on the first part and mate the other.

You CAN cut using sketches.  When I build a vessel with Long weld Neck flanges (a part in my routing library) I cut them in the assembly sketch so I don't have extra parts running around(the cut exists only in the assembly, allowing me to cut one part to many differant sizes for use in an assembly, especially when the part has many configurations)

Assembly sketches also help route plumbing.  create 3D sketch and mate your plumbing pieces to the sketch.  This is the basis for how Routing works.

• ###### Re: The point of sketching in an assembly?

For top - down design:

1. Layout based assemblies (simulate mechanism-like motion with 2D sketch blocks and once happy with the results, convert the blocks in assembly components by adding meat on them):

2. Skeleton sketches for defining the location of components.

• ###### Re: The point of sketching in an assembly?

In addition to the reasons stated above, I use sketched lines for the direction of Linear Patterns.  I learned a long time ago not to use the edge of a component.  They can be changed and lose the referenced edge.  My assembly template has a 3d sketch containing 3 lines, each one is at the intersection of two of the three planes.  (Two of them are on the top plane and perpendicular to each other at the right plane, and the other is vertical at the intersection of the front and right planes.)  These lines are in the right place for probably 95% of the linear patterns that I do.

• ###### Re: The point of sketching in an assembly?

Glenn, you made me curious, why use sketch entities instead of axes?

• ###### Re: The point of sketching in an assembly?

Oh I see I haven't gotten into the Top Down method. I figured that's what it was for but then I noticed that all of the feature tab were missing. That sounds like a realatively cool feature to have. So it's kind of like tracing for other parts to fit if I'm understanding this correctly? Thanks for all the info and clarification guys! Much appreciated!

~Corey

• ###### Re: The point of sketching in an assembly?

I did use axes to begin with but they are just way too visible!  And when I have sub assemblies it caused a mess.  I turned axes off and dont use them anymore (although it is still in my assembly template i just add the 3D sketch)

• ###### Re: The point of sketching in an assembly?

Richard Wehmeyer wrote:

I did use axes to begin with but they are just way too visible!  And when I have sub assemblies it caused a mess.  I turned axes off and dont use them anymore (although it is still in my assembly template i just add the 3D sketch)

I have the main axes in my templates, but leave the View > Axes turned off and select them from the FM. I find that much easier than having to Show the sketch and then zoom in to select the sketched line, and then turn off the sketch again. Not having the sketches showing also helps keep the graphics area clean.

• ###### Re: The point of sketching in an assembly?

No particular reason.  When I did it the first time it didn't occur to me to use axes.  The sketch works well, and it's easy to RMB on it and hide it when I don't need it.  And wouldn't it be simpler to have one sketch than 3 axes?

• ###### Re: The point of sketching in an assembly?

Glenn Schroeder wrote:

And wouldn't it be simpler to have one sketch than 3 axes?

It seems to me you can select an axis from the feature tree. You cannot select a sketch element from the feature tree.

Oops - Kelvin already stated that.

• ###### Re: The point of sketching in an assembly?

So you're saying I could select an axis from the feature tree to use for a linear pattern without making it visible?  If so, that probably would work better.

• ###### Re: The point of sketching in an assembly?

That is correct. Try it.

• ###### Re: The point of sketching in an assembly?

Thank you Alin and Kelvin,

I just tried it.  I named them "Front to Back", "Side to Side", and "Up and Down".  I'm pretty sure I'm going to like this better than the 3d sketch.

• ###### Re: The point of sketching in an assembly?

The axes can also be renamed to suit the intended application.

Pivot Axis, Cross-hole or Cross-pin Axis, Shaft Axis, etc.

• ###### Re: The point of sketching in an assembly?

Amen to that.  I do the same (though I have not incorporated it into my template yet).  But I use 3D sketch to do it.

• ###### Re: The point of sketching in an assembly?

Alan, I use sketches in assemblies for all manner of purposes.

As noted, you can create assembly level cut extrudes and revolves and holes which are very useful for field machining

Assembly 3D sketches are immensley useful for laying out wiring harnesses. Unlike mates, you can add external relationships to sketches contained in a subassembly. If you're routing a wire harness as a subassembly, you can't mate the connectors to the top-level assembly directly.  (yes, you can make the subassembly flexible, but you can't edit a flexible subassembly in place.)  However, you can create a 3Dksetch in the subassembly with incontext sketch relations to the top-level assembly and then mate your connectors to the 3Dsketch.

It's also very useful to have a single 3Dsketch for all of your wire routes-even if you have to make individaul wires or harnesses seperate parts for the sake of the BOM.

Also, you can't beat the speed and convenience of the sketcher interface for laying out top-down design.  If you derive your components from an assembly sketch instead of from eachother, than you can easily control clearances from that one sketch that  solves simulteneously instead of having a long history tree.  Plus, there are a lot more ways to constrain a sketch than there are ways to mate a component.  For example, the common problem, 'how do I constrain the motion of a pin to a slot' can be addressed with an assembly sketch and a path mate much more simply and effectively than it can with conventional mates.