Monday, September 06, 2010

How accurate should a SketchUp model be?

In the October 2010 issue of Popular Woodworking Magazine there is a letter about modeling drawers in SketchUp.  The reader asks how to model the small clearances required to make sure the drawers ride smoothly in their openings.  In "meatspace" this typically means the drawers are 1/32 or 1/16 undersized to the openings.  Bob Lang answered this question well, but in my opinion missed the most obvious response:  Why the heck would you need to model to this level of detail?

Look, I know more than most how tempting it can be to get every little detail correct in a SketchUp model.  I've spent time tweaking little bits and pieces to make sure they were just right, believe me.  While designing projects I can have multiple generations of a design, exploring new options and branching out into infinite possibilities.  So take it from somebody who has fallen down that rabbit hole - you have to know when to stop modeling and start building.

These days I am trying to remind myself that the goal is to make projects, not models.  My ability to create precision in SketchUp are far beyond my abilities for precision in the shop.  Wood moves with the seasons, small variations in tool setups introduce randomness during a build, and sometimes designs get changed on the fly. 

Here are a few questions I try to ask myself as I am making a model to ensure I am not sinking deeper into OCD territory.
  1. Will the extra level of detail make it easier to build the real piece?  By all means, if it makes things easier in the shop then add it to the model.  I am a strong believer in modeling details on joinery, curves, edge profiles, etc. as long as they make the time in the shop easier.  An exploded view of the project with a few key dimensions is invaluable to me as I build.  But leave out things that make no difference in the shop.
  2. Will the final dimension of the wood match the SketchUp model?  SketchUp is great at providing dimensions for raw stock.  Suppose you have a door rail that will be mortise & tenoned into the stile.  By all means, add the two tenons to the ends of the rail and use SketchUp to measure the total length of the rail.  But by the time you need to know the dimensions of the door panel, measuring the actual meatspace door is the best way to go.  A little variability could have crept in and suddenly the dimension of the panel in SketchUp doesn't match the door you built.  Until you have a CNC machine just spitting out all you project parts, you have to know when to abandon the perfection of the SketchUp planned dimensions.
  3. Does the design of the piece require a more detailed model?  If I am trying a new type of joint or I want to see how a curve would look, I add more detail until my question is answered.  Otherwise, keep it simple.  For example, when designing a piece with drawers I will often create a simple rectangle to fill the drawer opening instead of modeling a full dovetailed drawer.  Even a drawer-sized box is easy to make and fill the hole.  Until I need details about the drawer there is no need to model it beyond that point.  It's a heck of a lot easier to explore the overall size and shape of the piece this way.
Adding details to a model can be addictive, and frankly a great way to learn how to use SketchUp as a power user.  But take my advice, you have to know when to put the mouse down and back away slowly!


Morton said...

Yeah, I totally agree on all fronts. I too have spent lots of time in SU but find it most valuable for:
1) getting accurate measurements for initial pieces, etc
2) working on "block-level" models of new designs to picture a piece entirely before proceeding to a mockup or actual project.

Aaron said...

Morton, good to hear from you! Thanks for commenting on the blog - you are the first ever! That and $4.97 will get you a coffee at Starbucks.

Rob Bois said...

I just ran across this post again, because I linked to it in a post of my own from last year. The topic of Sketchup just came up again in a discussion I was in, and in re-reading this post I have to say I think I agree with it even more today than I did when I first read it last October. I don't measure anything from my models, I know how to do my joinery, and when introducing a lot of curves in design, sketchup really falls down. Aaron, I think this is now officially a "classic" post!

Aaron said...

Rob, always great to hear from you. I had to take a second to re-read the post myself. Many of the models I create get published, so they break all these rules. Good reminder not to overcomplicate things if nobody is looking at the model but me.