Yesterday I just had an intersting experience .. a lucky accident followed instanously by an epiphany.
I have been happily modeling various and sundry objects in Sketchup and then either using CADspan (if the number of triangles were not too many) or Meshlabs to convert from .dae files to .stl ... then AccuTrans to check for watertighness .. and I have successfully uploaded files to Print-A-Part and Shapeways. I have been mostly satsified ..
... except ...
Sketchup falls down when you get to small stuff. For example .. if you try to draw a circle that is under 0.018" radius .. it won't. A error screen pops up telling you that "Radius is too small".
This was a major problem when working in O scale / 1:48 .. after all .. that means that the smallest circle/hole you can draw in Sketchup is 0.018" radius .. a 0.036" hole. That's 1.728" .. pretty darn big to not be able to draw it. Crap.
The 'Workaround' has been to draw it larger like full-size and then scale afterwards. The problem is .. that you get all kinds of erratic behaviour once those dimensions drop to around that magic ~ .018" .. Sketchup leaves holes in the model .. basically just craps out.
I want to apoligize for being that .. obtuse that is. I suppose I could blame it on sucking up Agent Orange in Vietnam .. or the DU/Depleted Uranium in the armor of my tank in Desert Storm .. or even the Kuwati Krud everyone had in the last little go-around in OIF.
Ever since Chuck and Marc started to 'play' with 3d printing I was interested. I've had loads of fun and some success .. the major hang-up being that dang scale problem with Sketchup.
So. I was uploading a file to Shapeways using their form .. and forgot to check the radio button for size. They ask you to check .. ( ) Meters ( ) Inches ( ) Milimeters. When I went to upload the file I got one of those messages you see .. the "You fogot to .. whatever"
.....Please note: The STL file format has no native unit. A bit of a drawback for a 3D file format to say the least. The unit of measurement that you were using when making the model gets lost when the file is saved as an STL. So, a model that is 1 by 1 by 1, might be 1 cubic centimetre, 1 cubic inch or 1 cubic metre. This is why you have to choose the appropriate unit here so we know what size you would like your model to be.
Woah. DOUBLE WOAH. I read over that a few times and let it sink in. WOAH again. A .stl file is just units. NOT a specific measurement
I brought up my 6" gate valve as modeled full size in Sketchup. I punched a series of holes in the flange - 'drilling' thm to clear a 3/4" bolt. Divide that by 48 to scale to O and you have a hole that is only 0.016" dia. That 0.008" radius is well below the 0.018" minimum radius that Sketchup will draw. Tossed in the bolt heads .. and added embossing on the side (curious to see if that prints).
Ok .. now this is where it got interesting ..
- The valve is a 6" valve. The throat (opening?) of the valve body is 6". In 1:48 that is .125" .. or 3.175mm
- I scaled my gate valve using the 'throat' (or whatever it is called) .. scaling the 6" to 3.175". Used CADspan and created a .stl file.
- Uploaded the file to Shapeways .. and told it that it was in * Milimeters *
So. There you go. I just wanted to post this up for anyone who also suffer from not understanding some basic .stl stuff with apoligies to those who TRIED to explain to someone that's evidently too dense. :/