I was asked by Anthony P. and Kevin S. to create grates for an O scale storm drain system. Anthony provided photos of one being istalled. Using that as a reference I found this page from Jensen Prcast showing a 24″x36″ Curb Inlet with cast iron frame grate, and hood (6th down).

There are a variety of these on the page and gives me a good starting point. Since I have never been that connected to reality .. making an exact copy is of little interest.


Here’s one of the photos that Anthony sent me. If we say the sidewalk is 48″ then this one is about 24″ x 36″ which is the same as the Jensen product.

I only just noticed that this tapers from the front to the back. Look at the metal tabs that support the grate. The one on the far left is about half the height of the one on the far right. Now looking at the drawing at the top of the page I see the same taper.

Match Photo

I brought the photos into Sketchup to use Match Photo. Just how well this works depends on several things .. the camera used (lens design) and whether the photo has been cropped (Math Photo uses perspective and an uncropped photo to place the drawing at the exact angle the camera was at).

Since we know the grate is 24″ x 36:” we can use that to get at least the long dimension on the grate correct. The other measurements have to be taken with a grain of salt and some logical deductions.

From the above I can estimate …

  • The Cast Iron frame is 24″ x 36″ x 8″.  Walls are ~1″
  • Grate frame is about 2″ wide .. the grating sizing can be eyeballed in the drawing.
  • The Curb metal is very ‘wonky’ in the photos. Trying to get good dimensions is difficult as not only is it cocked at an angle but is curved. It is somewhere around 9-9.5″ tall and “in the vicinity” of 7″ wide. Perhaps half it’s height would be level with the concrete curb. A quick search confirms that curbs are between 4″ and 6″ high and about 6″ thick.

That gives me everything I need to replicate it in a CAD drawing in scale

Version I

I was pretty happy with how it came out. I did take longer than I expected .. that slope made for added complexity that isn’t that obvious at first glance.

Yep. I was pretty happy .. happy enough to run a test print .. happy. Until ….

I decided to brew up a .. call it .. blueprint. That’s when I realized I had managed to screw up the dimensions. The grate was supposed to be 24″ x 36″ .. or the opening it sits it .. with one or the other slightly larger or smaller for a good fit. What I ended up with as a grate measuring 18.4″ x 33.45″. Huh. Not that from a modeling perspective it matters one whit .. it just make my OCD itch.

Version II

I addressed the issues identified above in Version I – re-sized and made adjustments on thickness of various areas based on the test printing.


The test print came out well. The grate fits nicely into the cup of the frame

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Fantastic I can’t wait for these !!!