this is from JBLCAMRY on FLSPL
Ok, this is going to be a quick how to, using sketchup. This not a tuned box, it is just for demonstration sake.
Start off by measuring out your bottom piece of the box, and drawing it out.
Now that you have the bottom of the box measured and drawn, use the push/pull tool to pull it to the desired wood thickness. (Usually 3/4")
Now take your measuring tape, and click on the edge of each side and pull in 3/4" (or wood thickness)
Now draw lines with the guides still there, and then erase the guides
On this example I used a 3" wide vent, so take the tape measure again and measure 3" in from the inside of the walls, on the side and back. Then from those lines measure out another 3/4" with the measuring tape.
Then erase the piece in the front of the port and the guides.
Next is the 45 in the port, start out buy measuring from the corner to the interior edge and then measure 3" from the corner. (The little dot)
From that point, drag a square to the edge. And draw a line through the middle. Then from the edge of the square across till it turns a pink color (idk I’m colorblind)
Now erase the square and the guides, so there is only this left.
Measure from the middle of that 45, out 3/4" like this
Then draw a line and erase the guide, leaving you with this.
Now you have your layout finished for the box.
now you start to pull up all of the pieces of the box,
note that all of the pieces are up, you need to draw the lines that separate them. like so...
now you have an almost complete box.
next is how i do the top. i draw a line 3/4" up on the corner, then i draw a line the depth of the box, then back down 3/4". leaving this........
now pull it accross.
now is time for the hole cutout, first you want to find out where you want to but it, use the guides to do this. for this box, i pulled from the edge 14". then drew and X using the guides.
now draw the circle (this one is 5 1/2" radius) so there is an 11" cutout.
now use you push pull tool and push in 3/4" and let go. you will be left with this...
now erase the guides and your done, you have a finished drawing using sketchup
hope this helps.