How do you properly calculate a slot port around a corner?
For example, If a 2" x 12" slot port needs to be 25" and the box has an external depth of 14" using 3/4" MDF . . .

Here's what I've done, but is it right?
14" deep box minus MDF thickness for 2 walls (1.5") = 12.5" internal depth.
12.5" internal depth, but the port will go through the front wall, so that section of port will have a length of 13.25"
At this corner point, I consider the next section like a new length of port, and I would make the internal wall 11.75" for an over all length of 25"

. . . so in building the box, with the front face one continuous piece, the first internal port wall would be 9.75" long:
12.5" internal depth of box
- 2" port width
-.75" board thickness for next section of port wall
9.75"

But I had one person say to me that as long as the outside wall of the port is the length then you are fine. I argued against that saying it is overall volume of the port that is more important.

Have I been doing this correct?

 

I go by the middle of the port. Your first portion will be (14" - .75" for the back wall - 2" for the width of the port) = 12.25". You second portion will be from where the first port ends (25" - 12.25" - 2" for the width of the port)= 10.75"

 

Sorry I can't edit my math. The physical lengths are 11.25" for the first piece and 11.75" for the second piece (for the L shape). Using the center of the port gives a length of 12.25" and 12.75" for a total actual port length of 25".

 

Sorry another typo LOL. It's hard to describe without a picture. You want to measure the internal pathway of the port from the middle.

Check out the picture. I didn't factor the thickness of the port wood because it depends on how you assemble it.

Pictures by steveg789 - Photobucket

 

Thanks,

I have used that method as well and found that it produces the same results (although I'm more prone to making mistakes with that one).

I see that we came up with the same calculation as well.
For the second part of the port I said the wall would be 11.75 - so to take the middle of the port path, would be to add one more inch to that which is 12.75, as you stated.

Likewise, my first port wall was 9.75 Add .75 for the front face, add .75 for butting up against the next secion of port wall = 11.25 - then add 1" for taking the middle path of a 2" port = 12.25 . . .

Thanks for the verification!

(And thanks also for enduring a confusing verbal discussion that would be much better done through a drawing - words don't really do this much justice)

 

I think if you measured the length of the longest side, and add that to the length of the shortest side, then divided by 2 to get your average length, you'd end up with the "middle" length measurement.

Just for arguments sake: If the outside walls of your 'L' shaped port are 6" and 10" (total 16"), and and your port was two inches wide, then your inside wall should equal 4" and 8" (total 12"). 16 + 12 = 28. 28/2 = 14"

I think that might be the easiest way of getting your port length.

 

I like to use the middle path so that I know the overall length and then work backwards to find what size the individual parts need to be. Its easier to do when you aren't in a Venture Capital class and trying to bust out a verbal description and master a drawing in Paint too!

 

Let's try that on the model I gave up top:
Outside wall: 13.25 + 13.75 = 27
Inside wall: 11.25 + 11.75 = 23
27 + 23.5 = 50 / 2 = 25

Looks, like that Method works too.

So now I've got three ways to calculate port length:
1) Measure the middle path of the port
2) Add all lengths of port walls together then divide by 2
3) Treat each turn as a separate port and add together.

Thanks guys.