Phil - Big Problems - started building my top hat separator

[Howard In Toronto]

Hi Phil -

A 7-question beauty as I try my hand at building a new one this coming weekend......

I'm using 3/8" bendy plywood to form the walls of my top hat separator.
The upper and lower panels are 1/8" tempered hardboard glued into 1/4"-deep grooves routed into the bendy plywood.
I'm placing the separator on a 30-gallon fibre drum and the interior walls will hold it in place.

This past weekend I had big problems letting my 6" inlet correctly into the wall of the bendy plywood.

I'm using this type of 6" HVAC duct for trying this type of result - http://www.jpthien.com/smf/index.php?topic=249.0 to be let into the 3/8" bendy plywood walls.

When I use the software from your site - http://www.harderwoods.com/pipedocs.html
1 - what "join angle" should I enter?
2 - what "lateral offset" should I enter?

But then I saw this on your forum today - http://www.jpthien.com/smf/index.php?topic=110.0 and think it's a great idea.

I can buy the same kind of fitting at Home Depot - http://www.homedepot.ca/wcsstore/HomeDepotCanada/images/catalog/17074.0EB041006HD_4.jpg
3 - but I'm concerned about getting the sheet metal to accurately follow the curve of the top hat's walls while having enough meaterial to bolt or screw into the walls

But then I saw this configuration - http://www.homedepot.ca/wcsstore/HomeDepotCanada/images/catalog/17074.3TT06HD_4.jpg
I think it has a few advantages -
4 - because the area is shorter I figure I can get it to follow the wall's curve more easily
5 - and I can sheet-metal a small gusset into place for questions 6 and 7

With a 6" round inlet -
6 - should the opening into the separator be an equal number of square inches?
Is the following reasoning sound?
7 - 6" inlet = 3" radius squared = 9" x pi = 28.14 = 6 (this is one dimension of the square opening) x 4.71" for the opening into the bendy plywood's walls to match the square inches of the 6" inlet?

Thank you - I'd appreciate your help before I try this again on the weekend.

Howard

[phil (admin)]

For the joint template calculator:

The "Main Pipe Ext. Diameter" should be equal to the diameter of your top hat (let's say 24")
The "Branch Pipe Ext. Diameter" should be equal to the diameter of your inlet (let's say 6")
The "Branch Pipe Wall Thickness" should be equal to the thickness of your inlet (let's say .125")
The "Lateral Offset" in this example is (24-6)/2, or 9".

On the alternative inlets, I have to think more about those...

I'll post back again.