I'd been thinking about a spiral top hat for a while. At some point a while back, Phil mentioned having a "lead-in" section of the duct that curves to put the material on the outside of the duct before it enters the chamber.
I combined those ideas.
The spiral is an Archimedes spiral. In this design, every 90deg, the radius increases by 1/2in. My brother had been playing with Ruby script plugins for Sketchup to make spirals; so, I fiddled with the settings (initial radius and growth rate) to get a spiral I liked. The spiral is for 450deg. The last 90deg (or first 90 deg depending on how you look at it), represent the lead-in curve section of the duct. That kept the width of the rectangular duct cross section consistent.
I sized the top hat for an 18in diameter 10gal tub. I wanted a tub less than 20gal so if I can get a bag in the tub (without it sucking up into the top hat), the weight of the waste would be in the <20lb range. Sawdust density: http://www.engineeringtoolbox.com/density-materials-d_1652.html
I'm getting some by pass but I think it's because the outlet is too close the the shortest radius. If I were to do this again, I'd make the initial radius larger by about 1 to 1-1/2in (this would be radius from the center of the outlet duct to the wall at the closest point).
As you can tell from the pictures, my plexi bending skills leave a lot to be desired. I used metal duct tape to seal both sides of the wall when ever I had a break....
Cutting the spiral with a jig saw was the hardest part for me. Once I had one spiral mounting guide for the plexi, I screwed it to another spiral mounting guide and used a flush trim bit to even out any differences. (I wish I had access to a CNC for this.)
I followed the general top hat assembly techniques of several others here.
The top view picture of the top hat shows the path of the plexi following the spiral.
I think the initial 90deg curve in the duct is a really good idea based on watching the material fly around the outer wall of the top hat. If you build a spiral, make it a little larger that what I made. Using a spiral may be more trouble than it's worth unless you have access to a CNC (or better jig saw skills).
I've attached a Sketchup drawing and the Ruby script plugin for Sketchup along with a few pictures.
Hope this helps somebody.
Andy
I combined those ideas.
The spiral is an Archimedes spiral. In this design, every 90deg, the radius increases by 1/2in. My brother had been playing with Ruby script plugins for Sketchup to make spirals; so, I fiddled with the settings (initial radius and growth rate) to get a spiral I liked. The spiral is for 450deg. The last 90deg (or first 90 deg depending on how you look at it), represent the lead-in curve section of the duct. That kept the width of the rectangular duct cross section consistent.
I sized the top hat for an 18in diameter 10gal tub. I wanted a tub less than 20gal so if I can get a bag in the tub (without it sucking up into the top hat), the weight of the waste would be in the <20lb range. Sawdust density: http://www.engineeringtoolbox.com/density-materials-d_1652.html
I'm getting some by pass but I think it's because the outlet is too close the the shortest radius. If I were to do this again, I'd make the initial radius larger by about 1 to 1-1/2in (this would be radius from the center of the outlet duct to the wall at the closest point).
As you can tell from the pictures, my plexi bending skills leave a lot to be desired. I used metal duct tape to seal both sides of the wall when ever I had a break....
Cutting the spiral with a jig saw was the hardest part for me. Once I had one spiral mounting guide for the plexi, I screwed it to another spiral mounting guide and used a flush trim bit to even out any differences. (I wish I had access to a CNC for this.)
I followed the general top hat assembly techniques of several others here.
The top view picture of the top hat shows the path of the plexi following the spiral.
I think the initial 90deg curve in the duct is a really good idea based on watching the material fly around the outer wall of the top hat. If you build a spiral, make it a little larger that what I made. Using a spiral may be more trouble than it's worth unless you have access to a CNC (or better jig saw skills).
I've attached a Sketchup drawing and the Ruby script plugin for Sketchup along with a few pictures.
Hope this helps somebody.
Andy