Round to rectangular inlet question.

[RonS]

I am attaching the drawings I use to create the round to rectangular inlets. I'm not a draftsman I just do this as way to create some basic drawings before I make anything.
I use DoubleCad XT as my drawing package, it's free at this web site (http://www.doublecad.com/). I will attach some other versions of the file so it can be imported into other cad packages.

Here is basically the way I do it.

I use a modified version of Joe Emenaker's spread sheet to create the input for the drawing, which I will attach with Joe's instructions. Joe's web site (http://joe.emenaker.com/DuctEvolution/index.html) also has some help full information.

Using concentric circles draw the inner and outer radius from Joe's spread sheet,
also draw a third circle 1.5" smaller than the radius of the inner circle to serve as the round end extension.  ( you could also use concentric arcs for this also)

Use 10 concentric circles to draw the short tick marks on the inner radius circle. To locate the center of these circles, draw a perpendicular line from the center of large inner/outer circles to locate the center on the arcs to use for the circles.  The radius for these circles are calculated in a chart on the spread sheet.

Draw 3 concentric circles on the outer radius.  The radius for these circles are calculated in a chart on the spread sheet. These determine the tic marks for the rectangular section and corners where the bend lines meet on the outer radius.

Where these smaller circles cross the inner and outer radius lines creates the points needed to draw the diagonal bend/cut lines for the transition. Draw all the diagonal lines per joe's instructions and delete the parts of the circles you don't need.

Then add the dimensions  for the rectangular section at the bottom. From experimentation with paper cut outs I determined that you need to leave some material to connect it all together with rivets when your done bending it, unless your a good welder. These are marked on the drawings as connection tabs/leave this tab. If you use pop rivets you can get closed end rivets that are air tight.
(http://www.amazon.com/gp/product/B00137PW48/ref=oh_o00_s00_i00_details) I just used small rivets and a hammer.

Ron

Files attached Spread sheet (xls), Instructions (pdf), DoubleCat dwg (2cd), AutoCAD (dwg), AutoCAD (dxf), Pdf printout of drawing.

[Dougp28704]

Thank you Ron. I work at a machine shop. When we need sheet metal cut, we buy from a local laser cutting shop. I will have them quote this for me. I think it will be cheaper to have them cut the piece than what I could buy blank sheet for. I'll find out soon.

Thanks again for sharing your info.

Update: I was wrong about laser place. Cost is $45 for cut 22 gage. I went to lowes.

[Bulldog8]

Thanks for the drawing Ron. I'll give it a go in the next couple of weeks and add it to my system.

Steve