Design help needed

lumberjocks are awesome. Just sayin’. :)

I thought the largest diameter was 14”

The largest diameter would be around 14”, the smaller 8” and about 4” wide.

-- Dan, Sterling Alaska, Before you criticise some one, walk a mile in their shoes...then you will be a mile away and you have their shoes!

Thats better!

I got an inside radius of 6 43/64 and an outside radius of 11 43/64 if the unfold worked right.

-- Dan, Sterling Alaska, Before you criticise some one, walk a mile in their shoes...then you will be a mile away and you have their shoes!

http://thesheetmetalshop.com/pdf_manual/WilliamNeubecker/William_Neubecker_7.pdf

the piece you describe is called a concentric reducer in the sheetmetal trade.
Look at figure 589 on page 6….

Draw centerline then make two marks at points D and C thatll be your 4” length.
then draw a 90deg lines to the right representing the radius’ of both ends of your reducer(points D to E being 4” and C to F being 7”).
Next use a straight edge across points E and F and let it intersect the centerline and scribe a line to create point H.
Set a divider on points H and E and scribe a 360 deg circle then set divider on points H and F and scribe circle.
multiply smaller diameter times pi to get circumference (25-1/8).
Set divider to 1 inch and count out circumference in 1 inch (set divider to fraction at end) increments starting at point H and going counterclockwise on arc/circle.
scribe straight line from point H to end of smaller arc and through larger diameter arc. larger diameter’s circumference will work itself out.
youll end up with a patttern that looks like the one DaveR posted with points E and F on the right side and points M and L on the left.
Cut it out and roll across you thigh till the ends meet. I do this for a living and could explain better by showing you so sorry to confuse if this doesnt make sense. The pattern to make a cone is similar.
Hope this helps

-- Woodworkers theory of relativity - the quality of your scrap is relative to your skill level

Thanks everyone for your help. I got the template made, now I am going to cut the metal. Thanks again.

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