Thread: sheet metal development, square to rectangle offset.

Im having a bit of trouble working out how to layout this sheet metal duct, i know how to layout square to rounds but i cant work out a square to square offset. The program im using can give me all the measurements i require however i still would like to know how to lay it out without the need of a computer.

If you go to Conversions and Calculations at the bottom of the Metal Work Forum, then click on Printable Hub, Spoke and Spindle Templates - Metric. There is a large range of templates for various patterns, I couldn't see one for what you wanted, but if you click on Home then Contact Us, he/they may be able to come up with a program to do what you'd like.
Kryn

I can work all this shape out using maths but what I advise folks who have limited maths skills to do is first make up a cardboard mock up consisting on individual sides.

This shape is relatively easy because it has a right angle side.
Start by marking and cutting out, and joining (I usually use sticky tape) up the two sides that have right angles

Then mark cut out and pieces that cover the two openings - attach these the two sides already joined together - this is necessary to provide reference points for the following step

Then place the half complete model on its side onto pieces of cardboard and mark out the shapes of the other two sides.

Make sure it all goes together neatly and mark all the joins on each side A - A, B-B etc.

Then take it apart (discard the panels used for the openings) and select the panel you wish to make the join in and cut that along the line of the join.

Lay and stick all the necessary pieces down in sequence (follow the A-A B-B etc) onto metal and trace around the shapes

Sometimes its easier to make up a half size model and double the sizes.

I got this idea from my BIL who puts Al boats together. He makes up some of the most amazing shapes including curved pieces using this process.
Having a full cardboard model is very useful because you can test it to really see if it fits before you apply the snips to the metal.

Seems you guys are missing my question, maybe ive explained it wrong.
I have a good understanding id true lengths as well as being able to layout square to rounds with no lissues. I have the program, as show, that can give me everything i need to know and i wouldnt need to ask questions.
However my question is. If i didnt have a computer, how do i find the true lengths.

I do plan on laying out on some cardboard first then transfering to sheet.

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Ive just noticed but ive the screenshot has cutout the too view of the peice. Will reupload once i get home. But basicly its a flat on top and flat on side peice.

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I Assume you know A, B, D and L?

If so the most complicated maths needed is Pythagorus's right angle triangle rule.
This will allow you to work out the the lengths of the red and blue diagonals.
No need to calculate the dashed diagonal (X).
Just make up the model this far so you could then either measure X.
Or lay the model on a side including X and mark out that side directly onto the cardboard
Flip to other side and mark that out.
ETC
Screen Shot 2017-11-10 at 9.08.59 am.png

I'm not a sheet metal worker, the way that I'd approach it is that you would have to have 4 known dimensions, the base, top, height, and in your case, offset. Having those, I'd draw it up either in scale or full size, which would then give you your true lengths. I believe that this is how tradesmen of old would have done it.
Kryn

I dont really understand the problem.
Plan length over vertical height. Same as the square to round, just a lot less points to plot.

Originally Posted by Stustoys

I dont really understand the problem.
Plan length over vertical height. Same as the square to round, just a lot less points to plot.

Its really bugging me because i know its very simple to do, i just cant work it out. maybe its the offset that's throwing me out.

i know the top view needs to be drawn out, but which side view would need to be drawn as well?

The 5 panel shape on that diagram looks dead right to me.
Try printing it out on a piece of paper, cut out the shape and fold it at the joins and then join 0-0 to 8-8

Originally Posted by BobL

The 5 panel shape on that diagram looks dead right to me.
Try printing it out on a piece of paper, cut out the shape and fold it at the joins and then join 0-0 to 8-8

Yes i know its right. I just want to know how do i layout the patern without my software.

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I remember spending several days going through this, doing lobster backs, transitions and all sorts. 'Mechanically' laying out a pattern is all done with triangles - without getting into all sorts of detail, measuring/ drawing up things into triangles is how it is done.
Take the length of the mating duct and then measure from the two corners to each of the corners of the opposite duct (and the length of that duct side too). This will lock in the shape of the panels and hence the duct.
(Don't make me draw a sketch!!)

Michael

Originally Posted by brendanh

Yes i know its right. I just want to know how do i layout the patern without my software.

Make the model, removed the rectangle and square ends, slit it along one edge and lay it out on the sheet metal.

Ok this will be a little tricky as i dont like the way your software numbers. It would be easier to understand if the top and bottom had different numbers. But here goes.
The only line you dont know the tl of is 1-1.(well once you draw the side elevation)
Project the short 1-3 line to the right.
From where this intersects the long 1-7 line, mark out the length of line 1-1 from the plan view (7-7 is the same)
From the end of this line measure to the "other" 1 ( not the 1 you projected the line from)
This should be the tl of 1-1

Did that make any sense at all?

Originally Posted by Michael G

I remember spending several days going through this, doing lobster backs, transitions and all sorts. 'Mechanically' laying out a pattern is all done with triangles - without getting into all sorts of detail, measuring/ drawing up things into triangles is how it is done.
Take the length of the mating duct and then measure from the two corners to each of the corners of the opposite duct (and the length of that duct side too). This will lock in the shape of the panels and hence the duct.
(Don't make me draw a sketch!!)

Michael

Sketch please

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