non sheet metal guy attempts sheet metal, help!

metalmagpie · Apr 23, 2021

I want to make a square-to-circle transition. I have studied up on the layout and generated a half-scale stretchout drawing. It is visible here:

http://nwnative.us/Grant/images/temp/chuteStretchout.pdf

I can lay this out on sheet metal. I may even be able to cut the outline. I have friends with sheet metal brakes. However, looking at all the bend lines, I am intimidated! If I managed to bend along each bend line just the right amount, the inner edges would form a 4" circle and the outer edges would form an 8.5" square.

But how to know how far to bend?

oy vey

metalmagpie

metalmaster1 · Apr 23, 2021

360 degrees divided by the number of bend lines would be a good starting point

jz79 · Apr 24, 2021

press brake won't work here, there is no support where the bend lines converge so you won't be able to make somewhat precise bend there, pan brake may reach some, but not all bends

depending on how thick the material is, if that is aluminum, you could grind a tool to scribe lines to half material depth of more, then it will bend there, weld where necessary for strength, if is steel - use angle grinder to "scribe" the lines

for angles, instead of inventing math, use cardboard cutout, scribe, fold, tape it together and use as reference for the actual piece

rons · Apr 24, 2021

I use cereal box cardboard to figure out if my layout lines and hole patterns are right.

boslab · Apr 24, 2021

Get a sheet of poster card, draw the transition, then bend using a blunt tool on the bend line and a straightedge, it will help you know where the bends are.
I must have done hundreds of different transformers in school in Engineering drawing, all on thick paper, actually it’s quite fun!, lobster back spiral bends tees, oddly all the books with this kind of stuff are old!
Have fun
Mark

Peter from Holland · Apr 24, 2021

Make it out of 2 pieces Split the drawing in half That way you have a syncronic model which will form easier and look better
The 90 dgr bends on the square will be rounded Use a hammer to tap them with a sharp corner
By tapping eighter left or right you can slightly move the corner to left or right to get a exact square
Bend them a tiny bit more as 12.5 dgr It is always easier to correct a overbend as it is to correct a underbend
I have made plenty of them Asyncronic as asyncronic can be as well

Peter

jwearing · Apr 24, 2021

Add flanges to the long edges on the square end, and bend the flanges first. It will help hold the shape. If thin gauge, you can bend the rest by hand.

Scruffy887 · Apr 24, 2021

That would best be done on a press brake with either a Rolla-V die or possibly urethane die. I have done shallow cones with a Rolla-V type die from Trumph. My parts were laser cut and had the laser etch the bend lines at the same time. Price for Rolla-V dies will make your eyes water

deltap · Apr 24, 2021

Largely a matter of experience on a hand brake. Make in 2 halves and adjust with hammer on a stake. Bends are not all the same and there is no penalty for over bending a bit. Have a picture in mind of what it should look like and eyeball as you go. 16 ga hand brake will work up to 1/8 stock for that short a bend. Making transition longer will make bends less.

eKretz · Apr 24, 2021

Peter from Holland said:
Make it out of 2 pieces Split the drawing in half That way you have a syncronic model which will form easier and look better. *SNIP* Asyncronic as asyncronic can be as well

Peter

Neither of those are words in English. (Syncronic, asyncronic).Were you going for synchronous and asynchronous maybe?

jz79 · Apr 24, 2021

symmetrical/asymmetrical more likely

Peter from Holland · Apr 24, 2021

eKretz said:
Neither of those are words in English. (Syncronic, asyncronic).Were you going for synchronous and asynchronous maybe?

Oke How good are you at Dutch

Symetrical it is
Thats my English word for this day then

Peter

eKretz · Apr 24, 2021

Peter from Holland said:
Oke How good are you at Dutch
Symetrical it is
Thats my English word for this day then

Peter

Oh no, not even going to try that, haha. My German is passable, but I think your English is better...

And ah, symmetrical crossed my mind too, forgot to add that earlier.

adh2000 · Apr 24, 2021

I like syncronic better. It’s a cool word.

Sent from my iPhone using Tapatalk

petersen · Apr 24, 2021

Your drawing would produce a rectangle, not a square.

The midpoint and joining lines are too long.

Also;

Do you want a 4" circle to inscribe or circumscribe the twelve sided polygon
that you produce ??

Peter from Holland · Apr 24, 2021

Yes Looking closer the drawing is completly wrong
If numbering the triangles clockwise from 1 to 6 starting at 1 0clock
The triangles 1-3-4-6 need to be recktangles
No 3 and 4 put together should be identical to 2 or 5 Those (2 and 5) have the right shape
If you put together 1 and 6 this should have the same dimensions and shape as 2 and 5
If you split that drawing then verticcally you have the 2 pieces needed to make the square-to-circle transition
Here is a correct example Here ech 90dgr section has 4 bends but the more you make the more accurate to round it gets
How many you need depends on size also The bigger the more bends in general

Each of the 2 piece will look like this

Peter

metalmaster1 · Apr 24, 2021

Ron Covell videos might help

Winterfalke · Apr 24, 2021

metalmaster1 said:
Ron Covell videos might help

Lol was going to post one, he did just this sort of shape.
https://youtu.be/9wR4mj3M3q0

Strostkovy · Apr 25, 2021

A press brake with regular v dies will work fine. Just stay a bit on the narrow side and orbital sand the corner area a bit. Rolla V dies are pretty sweet for stuff like this. Alternatively, if you are often doing bump bends 160 degrees each, airbend into a 155-158 degree bend for good support without bottoming tonnage.

I wouldn't even worry about material thickness until you exceed 10 gauge,

TKassoc · Apr 25, 2021

I agree with splitting the pattern in half. I would also double the number of bend lines to reduce the amount of hammering to get the round end round. What material and thickness?

I like to keep the bend around 10 to 15deg each. Under 10deg like this part small errors in bend angle start to add up fast.

Roll a ring, tack weld it onto a flat plate, and clamp that down onto your welding table. Tack the two halves together and then start tacking it onto the ring. You should be able to work your way around tacking and hammering it round.

This is a 28" to 30" transition in 14Ga CRS with a 30deg angle and a 6" offset...someone ordered the wrong replacement RotoClone...

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