How do you make a tube/pipe

[Shedendman]

Sorry for the brief title,i'll try the best i can to explain what i'm on about.

ok,first off lets say you want to make a tube/pipe out of a flat bit of sheet metal,now i know theres a formula but the last time i did this was 30+ years ago at school,back then we did a seamed closeing ie you had two lap joints that you hammered together.

Eg if for a 4" dia pipe/tube you had to have a peice of metal so wide,there was a way to calculate this with the thickness of the sheet to make this(follow me so far?).

Also theres two types of joints one we did welded/solderd(unseamed) and one seamed as i explained above from what i remembered both calculations were different.

Theres more(sorry) how would one go about bending this sheet around something smaller than 4" because if we did that around a 4" pipe it wouldn't be 4" dia,anyone got any techniques on how you'd go about it.

Right i'll leave it there because its confuses me already.

Please jog this old memory of mine,as i said it was 30+ yrs ago i did this and a lot of beer has passed through these brain cells since then.

many thanks

 

[Paul.]

To find the circumference, multiply the mean diameter of the tube by Pi, (3.14159 is near enough) the mean dia is a line through the centre of the material, or the outside dia less one metal thickness.

How you bend it and make the joint will depend on the material thickness and the application, a slip roller is ideal for thin materials, with plate bending rolls used for thicker stuff,
If wrapping round a former you will need to allow for spring back, so a bit of trial and error needed, but as an example a 4" tube in 18swg (1.2mm) would probably need a 3" former.

 

[Shedendman]

Paul,thanks for your quick reply but i do get half that well to be honest just a slight bit of it.

But i want to make a cir not find one(is it vise virsa?),ok heres a flat peice of sheet of whatever how wide do i cut it to make whatever size dia of tube/pipe i'm after?

 

[Paul.]

Ok example
To make a tube 100mm outside Dia, from 3mm thick Material.
mean Dia is 97mm,
97mm x 3.14159 = 304.73mm,
So your blank size will be 304.73mm plus whatever you need to make the joint,
if a butt joint nothing, but joggles and swages will use some material, how much depends on the tooling and method, in 3mm you would butt it, but thin sheet is often overlapped or joggled, sometimes swaged.

 

[Shedendman]

GET THAT MAN A BEER RIGHT NOW

Cheers Paul,now the brain cells have kicked in

So,lets say for a 1mm thickness we come up with the following

99mm x 3.14159 = 311.01741 yes?

Also those terms joggled and swaged joints ring bells to.

Has anyone got some photos of joints like this in tube/pipe???????
Plus any methods you find best???????

cheers guys

 

[Shox Dr]

It's also worth noting of you are forming this tube in a set of slip rolls, the beginning and end will be flat, so you will end up with a a letter D instead of a O, to prevent this either cut the sheet long and trim to the dia you require, or once welded up, and ground down put it back in the rollers and smooth out the start/finish.

 

[Bsmith]

If you wish to do it by the old fractions, its the dia X 3 and a seventh.

 

[Pete.]

Dia x 22/7 is what I use as rule-of-thumb too

 

[Shox Dr]

If you wish to do it by the old fractions, its the dia X 3 and a seventh.

Dia x 22/7 is what I use as rule-of-thumb too

What's your preferred calculating machine, sliding rule or abacus

 

[Bsmith]

What's your preferred calculating machine, sliding rule or abacus

Atomic radio wave patern machine.

 

[Paul.]

3 and a 7th or 22/7 is fine for most practical purposes, it equates to 3.142, which is what we always used to accept as pi,
I have a habit of using 4 or 5 decimal places because some of the calcs i used to do in design work needed it.
the value of pi is still being researched, last time I looked it was up to 1241100000000 or so decimal places, a bit over the top for knocking up a tube though.

 

[TVT]

I don't know if it's relevant in this instance - it may be if you're joining the pipe to something else - Remember that Pipe is generally referred to by its Inside Diameter measurement, while Tube is measured by its Outside Diameter. Could lead to a couple mm mismatch on a 4 inch piece...

 

[Archie]

3 and a 7th or 22/7 is fine for most practical purposes, it equates to 3.142, which is what we always used to accept as pi,
I have a habit of using 4 or 5 decimal places because some of the calcs i used to do in design work needed it.
the value of pi is still being researched, last time I looked it was up to 1241100000000 or so decimal places, a bit over the top for knocking up a tube though.

There was an article on the BBC about it the other day. They've nailed it down to about 2.7 trillion digits so far!

 

[Paul.]

There was an article on the BBC about it the other day. They've nailed it down to about 2.7 trillion digits so far!

Crazy, some folk have too much time on their hands,
Apparently pi is an infinite decimal, its not going to help us bend that pipe up though is it.

 

[Shedendman]

Right gentelman no more maths please brain cells are on over load,
But many thanks for all your replys

Now i know someone mentioned about rollers,but when i was at school we had to bend this around solid bar with a double seamed joint,what i mean is with your flat sheet you bent over one end with a lap the other end the same but it went the other way,so when you hammered it round the bar the 2 joints met up,then you hammered both these together to make a seamed joint,follow me so far

From what i remember we used a bossing mallet to hammer it round the bar till both joints met,then sealed the joint by hammering the two laps joints together,as you can see not only did i pay any attension in maths lesson i didn't do in me english class did i.

 

[Hitch]

Start off at the edges, and work towards the centre.

Make youself a template from a bit of sheet, so you can get a guide to the radius as you start to form the sheet. Often called a 'sweep'.

The actual joint, id be inclined to weld it myself, what you describe sounds a bit like a lockform join...Cant remember much about that sort of stuff, only ever done it a few times. Perhaps one of the more 'sheet metal' types might be able to elaborate.

 

[Bsmith]

If its made of thin sheet, jubilee clips are handy as clamps for holding the edges together until welded or whatever.

 

[Paul.]

there are a few common types of sheet metal seams on this page, the name for the different joints varies a bit, for example a countersunk lap is sometimes called a joggled lap, and a single bottom seam is also known as a peened down bottom, another type of corner is the knocked up bottom, apprentices always seemed to find that funny, anyway this'll give you the general idea.

 

[Shedendman]

Sorry for not getting back to this,bloody PC went AWOL.
Thats the joints i was on about Paul esp the center one,you know i looked all over google for that didnt find it(wording wrong).
I remember doing that sort of joint and also doing what i can recall was a running solder weld(i think).
If i get time i might have a bash at one i have a load of thin sheet mind you when i say thin its 1mm thick,i'll try and keep you all informed if i do

cheers chris