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SactoWeld
04-15-2013, 12:45 PM
Can anyone give me some info or a site that gives info on cutting straight pipe and welding it together to create a bend? Are there formulas or anything to go by? Thanks in advance

assassin_works
04-15-2013, 12:53 PM
Well depends on how many sections you want to make the bend in and degree ex . Youu want a 90° and you want to do it in 3 sections you divide 90 by 3 gives you 30° on both side of the sections

SactoWeld
04-15-2013, 01:25 PM
Thanks, that seems simple enough. How would I determine the radius of the bend? And is there a name for this particular process?

04-15-2013, 01:36 PM
The radius of the "bend" is dependant on how far you space your cuts apart.

Smallest "bend" is with the cuts being pie shaped.

Dave J.

SactoWeld
04-15-2013, 02:05 PM
I get that much but I was just wondering if there is a formula so it's not so much a guess and check method. Say 1" gap in the inner part if the radius would equal a 7" radius etc.

zipzit
04-15-2013, 04:26 PM
I get that much but I was just wondering if there is a formula so it's not so much a guess and check method.

piece of graph paper, a pencil, a protractor and a ruler? If you want to save your pencil lead, its time to learn a CAD program (Computer Assisted Design).. Try google's sketchup. Its free. should do what you want here... The pencil / paper solution is quickest if you just want to get it done.

Zip.

SactoWeld
04-15-2013, 06:04 PM
Thanks for the replies. I think the pencil and paper route is the way I'll end up going.

VPT
04-15-2013, 07:18 PM
I've only done a couple pie cut bends in my life. What I did was just cut a bunch of random (all the same but never knew size/dimensions/degrees) and just kept welding them together till I had the bend I wanted. If the bend ended up a bit more than I wanted in the end I would just cut it to what I needed after all welded up.

I soon realized pie cut bends are a waste of gas, filler, electricity, and time. I just buy pre bent 180 degree tubing now in the size I need and cut out the bends I need at the time.

MikeGyver
04-15-2013, 09:28 PM
I soon realized pie cut bends are a waste of gas, filler, electricity, and time. I just buy pre bent 180 degree tubing now in the size I need and cut out the bends I need at the time.

And compared to a mandrel bend, they look worse, flow worse, are all heat affected zone, are more prone to weld failures like pinholes/cracks, etc. Sometimes you do what you gotta do though.

SactoWeld
04-16-2013, 01:36 AM
thanks for the info, thats good to know. i was thinking it may save me some money on future projects but i guess i'll just stick to the mandrel bends

Oscar
04-30-2013, 04:48 AM
Well depends on how many sections you want to make the bend in and degree ex . Youu want a 90° and you want to do it in 3 sections you divide 90 by 3 gives you 30° on both side of the sections

This ^^^^ is incomplete as it does not take into account the width of the tube at the inside part of the bend.

The inner (shorter) part of the tube has to have some kind of width so that the tube looks like a trapezoid when you look at it perpendicular to the radius of curvature (light hitting it at 90° would cast a trapezoid shaped shadow on the ground), otherwise you'd have a heck of a time trying to weld up a wedge with a corner that vanishes into nothing.

OP this is what you'd be looking at:

Lets say we need to cover a 47° bend angle from one tube to another:

http://i169.photobucket.com/albums/u235/musico79/welding/LobsterTurn01_zpse5d0845e.jpg

Lets say we want to use 3 wedges to keep things simple. So the question(s) now become in [blue] and [red]:

http://i169.photobucket.com/albums/u235/musico79/welding/LobsterTurn02_zps3ac2f155.jpg

Lets use some numbers...

http://i169.photobucket.com/albums/u235/musico79/welding/LobsterTurn03_zps8d02326e.jpg

Ignore "Inner Radius". Not needed for this methodology.

I devised three formulas. If measuring precise cutting angles is not an option, the other method relies on simple linear measurements.

http://i169.photobucket.com/albums/u235/musico79/welding/Lobsterturn05_zpsd19a872e.jpg

Using Method A, each of the 3 "lobster tail" wedges needs to be ~3/4" long on the "outer width" (bold red line in previous picture), and the cutting blade is to be set at ~8° inward on each side (the "blue" angles in the previous picture).

http://i169.photobucket.com/albums/u235/musico79/welding/OuterWidthAngle_zps07a87c24.jpg

Or to make equivalent cuts using Method B, each of the 3 "lobster tail" wedges needs to be ~3/4" long on the "outer width" ( longer bold red line in previous picture), and the two smaller sections on the opposite side (short bold red lines in previous picture) each need to be ~1/4" long, which would leave ~1/2" in the middle.

http://i169.photobucket.com/albums/u235/musico79/welding/OuterWidthSmallLengths_zpse8659ba2.jpg

One must be careful to not choose a bend radius that is too small, or way too many pieces (nor both), because then the inner-width of the wedges becomes very very short with respect to the wall-thickness and might present yet another challenge to turning out a successful weld.

BUT, of course it's BEST to use pre-made mandrel bent tubing to simply cut out the necessary pieces. Lobster-tail'ing is more like a last resort sorta thing because it won't flow as good and all that stuff that MikeGyver mentioned.

Class dismissed. Homework due next Tuesday. :laugh:

drujinin
04-30-2013, 11:54 AM
Like High School Math, I got lost after the Teacher introduced himself at the top of this post!

Hard Times
04-30-2013, 12:00 PM
I make my own and roll them, You can do increasing tapers that form what ever you want it to. Lot of drawing time to do this though.

http://i268.photobucket.com/albums/jj39/chick_in_Indiana/100_4234_zps564b3401.jpg (http://s268.photobucket.com/user/chick_in_Indiana/media/100_4234_zps564b3401.jpg.html)

http://i268.photobucket.com/albums/jj39/chick_in_Indiana/100_4240_zpscf9647d6.jpg (http://s268.photobucket.com/user/chick_in_Indiana/media/100_4240_zpscf9647d6.jpg.html)

http://i268.photobucket.com/albums/jj39/chick_in_Indiana/100_4042_zps53e72e80.jpg (http://s268.photobucket.com/user/chick_in_Indiana/media/100_4042_zps53e72e80.jpg.html)

http://i268.photobucket.com/albums/jj39/chick_in_Indiana/underbelly014_zps085fe465.jpg (http://s268.photobucket.com/user/chick_in_Indiana/media/underbelly014_zps085fe465.jpg.html)

ezduzit
04-30-2013, 02:31 PM
Oscar--I like your illustrations. If I may make one suggestion it would be, instead of 90 degrees, angle the ends of the straight tubes such that the weld joint bisects the angle between the straight tube and the first pie-shaped section. And to evenly divide the angular change such that the 3 small sections are identical to each other, rather than asymmetrical.

Oscar
04-30-2013, 03:31 PM
to evenly divide the angular change such that the 3 small sections are identical to each other, rather than asymmetrical.

Thank you :) But please read the "note" at the top of each diagram ;). All cut pieces are identical even if the diagrams don't show it. This whole methodology begins with the requirement of using 3 identical cut sections in the first place. The ends of the tubes to be "joined" need not be modified in any way to use these 3 identical cuts in this hypothetical scenario. :drinkup:

Using Method A, each of the 3 "lobster tail" wedges needs to be....

...using Method B, each of the 3 "lobster tail" wedges needs to be...

see? :D