cut pipes to weld a "T"

Larry Jaques scribed in :

the 'OP' wants to join 2 bits of 6 inch pipe

if that makes a tool handle, I'll be jiggered

swarf, steam and wind

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On 06 Nov 2003 02:01:37 GMT, snipped-for-privacy@aol.com (JMartin957) brought forth from the murky depths:

Take 1" (example) pipe, cut in half. Hold end to paper, draw 1" circle. Fold paper in half at circle. Cut out 1" x 1/2" semicircular arc. Fold paper around end of one pipe. Draw arc. Rotate pipe 180 degrees, draw arc. Cut out arcs. Grind to fit pipe. (requires no math ;) Weld together.

What won't work?

-- Friends Don't Let Friends Eat Turkey and Drive --

On Thu, 6 Nov 2003 14:50:44 +0000 (UTC), DejaVU brought forth from the murky depths:

Oops. I must have combined two messages. Mea culpa.

(Note to Jim: Now I clearly see why you wanted to use pipefitting techniques or whatever.)

-- Friends Don't Let Friends Eat Turkey and Drive --

I guess you didn't try it, did you? Because if you did, you'd know exactly why it won't work.

You are talking about using the pattern to cut the point on the end of a piece of pipe, rather than a vee in the middle, but no matter because it's the same thing.

Given your example, the two ends of the arc on your pattern are exactly 1" apart. On the piece of pipe you want to cut, the two points or the bottoms of the vees will be 1" apart, as that is the diameter of the pipe. But, when you wrap your pattern around the pipe, the ends of the arcs won't make it halfway around the pipe - because halfway around the pipe is really 1.57", or pi over

1. Because the paper has to wrap around the surface of the pipe, doesn't it?

And not only will your pattern not stretch halfway around the pipe, as it should, but when you trace it you'll find that the ends of your arcs meet the square end of the pipe at an angle (tangent) of 90 degrees. Not at 45 degrees as they should.

The poster who suggested using a rubber ring as a pattern will get the same cut you do, although with the flex and stretch of the ring he'll get closer.

John Martin

On 06 Nov 2003 22:25:59 GMT, snipped-for-privacy@aol.com (JMartin957) brought forth from the murky depths:

No, I didn't.

Um, to me, ARC and VEE sound pretty similar. I was talking about cutting the relief in the pipe.

OK, you got me with the actual size, but I said to hold the end of the pipe to the paper and draw the circle.

With a 1" pipe, yes. Not even close with a 6-incher.

See above re: stretchmarks. As to the angle, why would a cut which was radiused to the OD of the pipe -not- fit? The ends of the arc would be to the outside of the pipe, not the inside, so there would be no 90° step. I'll give you the fact that I didn't address the proper fit for a certified weld, but I'm a certifiable jury rigger. So sue me. ;)

-- Friends Don't Let Friends Eat Turkey and Drive --

Larry:

I've seen other posts from you here, and you seem like a decent guy. I really haven't had any intention to insult or demean you.

What you wrote here, however, was simply wrong. I tried to point out to you in a couple of ways exactly why it was wrong. I suggested at least twice that you actually try what you had recommended. Nothing more complicated than tracing the end of a pipe (or even a can) on a piece of paper, cutting along the line, and wrapping it around the pipe to see the pattern. You couldn't be bothered.

I tried going through your latest reply, but it's just gibberish. "See above re: stretchmarks." What above, what stretchmarks? "a cut which was radiused to the OD of the pipe". Whatever that means. "The ends of the arc would be to the outside of the pipe, not the inside, so there would be no 90° step." Simply can't follow you there, either.

Obtaining the proper fit for a certified weld has nothing to do with this, as the method you proposed won't even come close. But, since ou couldn't be bothered to even try it, I guess you'll never know.

Over, and out.

John Martin

What won't work is trying to stretch a diameter around half a circumference. In other words, the part you need to mark and cut is 1.57 times longer than the template you're wrapping around it.

Now if you were to leave your template *flat*, and project lines down from it to the circumference of the pipe you want to mark, it will describe the correct curve you need to cut in the pipe.

Gary

On 08 Nov 2003 05:11:34 GMT, snipped-for-privacy@aol.com (JMartin957) brought forth from the murky depths:

Ah, the light dawns. I just tried to visualize doing that and see exactly what you meant. When wrapping the paper around the pipe it gets narrower (from a 2-D standpoint) due to the wrap. I was thinking in 2-D and trying to work in 3-D.

You're absolutely right. I sit corrected. (too lazy to stand.)

I was thinking 1" pipe when the OP had 6" in mind. The paper would have stretchmarks trying to fit the 6. (Eez joke, mon.)

Ditto. And thanks for following through and helping me to see my error.

-- Friends Don't Let Friends Eat Turkey and Drive --

On Sat, 08 Nov 2003 02:21:57 -0500, Gary Coffman brought forth from the murky depths:

I picked up on that this morning when replying to John. Thanks.

-- Friends Don't Let Friends Eat Turkey and Drive --

And I assume that you didn't try the ring gasket wrap method because if you did, you would have seen that it does indeed work! I do it all the time. Don't need no formulas or pi or calculators. Turn off your calculator, get off your ass and go out in your shop and try it.

Geez, the guy asked for help laying out a piece of pipe not a lesson in math. Hell, if we all understood how to mathmatically design a template for this stuff we wouldn't ask for help.

Instead of telling everybody else how wrong they are and why according to your calculator, their idea stinks, why don't you whip up a template for the guy so he can get his pipe cut because all the rest of us don't know what we're talking about.

I'm gonna go cut some pipe.

James

You're welcome. It should be obvious that what you really have to do to project a 2D figure onto a 3D surface. What may not be so obvious is that wrapping the 2D figure around it won't do that, because the projected figure on the pipe surface is an ellipse, not a circle.

The easiest way to generate the correct figure is to hold the 2D template *flat* above the pipe, and drop perpendiculars down to the pipe surface to form the required curve. (A stiff template and a long marking pen will do for the precision needed for welded joints.)

BTW, the flat projection method will also correctly describe the elliptical mating hole you need to cut in the other pipe.

Gary

On Sat, 08 Nov 2003 19:13:39 -0500, Gary Coffman wrote something ......and in reply I say!:

Just mumbling....Place a highly directional light directly above the work, then trace the shadow? Saves the steady hand requirement.

****************************************************************************************** Until I do the other one,this one means nothing Nick White --- HEAD:Hertz Music

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The light source would have to be at virtual infinity (sunlight would work). Otherwise you'd get geometric distortion of the shadow.

Ray trace on a piece of paper and you'll see why.

Gary

On Sun, 09 Nov 2003 19:25:10 -0500, Gary Coffman wrote something ......and in reply I say!:

*highly directional* as in spot, would, as we have all seemed to agree, be enough for non-mil-spec non-HP welds IMO. I reckon it would give as good as using a marker pen, unless you jigged the pen.

But yes, the sun would be good. You would of course have to allow for the movement of the sun in the sky between drawing one side of the pipe and the other. .......

****************************************************************************************** Until I do the other one,this one means nothing Nick White --- HEAD:Hertz Music

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While that is theoretically true, I doubt that the error induced from a light source a few feet away would matter for a welded joint. Just use a short piece of offcut from the pipe for producing the shadow.

Ted

I think one could use a laser pointer. Set the pointer on the inside of the perpendicular pipe and draw the outline on the other pipe. Then do the same with the laser pointer moved around the outside. The proper cut should be between these two outlines. Cheat a bit to the large size and cut.

One more time. I've watched this done hundreds of times in commercial shipyards. A new piece of soapstone is flat, and about 6" long. If you sharpen one end, and then lay the soapstone (available at any welding supply store) on the pipe so it projects over the gap onto the target pipe, then you can move the soapstone around the pipe and scribe the line of intersection. Cut this line with a torch and clean up a little with a grinder, then slide the other pipe into the cut and scribe it off the edge of the cut. Then take the other pipe back out and cut to the scribe line and clean it up with a grinder. Then fit up and weld. This process is called "scribing in" and is used in many ways in shipbuilding. You can cut the pipes in either order.

The scribing only takes a few seconds. No need for a precision light source!

Grant Erwin