Thread: Welding pipe at 90 deg.

I wonder if some of the metal fab experts can help me.

I will be welding some 150mm pipe at right angles and I want to cut the pipe to form a neat "tee."

I intend to make two 45deg vertical cuts at the end of the pipe. I have briefly tried this allowing for pipe thickness but I obviously got my calculations slightly wrong as it nearly fit but not quite. I was practising with my drop saw but it is too small for this size pipe and I had to finish off the cut with a cutting disc in my 9" grinder. This may be where I have gone wrong.

I wondered if there is a formula for gauging the cut. With smaller pipe I can normally fudge things, but with larger section there is an awful lot of fudging. It's time I got it right first time.

I will have access to a bandsaw when I want to do the cuts for real.

Any help is appreciated.

Regards
Paul

Try this bit of software

Thanks DJ

It is nearly there but not quite. Two 45 deg cuts on either side of the pipe produce the correct shape but working out how far back on the pipe is the trick and I don' have that.

Regards
Paul

If you have a lot of them to do, I would cut and grind one to fit and then make a sheet metal template to transpose it to the next.

Robert

Hi Bushmiller,
Lets go back to the outcomes you probably want to achieve.
A neat 90 degree fitting from one pipe to the other to minimise gap and maximize your weld appearance.
What other aspects of the fitup are important to you? Is the pipe used for air or liquid transport and will the inside finish affect flows?

Smaller pipes allow one to fudge as you say.As diameters get larger things are considerably different.
The mitre cuts work OK for thin wall material but I suspect that your pipe is perhaps in the region of 6 to 10mm s wall thickness range. If this is so the wall thickness will prevent a match of the the two pipes.Material from one pipe or the other will need to be removed around the 90 degree and 180 degree areas of contact.
The best fit can be achieved by a wrap around template made by the development method. Some good cardboard sheet from the newsagents will make a wraparound template which can be aligned on marked center lines on your pipe. Normal 12 segments are used as a divisor but if better accuracy is required you can go to 24.

If the pipe is 150 Od the maths would be 150 x 3.1416 = 471 circumference and divide that by 12 or 24 to get 39.23 or 19.23 respectively.Drop the decimal places and work on whole numbers- it will still be close

A description and drawings are here

http://www.woodworkforums.com/f160/w...ural_steel.pdf EDIT - link not working checking on it _Grahame

Scroll down to p 3-20

better example below

Cheers Grahame

Try this
1) Draw two circles around the pipe 150 mm apart.
2) Drill two small holes 180º apart on one line and partially screw in two small self tappers.
3 Repeat 2) on the other circle with each screw exactly parallel to the ones on the first circle.
4) twist tie two diagonal loops of flexible wire constrained by the diagonally opposite screws on each line.
5) Scribe or mark along the wires.

BTW to mark the original circles use the same wire method but of course no screws.

Thanks for the advice. I should have given a little more information as to use. I am making up a tank stand for a head tank on the house. It is only a small tank, but I am sure I don't have to tell you that a 5000L tank weigh 5tons! So as usual I am overbuilding particularly as I have had this 150mm pipe (most of it would have been old fire mains) for fifteen years or more.

So no liquids, just lots of strength. The development drawings you have drawn up and referred me to are impressive but a little more acurate than I require. I should be able to make two 45 deg cuts and maybe a quick touch up with an angle grinder and I'm done

Just to give you a better perspective of what I am trying to achieve, I cut the end of the single cut I made and then completed the second 45 deg cut. As you can see in the pix., I didn't cut the 45 deg far enough back. It's all a bit difficult because the drop saw just ins't large enough.

The essence of my question is how far back to cut. Is there a formula based on the diameter and thickness of the pipe? I will eventually get there by trial and error, but in my normal impatient fashion I want to be there immediately.

The wall thickness is only 4mm, although some others in the pile are 6mm.

Regards
Paul

Too bloody easy!

Using pics 3 & 4 for reference

In the pipe that you cut the birdsmouth on.

PIC 3
Draw a centerline done the highest point-at the gap end
Run rule on edge to align with center line -projecting over gap until rule end contacts other pipe.Mark where rule touches

Measure dimension- I would guess about 25 to 30mm- take some off for wall thickness as pipe projected down will hit on the inside- so take at least the wall thickness ( you said 4mm) you still probably need to taper the inside with the AG- Are you sure the 9" AG is big enough

PIC 4
Measure to close up gap at top of the birdsmouth.If actual measurement is 25 , say take off 4 and measure up and cut 21.

Easy Peasy Japaneasy!


Of course we will want to see the pics of the results. EDIT pic 4 I see the back lower cut appears to be out of parallel with the front curve-or is it the angle of the pic?2nd EDIT oops i see its the other pipe.
Cheers
Grahame

Tube Coping Calculator

Thank you everybody. I have taken a little bit of knowledge from each of you. Woodwould's coping calculator was very helpful. Initially I thought it might only work for tube but it worked for pipe too (in theory).

I am about to head off to NSW for about ten days or so, but will get back into this on my return. I am instructed (by SWMBO) to be back in time for son's birthday on 1 July. Not unreasonable I hear you say, except that he's thirty! Actually the tank stand is a matter of priority as the tank (along with two more tanks) is ordered and partly paid for.

Pictures Graeme? Pictures?? Oh, allright, I will see what I can do. I'll be the one crushed under the platform as I am not quite certain how I will be lifting it into position. One 2m length is heavy, two are a grunt and the platform will have six.

Regards
Paul

I generally go for about an inch or 25mm on the flat in the centre, and trim back from that. A large angle grinder to trim the flat tapering on the inside.
It should be about 70mm back from the square edge of the pipe ie.half the diameter less the wall thickness of the pipe.
Hope this helps.
Kryn

Gentlemen

Thank you very much for your help in this project. I have started a thread to detail the process and the result. I hope it is apparant why I really needed that strong weld profile.

http://www.woodworkforums.com/f245/h...1/#post1574823

Thanks again

Regards
Paul