pipe miter

[ieezitin]

Hi guys.

I need to make a handrail so I need to miter the pipe to make the joints, in the attachment is a hand sketched Iso it shows my runs, angles of rise and angle of turn.

What is the formula to making a swing joint off set miter joint. I really want to make a template out of card so I can wrap around the pipe and trace the line to make the cut on the pipe.

Or is there a simple program I could use to get the same effect.


I than you in advance.         Anthony.

[Gadget]

Try this, I've got other links if this doesn't meet your needs.

http://www.metalgeek.com/static/cope.pcgi

[Bernd]

Just off the top of my head I'd say two 18º angles. How did I get there. Well 180º minus 144º divided by 2 = 18º.

Ya I know I'm wrong? Right? 

Bernd

P.S. Try it withsome cardboard first before you cut the pipe. 

[ieezitin]

Berned.
Your math is correct for a level miter, but I have a rise and angle projection together. I called that a swing joint( maybe wrong here).

In essence  my y value from left to right on the sketch is 71.58* rise from level heading to z,  my run is 64.875 then I hit my miter joint,  then at the joint I  rise 69.35* in z travel while 144* away from x value.

Yep before I cut the pipe I certainly will slice into card. This is a brain teezer, believe me I was at my welding table for an hour tonight fiddling with pipe and propping up silly stands trying to get a visual on this.

thanks

Anthony.

[HS93]

Simple way to do it, I served my time as a joiner so had to do a lot of jobs like this in my time, we simply drew it out on plywood,then used the same bit of plywood to make a mitre box, using this methoud you can have two different sized tubes and still get the correct angle.
this is just an alternative way to do it and just posted so you can have alternative fall back, if you have one of these cheap power miter saws with a metal blade in use the piece of ply as a temlet to set the saw.

Oh and when you draw it out devide by 2 or  4  the two lenght's  but not the pipe size to make it managable to draw
Peter

[Bernd]

I don't think the rise angle will have anything to do with the angle you need to cut the pipe to give you the 144º bend.

Tin on HMEM confirmed what I said here. I think your making this more complicated than it needs to be.

I would use two pieces of wood and cut them as Peter suggests and see if that's what you want. Make the two pieces of wood the width of the pipes dia.

Bernd

[ieezitin]

Gentlemen



This is a rolling off set, the miter has to do two functions swing an angle (off set) then roll up at an angle.

Allot of people have answered my question I thank them but all the answers I am getting is just for a general miter.

My first sketch has the wrong angles I have amended this with another sketch. All so read the drawing as an Isometric three dimensional.

I did not mean to complicate it its my fault for a bad drawing.

Berned I think your right I maybe making this too complicated, I have read a lot of peoples answers and gone into the shop and tried it just don’t seem to work, where I offer the two pipes in the air at the given  elevation changes  and the angled off set I see the joint of being a mixture of both angle change and elevation in the angle from one pipe to the other.

I think this is one of the hardest times I have had to put into words a complicated math problem.

Hopefully this next sketch helps.

Thanks to all again.   Anthony.

[ieezitin]

This is the best drawing yet on my problem

Compound Miter is the term that eluded me.

Anthony.

[Bernd]

Now that last drawing made it perfectly clear. You are going up and then around a corner. And yes that will be a complicated bit to figure out on paper.

If I were going to do that I would actually try to use the pipe mount it to the side of what ever you are going to mount that pipe on and have at it with a saw were they meet. If possible that is.

And this is were I drop out of sight with this problem. 

Good luck. I'm sure you'll let us know how it turned out.

I would have though Marv would chime in on this math problem.        

Bernd

[dsquire]

ieezitin

I think (and that is sometimes a bad thing) that we are taking a simple problem and making it complicated. The math has escaped me at present. When these 2 pipes are mitered and welded it will be the same as 1 long pipe with a bend of X degrees somewhere close to the center. Now if we take that pipe and lay it on the floor with nothing supporting it, it will lay flat on the floor. In that position you can see that there is only 1 angle involved. Divide that angle by 2 to get your cutting angle.

This is easy to do after the fact. Now we see how it can be worked out mathematically or making a mock-up. Take 2 pieces of something of proper length and make a mock-up the way it will be installed then measure the angle formed, divide by 2 and cut the same angle on both pieces and they should line up as perfect as what you measured.

Hopefully this will help rather than confuse.

Cheers 

Don

[Gerhard Olivier]

Hi ieezitin

Don is right here as it is round pipe there is only the angle between the two pieces that is important - it would only be a compound miter where there is a difined top ( as in a stair railing that is square or profiled) but as yours is round pipe anywhere on the circ of the pipe can be the top.  Hope this helps.

Gerhard

[mklotz]

I would have though (sic) Marv would chime in on this math problem.

No point.  The OP has already calculated the angle between the two pipes somehow.  Since two lines define a plane, that's all there really is to know.

I don't think anyone here really wants a mathematical solution but I'll outline the technique anyway.

Each pipe can be considered a vector.  Then calculating the dot product between the two vectors will yield the angle between them.

Define an xyz coordinate system with its origin at the point labeled "start point" in the diagram.

Determine the coordinates of the end of the first pipe, which is the point of intersection, and label them x1, y1 and z1.

Using the same coordinate system, determine the coordinates of the end of the second pipe and label them x2, y2, z2.

Define L1 to be the length of pipe #1

L1 = sqrt (x1^2 + y1^2 + z1^2)

Define L2 to be the length of pipe #2

L2 = sqrt ( (x2-x1)^2 + (y2-y1)^2 + (z2-z1)^2 )

Then:

cos(phi) = [-x1*(x2-x1)-y1*(y2-y1)-z1*(z2-z1)] / [L1*L2]

where phi is the angle between the two pipes.

[Bernd]

I would have though (sic) Marv would chime in on this math problem.

Ya I know. I have a spelling problem at times.

I'm now sorry I asked. 

Bernd

[ieezitin]

Marv.

Thanks for the solution. And a good reference for people.

 Your right! You knew I did my math as I already had the length and angle.

Don. Gerhard.

My original question was “   What is the formula to making a swing joint off set miter joint. I really want to make a template out of card so I can wrap around the pipe and trace the line to make the cut on the pipe.”

I used the term (swing joint) (offset) this confused a lot of people, and then through discussion the term (compound miter) came into play which is the correct term.

I admit I was confusing, I have a tendency be like that just ask my wife!  HS93(peter) showed me a little trick and this was offered by a few people in various forms but all much the same and it works sufficiently to get a joint weld able.

I also was over thinking this problem.

I would like to thank everyone for there efforts in trying to help me, a lesson I have learned here is im nearly 50 now and I need to stop being so stubborn.

Do I hear something about dogs and tricks?   

Anthony

[dsquire]

Anthony

I'm glad that you have the results that you were looking for. I am sure that a few people learned something from this exercise, I know that I did. Sometimes I can complicate a simple problem just by thinking about it too much so you have to stand back and look at the bigger picture. 

Cheers 

Don