Thread: 4th Axis for pipe cutting?

1. 4th Axis for pipe cutting?

I'd like to fab a set of rollers , similar to torchmates, to rotate pipe, while the plasma copes, or cuts angles. The engineering is simple, but how do I control the revs, verses the x axis movement? I use autocad/sheetcam/mach2. Unrolled, a coped, or angled piece of pipe would resemble a spline, or polyline.
How do I come up with the g-code for that?
A polyline in autocad in 2d ? Two intersecting cylinders in 3d , then delete one to get the cut?
kind of new at this, so any help would be apreciated!

2. A section through the cut is an ellipse. Here's something that might work. First, figure out the height of the angle. on a 2" tube, a 45° cut would be 2" high. (low point to high point) Draw an ellipse with the height as the X value, and make the Y value 180. (180°). Erase half of the ellipse (left or right half), copy flip and paste as shown. It should now be 360 tall, for 360°. The X should be the distance traveled. Save as R12 .dxf, and the ellipses will be converted to polylines automatically. Create gcode, and swap the Y with the 4th axis A? C? Because it's so tall, the resolution may not be good enough. The picture is not to scale, it will probably be much taller.

You may also be able to do this with an Excel spreadsheet.

3. First off you only need the circumference of the drive wheel to program your x axis. An inch is an inch, only on the pipe it's round, not flat. I saw this link here a while back for tube coping, I haven't used it yet, so let us know how it works.

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

4. Originally Posted by DSL PWR
I saw this link here a while back for tube coping, I haven't used it yet, so let us know how it works.

http://www.metalgeek.com/static/cope.pcgi
Looks like it just gives you a pattern to print.

5. You should be able to import the image into your cad program and scale it to the proper dimension.

Right???

6. Originally Posted by DSL PWR
You should be able to import the image into your cad program and scale it to the proper dimension.

Right???
Could you do it accurately enough? And again, how do you get the 2D template into 4th axis + X g-code? Also, it seems like it possibly adds notches for tubing maybe? I changed the settings, and got a quite different looking template than the original one on the page.

7. Hey BigBlock,
I'd imagine you are making race car chassis but can you tell us a bit more the process you are hoping to create? Are you hoping to use this for (A) one off work where each joint is treated separately? i.e. do your bends then cut the tube to length where it intersects with the other tube, measure you angle, make a reference mark (for zero degrees) then cope the ends by cnc? Or are you hoping to use this for (B) true mass production type work where you design the whole structure in 3D CAD (maybe even using one of the true 3D tube/pipe design programs) then you make whatever number of units you need of the same part? I.e. where you load a length of tube into the machine and the rollers notch (cope) one end then automatically advance tube the appropriate distance and cope the other end but keeping the correct reference angle to the first cope so that tube is then loaded directly into mandrel tube bender. The reason for my question is that depending on what you are aiming for it will probably affect what process you choose here as per your question. Even though I'm a cnc "aficionado" I can't help thinking that if your's is the first case, a manual tube notching machine is the best way to go. For those that don't know what that is, it's basically a machine that has the equivalent to a hole saw (whose O.D. = tube I.D.) without the centre drill, tube is firmly fixed in machine and intersection angle adjusted and piece is cut. Certainly if your's is the second case (i. e. going into mass production) the design and programming time is considerable but this is far outweighed by the repeatability and accuracy gains.

Getting back to the main question here. If I were my project and I needed it for (A) but was determined to use cnc, I would use the coping program above to get all the standard angles and tube sizes you use, then import and scale them in AutoCAD, then take all your measurements (movement in X axis direction and rotation in degrees) because the drawing as it is, is only good for cutting a shape from a flat piece of metal and rolling it up to be a notched tube. Also, for those that didn't realise the importance of the stating the wall thickness of the tube, it's because it's the I.D. of the notched tube that intersects with the O.D. of the untouched tube that determines the elipse created. You then input this data into an Excel spreadsheet so that you have each angle and tube size entered. From there, if you have already input the specs of say 2" tube at 30deg. and also 45deg., Excel can easily output (calculate) a notch of say 34deg. or whatever angle you want. Once you have this part done, getting the g-code done will be a simple matter.
The mass production route via a complete 3D structure design in CAD to directly cutting full lengths of tube would be out of my league but in my case I would probably still use much the same route but manually program the X axis distance and angle change from one notch to the next. In the case of mass production it wouldn't matter if you wasted a few pieces trying to get the correct distance/angle references between notches.

Anyway, this is an interesting project that I will be following closely. Good luck with it.
Skippy

8. Intended application

Thanks guys, for helping out! Sorry, I guess my handle is misleading. I own a Marine Fab/Machine shop, and am getting into the cnc thing for production work, the pipe deal is for one off work. I do alot of handrailing, hydraulics ie: 1" - 2" material, but also do a considerable amount of exhaust work ie: 4" - 12" pipe.
It is very difficult to hand cut bend segments in 6" and up , when the stuff wont fit the saw! I thought the cnc might save alot of hassle.
Program one working for a cope, a few for angles, then scale to fit may different sizes.
I am a ways from implementing this but have it in mind to do, cnc is supposed to make life easier, right?
I understand the roller circ. verses pipe circ., but they are interdependent . the speed of rotataion is not only the y axis , but also feedrate, right? could get tricky.
I will play with it, but might waste alot of pipe, hair & patience! Thanks for all the ideas, I'll try them!

9. This program gives the pattern height, so you only need to make sure the imported drawing is the same height as the pattern. Get the 4th axis idea out of your head. You will be unhooking the gantry axis and putting that imput into your new rotary axis. Thus you still have a 2 or 3 (I'll count thc as the 3rd) axis.

Lets assume you have a drive wheel that is 3" in circumference, and is a direct drive off of a stepper 1:1. Say the pipe has a circumference of 6". The drive wheel needs to turn 2 times to rotate the pipe... easy to picture. The pipe is 6" around, so the machine thinks with 2 rotations of the drive wheel you've moved 6" but you've only turned the pipe one rotation.

The only way you would need to get as complicated as skippy suggested is if you had a lathe chuck for the pipe and you spun the pipe from the center, instead of the edge. This would be a true 4th axis, requiring you to figure every thing out in deg.

10. For the hand rails/hydraulics forget cnc as you won't beat a manual notching machine in terms of time. (Sorry I'd never heard the word cope until now. Presumably we are talking about the same thing?) Go to a race car fabricating shop to see how they work.

Re the 4" - 12" pipe that's a different matter. A 5% error can't be seen in a 1"pipe but a 5% error in a 12" pipe is a disaster.
It is very difficult to hand cut bend segments in 6" and up , when the stuff wont fit the saw! I thought the cnc might save alot of hassle.
My only concern is that I'd imagine that apart from using straight pipe you also buy/use bends. In my case I tended to use more bends than straight pipe. Trying to set this up in a machine for coping in a one-off situation might prove difficult or unfeasible timewise.

I understand the roller circ. verses pipe circ., but they are interdependent . the speed of rotataion is not only the y axis , but also feedrate, right?
Turning all this to g-code is no big deal but first do your homework to see if the whole concept is feasible in your case.
Please keep us up to date with it all.

11. You're X axis will use a series of G1 moves, of varying lengths. It's not so simple to just say rotate 720° during the X moves. Each seperate X move will require a different amount of rotation.

12. I still think my way might work, btw, and it's pretty simple.

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