[Normsthename]

I have been reading a few old threads about using cnc plasma to 'fishtail' tubing
I am interested in learning a bit more because I have a potential customer who at present has to have this done on a 5 axis Laser machine which costs them a fortune
I understand the basic theory but I have a few gaps in my limited knowledge
I know I can use the X motor driver on my CNC Plasma to power the A Axis motor, can this motor be programmed by angle instead of distance?

E.G
If the A Axis motor used a 5mm leadscrew, to rotate to 180° I would tell the A Axis to travel 2.5mm etc
Can you program the A Axis motor using degrees in Gcode?
It would make life much easier when I write the Gcode
I can output the developed shape in my 3D Cad program, and I am sure that I can write a program to generate the Gcode automatically from the co-ordinates of the developed shape
Next question, I have seen that these contraptions can also 'fishtail' square tube, how do they do that?
Do they just rely on the THC to lift the torch up and down when it goes over the corners??

What is the best / easiest method for holding the tube?

Thanks

Andy

[Torchhead]

It's not that hard. Consider the rotary axis as the cutting surface of the round pipe. It's in fact the circumference of the pipe. use a standard rotary table (vertical mount) and by making your drawing the same width of the circumference you can cut any shape you want. If you use MACh I have a screen and macros written that only requires you put in the steps required for your motor to turn one REV, the ratio of the rotary table (usually 45:1 or 90:1). From that point on you just click the "Calculate" button and it walk you through a quick set of single line inputs. All you have to know is the diameter of the pipe/tube. No angles, no scaling factors.

Square and rectangular is not as easy. The corners present problems for the torch and THC. It could be done but I am working on a rotary index program that cuts each side as a separate layer. That way you can cut any shape (even inside shapes)
That you want. Operator will just have to enter the Width and Height of the piece. The 90 degree index will be handled automatically..

You can download the MACH profile , screen and macro installer off the CandCNC website (manuals section). It won't work with other setups but you can play with how it works in simulation.

TOM Caudle
www.CandCNC.com

[Torchhead]

I read that first part I wrote again and realized it's not clear what i am talking about. It's basically taking a flat design and wrapping it around the circumference of the pipe. Instead of moving the torch on a flat piece you fix the Torch in X and rotate the piece under it. only trick is you have to re-calibrate the movement (surface travel in inches) for each diameter of pipe. That is what the custom rotary plasma macros do. It even calculates the width of your max drawing size for a given pipe. The smaller the diameter the more steps per inch you will need to move the surface at the right feedrate. At some point you will runout of motor RPM. If you are running steppers the macro will warn you if the steps per exceed the MAx velocity (possible loss of steps) and tell you the fastest feerate you can cut at.


TOM C

[scrambled]

Tom-

How would this work if I needed to notch a 4 inch sch 40 tube to fit a 5 or 6 inch tube at an angle such as 45 deg.

Is that question clear enough? Do you have a picture of what the cut path would look like?



Thanks


Steve

[Normsthename]

Thanks Tom

How would this work if I needed to notch a 4 inch sch 40 tube to fit a 5 or 6 inch tube at an angle such as 45 deg.

I have attached some pictures of what I think you have in mind
I would also be interested in how the macro can do this
Can the macro also cut the corresponding hole into the tube wall if required?
The way I was thinking of doing it would allow either way

Andy

[scrambled]

Andy-

That is exactly what I had in mind. I wanted to put a tubing notcher on my table, but I thought it would be to complicated to program. Looks like I was wrong---again.



Steve

[DanOSB]

i have found some site with those info.. heres one of them.. cant find others i had saved.. http://metalgeek.com/static/cope_custom.pcgi


would be awesome if someone could program this to a screenset for mach or gcode converter..

would be nice to be able to draw up the pipe layout then it can cope both ends to match the drawing and nest them then basically load up all pipes and it will cut out everything automatically inculding nesting to minimize the waste of pipe (would be nice for a hand rail job)



if someone knows that kind of software out there pls let me know

Cheers
Dan

[Normsthename]

Dan, you can download the Gcode from that site

Andy

[DanOSB]

andy i never noticed that.. pretty cool

but is there a software that can build all hand rails and then automatically nest and output gcode then i can throw in full stick of pipe and let it cut all of them then load up next pipe till the job is done then weld up everything

that would be a sweet feature

[Torchhead]

There is software for virtually anything you want to do.....all you need is enough money to buy a small country!

[WSS]

Here is a link that shows something similar to what is being discussed here:

http://military.discovery.com/videos...e-cutting.html

WSS

[Hi-Vac]

Here is a link that shows something similar to what is being discussed here:

http://military.discovery.com/videos...e-cutting.html

WSS

A Perfect Example!!!! Thanks!

[Normsthename]

Thats just how I thought it would work
The hardest thing is to work out how to hold the tube and drive it from the 'A' Axis motor.
The tube needs to be easy to load and also accurate with possibly end stops for batch runs.
Wonder if you could use a chuck off of a lathe?
I don't think writing the Gcode is difficult, I have a pretty good idea how I will go about that
I also want to be able to cut holes and shapes into the tube side wall

Andy

[WSS]

You could do a "pipe roll" kind of set-up with a pressure adjustable idler on top to keep it from skipping when accelerating. That way you could utilize endstops for repeatability. We use both rolls and lathe chucks for positioning under our weld heads. The difference is the speed! Ours crawl compared to what plasma needs.

WSS

[DanOSB]

to keep pipe in place place one of those type of pipe roller (attached image from other website for the concept..) spaced out every 4 feet or something after it cut off smaller section ti will fall and work your way toward to the lathe chuck for last cut..

this stuff i attached could easily be built from our cnc machine

[WSS]

Take a look at this:

http://cgi.ebay.com/CNC-Plasma-Pipe-...#ht_590wt_1167

WSS

[Torchhead]

Little late night project for MACH3 for a rotary axis on a plasma machine. Goes into service next week. Does not (yet) do cutting with a "Wizard" (just put in the parameters and it does the calculations for pipefitting.) but it will take G-code from flat drawings through SheetCAM and cut the shapes in round or square/rectangular tube.

[DanOSB]

torchhead that screen looks really nice..

[dgapilot]

What is the smallest diameter tube that a plasma could cope? I want to build an airplane and tubes go as small as 1/4 X .025. Most are 5/8 X .035. Could this be done on a plasma? I was thinking of building a mill to do it, but plasma may be easier.

On another note, when yoou make your wizard what would be the chance for coping a cluster with multiple tubes joining at a common point. I know it;s a lot more work, but that would be nice.

Thanks

[Torchhead]

The issue with small tube is the surface cutting speeds. I won't bore you with a lot of math but the smaller the tube is the faster you have to spin it to reach a certain surface cut rate (feedrate in IPM) We all know that the proper feedrate in plasma is critical to a good cut. Here is where the math comes in. The max RPM you can spin a rotarty table is dependant on the max RPM of the driving motor divided by the ratio of the rotary table. At 1" using a normal stepper (maX RPM aboout 800 RPM) and a 45:1 rotary table the max RPM of the rotary is about 20RPM. Now the circumference runs at PI times the diameter of the work. Spinning the rotary axis at 20 IPM yields a surface speed on 1" tube of approx 60IPM....not fast enough for thin tubing. Either we have to build a rotary axis that has a lower ratio OR find a faster motor (aka servo).

Bottom line is that with fine cut tips, a low ratio rotary axis and/or a servo as the motor you could cut small diameter tube. The software won't care but it will warn you if the IPM you have as your velocity setting in MACH is lower than the IPM you need at a given diameter. You need some ratio to get the torque you need. The nice thing about small tube is that standard lathe chucks have a through hole big enough to pass 1" or larger material.

So the answer is (in pure English). You can cut small tubing with plasma if you can spin it fast enough. A rig designed for tubing up to 3.00 dia might not work for cutting 10" pipe!

About the multitube cope: It shouldn't be too hard (he said confidently) . Doing it with three different sizes of tubes might get a little dicey........

Whatya building an Lunar Lander ? (:-)

TOM Caudle
www.CandCNC.com