Plasma Based Tube Notcher / Fishtailer

[hotponyshoes]

Hi,
I have nearly finished my cnc table (waiting for a machine torch to arrive) and, not being the waiting around sort, am starting a tube notcher.

I will be cutting tube up to 2.5"o/d and up to 3' long

I have searched but have not found much info on plasma tube notchers. I would like to build something capable of both notching tubes (like roll cages) and cutting holes into the sides of tubes (like ducting).

My first thoughts (pics to come later) are to make somthing along these lines:

A bed of about 4' long by 1' wide, the tube lies along this axis and can be rotated 360. The plasma torch sits above the bed and can be moved left/right to cut the profile.
I will see what the cut is like before I consider THC.

To turn the tube I have come up with the following: I could either mount a chuck (I have a spare 6-jaw) at one end of the bed and support the tube using and adjustable roller, or,ideally I would like to mount the chuck in the center of the bed and feed the tube through it so I could notch both ends without loosing my start position (so I could offset notches on either end exactly).

I could either move the chuck along the bed to position the tube under the torch or move the torch from one end to the other by a known distance. I could just locate the tube, mark the start position, cut one end, then turn it around to cut the other end but this means I would have to mesure the length between cuts by hand.

Anyway, first problem I have come accross is with my 6-jaw chuck. I thought this would be ideal as 6 jaws is less likley to mark the tube (I will mostly be using highly polished stainless).
The problem is it is a 6" chuck but only has a 2" through hole. I trundled off to have a look at a 10" yesterday but this also only had a 2" through hole.

Are chucks available (commonly - like second hand) that I could fit a bit of 2.5" tube through or should I be looking at another way of holding/rotating the tube?

I did toy with the idea of rotating the torch but cutting upsidedown looks like the wrong way to go!

[The Inventor]

You'll need an "A Axis" to rotate the tube cw/ccw... by rotating the tube/pipe
your torch will always be at the right height.

Why not make it a quick change type by make stubby cones that will fit
inside the end each tube/pipe?

Make the spindle of the "A" so you can either slip them on and lock them in
place with a couple of set screws... or even make it a thread on type like
you would have on a lathe.

Put 3 or 4 'L' shaped tabs around the outside of the cone with 'thumb screws'
to hold the tube on place.

I've seen some videos from Dynatorch and Torchmate (I THINK these are
the right companies!!!) that shows how it works.

You might try searching Google Videos or YouTube, as well.

[jcc3inc]

Good afternoon,

What wall thickness are you expecting to cut? Thicker walls ==more problems with fitting to the existing tube unless the cut is also bevelled.

Regards,
Jack C.

[20B3rdgen]

Torchmate has a Automatic Tube & Pipe Cutting Attachment. This ebay listing might give you some ideas.

http://cgi.ebay.com/ws/eBayISAPI.dll...1976&rd=1&rd=1

[DeviousMW]

Since you arent touching the tube with the plasma cutter.. why not something like a pair of smooth rubber tires to spin the pipe on a set of rollers. I guess if there is enough Z axis travel, a unit could be made to sit right on top of the slats you normally cut on. Could be something you pop on and off the table as needed and plug in as a 4th axis.

DeviousMW

[hotponyshoes]

I will be cutting tube up to 2.5"o/d with a thickness of up to 1/8". The fit between the pipes has to be up to tig welding. so close but not that close

As you get a slight bevel with the plasma cut I was hoping I could use this to my advantage - ie I could 'align' the bevel somehow so it would be correct to what I planed to join. mostly I will be cutting holes into the sides of tubes to put a second tube into it rather than welding a tube onto the outside of another tube so the bevel thing may not be an issue.

I have thought about the 'wheel' arrangement. I thought about putting a pair of bearings on the base of my taable at one end and a second paair (maybe on some sort of carrage on my x axis) that I could slide along to adjust for diffrent tube lengths. on the fixed bearing mount a solid rubber wheel that can be pressed against the tube and rotated with a controled motor. providing I could acuratly rotate the tube 360 I could plug this in as an extra axis.

I am thinking if i used something like this:
http://metalgeek.com/static/cope.pcgi
(it generates a line as if you had un-rolled the tube) I could set the wheel as my x axis and the left/right movment of the torch as my y and it should work ok.

From my experience of cutting tube by hand I don't think I will need THC for tube but I could come up with some way of using my table 'as is' and just flicking a switch box to change between the normal x and the rotary x.

I am still trying to come up with a way to hold the pipe, I think if I use cones at both ends they will be in the way of at least one cut. Also I would like to be able to put a cut on both ends of the pipe and be able to offest them by a known amount. To do this it would be better to leave the tube mounted so I could rotate it by a known amount before making the second cut.

I would like a chuck but I would need one with a 2.5" through hole. The rubber wheel would work providing I can make it rotate the pipe with enough accurecy.
Thanks!

[Mike@Torchmate]

We do offer a Tube Cutting attachment with our machines, that works on that same basis as The Inventor was explaining.

The problem with fitting them together with tight tolerances, is that the torch itself is always in the same position relative to the pipe, so the bevel and cut angle is always pointing toward the center of the pipe. It will be more noticeable on the thicker cuts then the thinner cuts of course, but most of our customers are MIG welding it together and not using it in places where tolerances are key.