Re: Tubing Notcher

Many thanks for your ideas, Gary.

You write: "the pivot point of the second rotary axis [ie., the axis
being used for torch cutting angle control] must be aligned and at
the same radius as the ID of the pipe being notched" This is the
part that I don't understand and should appreciate clarification.

Please clarify how you control the cutting angle using just a single
rotary movement of the torch. Surely the torch needs to be rotated
in both the planes along the length of the pipe and transverse to
the pipe axis? Did you use a clever approach to implement this
using just one rotational movement?

Are you able to send me a sketch illustrating the overall the layout
and axis movements?

Regarding the machine architecture, the question arises whether to
move the pipe or the cutting torch for particular linear and
rotational movements. With a machine such as yours which cuts large
and heavy pipes, clearly the best approach is to drive just the
torch. For my application, the tubes are smaller and lighter (tube
diameter will be a maximum of about 2in/ wall thickness 0.125in and
maximum length of tubes about 6ft). Although such tubes are still
heavy relative to the weight of the torch, I am wondering if the
hardware could be simplified by moving both the tube and the torch -
for example, rotating the pipe whilst moving the torch in the linear
axis along the length of the tube and also moving the torch to
control the cutting angle. Apart from possibly simplifying the
hardware, such an approach may improve accuracy. If only the torch
is moved, each part of the motion control hardware has to carry the
weight of the other part and errors in each axis become cumulative.

I should appreciate people's ideas for the architecture and how I
should best implement the hardware for the combination of
movements. Also, ideas for how the workpiece (tube) should be held
would be of interest.

The required linear movement is quite small - for example, for a 2
inch tube meeting another tube at 30 degrees the length of cut is
about 4 inch.

Notches are only required to be cut at the end of the tubes. A more
general solution would allow cutting notches or holes anywhere along
the length of a tube but I do not require this for my application.

Douglas

--- In CAD_CAM_EDM_DRO@yahoogroups.com, gary <garyclick1@c...> wrote:
>
> A couple of partners and I developed an in-house machine for the
company
> I work for in the mid-80's to do what you describe. We had to
produce
> large space frames fom T-1 tubing where the main members were 8"
O.D and
> the bracing members ranged from 8" down to 2" with as many as 8
members
> intersecting at a node and up to 5 members in a given plane. Wall
> thickness ranged from 1" to 1/4" and there were 15,000 or so ends
to be
> notched. The machine had one linear, two rotary axis and used an
> oxy-fuel torch to cut the pipes. The linear axis was used to move
the
> torch parallel to the axis of the pipe being notched. One rotary
axis
> was used to rotate the pipe to develop the notch and the other was
used
> to tilt the torch to maintain a constant angle Vee-Groove for
welding
> between the notched pipe and the through pipe.
>
> Programing was done using APT and the pipes were defined as
cylinders in
> space with each pipe having an ID cylinder and an OD Cylinder.
Splines
> were defined on each intersecting cylinder and the distance
calculated
> from a plane defined perpendiclular to the centerline of the
cylinder
> axis to the first intersection of the intersecting cylinder. The
> intersection lengths from the ID cylinders were used to define a
splined
> curve that if wrapped around the pipe would define the
intersection of
> the pipe I.D. to the through pipe. These numbers were used to
drive the
> linear axis and notch the end of the pipe for the pipe ID
intersection
> as the first rotary axis rotated the pipe.
>
> The intersection data from the OD splines was used to calculated
the
> instant angle formed by the end of the notched pipe to the through
pipe.
> For example for an 8" pipe intersecting and 8" pipe at 90 degrees,
the
> cut angle of the intersecting pipe is 90 at the deepest cut, 180
degrees
> at the points of the notch and varies constantly in between. The
welding
> Vee -Groove angle was input into the program and subtracted from
the
> calculated cut angle. This angle was used to program the second
rotary
> axis.
>
> The only thing else required was a manual axis mounted
perpendiculat to
> the linear axis. Since the notch is defined at the ID intersection
to
> the intersecting pipe, the pivot point of the second rotary axis
must be
> aligned and at the same radius as the ID of the pipe bing notched.
>
> This worked quite well after a short period of debugging.
>
> nitewatchman
>
> douglasr987 wrote:
>
> >I am interested in developing a tubing notcher based on CNC
plasma
> >cutting with a rotational and linear drive mechanism. Such a
> >machine would be used to prepare pipes or tubes for joining (by
> >welding) at various angles.
> >
> >There was some discussion of such a machine on this forum back in
> >2000. (Refer message number 5920 and it's thread)
> >Unfortunately, I am unable to contact Joe Vicars who started that
> >thread and was developing a similar machine which he refers to as
> >his R-theta tubing notcher. Joe's email address from this
bulletin
> >board is non-valid - does anyone know his current address?
> >
> >Since that posting back in 2000 there appears to have been no
> >further discussion on this subject. My search for "notcher"
returns
> >no relevant results.
> >
> >The sort of machine that I am talking about can be seen at
> >www.cypressweld.com/saddle.htm
> >
> >The intention is that the new machine to be developed will be
more
> >versatile and much cheaper than the available product from that
> >company!
> >
> >I should much appreciate any guidance and ideas that anybody can
> >offer. In particular, ideas for the system design and components
> >that could be used.
> >eg.,
> >Rotary and linear drive mechanisms
> >Workpiece holder (tube diameter will be a maximum of about 2in/
wall
> >thickness 0.125in and maximum length of tubes about 6ft)
> >
> >It seems that the ultimate machine should offer control of the
> >cutting angle relative to the surface of the tube to optimise the
> >fit of the tubes for subsequent welding. Also, how should I
control
> >the plasma cutting torch stop/ start, gas supply etc.?
> >
> >I have a background in electronics so developing the machine
control
> >and software for the system should not be a great difficulty
whilst
> >the mechanical aspects of the machine will be more challenging
for
> >me. Nevertheless, I should also be interested to learn details
of
> >suggested electronic control systems and software that could be
used
> >in the implementation.
> >
> >Thanks in advance,
> >
> >Douglas Reid
> >
> >
> >
> >
> >
> >
> >
> >
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