Plasma cutter tracing machine.

[CNC Dan]

It appears to me that there would be a lot of looking up and down, making it easy to have the stylus slip off the pattern.

no need to look down, just need to watch the pattern/stylus.

 

[yomax4]

ESAB had or has a motrized version of this. Uses a knurled drive wheel to move along the part. Does a nice job. The down side is after a while you have a hundred cut out template parts hanging around that you need to keep. This unit is a fraction of the ESAB cost..

 

[mjncad]

no need to look down, just need to watch the pattern/stylus.

That sounds good in theory; but I know I'd be checking cut quality from time to time as I'm moving the stylus against the pattern.

 

[uhmgawa]

That sounds good in theory; but I know I'd be checking cut quality from time to time as I'm moving the stylus against the pattern.

That was sort of my initial concern. I've looked at this with some interest for quick one-off
prototping as it seems to be easy enough to implement. But had a few concerns.

Usage appears to me quite awkward given the pattern is suspended above the work piece.
This may be ok for small area coverage but I expect would grow unwieldy with larger work.
I'd prefer having the pattern situated in the same viewing location as the work relative to
the operator, resulting in more natural operation.

As stated above there is a need to assure the torch travel plane is exactly parallel to the
work piece given the rigid torch mount. This again becomes a greater issue with larger work.
In contrast the horizontal pantograph mechanisms have sufficient vertical flexibility allowing
the torch to follow even an irregular work surface which isn't possible with this mechanism.
Another usage consideration is the torch cutting point must be exactly collinear with the
torch pivot point (and ideally trace stylus point) otherwise error will be introduced as the
torch arm rotates in an arc.

Note this isn't a vertical equivalent of a conventional parallelogram/pantograph linkage, but
essentially a 2 arm, 3 point linkage. In any case the useful precision of both mechanisms
is limited by rigidity of the members in effect from pattern to torch as the mechanism itself
is transferring the x/y position. Eg, any flex in the mechanism from stylus to cutting arc will
result in positioning error of the cut. Here distortion of the frame due to rotational torque
would be the primary concern. While the stress transmitted from stylus to torch should
be minimal in this respect, vibration will deflect the frame particularly near its resonance.
I suppose damping could be added at the cost of increased mass. Horizontal mechanisms
are less of a concern in this sense depending upon degree contact with the work and/or
supporting table.

 

[Arc weld]

I believe Airco invented the Camo-graph years ago and other's including Victor also made them. They used knurled magnetic rollers on the template powered by a variable speed DC motor. Different size rollers would change the part size but they recommended cutting the template smaller so the cut part would be the right size. On a manual machine, I think it could be hard to keep a steady speed on thicker material. The stylus and the torch need to be a fair distance apart in order to have the highest accuracy.

 

[ThomasH]

That was sort of my initial concern. I've looked at this with some interest for quick one-off
prototping as it seems to be easy enough to implement. But had a few concerns.

What about using a digitizing arm, which helps you "map" out the piece so a drawing can be imported into your CAD program? Then you can edit the drawing, and send it to the CAM program, then to a conventional plasma cutter can be used on demand or the drawing sent to a cutting shop. The arms used to be really expensive, but have dropped down into a price that might be affordable on the right kind of job.

 

[Arc weld]

If you can draw the piece you want, they've had electric eye pattern cutters for 40 years or so. Nowadays everything is CNC. I think the whole thread was about an inexpensive way to accurately cut shapes. If you're going to get into digitizing arms and cad/cam drawings, etc., why not just go to a shop and have it done. Probably save money and time in the process.

 

[ThomasH]

Well, even if it isn't affordable ($30k or so) the Faro 3D arm is cool to watch:
https://www.youtube.com/watch?v=q3SVTBrKyZk

 

[jwmorris]

I have a CNC plasma and often have parts CNC water jet and laser cut; however, I built a pantograph 15 years or so ago and sure wish I had it 30 years ago.

It takes little to build them. Actually if you can't build one yourself you likely won't have much use for the parts that they make.

I built mine from scrap that I had.

There are some photos of the one I built, in post #30 here.
http://www.tractorbynet.com/forums/build-yourself/273086-show-what-tool-you-made-3.html

It is a gear reduced motor on top using a '86 RX-7 dash light dimmer for the speed control. There is a magnet inside the aluminum housing to keep it attached to a metal template and heat shrink tubing around the top for traction, all mounted in another bearing to keep a straight line from being waves.

A section of piano hinge hits the cut lever on a torch or remove the stand off's with a 9/16" wrench and drop the plasma torch into the ring with the hose clamp. I used an eyebolt an wing nut to hold a regular handheld torch, quick ad easy.

You can make a single part faster than you can draw one in a cad program and it is also much faster to set up on drop steel than using a CNC and making sure the scrap/program are in the right place to get a complete part.

The parts that it makes have an edge that rivals what comes off of CNC equipment. The parts in that post are 1" thick steel.

 

[jwmorris]

After watching the video in the OP again, the reason you want a motor drive is so you don't have to edit the video when you jerk the torch and loose your cut.

The smooth cut is made by consistant speed.