Water Jet Cutting of Metal Art and Metal Artwork
Introduction
I used to cut all my copper-wood laminates by hand with a scroll saw and as thin a blade as possible. I drilled a 3/64" hole and used a #7 or smaller blade with a 22" Delta Scroll Saw. It took a long time, was arduous physical labor and was difficult to do accurately. Many. many blades broke, some of which scratched the surface patina. It required a lot of sanding afterwards, and the combination of the cutting and sanding necessitated a lot of re-gluing. I actually got very quick and good at it. But the final straw was the decision to start adding a metal back to the laminates. That increased the weight of each piece and make the whole process doubly difficult.
A Better Way - but still not perfect
I recently had some copper-wood-copper laminates cut by Midwest Waterjet in Michigan City, Indiana. Super-friendly and smart Pete Scherf takes your design and translates it into a CAD-CAM design which runs the water jet cutter.
Weldwood-Dap Contact Cement was the Glue - about 10% of the glue came unglued, in some cases caused by the force of the water jet itself, in others perhaps because of the exposure to water. Repaired with 3M DP-190.
The warped copper is attached to the wood and glue by hammering - by hand. This doesn't create as smooth a surface as would a large hydraulic press with a urethane pad.
Some of the marine plywood itself fractured, caused by the force of the water jet - 60,000 psi - repaired with gorilla glue.
The marine plywood between two sheets of .020 copper tends to have a convex rough surface. This takes a lot of bondo or wood filler to hide. Too labor intensive. Switch to 1/4" aluminum.
Flat untorched copper (not hammered) had the least amount of glue problems. That was probably because of the 100% contact between the copper and the glue and the wood. Also, that particular piece had sat around for a year with the primer curing on the back. Need to test whether the time curing of one year was more of a factor, or the flatness of the metal.
The pieces should have corner angles that are exactly 90 degrees. But when laid out on my pegboard table, there appears to be some inexactitude, though better than the hand-cut pieces. Does the force of the water jet cause the pieces to rotate on the table? Even one-quarter of a degree is less than square. Or is my pegboard table less than accurate? It only matters when I am doing large 90 degree layouts - like the Thunderbird, Stairstep, etc.
They had some problems with the outsides of pieces. I will have to ask them to be sure to be careful when cutting the outside of the pieces again. In one case, the waterjet caused a large gouge on the bottom side of a a copper/wood/copper piece (the top is okay). This happened because the copper caused the high pressure stream to bend inwards, much as your finger at the opening of a hose will cause the water to bend towards it.
In another case, they lined the piece up incorrectly and trimmed off the wrong end, leaving wood visible. Now I will have to mask that mistake with wood filler and paint.
They want to be able to clamp onto the piece on the outside. It helps to give them a piece of metal that is larger than the final design. They start their cuts in the middle - the outside pieces are cut last.
The center pieces are the smallest, so they are 'tabbed'. The tab is about 1/4" wide and is cut by hand later.
Tiny pieces of garnet are used in the water to facilitate the cutting. This splashes everywhere as a sandy water and can ruin a patina. Protect the patina with lacquer and window film prior to cutting.
After cutting - you may have to strip off the scratched-up lacquer and then reapply it. Or you may just be able to clean up the surface and respray the lacquer.
What else can go wrong - March 2008
They started in the center with a pierce cut on a copper/aluminum laminate. This metal-metal laminate was double glued with Weldwood Contact Cement and the copper had been hammered very flat. The glue had been allowed to cure for two weeks prior to the scheduled cutting.
The waterjet pierces the copper instantly, then takes about 2 seconds more for the waterjet to pierce the 1/4" aluminum, alloy 5052.
This time, instead of piercing the aluminum, the water jet found a small void in the glue and, following the path of least resistance, filled up the center of the design with high pressure water under a copper bowl. The operator stopped the process right away - perhaps one second after start-up.
Was there garnet in the water, I wondered? Pete said that if there was a divot in the metal under the copper hole, then the garnet had been omitted. I found no divot but a very tiny hole all the way through the aluminum, so yes, there had been garnet in the water.
Could the cut have been made at low pressure? Pete says that requires a changeover to a low pressure nozzle, so that wasn't the cause.
So this was bad luck. How to prevent it recurring in the future? Pete will have his cutter pre-drill a hole for the first piercing. This is the most problematic piercing, because it is in the center. All subsequent piercings will have an escape route for the high pressure water, after the first piece is cut.
What Instructions to Give Them Each Time
Draw lines on the front of the piece prior to taking it in for water jet cutting. This gives the operator a way to double check if Pete has got the right design keyed up. (Not that Pete makes mistakes, but we are all human.)
Do a dry run before the actual cut. Check to make sure that no cuts are outside the copper. No aluminum should be visible from the front after the cutting.
When the location of the first piercing is identified, predrill the hole with a 1/16" drill bit. Don't let the drill touch the patina - use a cardboard drill guard with a small viewing hole in it.
If bowling occurs, skip outside the bowled area and continue with the cutting - be sure to predrill that first piercing. The bowled area will be easier to remove and repair than trying to remove and repair the whole piece of copper.
Laser Cutting?
Laser cutting is great for steel and stainless steel, but difficult with aluminum and copper, due to their high heat absorption factors. I was told by one laser cutting company that any type of copper or copper alloy reflected electrons back up into the lens, destroying the lens.
Also, the heat of the process could possible damage a copper patina or warp aluminum.
However, further developments in this process might make it feasible in the future.
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