Water Jet Cutting

water jet cutting metal

Water Jet Cut Squares

Introduction

I used to only use thin copper laminated to 1/2″ plywood for my wall sculptures because I knew I could cut it myself with a scroll saw. At the time, my concept of an artist required me to do everything myself, which precluded my having someone else do my cutting for me. This was when I was just starting with my wall sculpture puzzle designs in 2000. I 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. This was very high-focus work, trying to keep that skinny blade inside the extra-thin sharpie line. 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 much 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.

There were other good reasons to use the copper-wood laminate approach. I achieved the beauty of metal with the lightness of wood. I edge-blacked the wood, so it looked like solid metal. The wood made it easy to change hangers and hang the wall sculptures in different orientations. But most people at art shows were expecting solid metal and couldn’t understand the laminate process. So then I started adding a metal back to the  laminates – it wasn’t solid metal, but it felt like it from the front and back. Hangers were still easy to attach and change around. But the extra metal also increased the weight of each piece and made the whole cutting process doubly difficult. So I switched to using water jet cutting.

Water Jet Cutting – A Better Way But Still Not Perfect

October 2006:  I recently had some copper-wood-copper laminates cut by Midwest Waterjet in Michigan City, Indiana. Pete Scherf takes your design and translates it into a CAD-CAM design which runs the water jet cutting machine. I used Weldwood-Dap contact cement for the laminating glue. During the water jet cutting,  about 20% of the glue came unglued, caused by the force of the water jet itself.  The high-pressure (60,000 psi) very thin water jet (.060″ wide) penetrated the copper like butter, but then hit the wood and radiated outward for a few milliseconds, enough time to cause the delamination. The bottom laminations also had problems with the glue.  I repaired the delaminated areas with 3M DP-190 epoxy and kept them tightly clamped overnight. Some of the marine plywood itself fractured, caused by the force of the water jet – also repaired with epoxy. Repairing the delaminations  took about 4 hours – about the same time as it would take to cut the pieces by hand and sand the edges. The edges of the marine plywood between the two sheets of .020 copper tended to have a convex rough surface. This took a lot of bondo or wood filler to hide and the whole process became very labor intensive.  But at least I was not cutting the pieces by hand with the scroll saw.

The pieces should have corner angles that are exactly 90 degrees. But when laid out on my pegboard table, there appeared to be some inexactitude, though better than the hand-cut pieces. Did the force of the water jet cutting cause the pieces to rotate on the table? Even one-quarter of a degree is less than square. Or is my pegboard layout table less than accurate? It only matters when I am doing large 90 degree layouts – like the designs for the Thunderbird, Stairstep, etc.

They had some problems with water jet cutting the outsides of pieces. I will have to ask them to be sure to be more careful next time. In one case, the water jet cutting 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 water jet cutting 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. Then I had to mask that mistake with epoxy 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 with the scroll saw.

Tiny pieces of garnet (alumina abrasive) are used in the water to facilitate the cutting. They cut over a large water bath filled with muddy garnet-filled water. 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.

Water Jet Cutting – what else can go wrong

March 2008:  I have started doing my layouts with CAD dxf files – Viacad 2D only $39.99! – and I have switched over to laminating copper to 1/4″ aluminum. Pete’s helper started water jet cutting in the center with a pierce cut on a copper/aluminum laminate, copper facing up. 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. I had done the gluing in the summer and the gluing was perfect this time.

Normally, 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 couldn’t find a small void in the glue to relieve the pressure and, following the path of least resistance, filled up the center of the design with high pressure water and created an upside-down copper bowl right in the center. The operator stopped the water jet cutting 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 water jet cutting 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.

Water Jet Cutting – What Instructions to Give Them

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 water jet cutting. 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 water jet 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.

Water Jet Cutting – New and Improved

water jet cutting

Waterjet Cut Circles

October 2011:  Well Pete doubled my prices and wasn’t returning my email request for a quote, so I did a search for water jet cutting services within a 30 mile radius of Harbert, Michigan. I was very surprised to find three: Wynn CNC in Stevensville, MI; Liberty Steel in Benton Harbor, MI; and RS Precision Machinery in LaPorte, Indiana. I asked all three for quotes and Rudy Schlager at RS Precision came in the least expensive.

Rudy was very friendly and professional. He has a brand new Omax with an incredibly small kerf. Pete’s machine is 15+ years old and has a kerf of about .040″. Rudy knew right away that the copper should go face-down when cutting an aluminum/copper laminate. He finished 7 designs in less than a week (Pete usually took 2-3 weeks.) The edges were cut very vertical (Pete’s were sloped) and glistened like jewels – none of the banding that I got with Pete’s machine. And no delamination at all!  I am very pleased.

You can see from the image on the right how small the kerf is. I measured it – about .015″! You can also see there is a small divot where the high pressure stream first hit the metal before piercing it. No problem – that’s the back side.

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.

If I could afford one, I would buy a water jet cutting machine myself, but a large-table Omax costs about $250,000. I expect I will have outside services do my water jet cutting for many years in the future.

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