Troubleshooting "Banana Cut" Problems with Melamine

Humidity issues cause some panels to curve or bow when cut. Here, CNC operators discuss possible solutions. December 6, 2006

We recently started a new line of frameless cabinets using melamine. We use a beam saw to cut parts and a CNC machining center to machine the ends. We have problems cutting the melamine on the beam saw. Seems there is stress in the melamine that is caused by humidity. When we cut, say, a 24" rip, there is a 1/8" bow in the cut due to this stress. This causes parts to be out of square and not line up in the finished cabinet. We have to cut, then trim cut, each piece to get good square parts. This doesn't work with our optimizing software, so we have to manually enter and cut these pieces, which kills our efficiency.

Should we cut the blanks bigger on the beam saw and trim the pieces on the machining center? That will require some software modification on the parts ordering and a different way of edgebanding (after, rather than before, machining), plus all new programs for the MC. We didn't figure these headaches into the bottom line and the schedule to maintain our other line of custom cabinetry. I know a nested base router would solve our problems, but we are not sure of the volume of sales and don't have a good footprint on the floor for one. Any suggestions on how to streamline this line?

Forum Responses
(CNC Forum)
From contributor T:
What software are you using?

From the original questioner:
We optimize with Cut-Planner on our Schelling beam saw and program our Busellato Jet 4000XL with Genisis 2.0

From contributor T:
Are you using any design software? If not, how do you create the cut list that is fed into cut planner?

From contributor A:
I used to see this years ago when I was in the Florida market. Our sheet good supplier described the problem this way. The faces of the panel are nearly impervious to moisture. The edges are effectively open pored sponges that take on or give off moisture as soon as the panels are subjected to humidity conditions different from the plant where the panels are made. Panel edges are prone to taking on moisture due to high humidity or losing moisture due to evaporation (think about a load of panels driving down the highway at 60 mph for a 2 hour trip!). Both will cause the bowing problem you described. Our solution at the time was to buy only full units that had some sort of protective wrapping on the outside. Also, we cut the material from the center outward, trying to leaves the edges as falloff.

From contributor K:
If you want true parts, you will have to cut them bigger. .250" works good and doesn't seem to hurt yields too often. Also, you should be able to offset all of you programs in the x and y. We have 10 CNCs - 3 kinds and 3 cam packages - and I could fix them at the machine or in the software, but I don't know Busellato. Your PS programs could be fixed quickly if you have product planner with cut planner.

From the original questioner:
We don't use any name brand software to list our parts. We've developed our own software for listing parts and creating a bill of materials based on model cabinets and a team of tech service people to interact with the dealer and enter the information into our network. Cut lists are downloaded from the network to the optimizing computer at the saw. Changing the sizes for the cutlists is easy; getting cut planner to automatically trim, cut, rotate the piece, then trim again is the hard part.

To give you an idea of the scale of things, we are doing about 800 units of custom cabinetry a week and opened the frameless line to our dealers to allow about 50 units a week to start. If the frameless takes off, then I'm sure we would get the nested base router and make room for it, but for now, we're cutting our teeth the hard way and getting a toothache.

From contributor M:
Why can't you allow for the trim in the Cut Planner software? If you want to cut each part 1/4" oversize, then allow for that in part width and part length adjustment. But if you do that, you can set the trims to zero in Cut Planner and not make a trim cut at the saw. (Unless the sheet factory edges are worse than 1/8".)

From the original questioner:
Contributor A, does your optimization software tell the saw to cut from the middle out or is that done manually? If Cut Planner would allow us to do that and create cut patterns to cut and then trim cut automatically with the operator rotating the piece, that would be great. It would take a little more time, but would eliminate the manual entering of all the cuts and would enable the label printer to follow the cut pattern.

Contributor K, our Busellato does have offset capabilities. The problem as I see it is that not only our ends, but tops and bottoms, would need trimmed to get true parts and that would take too much production time, not to mention all the reprogramming. Currently, only the ends are machined at the MC. Tops, bottoms, stretchers and such are machined at the dowel insertion machine.

From contributor I:
Do you allow the panels to acclimate themselves to your shop (24-48 hours) before you cut them? This can make a big difference. Also, is your shop climate controlled? At a place I used to work, we cut thousands of sheets of melamine clad material and never had a problem like you described... and we had the same equipment you have.

From the original questioner:
We are located in south central Pennsylvania and right now, it's about 90 degrees and you can cut the air with a knife. Our shop is not climate controlled, but my office is quite cool (I'm spoiled). The bundles of melamine have been in the shop since last November. We were told by our supplier that this condition would effect us the worst in the summer and winter, very humid or very dry. We have a large facility and air conditioning would be nice, but extremely expensive.

From contributor M:
In my opinion, there's something wrong with the material. You shouldn't have those problems.

From contributor S:
Your Schelling should have relief cut capability built in. If not, call Schelling and they can update you via internet access. They also need to tweak some settings. I've used this before on the Schelling I used to run.

From contributor L:
I have always heard this problem referred to as a banana cut. We have had a problem with this mostly in the wintertime. It is a problem with some melamine much more than with other melamine. We are a small shop with a beam saw and point-to-point machining centers. We had a greater problem with a Canadian board that we were using for a particular job. The only way we could solve the problem was to cut the panels oversized and route all the way around the panel on the point to point, basically sizing the panel prior to other machining operations. When we had the problem, I spoke with several representatives from a few different mills and I was told that the problem is worse if the mill does not let the panels cool before they are stacked and banded together.

From contributor E:

I would agree with the folks suggesting oversize blanking and finish size on the router/P2P.

Your suggestion that a nested approach would solve all the issues is a little optimistic. If the edge ripped part is long, and the nest dictates that it be cut from the edge, the stress is there regardless of how (saw or CNC router) you cut it. I use a nested base machine and I have (on rare occasions) observed just the same results you describe when machining a narrow but long part from near the edge, something like 9" wide by 92" long.

Alternatively, you could consider outsourcing the work to a job shop. Sometimes it makes sense to outsource work that is not efficient with in-house assets. This does not preclude tooling up for the work, expecting to take it in house at some logical point. As a job shop, I have done many projects for customers that involved taking a product/component from prototype through initial production levels. Some of those projects have stayed with us for years, others move to the customerís facility as soon as they are geared up. It may just make sense to find a shop with a nested based machine to do some of the work for you.

If not, I guess you will have to review your reprogramming investment, capital equipment options, or methodology and see which is most easily adjusted.