One moment you are working away quite happily, the CNC is humming along and everything is just so.
The next, things are NQR – items are breaking loose, engravings are either too shallow or too deep, and the vacuum table is not doing its job.
It is the afternoon of a warm day, and the MDF spoilboard had suddenly started to warp and flex, pulling away from the vacuum table. It wasn’t something I had experienced with very thick MDF, but once the thickness had come down to around 8-12mm or so, it was a real problem.
I first thought the solution was easy – buy more 32mm thick MDF, after all, the first lot came from Bunnings. But there was a problem. That was apparently intro stock for the new store, but not something they were going to carry in the long run.
I got to thinking, and one thing that I had tried unsuccessfully, was to place a piece of 3mm MDF on top of the spoilboard (on top of the vacuum table). As a trial it was unsuccessful – to many losses in the system. But what if I ditched the spoilboard altogether, what then?
So I milled the base really flat, (still a sacrificial piece), then instead of placing a spoilboard on top, I placed a simple sheet of 3mm MDF on top. It is thin enough that air is drawn straight through it without having to mill off the heavily compressed portions top and bottom, and it is a very uniform thickness. Also, rather than having to mill, and re-mill it flat as it gets chewed up, it can be flipped over and the other side used, or simply discarded and another $2 sheet bought in.
The other main drawcard of the 3mm spoilboard, is it is thin enough that the vacuum base pulls it flat whether it wants to tend to curve or not.
The first few runs really proved how effective it is. Not only was the sheet being cut held down well, and very flat, there was significant vacuum that kept the pieces in place as they were cut free, and drove the dust deep into the cut groove. This was packed rather tight, so the bits did not move even though no tabs were included, even when the entire board was picked up and turned over to sand the other side.
Small refinements to technique, as a result of an adverse situation. Happy days.