Sometimes Things Don't Go Right

The chairs I've been making recently have four curved bars across the back. I've been cutting them on the Maslow. They look like this when they are finished:

I cut them with a router set to about 60mm depth and a toolpath that runs up and down the concave side taking off 2mm at a time. It then runs back and forth across the conves side taking off 2mm at a time. I hold the blanks to the Maslow base using a couple of 70mm screws. This is fine, except that on the latest part I was cutting the screws came loose, I think because the vibration of the routing and pressure of the tool was wearing the holes in the base. It's made of chipboard and the screws just got loose. Once the part started moving, the router made a hell of a noise and did this to the workpiece

The bit has ripped the wood apart.
I'm now going to try to use some 6mm studding through the workpiece and see if that lasts longer than the screw method. I only have seven more to do I think, so hopefully it will stand up for that long. I need a new blank now too...