![Shocked :o](http://newforum.arcadecontrols.com/Smileys/default/shocked.gif)
Seriously, don't try that again!!
Im suprised you escaped without injury.
Those discs you are using are designed to chop off metal bar etc, not to cut wood. Those discs work by grinding away the material, you cannot grind wood. All that will be happening is that the disc will try to cut but it will only burn the wood. If its MDF it will probably heat the glue in the wood up and become hard as the wood/glue/sawdust compacts together as the dics have no means of clearing the wooddust etc which is why you cannot 'cut' any deeper than 1/4".
The fact that the discs are 3" wont help matters either. The edge of the disc will be further away from the spindle than necessary which means the router will be over hanging the material more which in turn means it will be harder to keep the router flat against the wood. I dont want to know what would happen if the router tipped slightly with the brittle disc against / 1/4" into the material.
You want a propper 1/16" slot cutter and the appropriate spindle for it. Something like this:
Product linkYou can scrimp on some things by taking shortcuts and not always using the corret tooling but dont scrimp on something thats spinning at 20,000RPM a few inches away from your b0llocks!