Quote Originally Posted by pauley555 View Post
i mainly cut 18mm mdf shapes and letters,and would like to know what bit would be best for this and where to buy?
Depends on the size of the letters and shapes. In general you can't go wrong with these:

http://www.ebay.co.uk/itm/5x-6mm-Car...item20b95dbb6d

Having only one flute means there is plenty of room for the swarf to eject, so you can use a large depth per cut assuming the spindle is up to it. They last for a very long time. I've cut through 18mm MDF with one of those in one pass before now...but start with something a bit more sensible like the width of the cutter. It looks like your machine will only do 2.5m/min (another reason for getting single flute tools - the feedrate required is proportional to the number of flutes) and you don't want to be applying a high cutting force at that speed, so I'd start a bit slower - say 16000rpm at 2m/min with the 6mm tool. But do experiment to find the optimum.

Clearly if the radii on your shapes/letters is less than 6mm you will need smaller cutters, but those single flute cutters are available in various sizes so that shouldn't be a problem. Don't get a small cutter if you can help it as they're much weaker, increasing the chances of breakage.