Camframe can cut one-off single and multiple window mounts. We stock a comprehensive range of mount card and may even be able to cut a mount while you wait, how great is that!
Mount cutters need to be regularly re-calibrated. This is done by cutting a few test windows and checking to see if the blade has overrun in the corners.
The devil is always in the corners. A well-cut mount will not overrun in the corners by more than just a few mills. If you see cut marks of a centimetre or more you should point it out to the framer and ask them to re-cut the mount for you. Their reputation is hanging by that centimetre.
Mount cutting is not difficult, you just need good equipment and a sharp blade and above all high-standards.