Next, pressing the mount board firmly use the ruler part of your cutter as a guide. Lay it just inside your pencil lines - this will make sure that the mount is almost exactly the same size as the frame's interior. It should be a nice snug fit when cut this way. I prefer to use a heavy Stanley knife to do the actual cut - I don't have to press too hard and risk moving the mount and it give an easy smooth cut. Lay the blade of your Stanley knife against the ruler and cut from the outside of the frame inwars - just past the corner if that makes sense. You should now have your basic mount rectangle.
Don't forget if you're framing it to check it does indeed snugly fit your frame at this stage. You don't want to do the rest of the work only to find out you messed up up at the very beginning.
Next you need to measure the dimensions of your image and then do a couple of calculations. Lets says your mounting board is 40cm by 30 cm and your image for the sake of argument is 30 cm by 20cm. You need to mark out a window exactly in the middle of your mounting board. So that the photo is held firmly onto the mount I like to make this window about 2-3mm smaller on each side - so you'll be loosing a little bit of your image on the border on each side. On a 12" x 8" you really don't notice this at all. As our image is 10cm smaller we need a border of 5 cm + 2-3mm top and bottom. We need a border of 5cm + 2-3mm left and right as well as the photo is 10cm narrower. On the back of your mount mark 2 points clearly on the left and right sides 53mm down from the top. Repeat - with 2 points left and right 53mm up from the bottom. Joint the 2 bottom marks together with pencil and join the 2 bottom marks together.
We're going to repeat this process for the side border - so again mark 2 points - one top, one bottom 53mm from the left edge and again 53mm from the right edge. Connect the left top and bottom marks with a pencil line. Connect the right top and bottom marks with a pencil line. You should now have a square marked out. Lay your print on top to check it fits - it should overlap the lines by a little. The key to all of this is just to take your time and check everything as you go along.
Now we're going to cut out our bevelled mount. Lay your cutter on the outside of the pencil line so that that it lays exactly against it. Slide your cutter onto the guide rail - making sure the to line up the little silver marking line (circled in red) matches exactly
the pencil line as shown in the photograph. Press down your cutter and sill pressing down push firmly and slowly away
from yourself. The cutter blade is spring loaded - and as the silver line reaches the pencil line at the other end lift the pressure so that the blade will spring up and out of the mount. Your first edge is cut.
Rotate the mount anticlockwise and repeat this exact same process for the other 3 edges. Do not go beyond your pencil lines - if you have placed the cutter and guide as I've described everything will line up perfectly. The centre of the mount should fall out as you lift it leaving you with a perfect bevelled edged mount. Keep an eye on your cutter blade - if it starts to become blunt change it. Your cutter should come with spares and you can source more from any half decent art supply shop.
We're now going to attach the mount to the print. The first thing to do is cut out 4 small squares of masking tape and attach them to the back each corner of your print so the sticky side is facing towards the front of the print. Turn it over so that it is facing you. Now take your cut out mount and turn it the rigth way up so that the front is facing you. Carefully hold it over the print so that everything lines up (don't forget your overlaps) and then place it gently on the print and press down in the corner.
Don't worry - this isn't how we're attaching the board - the tape on the corners is just to hold things in place whilst we finish everything off. Turn the board with the print attached over, face down. Take and stick roughly 50% of the width on the print back and 50% to the board on each of the four sides. Press it firmly removing any kinks or air bubbles.
If you're mounting this for a competition then I would recommend next that you use 2mm - 3mm thick card (I get mine from my local arts supplier in Redruth). Cut it so that there is a 2cm - 3cm border compared to your mount. Some people just use masking tape again to affix this - I like to be doubly sure and use some craft glue - also putting a small couple of dots on the back of the print (make sure the glue you use will not damage the print - some will). This is then stuck onto the back of the mountboard - with masking tape round the edges both to hold it in place while it dried and help keep everything together. If you use rubbish masking tape it will peel off and your mount will fall apart. This is why you'll see many people also stick some tracing paper onto the back of the board - it can be brushed back when showing and left over the front of the print in storage so that if someone's tape comes off it will not damage your print.
If I'm mounting this in a frame I will use 160gsm card as my backing - as that is what the frames I use will fit. Yours may well be different. I make this backing board the same size as the mount and again use craft glue to affix it - with double sided tape on the four edges between my backing and mount board to help hold it together.
I then title, sign it, pop it into the frame - and we're done ! Remember - if you take your time and do everything methodically you'll be fine.