To avoid having frayed edges, we folded the baize over every edge, added an extra crease in the overlap and stitched through all of those layers (3 layers of baize and 1 of leatherette).
The tricky bit about this project was getting the size of the baize right, since ironing creases into the edges shrinks the material around the outside. We tried to reduce this effect by ironing the baize all over before starting, and stretching out the baize before sewing the pieces together. There may be a better way of doing this, however.
Step 1: Get the materials
You'll also need some good scissors, a ruler, a measuring tape, tailor's chalk, an iron, a sewing machine and thread to match the colour of the baize.
Step 2: Measure out the leatherette
Carefully mark out on the back of the leatherette the intended final size of the mat, making sure that it's rectilinear using a large right-angle or repeated measurements. It might be worth checking that the diagonals measure the same to check that the rectangle isn't skewed.
Step 3: Cut the leatherette to size
Step 4: Iron the baize
Throughout this project we used the iron on its wool setting and with steam. However, if you can get away with doing it on a lower setting and without steam, this may reduce the shrinkage. We found that we needed steam in order to press in the creases, however. Another point to note is that there appeared to be some water staining from using the steam but it isn't so noticeable that it bothers me.
Step 5: Measure and cut the baize
Lay out the baize on the table, put the leatherette on top, making sure that there's at least a 3cm margin (seam allowance) on each side. Use the chalk to mark all around the edge of the leatherette on the baize.
Then measure an extra 3cm seam allowance all around the edge and mark it with chalk. Finally cut it to size along that outer line. At the end of the step it should look like the picture.
Step 6: Pin the edges of the baize
Step 7: Tack around the edges
Step 8: Iron the first crease into the baize
After you've done this ironing, unpick and remove the bright thread you used for tacking.
Step 9: Mark out the second crease
Step 10: Fold in and pin the second crease
Step 11: Iron in the second crease and tape to the leatherette
Then lay the baize out with the creases facing up, and lay the leatherette over it. Now lift the creases, fold them around the edge of the leatherette and tape them down with invisible sellotape (a.k.a. magic tape). Make sure that the edge of the leatherette goes right into the crease, so that you'll be able to sew through all four layers in the next step.
At the corners you should trim a triangle off the baize in order to reduce the amount of overlapping material, while making sure that there still is some overlap to sew through - i.e. don't cut the triangle right to the corner of the leatherette. Ideally this cut should go through the point where the second creases would meet.
You might find that the baize has shrunk from the ironing, so at this point we stretched it out, weighted down the corners with books and left it overnight (as shown in the second picture).
Step 12: Sew the baize to the leatherette
The leatherette is quite stiff and heavy, so you may need someone else to support and gradually move the mat as you're sewing around the edges.
Step 13: Finish off the trailing threads
When you're rolling this mat up for storage, we found it's best to fold it over once before loosely rolling it up - this seems to minimize creasing of the baize and leatherette. (See the third picture for this step.) Even so, it's difficult to roll it up without crumpling the baize to some extent, but as yet it hasn't been difficult to smooth it out when you lay the mat out again - time will tell whether this is a problem in the longer run, I suppose.