When you have the upper portion of the jewellers saw blade clamped securely and squarely in place, you will need to create a proper tension to fix the bottom of the blade in place before beginning to cut your miniatures or model parts.
Tensioning a Blade in a Fixed Frame Jewelry Saw
To tension the blade in a fixed frame jewelry saw, you need to press the saw frame so that it comes closer together at the blade opening. Most people do this by holding the handle of the saw firmly and pressing into an upright edge of a workbench, closing the jaws of the saw at least 1/4 of an inch, and while the jaws are partially closed, inserting the bottom end of the saw blade into the clamp and tightening it. When you have tightly clamped the blade into the saw, you can let off the pressure on the saw handle and allow the saw to return to its normal shape, pulling the blade into tension as the saw frame straightens. You should be able to pluck the back (non toothed side) of the blade gently with your finger and hear a 'ping' similar to that of an instrument string. If your blad 'thuds' rather than 'pings' you need more tension and should repeat the process again. You don't want a high pitched 'ping' that shows you the blade is very tightly held under too much tension. It may break more easily when you use it.
Tensioning a Blade in an Adjustable Frame Jewelry Saw
If your saw has an adjustable frame, you can insert the blade into the lower wing nut and tighten it in place, then adjust the tension by loosening the wing nut on the back of the saw, and pressing the end of the saw frame down on a work surface to enlarge the size of the saw, tightening the back frame screw into position when you see that your blade is tight. For some people this is an easier way to tension the blade than doing it by putting pressure on the front of the saw. For an adjustable saw, try both methods and choose the one that suits you best. As with the non adjustable frame, a properly tensioned blade should 'ping' when you pluck it.