Zammo,
There are a number of things that'll stop you drilling straight holes; poorly ground drills, blunt drills etc. The frame that you mention will only go so far to helping you drill straight holes every time - I think the frame would require itself to sit wholly over the steel being drilled - so your knife blank would need to be in the middle of a large sheet!
To help yourself without having to buy loads of gadgets, Start drilling into the material then stop once the hole is established . Loosen the chuck and remove the drill from the drill-bit, you can then check your progress with an engineers square (a piece of paper folded twice gives a very accurate 90 degree angle). If you need to correct, do so slowly and check it again. You can also use the reflection in the surface of the metal, you're looking to keep the drill-bit and the reflected image of the drill-bit in line, but make sure you view it from several angles. Then theres using a pilot drill, smaller than the size of hole you want to make but removing material in stages until you reach the required diameter.
Hope this helps.
Ogri the trog