If you want to be a compound coach, do you need a bow press or at least need to know how to use one? I think the answers are “yes” and “yes.” Compound bows were invented before the bow press. In those early days (the 1970s and 80s), it was the practice that to work on a compound bow, you slacked the string and cables or even dismantled it by backing out the limb bolts. This was a clumsy process which could be dangerous and, for one, screwed up any chance of finding your previous bow setup and tune accurately.
For those of you not in the know, compound bows use mechanical advantage to bend very stiff limbs, very short distances. In those early days, again, there were even kits to convert recurve bows into compounds: they involved cutting off the recurve sections and bolting on wheel hangers, etc. These bows, even without their springy limb tips were invariably weaker than purpose made compound bows, which used much heavier limbs (over 100 pounds of deflection force at a minimum).
Technicians in shops and manufacturers responsible for assembly, repair, and adjustment of these bows quickly realized the need for a device such as a bow press and voila!
The photo shows a couple of common modern designs, the yellow one was designed for older bows, the other for more modern bows. The yellow one worked until the past decade or so. The bow was placed so that the limbs rested on the outer rubber rollers, which were adjustable to make a correct gap between them. Then a winch pulled the riser, which was hanging below, downward, causing the limb tips to bend closer to one another, slackening the string and cables (see photo at bottom). The original presses were more like the yellow one, but they involved a single center pull (at the pivot point of the bow). It only took a few dozen bent or cracked risers (they were wood or cast, not forged, aluminum then) to suggest the improvement of having a double pull (note the two central rubber wheels on the yellow press), this perfecting the design.
That design lasted until compound bow’s evolved toward what are called “parallel limb” designs. These bows have limbs that are parallel to one another or even past that point. The original design of bow press no longer worked because the limbs didn’t stick out far enough to get bent; the bow just pulled through the outside rollers!
The other bow press has “fingers” that approach the limb tips on both sides of the eccentric on both ends of the bow (see detail left). Then a screw drive (powered or manual) brings those two ends of the bow closer together, getting the job done. This new type of press will work on newer and older style bows as long as the bow is short enough to fit between the fingers! In the early days of compound bows, the bows weren’t short like they are now. Instead of 30˝-38˝ axle-to-axle bows as are currently in vogue, they had 48˝, even up to 54˝, axle-to-axle bows. Modern bow press manufacturers are unlikely to make their presses accommodating of these very long compounds as so few still exist.
Danger! Danger, Will Robinson!
Using a bow press is inherently dangerous, so be sure to get a seasoned veteran of their use show you how to use one. The forces involved are great (hundreds of pounds of force) and, trust me, if you make a big mistake, changing your underwear will be the least of your worries.