By: Anonymous: Tony () Thursday, 21 July 2011 @ 09:20 AM ICT (Read 2449 times)
I recently helped a friend and his dad put new tires on his motorcycle in their home garage. When I grabbed a wrench and started to loosen the rear axle, his dad stopped me and said I was using the wrong end. It was a 24mm wrench with open-end jaws at one end and a box wrench at the other. I had tried to loosed the nut with the open end, but he said I shouldn't do that because the jaws can spread easily and allow the wrench to slip. He said I instead should use the box end. Is he correct or just being very cautious? It seems to me that a 24mm wrench is a 24mm wrench, no matter what type it might be, and I can't imagine the jaws on a wrench that big flexing enough to slip.
By: news (offline) Friday, 22 July 2011 @ 06:27 AM ICT
Your friend's dad is correct in telling you to use the other end of the wrench, but not for the reason he expressed; unless an open-end wrench is of very poor quality, jaw spreading is not a major concern.
A box-end wrench or a socket always is preferable to an open-end wrench except when neither can be slipped around the fastener – such as when the hex is on a hydraulic line or a turnbuckle or located so close to something else that only an open end wrench will fit. With an open-end wrench, the jaws only make meaningful contact with two of a hex's six corners, and that contact occurs right at the very edge of the corners.
If the force required to turn the fastener exceeds the strength of the small amount of metal right at those two corners, the wrench will slip and round off the corners. A box-end wrench or socket, how-ever, makes contact with all six of a hex's corners, so they theoretically are three times less likely to slip and round off those corners.
By: ThaiDesign (offline) Friday, 22 July 2011 @ 08:40 AM ICT
A basic six-point box wrench or socket is, in essence, just a simple inverse hex, with six sharp external corners. Even a basic 12-point wrench has sharp intersections in all 12 of its corners. This means that when a six- or 12-point box-end wrench or socket tightens a hex, it applies pressure right at the very edges of the fastener's six corners. Normally, this is not a problem; but if the fastener is well-used or has less than perfectly sharp corners, the wrench or socket can slip and round off the corners altogether.
I used the word 'basic' in describing the aforementioned wrenches because there is a more-effective type. About 50 years ago, an American tool manufacturer addressed the problem of rounded-off fastener corners by patenting what it called Flank Drive. This involved putting a small relief at each internal corner of a box wrench or socket so the force of turning would be placed not at the very corner of the fastener but rather a short distance from it, on the hex's flank, hence the name. This allowed more of the hex's metal to resist the force of turning, making it less likely for the corners to be rounded off. In fact, Flank rive was so effective that a wrench with that design often was able to loosen nuts and bolts that already had been rounded off.
The patent for the Flank Drive expired years ago, so most reputable tool manufacturers now use some form of flank drive on their box wrenches and sockets. The original Flank Drive developer has even introduced Flank Drive Plus for open-end wrenches. This design uses special notches of the wrench's jaws that apply the turning force a short distance from a fastener's corners rather than right on the corners' edges.