I love fiddling with my swing, and though my scores suggest that's not a great idea it's one of the main reasons I enjoy this pastime. There is not one perfect way to swing; the clones turned out by most of today's swing schools are effective but so were Lee Trevino, Jim Thorpe, and Arnold Palmer. A modern swing coach witnessing their forms, especially those of Trevino and Thorpe, would pass out from shock, and some still do when they see Jim Furyk.
None of these guys uses a single-axis swing (Thorpe may be up to a quadruple-axis), but in the spirit of golf diversity I point you to the Single-Axis Golf site. There are separate sections on Natural Golf, the Ideal Mechanical Advantage, the Heard Super Swing, Big Grip Golf, Graves Golf, and the aptly named That Other Method. Photos, video clips, and a lively forum where a current discussion concerns a golfer who finally found a swing key that works after 35 years of experimenting. So according to that I've got about 25 years to go.
From that link, here's the tip:
On your backswing merely pull with the middle fingers of your right hand (right handed golfer) against the shaft / thumb of your left hand. What you are doing is creating the angle (90*+) of the clubshaft to the left arm and a flat left wrist. Try to feel the leverage of this pressure point creating pressure against the heel pad of the left hand. You may be able to work in a push of the left heel pad to really force the angle.
When I say "merely" I am understating, you "really" have to pull to create this leverage. (beads of sweat cascaded everywhere) The first few buckets, and in fact for the first few weeks, my right bicept was getting very tired. The straighter you can keep your left arm the better - tension seem to be everywhere- definitely no "loose" arms. (After six weeks of doing it, I can now achieve it without as much tension in the arms, in fact at times I can get pretty loose and more clubhead speed is appearant. but definitely work with tension first.)
As you swing down, do everything you can try to keep the tension and hence the angles and DO NOT RELEASE, let the whole arm triangle assembly sort of rotate down and around. Feels different, if not, you are not doing it properly.
Another visualization, when you pull against the club/thumb, feel as if you are forcing a straightening the left arm and never letting it relax.
Also, if you are not used to letting your left arm rotate through on the downswing, you may have to overcreate the sensation. Insure that the back of your left hand is in line with you left arm (flat), no cupping. I started with the feeling that - from the top of the back swing - the back of the left hand immediately feels like it's flat and facing the ground just off my right (back foot). This seems to force the right elbow into the the side (very nicely). If you then carry the whole assembly through impact, the angles will be maintained. DO NOT FEAR holding the angle for a seemingly ridiculous amount of time. And in order to hit the ball, you will find your body providing the necessary bending....
Yes. It's just that simple.

