Howdy,
First of all, 'rakers' went out with scratcher chain and crosscut saws. Their function now is as depthgauges. The depthgauge limits how much bite the cutter can take and how far the cutter can pivot backwards in response to the forces of cutting at the cutting edge. As the depthgauge is lowered, the cutter tips back further, the cutting edge goes increasingly blunt angled (as seen by the wood), and the force required to pull the chain through the wood increases. (It pulls the saw down so it feels like it is really cutting, although the cutting speed may actually be slower). Lowering the depthgauge too much too soon, results in greatly increased vibration and shock loading on the chain saw motor and saw chain. This punishment may not be obvious to the operator due to the extremely effective antivibration isolation of the handlebars these days.
.025 is the preferred setting for the cutter as factory new. As the cutter is filed back, the angle between the depthgauge and the cutting face becomes reduced, and increased setting (lowering) becomes necessary, say to .030, (just to stay in the same relationship as new). By the end of life, the setting may need to be as much as .035 on a standard 3/8 chisel chain in order to maintain the as-new performance level. There is only one tool that accomplishes this "progressive" lowering of the depthgauges accurately and that is the Carlton file-o-plate. It does not work on all models of chain, as it is designed to fit up correctly to the Carlton cutter. This system also means that the cutters do not have to all be the same length, as is the case with other depthgauge setting systems. (Since they have all been rendered equally 'hungry', who cares if they are different lengths! They can even be all long on one side and short on the other, but otherwise properly sharpenend, and the chain won't lead).
There is a downside to progressive lowering of the depthgauges, and that is that kickback potential and kickback energy increase as the depthgauge is lowered. Rather badly by end of filing life, in fact. This is one big reason that the factory recommendations usually are for maintaining the .025 setting only. Even at that, the kickback energy does increase at the end of life! (This is why those radical guardlink designs these days, that literally run out of cutting ability by end of cutter life).
For ripping, (milling) you want less depthgauge setting than mentioned above. .025 is actually too much, at least until the cutters are back a ways. This is because of the greatly increased cutting resistance because of cutting the fibres off directly across the fibre bundle, instead of running the topplate between the wood cell fibres as is done in a bucking cut. Taking off every other cutter pair's topplates reduces the increased loading, (by having fewer cutters actually cutting the full kerf width) which is why this modification works.
Regards,
Walt Galer
