Thanks, Bob
Very interesting....my chain is only about 10 cuts old...
Would the rakers be wrong after 2 sharpens?
The first thing i do with stock chain is drop the rakers.
The KPI for rakers are the angle between the raker/cutter tip/wood (or on the picture above, the ruler. I call this the "raker angle".
On new 3/8 chain chain the raker depth is 0.025" which converts to a raker angle of 5.7º.
Another way to look at this is the "gullet width" (0.25" on a new chain) to "raker depth" (0.025") ratio, on stock new chain this is 0.25/0.025 or 10:1
As the cutters wear, to maintain the same ratios the rakers have to be dropped even further. so when the gullet reaches 0.3 teh rakers should be at a minimum dropped to 0.03"
On my 880 and 076 I like to use a raker angle of 6.5º or a ratio of 9:1, which corresponds to a raker depth of 0,28 on a new chain. but I usually set it to a bit more eg 0.03" to just get me ahead of the game. On my 041 with 25" bar and Lopro chain I use 7.5º which is a ratio of 7.5:1 on new chain this is a raker depth of 0.033"
2 sharpenings might not seem much but it depends on how much metal you removed. For low dust cutting a minimum raker depth should be 1/10 (corresponds to about of them gullet width but with a big saw like an 076 in Aussie hardwoods, 1/9 is a better ratio to work with and if teh logs are narrow I swap from a 7 pin drive sproket to an 9 pin,
If all this maths is not your bag just use the method my dad used. Drop your rakers by taking 3 swipe of each raker and try a full bar length cut. If it goes OK, swipe 3 more times of each raker and try again. and keep doing this until the the chain starts to grab and it might even stall the saw, This means you have gone too far so now take a few swipes off each cutter to get you back to optimum, Measure the raker depth with feeler gauges and that is your sweet spot BUT only for that power head that specific cutter length, that chain.bar length, in that wood etc.
Better still, measure the gullet width and raker depth and work out the ratio and that will be the ratio for ANY cutter length but once again, only for that power head, that chain.bar length, in that wood etc.
Confusing as heck.??? but cuts like a hot knife thru butter all through the life of the chain.