After some testing I found the washboarding effect to be due to a synchronisation between cutting speed and chain speed.
Below is my goto photo to demonstrate this.
Same log, same chain (3/8 full comp, hand filed with 6.5º raker setting, )
The finish on the left is while making a narrow cut near the top of the log - the one on the right is a wider cut near the middle of the log, with the chain touched up somewhere in between the two.
Trying to do something about washboarding is tricky because an operator can't see the cut surface while making the cut and take appropriate action
As I usually only make narrow cuts at the top and bottom of most of the logs I cut I don't usually worry about it because those slabs usually end up going through the chipper.
Chain speed can difficult to control via a standard CS trigger but using a remote locking throttle can help set the throttle back a couple of hundred rpm from WOT.
Cutting speed is determined by things like wood hardness, how aggressive the cutters and rakers have been set, and how much pressure is applied to the cut by the operator.
If the chain is already at maximum cutting speed it can't go any faster, so the only thing would be to make less aggressive by either blunting the cutter or removing some of the cutter length to make the raker angle lower. In the narrow logs that are typically placed onto a logosol it may be worth doing this but if the log is a wide one, making the chain less aggressive for the narrow initial cut will be counter productive when milling the wider section of the log.
Reducing the pressure slightly in the cut by the operator can also help, but if the cutters and rakers are optimised the chain will be self feeding so it may be difficult to do this.
I can't see what grinder versus hand filing has to do with washboarding as chains can be made just as aggressive with either sharpening method.
With some care I can get better finishes with my CSM than I can with the BSM.
