i used to make drill bits for someone...3 inch diameter, machined lip to take carbide insert. takes some doing, sharpening a big carbide drill on a standard greenstone. they wear away really fast. make a mess.
also sharpened a few masonry drills for the cnc lathe a few times. once again, silicon carbide "greenstone". or a non segmented diamond wheel on the angle grinder
makes less mess, that one. rougher finish unless you got a diamond file to hone it with. dont make carbide as "sharp" as HSS. even put a 0.2mm flat on the lip. makes it stronger.
i hate drilling hard stuff, especially if the holes already there! ruins drills.
but balancing. pffft.
best option is lightening everything. whole crankshaft to reduce rotating weight. lighten piston to reduce oscillating weight and counterweight required, which also reduces the rotary vibration.
why is a vtwin better balanced? in a single cylinder, piston goes up and down. the counterweight goes down and up. but the counterweight rotates. so it also creates a side to side vibration.
a 90 degree v twin sticks another piston here, at the side. so the side to side vibration is also countered by a piston travelling the opposite way. making for a smoother engine. next option is four cylinders, in line...
reducing total weight will reduce vibration in total.
reducing counterweights/piston weights will reduce oscillatory vibration that shouldnt really be RPM dependent at all, as the g forces increase at basically the same rate in both directions... piston goes faster? so does counterweight. it is rpm dependent though, because the piston travels linearly, and the forces are constantly changing,from dead still to full tilt, whereas the crank experiences a relatively static loading, centrifugal force only...
but even when you get this right, if the counterweights just heavy anyway, its still going to vibrate side to side no matter what you do to the piston, pin, or rod!
reducing weight will allow for faster pick up when the throttles opened. less weight to get spinning.
reducing weight will reduce bottom end torque by removing all that rotating mass!
best to leave it all alone, methinks
has anyone tried turning up acrylic/nylon/alloy weights instead of the stock steel? and looking at the crankpin earlier...theres heaps of space to machine out and press in a new crankpin at a larger offset... more stroke. more grunt