Getting a VFD was definitely the right thing to do for Japanese bits.
The Robinson machines motor speed is 2840 rpm. Delta wound three phase. 4hp.
Fine for chains and the British pattern double twist bits. But Nakahashi bits are designed primarily for softwoods and approx 1400 rpm.
So for this test, a 22mm bit, which is still okay with softwoods but pushing your luck on hardwood.
Test timbers were Baltic pine and New Guinea Rosewood.
The Baltic was very happy at around 1000 rpm and would still cut okay at 800.
Higher than that and the resin content disagrees with the auger.
NGR was happiest at recommended speed set at frequency of 25 Hz. Half usual motor speed. Breaking through the skin was slightly tough but cut nicely once the points were sunk in.
I never skim the bottom once the full length is cut. I lift enough to clear and take over lapping cuts to clean out the bottom.
I know most people use a coin to set the auger height correctly but that's not how I was taught to do it. I square up the chisel, lock it to the collar then let the auger drop until the cutting edge is a tad lower than the point's. Then tighten it. This is especially important on larger chisels where you need to break the corners out easier by weakening the wall around the auger lower down.
I once tried to mortise oak with a 3/4 bit.
The Oak wouldn't accept it. So I turned to the old hand and he smiled. Listen ooop lad, sometimes tha has to cheat to get it reet.
Yorkshireman. Tough as old boots.
He grabbed a power drill and drilled down the four corner's by eye. 15/16" long Brad point.
" Now she'll give lad " .
Thanks Tom. You were a diamond Geyzer.
It worked. All the way up to 1and1/8".
Tom must have been in his seventies at least and had a heart condition so I did all the heavy lifting. We were often milling 3 to 5 inch thick mahogany boards. " Eee that's a heavy basturd mate, have a blow !"
That meant put it down for a moment and give him a rest.
A good man to learn from and a true gentleman. 
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