The oneway is simply to use but us expensive. The McNaughton has a learning curve but is more versatile. I have the McNaughton and found it hard to use but have only cored about a dozen. I simply don't do that much of that stuff so haven't gotten past the learning curve and it's struggle. I have been reading more and think I know at least some of what I was doing wrong.
You need to do some research on entry angles if you buy the McNaughton. I just wrote an article on building your own coring tools for Woodturning Design magazine. Actually it was on cold bending tools to make your own boring bars but I build the jigs to build more sizes of coring tools for my McNaughton system.
I have the McNaughton purchased used. One of the large knives has a "flat spot" which I need to correct since it causes the knife to be off track and rub on the side.
As John mentioned, the McNaughton has a big learning curve.
I normally use the McNaughton with my friend. Helps a LOT to have someone to assist with placement of the knife/entry angle and especially to have one finger over the "OFF" switch.
We have cored a few piece. The cherry cored easily. We took down the remnant of my friends walnut tree and this proved to be the wood from hell. Many dismounts and lots of vibration.
The last of the walnut pieces we managed to get two bowls, the outer and next. Dismount and other hiccups caused the inner core to be a failure.
This piece was about 14in in dia but we were not able to get this up to 400 rpm even though it was turned round at my friends. The reason was the sap wood vs heart wood density difference caused the imbalance.
Our learnings from using the McNaughton are :
a) Hone the knives frequently.
b) Spray dry-lube on the turret and knife.
c) Stop often to clean out the shavings. If any rubbing, widen the groove.
d) Find the entry angle and be prepared to adjust as you get deeper. Too shallow and you will bust through the bottom.
e) You need more power on the lathe than you may expect.
f) You need a REALLY strong tenon. Most of our dismounts with the walnut were due to the tenon breaking. Finally glued on a large base to which we screwed on a face plate.
g) Watch the Dale Bonertz video. Very useful. I have not been comfortable going much about 500 rpm. Dale recommends 800 rpm. Need a REALLY balance blank for this.
h) Be prepared for catches. We had a LOT on the walnut. Some caused tenon to break, some stopped the lathe, all in all, a bit of white knuckle turning. The knife does want to pull itself into the groove, so be prepared to control the feed rate. Very important.
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