I so still recommend a square tip on the cutter. I have retipped a couple of my blades with tantung, which is what the cutter material on my Big Ugly tools are made from. I kept the same shape. I also have one cutting tip from Oneway that I had them send me that was hardened but they didn't cut that chip breaker tip on. I tapered it slightly so it wouldn't bind in the cut. It cut far better than their original design. I was told that that point helped keep the cutter on track, rather than drifting. Not that I could tell. Woodcut also uses a square tip. The only advantage with the spear point on the McNaughton is that when coring larger blanks you can 'fish tail' as Mike Mahoney says, which is a gentle side to side sweep as you core. This opens up the kerf. This is not necessary on smaller cores, but you can't do a larger core, like a 12+ inch by 6 inch bowl without opening up the kerf. This has to do with the geometry of the blade. They do not follow a perfect arc of the circle, with the last 1 1/2 inches of the blade going more straight. This is why they always drift to the outside. This causes the blade to bind in the cut. Add being slightly below center, and this adds to catches. Mike was the inspiration behind the spear point design, which he said helped when you had to cut the core totally off rather than turning down close and then breaking the core out. Again, for me, I have found that if you want to cut a blank totally off, like when you are coring end grain, burl, or crotch wood, you have to have that tip at dead center, pretty much the same thing you have to do with a gouge or NRS if you want to clean up dead center. I have learned to feel it when the blade is below center. Most of the time, since I tend to use long handles on my McNaughton, I just lower the handle a bit. Note here, this is master class only... You can also raise the tool rest a bit, which is 'safer'.
There have been comments, and I don't remember who, about the spear point helping to keep the blade on track, kind of like with the Oneway bit. I had the original McNaughton blades, and the cutter was dog eared off to the outside of the bowl with a bevel angling back from the point, so kind of half of a spear point. I had heard others were using different grinds. I tried it angling to the inside, the outside, and straight across. The straight across seemed to work best for me. As I said about the Oneway, the straight across grind cuts far better for me than their spear point does. There was no problem with it tracking off center. I also tried a slightly rounded nose, which I do on some of my new McNaughton blades just so I don't grind away so much usable metal. I still prefer square nose.
As near as I can tell, the main cause for making funnels with the McNaughton comes from aiming wrong. The tendency is to try to match the outside curve of the bowl with a blade that has the same curve. That does work, but then when coring, the tendency is to try to aim for a cut that gives you an even wall thickness all the way to the bottom of the bowl. This method would work fine if you are making the tipsy/earthquake bowls which have a round bottom. If you aim for even wall thickness, you come out right on your chuck jaws. If the curve of your blade is smaller than the outside curve of the bowl, then you can start out for even wall thickness as the extra curve will steer you away from the chuck jaws. If you have a blade that is flatter than the curve of the bowl, then you have to aim more to the center of the bowl rather than down the side. I used to hold my blades up over the bowl in the arc I planned for my cuts, which I think is essential for helping you aim. Now, with experience, I don't need to do that all of the time, but some times I do. I did see one video of a turner who actually penciled in lines on the bowl where he wanted the bottom of the core to be. Then he held the blade up over the blank to see where it should go. Great visual for beginners. Now I have to see if I can find that video. He did say that he liked his cutter slightly below center. For me, that is NEVER. When using scrapers on the inside of a bowl, you ALWAYS have the cutter at, or slightly above center.
The McNaughton had a lot of flex built into the system. To set the height, use the longest blade you have. Really pull up on the handle to get the cutter as low as it will go. This gives you a point that is 'close' to where you should be cutting. This does not take into account what happens when the cutter is actually cutting. That is a lot of pressure on the tip of the blade. If you ever have broken off a core, and then try to cut that stub off with the coring tool, if the cutter is at dead center with no cutting pressure, put the tip into the wood and it will drop/flex as much as 1/2 inch. I always use a collar under the tool rest. This keeps it from vibrating loose and down, which you don't want. You can also, as you get near the bottom, raise it slightly off of the collar to keep cutting height near or slightly above center. I guess you could make spacers as well for 1/4 inch increments. If you try to get your collar height set by using one of the smaller blades, you will be way below center when using a larger/longer blade.
Not sure if they are still doing it, but Woodcut used to have their cutter, which is made from Stellite, slightly concave on top rather than flat. It was supposed to help with chip ejection. I don't have as much experience with it as I do the McNaughton, but it did seem to help. The problem with the McNaughton and the 'fish tail' method was that it seemed, to me, to make the sides of the kerf more jagged, as opposed to straight and some what smooth, and I would get more chip jams when coring. Same with making 2 passes down to open up the kerf. Single straight down cuts seem to have less chip jams.
robo hippy
