McNaughton coring cutter shape

[Kevin Jenness]

I have the newer design with pointed tips. Robo hippy has a video in which he endorses regrinding to a square profile for a smaller chip. What is the supposed advantage of the pointed shape? Has anyone used both and is willing to compare them?

 

[Darryl Fective]

Not sure the difference that direction, but a bit of negative rake can help keep it from being too grabby.

 

[robo hippy]

Well, you can't do a negative rake on the McNaughton blades because the cutting edge is a micro thin piece of hardened metal. If you go negative on it, you remove the cutting edge. The idea of the spear point came from Mike Mahoney. If you watch him core, he "fish tails" which means he sweeps a bit side to side as he cores to open up the kerf. Oh, also, he said it makes it easier to cut the core entirely off with the tool. This is handy with burl, crotch, and end grain cores because if you try to break them out, they can tear through the bottom of the bowl you are coring. For me, the problem with totally cutting the core off comes from not having your tool rest high enough. I have learned to "feel" when the cutter is below center as I near the end of the cut. This is why I have my cutter set 1/4 to 1/2 inch above center with the longer blades on and lifting up against the gate. There is a lot of flex designed into the unit, and with scrapers, on the inside of the bowl, you ALWAYS want the cutter at or slightly above the center point of the bowl. If you are below center, you get bigger catches. If you have ever tried to remove the stub left when you break out a core with the blade in place, at first contact, the blade drops way down, and that puts it below center. I do consider the square cutter point to be better since I tend to try to make the plunge cut all the way to the bottom in one pass.

robo hippy

 

[Neil S]

.
I went with a halfway in between profile, with just some of the tip squared off. The one on left is the original spear point and the on one the right is my modified tip.



I found it is important to align the squared off tip so it is cutting in the direction that the bar wants to follow, ie the square edge is in line with the radius.

I made this modification to reduce the butterfly shavings that I was getting with the spear point, which were more prone to clogging inside the kerf.

.

 

[robo hippy]

I think I heard some where that one thing the spear point did was let the shaving fold in half so they would eject easier. Mine seemed to expand rather than fold and I would get twice the jam ups that I did with the square tip. I do think the spear point works better if you are fish tailing, which I don't do. That is a lot of cutting area at the end of a long bar. Most hollowing tools are not 1/2 inch wide. Maybe 1/4 inch max.

robo hippy

 

[Neil S]

I think I heard some where that one thing the spear point did was let the shaving fold in half so they would eject easier. Mine seemed to expand rather than fold and I would get twice the jam ups that I did with the square tip.

That was also my experience with the full spear point too.

 

[Adam Vila]

Interesting and helpful observations, robo hippy. Curious if anyone is still retrofitting carbide tips on these knives. I contacted someone that once did, but no longer. Seems that with the right equipment someone could tap the tip so replaceable carbide cutters could be substituted in.

 

[robo hippy]

Hmm, trying to remember.... I am fairly sure I had Mike Hunter retip one of my old blades. First one was too long and pointy. Second one was much better, but I ended up silver soldering some tantung on the end of my blades. You might contact him to see. I know it can be done. Most difficult part was to drill the hole for the screw to seat the insert.

robo hippy

 

[Adam Vila]

Hmm, trying to remember.... I am fairly sure I had Mike Hunter retip one of my old blades. First one was too long and pointy. Second one was much better, but I ended up silver soldering some tantung on the end of my blades. You might contact him to see. I know it can be done. Most difficult part was to drill the hole for the screw to seat the insert.

robo hippy

Brilliant. I remember contacting Mike hunter of Hunter Tools last year and he said they're no longer doing the retrofittings. Hope that changes, or someone else takes it up.

If you happen to have a picture of your tantung-tipped coring tool, would love to see it.

 

[Bill Blasic]

You know if they gave out awards for inventions in woodturning products I believe Mike Hunter would lead with the most awards. His nano carbide woodturning tools and especially the Korpro cutter which really change for the good in coring for me. Brent English would also get an award for the Robust lathe as to bring out a new lathe when the market already had so many outstanding lathes took a lot of courage. How about you? What say you as to who would get an award.

 

[robo hippy]

To me, worst coring cutter design goes to Oneway. Pretty much worthless. I did have them send me one of their tips that had been hardened, and ground the sides down to I had a trapezoid, about the width of the blade on the mounting end and opening up to maybe 1/2 inch on the cutting tip. It worked FAR better than their standard tip. I asked them why they didn't make their tips like this and they commented that it was too aggressive for the average user or some thing like that. But it cuts SO much better and you don't have to take it off to sharpen it. Nope, we are not going to change it. I never learned to post pictures here, and may never get to that.... So, think of the spear point on the McNaughton, but the spear is ground down to square. That is the shape I use. I would expect M42 HSS to be sufficient, or tantung or stellite if you can find it. I used silver solder to adhere mine to my old coring blades.

robo hippy