McNaugton coring blade retipped with Hunter Korpro cutter

[Pat Scott]

I've been using the McNaughton coring system for 12 or more years. I use the medium curve blade from the Standard set for 99% of the bowls that I core. The cutter started out new at 3/8" wide, and as it's been sharpened many times over the years it gradually became smaller and wasn't cutting as wide of kerf. I debated about buying a replacement blade for $75, but after talking with Hunter Tools I decided to send my blade to him and have him retrofit it with a Korpro cutter for $100. In my mind the extra $25 was a no brainer from not having to sharpen, ease of cutting, etc. (As a side note Hunter doesn't do the retrofit himself, he subs that out to someone else because a precise recess has to be milled in the end to fit his Korpro).

Has anyone else had their McNaughton retipped with a Korpro? I'm curious to hear your thoughts. I'm having nothing but problems.

As you can see in the pictures, the Korpro is only 1/32" wider than the blade. As soon as I get about 2" deep into the cut you can feel the blade bind up in the kerf. Trying to widen the kerf is a PITA because it's hard to get the edge of the cutter to bite into the sidewall. Shavings are almost welded (for lack of a better word) to the side of the blade to the point where I have to constantly withdraw the blade and use a wire wheel in my drill to remove caked on shavings. The shavings also build up on the tip more so than the McNaughton tip and again I have to use the wire wheel to clear them. As you can imagine with the blade rubbing on the sidewalls the blade gets really hot.

I contacted Mike Hunter and asked if I got the wrong Korpro installed and can I get a bigger cutter. He said I had the right cutter and since the Korpro cuts so easily and quickly that I need to clear shavings more often. I didn't think that was the problem but OK I'll try it. Tried it and no change. I'm not a Mike Mahoney or anything but I've cored enough to know somethings not right. When it works it's nice and easy to cut, but that's not very often. I fight with it every cut and it easily takes 2-3 times longer to make one core than it used to.

I debated about switching over to the Oneway system, and I've read great things about the Korpro cutter with that system. The pictures on Hunters website clearly show the Korpro is wider than the Oneway blade. In the end I spent $75 instead of $750 and bought a replacement McNaughton blade but I don't have any wood to core at the moment. The new McNaughton blade isn't without it's problems, you can see the blob of extra metal on the side of the tip that I need to grind smooth.

I'm just curious if anyone else has done this and if you've had any problems like I have before I contact Hunter Tools again. I thought maybe my Korpro blade was bent or twisted but comparing it to the new blade shows them identical (1st pic shows Korpro blade on top of new blade)
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[Reed Gray]

Mike did retip one of my McNaughton blades some years back. I since have gone to tantung, which is the cutting material that I use for the Big Ugly tool. It has to be silver soldered onto the blade. First one he did was a long spear point, which did not work at all. The second tip was a square one. I would want a square to sit at least 1/16 inch proud of each side of the blade. He just drilled a hole in the blade, and I think it was recessed a bit to keep the square cutter from rotating, can't remember. It did work, but it does need to be wider than the coring blade. A round cutter would also work. The 1/32 clearance is not enough to compensate for the height of the coring blade, which needs a certain amount of clearance when coring.

robo hippy

[Jeffrey J Smith]

Pat - for what its worth, I've been using the same set of Macnaughton coring blades for somewhere north of 15 years. Like you, its the mid-curve blade that gets the most work. In that time they've only been on the grinder two or three times as I recall. I do hone the tips every time they're used with a cbn hone, but other than that, unless I drop them or damage the tip somehow (hitting buried metal) they're good to go and continue to cut well with just the honing.

[Pat Scott]

Pat - for what its worth, I've been using the same set of Macnaughton coring blades for somewhere north of 15 years. Like you, its the mid-curve blade that gets the most work. In that time they've only been on the grinder two or three times as I recall. I do hone the tips every time they're used with a cbn hone, but other than that, unless I drop them or damage the tip somehow (hitting buried metal) they're good to go and continue to cut well with just the honing.

Thx Jeff, I've never been much of a honer (which sounds like a dirty word!) on any of my tools but maybe I should give it another shot with this new blade. I just never got the results from honing and it never seemed to cut like I wanted. I touch the tip to the grinder and back to coring. I figured 15 years out of the blade is good.

[Reed Gray]

Use a coarse, like 220 or 320 hone. I go sideways on mine. It does raise a fairly good burr. A fine hone doesn't make for much of a burr other than for a NRS. I generally just barely touch it to a 320 CBN wheel.

robo hippy

[Jeffrey J Smith]

Use a coarse, like 220 or 320 hone. I go sideways on mine. It does raise a fairly good burr. A fine hone doesn't make for much of a burr other than for a NRS.
I use a D-way hone - 320 one side, 600 on the other. I seldom check which one I'm using when in a hurry, doesn't seem to make much of a difference. I do remove any burr completely before honing once in a while.

[Pat Scott]

I've only tried a 600 grit hone, never thought to try coarser!

[Richard Casey]

Pat, from the moment I saw this post I knew it was never going to work due to insufficient side clearance. I had given some thought to modifying mine to take a round carbide insert. Maybe someone like Reed Gray might have the skills to calculate the required cutter diameter to provide the necessary clearance. I think it could be practical.
Regards,
Richard.

[Reed Gray]

Well, I like a square nose on my cutters, about 3/8 wide max. I do taper the sides a bit, so by the time I get to the end of it, it will be 1/4 wide maybe. I did have some McNaughton blades that I wore out, and the cutter was about the same width of the coring blade, and I had to do a double kerf.

robo hippy

[Karl Loeblein]

Got any pics of your square nose cutter?

[Reed Gray]

No pics, don't know how to post them. 3/8 wide at the cutting part, 1/8+ at the base. Had to grind the shaft down flat, then silver soldered the cutter on. Not sure if this is a trapezoid or not. Just a square nose. Very similar to the Woodcut cutters.

robo hippy