McNaughton revisited

[Eric Gourieux]

I bought a McNaughton Center Saver system a few months back. I've practiced a lot and have cored a bunch of bowls, but the blade seems very "catchy". I've sharpened it (kept the same grind), opened an adequate kerf, cleared shavings, adjusted speeds and still get a LOT of vibration and catches. I've watched Mahoney's video several times.

Reed was kind enough to share his video instructions on the system, which I found to be very helpful. Has anybody changed the grind on the cutter, as recommended by Reed?

As anybody had the same issues and found a good solution?

[mike ash]

Yep, I changed my grind to the flat pattern that Reed has found to work better, and conclude that Reed is right on.!!!!

[Dale Bonertz]

Eric,

What size blades are you coring with? What type of wood are you coring? How fast are you coring? What is your lathe you are coring on? This will help to diagnose your issues.

Turn the speed down as the blade extends further from the rest. Not always a good idea to widen the kerf since chips can jamb between the blade and kerf causing catches and binding. Make sure that when you a setting the cutter height that you extend the blade to its fullest reach out of the turret and then set the height to center or better yet slightly above to allow for torque. I leave the point on the blade but I do flatten the factory angle over several sharpenings.

[Reed Gray]

The chattering seems to be a problem. Much more so with hard woods like locust or osage. I do keep my cutter above center, just like I do with any scraper. Other than that, some times it just does. It does take a light hand and let the tool cut and feed by itself. Perhaps the most difficult thing for me to learn was to keep the blade up against the top of the T bar (now a square tube thing) because with all the blade hanging out, it is almost impossible for the turner to keep it from dipping when you contact the wood. With the Mark 8 system, there is an underneath support bolt/bar that you need to use. This keeps you from dropping the handle. If you haven't checked out Dale's You Tube clip on the McNaughton, it is pretty good.

robo hippy

[alex grams]

I will have to revisit and look at your grind Reed. I've used my system with some good success, but have had some chatter/catch/binding issues on some larger osage I've worked with. Do you have a link/picture of your grind?

[Reed Gray]

No, I don't have any still pics of my grind. What I did was to grind the tip down to square rather than triangular. Main reasoning behind that is that you get less surface area into the wood at one time. Some do use the 'fish tail' method where when coring, they sweep the cutter back and forth a little to keep a more open kerf. If you do this, you are using one side of the triangle, then the other. How ever when you get to the bottom, you aren't sweeping as much, and the whole tip becomes engaged. Ever notice that all hollowing tips are pretty small?

The biggest problem is in dealing with the 'drift' as in the blade always drifts to the outside of the kerf, rather than following the arc of the blade. As near as I can tell, this is because the last inch or so of the blade goes straight rather than following the curve of the blade. If your support fingers are locked down, or you have a bending jig like shown in the latest issue of Woodturning Design, you can fine tune and tweak the tip in just that tiny little bit, and this makes it run a lot more true to the curve. I have tried to convince Kel of this, but he doesn't agree. Last time I talked to Mike Mahoney about it, he said, 'you might be on to some thing there'. I have one that I tweaked in just a tiny bit too far and it now curves to the inside of the cut rather than to the outside. If you have one of the plastic circle templates, lay your blades on the circles and check them out. The bends with the newer Mark 8 system are pretty good. The older blades tended to be rather wild some times.

robo hippy

[Eric Gourieux]

[QUOTE=Dale Bonertz;2208668]Eric,

What size blades are you coring with? What type of wood are you coring? How fast are you coring? What is your lathe you are coring on? This will help to diagnose your issues.

Dale, I have the medium blades and have cored fairly dry hard maple, wet ambrosia maple and cherry. Most were about 12" diameter. I have a Nova DVR and usually have the speed around 600-800 RPM's. One problem with coring with the Nova DVR, in my limited experience, is that the banjo tends to move even when I crank it down pretty well. That may be due to the vibration, though.

[Dale Bonertz]

That helps, your coring woods that should not be to much of a problem. I have never cored on a DVR but I have heard other complaints about the banjo loosening so that may be part of the problem. One thing that never seems to come up is the opening of the kerf. The blades are designed with the tip wider than the shaft to allow for free travel of the shaft in the kerf. By widening the kerf you not only can chips get jammed between shaft and blank but also you will get more twisting of the shaft due to the torque which can cause a catch.

My first suggestions would be to make sure your tenon is large enough. To small of a tenon and you can get blank vibration. 12" blank should have at least a four inch tenon until you become pretty handy with the tool then you can go smaller if you choose. Take your biggest/longest curved blade from the standard set and put it into the turret. Fully extend it out of the turret as though you are coring a deep bowl. Now align the cutter tip at 1/8" above the center of a bowl or drive center - make sure you are holding the shaft up against the T support or U support on the M8 while setting the height. Start your core around 700 rpm an as you go in about an 1 1/2 inch slow it down to 600 after 3 " in down to 500 and as you approach the end of the cut to 300 to 400. One last thing do not pull the handle to the left and try to force a curve. Push straight in and allow your body to move to the left so the tool can make the curve. Move your body much like you would using a gouge. Try that and report back to see if that has helped you. If you want to email me directly or call me while your in the shop send me a PM and I'll give you the information.

[Doug Herzberg]

Eric, I haven't had this problem since I watched Reed's video. The changes I made were 1) the spacer under the toolrest, 2) locking the turret and 3) a 4" (approx.) recess instead of a tenon. I had tried a smaller tenon on small blanks, but I also had been using tenons sized for the 130mm SN2 jaws. I did not grind the knives flat. My knives are also medium (standard). I haven't reduced the speed as Dale suggested, but it sounds like a good idea. I have done pine, osage orange and maple without a catch or any chatter. The locking mechanism on the banjo of my Grizzly lathe has a bolt through the bottom clamp with a nut that is used to adjust the clamping pressure. It's always working loose, so I'm always tightening it up. I don't know how the DVR banjo works, but I would think there would be some adjustment for cam wear.

[Eric Gourieux]

Doug, Reed and Dale, thanks for your replies. I have had the same problem with my banjo bolt working loose and was always tightening it. Finally, I tightened the lock nut on the underside of the banjo, and that has kept it pretty tight. I may consider a thicker, wider washer on the under side to see if that feels more secure. I'm planning on working on my coring tomorrow or this weekend, so I'll let you know how it goes. I'll review the videos one more time, too.

[Mike Cruz]

Eric, I've found the BEST solution to catches (the kind that will rip the blank off your chuck and crack a perfectly good tenon!) is to put your lathe in high gear (the one that allows for the fastest speed), and turn the rpms down to 600 or so. This gives you less torque. So, instead of the lathe powering through the catch, it simple slows the lathe down or stops the lathe. Once you get accustomed to doing it more, you'll get to know the sounds of when you are getting close to stopping your lathe. Just ease back and continue.

As for shavings, yes, shavings clogging the kerf screws things up. So, I feed the blade in with my right hand and hold the air nozzle to the kerf with my left. This keeps the shavings ejecting. You don't need a death grip on the knife anyway...as long as you keep the handle pulled up in the back!!!

[Reed Gray]

Another solution is to slack off on your drive belt a little. I don't bother any more, I am so used to it. I still keep it in mid range (3 speeds on my Beauty). Never tried an air hose, just too much to hang onto. I did find that with the squared off tip, I get way less clogs. The more I pull the blade out and stick it back in, the more it clogs, which I think is due to notches in the sides of the kerf from starting and stopping.

robo hippy