advice on McNaughten 8 coring

[Michael Ginsberg]

Hello All.
I am intersted in getting the McNaughten coring system. I have a Nova 1624 lathe. In the Craft Supply catolog, they offer the Standard System which stated is for lathes 12-16 inches. The Jumbo system is for lathes 16-20 inches. Obviously, my lathe falls right in the middle. Does anybody have any ideas as to which would be the better situation OR should I by the complete set of the two or is it redundant? If there will be applications for both sizes, I don't want to get caught without the proper size to do the job at hand when needed. Please feel free to suggest!!

[Terry Gerros]

Not that I am any expert by any means, but I think you are going to find you use 1 or 2 blades for 95% of your coring. I have both sets (older system) and have yet to use the jumbo set. Not that I regret buying them....you just never know..... You might try to get in touch with Reed Grey in Eugene, OR and get his opinion. Reed has cored hundreds of bowls and has extensive knowledge of the tool.

[Nathan Hawkes]

Michael, its most likely that you'll need only the "regular" sized coring knives. I turn on a PM3520, and have the regular set and one of the large knives which can be purchased separately. I'm not sure exactly what the McNaughton specifies the maximum core you can remove with the regular set, but in practice I found that you should reduce that by an inch or so, just my experience. I can remove about a 9-10" core easily with the regular set, maybe a bit larger, provided the bowl isn't too deep. I've cored out a 15" bowl from a very large blank with one of the "jumbo" knives. Mostly, I stick to the largest knife of the regular size set. Hope this helps.

[Michael Ginsberg]

I just spoke with Mike Mahoney. He also said stick with the Standard set.


Michael, its most likely that you'll need only the "regular" sized coring knives. I turn on a PM3520, and have the regular set and one of the large knives which can be purchased separately. I'm not sure exactly what the McNaughton specifies the maximum core you can remove with the regular set, but in practice I found that you should reduce that by an inch or so, just my experience. I can remove about a 9-10" core easily with the regular set, maybe a bit larger, provided the bowl isn't too deep. I've cored out a 15" bowl from a very large blank with one of the "jumbo" knives. Mostly, I stick to the largest knife of the regular size set. Hope this helps.

[Reed Gray]

For learning, you should go with the standard set of blades. You can core up to maybe 14 inches with the flat curve, and the medium curve will remove a 12 inch core easily. If you are going for bigger bowls (ones over 14 to 16 inches are more of a specialty market), then you would need the two curved blades for bowls that size. Do learn to use the standard blades first before trying the large blades. Do start with green wood, and smaller pieces (10 to 12 inches) for the first few cores before trying some thing larger.

If you encounter any problems, let me know.

robo hippy

[Bob Bergstrom]

+1 on what Reed says. If I turn a big bowl, I usually just take the biggest I can with the standard set, and then rough out what is left.

[Edward Orecchio]

I have a NovaDVR3000 wired to 220 to get 2hp. I just purchased a Mark 8 McNaughton system,standard set and got 2 extra blades(medium mini and micro). Frankly the Nova does not have the guts to core a full 16in chunck of wood-that puts alot of stress on the machine with it stopping very frequently(and I do have it weighted down). I don't think the Jumbo blades will be of much use. I think the Nova works fine with the smaller bowls and I think buying the mini blades may serve you well along with the standard blades.

[Michael Ginsberg]

Thank you all....I will be getting the standard for now...perhaps the jumbo when I get my New larger Nova or PM3520.

[Reed Gray]

Edward,
I would think that you should have plenty of power, which to means some thing is wrong. I have turned on a Nova DVR with 110 and it felt like it would core fine.

Most common problem is the blade binding in the cut. Most of the time, this is because the blade tends to drift off towards the outside of the cut as you core. The kerf needs to be widened out a bit.

If you are coring at slow speeds (less than 500 rpm) it will tend to bog down more than if you are coring at higher speeds (800 or so rpm), but this is a 'comfort' level thing. The blades can be pretty aggressive some times, and need little pressure for coring, and if you let them, they will self feed.

One thing that I did (Kel McNaughton was very surprised to hear this) was to grind the spear point down to square. Much less steel on the wood at one time.

robo hippy

[Michael Ginsberg]

Reed,
So you are saying if I understand you right.... that I could use the jumbo on my 1624 with a light touch?
Michael

[Reed Gray]

Probably, but, and there is always a but, or a 'theoretically' involved. Figure that the cutter is a scraper (all coring systems are scraper type cutters). With both sides of the spear point, you have a 1/2 inch wide scraper. If you can peel off shavings with a 1/2 inch wide scraper fully engaged, then you "should" be able to core with the large set of blades. The cutter is actually the same size on the mini, standard set and the jumbo/large set. The micro set the cutter is 1/4 inch wide or slightly less, and is designed for mini lathes.

If you watch Mike Mahoney's new bowl coring DVD (better than his old one) you will notice how much he opens up the kerf with his 'fishtail' method of sweeping the cutter back and forth a bit. This does three things. One it opens up the cut so the shavings eject better. If you have the full tip engaged, the shaving is 1/2 inch wide, and if the cut is 3/8 inch wide like the cutter, you get almost instant plug ups. The second thing it does is that the wider kerf helps to counter the drifting tendency of the blade (wider = less chance of binding). The third thing here, as you swing from side to side, you are cutting with one side of the tip, then the other.

With my ground off tips, I can get away with a narrower kerf, and the chips eject fine without having to open up the cut any more. Also, I fine tune the blades. I have talked to Kel about this a few times, and we disagree. The arcs of the blades can be a bit off, and this is mostly right at the tip. This was more of a problem in the past. I tweak the tip of the blade in just a tiny bit, maybe 1/16 of an inch, which on the end of a 6 to 8 inch lever can make a difference. This seems to help prevent the drifting, and one blade I had actually drifted to the inside. I think most of the time the blades don't need this, and most turners just got used to working with the drift.

Steve Russel developed a 'pulse' method for coring on the smaller hp lathes. Mostly it involves letting the speed build up and then plunging in a bit, let the speed build again, and plunge some more. I believe you can find his article on his web site as well as the McNaughton/Kelton tools web sites.

Do let the tool cut by itself. I push mine into the cut as I am a production turner, and I have a 3 hp Robust American Beauty. I did the same thing on my old PM3520A.

Perhaps the biggest problem with the lathes bogging down is a combination of the pressure/resistance of the cutting tip, and binding of the blade in the cut at the same time. If, when you remove a core, there are burnished or burn marks on the wood (most often on the bowl wall, and not on the core) it is the drifting. With a bigger more powerful lathe, you can get away with it. On smaller lathes, you can't. Perhaps the most difficult thing to do when using the McNaughton, other than learning how to aim, is to make a smooth even cut with it. Every time you remove the blade to clear the chips, you will leave a small bump. That bump can act as a lever and push the blade away from the cut, and make a catching point for the shavings.

10,000 more times grass hopper.

But teacher, that is what you said last time.

10,000 times more.

robo hippy

[Michael Ginsberg]

Thank you Reed for your insight.

[Josh Bowman]

Michael,
I just bought one with the standard and large set. After coring several bowls, none larger yet than 10", the smallest blade in the stardard set is all, I've really needed. I tried the next size up and made the top bowl too deep and cut the bottom out of the 10" bowl.:o
I did get the Mahoney DVD. It's not really needed, but watching it really helped me see problem areas. The blades will almost feed themselves, so if you get very aggressive, be prepared to duck!:eek: Wouldn't know why I know that.:D

[Bob Bergstrom]

Thanks to Reed also. Coring has a learning curve and it is well worth listening to those who have been the grasshopper and are now the master. I only have 9,900 more bowls to core and I can start on the next 10,000.:rolleyes::rolleyes:

[Fred Perreault]

Reed,
You mentioned that you put a modified grind on the coring knife tip. Is it possible that you could show a "before" and "after" pic of the grind? It seems from your extensive explanation that there is improved performance with the change in grind.
Thanks

[Ken Whitney]

I just started using the McNaughton 8 coring system. First try orbited the blank. Watched the Mahoney video. Second and third tries went fine. Slightly higher speeds helped.

Although I've never used the old style gate I do not like the the new version's bar and knob cutter support. It is supposed to keep the cutter/handle from dropping, but it really doesn't stay adjusted for me. In Mike Mahoney's video he seems to ignore that feature from time to time.

Reed, do you grind the wings of the cutter and leave the point or do you grind the tip square?

[Reed Gray]

I do modify the tip by grind it down square across. I never got around to the picture taking or posting stuff yet. It is a modification that I made, and neither Mike Mahoney or Kel McNaughton understand why I did it. It just works better for me.

The spear point was a Mike Mahoney idea. It is supposed to make it easier to cut a core all the way off, rather than cutting mostly to the center then breaking the core out. The breaking out method works fine for most straight grained woods. For end grain, burl or crotch wood where the grain goes in different directions, if you don't cut it all the way off and try to break it out, you can rip right through the bottom of the bowl you are coring. To me the biggest problem with cutting a core all the way off is the blade usually is below center when you get to that point. If you try to remove the stub at the center of you bowl with the coring blade, as soon as it engages the wood, it goes down below center. That is a lot of pressure on a 6 to 8 inch lever, and the system is designed to flex. When coring, after doing a whole bunch of them, you can feel this. You can raise the tool rest to keep it at center height. You can also lower the handle (which raises the point), but this is a PROFESSIONAL DRIVER ON CLOSED COURSE DO NOT ATTEMPT type of thing. It can be done, but is risky, and I will not recommend it for anyone.

The original McNaughton blades had the cutter dog eared to one side. The newer spear points have the cutter centered on the blade, which was a huge improvement. I had the original blades. I heard others were experimenting with different shapes on the cutter tip, so I experimented as well. I did square across, dog ear to the inside, and spear point. I did not notice any difference in how the blade tracked (went along the intended path), feed rates, catches, or general cutting ability on any of the different profiles. When the spear point first came out, I used it for a bit, then ground one tip down square. I liked it. My goal is to make the core in one pass without having to widen the kerf. With the spear point, this is impossible. A 3/8 inch wide kerf and a 1/2 inch wide shaving equals instant chip jam. I still have to widen the kerf a small bit because of the drifting, but not much. There is less cutting pressure with the square tip with it fully engaged that there is with the spear point fully engaged. The biggest advantage to the spear points as far as I am concerned is that you can remove some of the wood on the inside of the cut, which you could not do with the older blades.

Trying to get the McNaughton to core in one swipe, like the Woodcut or Oneway, without having to change the tracking, or tool rest has been an obsession with me. In theory, you should be able to do it, just by keeping the blade centered in the cut/kerf.

Shameless plug, I have a DVD on using the McNaughton as well. PM me for more info.

robo hippy

[Edward Orecchio]

Gee Reed that is very helpful. The learning curve is steep with that tool. Widening the kerf is a thought-I thought I was but maybe it wasn't enough. The speed thing-I have not been over 300RPMs,should I go up to 500 or more. On his DVD Mahoney says 600-700. I haven't had the courage to go that high but should I? Ed

[Reed Gray]

300 rpm is too slow for me. I would compare it to running a chainsaw at too slow of a speed. You want high torque, but you also need a certain amount of speed as well. If you turn up the speed, use very little pressure on the tool. Bill Grumbine told me he cores some natural edge forms at 1000 rpm. Since I don't have any readout on any lathe I have ever had, rpm is guess work for me. I would think that I core most of the time in the 700 or so range, and up to 1,000 some times. Probably 500 or so on large pieces. I will turn smaller bowls (8 to 10 inch) at 2000 rpm. Fast enough so that some think I am crazy, faster than most will ever try, and probably a 'professional driver on closed course, do not attempt' thing for a lot of people. I used to use slower speeds, but as I eased the speeds up, the coring got easier.

For the under support on the new Mark 8 coring systems, I do not have mine on the tool. I learned without it. When I first started (old style T bar on top or the blade, I would hold the blade down and not in contact with the T. Really doesn't work well that way at all. The under support bar is a good idea for beginners to remind you to keep the bar up, but it is not essential once you have learned to use the tool. It also keeps you from dropping the handle when you are removing the blade to clear the chips. If you have ever had a catch with a scraper on the inside of a bowl from having it pointing up, you know what can happen.

Pat's Fan on Woodnet Forums said it well when he said, "When sphincter tightening exceeds chuck tightening, you have a problem." Stay in your comfort zone.

For what it's worth, I have never had a bowl fly off while coring. I have had them come loose from the chuck for lots of reasons, but nothing goes flying. The blade in the core keeps things in place. I have had cores go rolling across the floor though.

robo hippy

[Ralph Lindberg]

I'm not up to Robo or Bill's coring, but I do have a digital readout on my lathe

I find 750 to be a nice coring speed.

I doubt I have the nerve to try 1000

Robo, BTW, I took the coring knife I was having troubles with to the last "turning day" the consensus of GeorgeK and Hinkie was that the angle was too sharp, When I checked it at home, that knife had a 50-degree angle, while the other knives were at 60. Could explain why that knife was grabbing so much

[Reed Gray]

I do remember reading or hearing that scrapers with a sharper bevel angle are more grabby/catchy than a blunter angle. I think mine are about 70 degrees or so, but never measured. Locust and Osage are two woods that tend to chatter a lot when coring, no matter what you do.

robo hippy

[Jeff Nicol]

Michael, I have the standard set and after a few practice runs on different types of wood I can now core an 18" bowl on a 19.5 blank and on down the line. Like Reed says you have to put in some time and figure out what works for you and everyone is different. The lathe power and capacity are really your only limiting factors. Alos making sure that the cutter is cutting at the very center or a bit high is a key point to remember with the McNaughton system. I ended up making a permanent spacer that I keep on the tool post of the gates which starts my cut at about 1/8" above center but it finishes at the center due to the torque and small amount of flex in the knives. If the cut is below center at the start and or finish the knives will grab for sure.

Thus practice makes perfect,

Jeff