Selecting the right McNaughton knife radius

[John Washam]

I, like many others have struggled with my McNaughton Center Saver system. The system was a “freebie” when I purchased my used 3520 a few years back. I have the standard set of 3 radius and one straight blade knives. My question is do the knife radii correspond to a range of bowl (core) sizes? For example: does the smallest radius knife cut cores that are 5-7 inches; the middle radius cut 8-12 inches, etc?


Reed Gray, Dale Bonertz and other turners do an outstanding job with their YouTube vids and I have reviewed them so many times, I can almost quote the dialogue!!! 😀 I know that Dale suggest matching the knife radius to the out side of the original blank but what about the inner cores; how does one know which knife to use? Guess I’m just a very slow learner.


Would appreciate any guidance on selecting the knife size to use for a given core diameter.


Thanks in advance,
John

[Edward Weber]

I would need more info before I could answer.
McNaughton has 4 different ranges of knives for starters. The other thing is that diameter is only one measurement, depth is the other.
For example, a 10" diameter core could be shallow or deep, different knives would be needed for each.

[Jeffrey J Smith]

I'm not in the same league with Robo or bonertz, but I've been using my Macnaughton for nearly two decades - mostly to core 3 or 4 bowls to save from turning them into shavings, seldom to create nested sets of any more than that. I find that, for the bowl shapes I prefer (slightly open forms) and the typical sizes (16 - 18" for the largest) the cores all wind up using the middle curve of the three curved blades of the standard set. I wind up with a 16, a 14 or 13", a 10" and usually a 6" blank for the drying shelf.

These blanks are typically 1-3/4 - 2" thick so there's a lot of latitude to reshape when final turning.

Its very rarely that I need the smallest and equally rare that the largest (shallowest curve) is used. I do use the straight blade a fair bit to separate either a lid or a platter from a deep blank.

[Reed Gray]

I end up using the medium curved blade about 90% of the time. The other 10% is usually the small curve blade. I do wish there was a little more variation in curves.

robo hippy

[Richard Coers]

Always good to go to the source. https://www.kelton.co.nz/McNaughton%20Center%20Saver.html
The Micro system has been designed for those whose work is probably in a size range from 100mm to 200mm (4" to 8") in diameter or those wishing to take very small cores as part of nested sets where larger blades are used for the remaining cores. If you typically work with blanks in the size range 100 mm to 250 mm(6" to 10") diameter, then the Small set will probably fulfill your needs. For work in the 200 mm to 350 mm (8" to 14") range, then you might opt for the Standard system. If you routinely handle work in the 250mm to 450 mm(10" to 18+") diameter range, then the Large or even the Combo would be preferred.

[Jeffrey J Smith]

I think, in practice (at least for me), if the goal is to keep the wall thickness somewhat consistent, the radius of the blade typically stays consistent from one size core to the next in the same blank. I tend to work from the largest core to the smallest so the wall thickness is set by the outside form the blank has been turned to. Pick the blade that matches best and start pulling cores.

I push the limits of the standard set fairly often by going as far as 18" dia - I usually have to knock out that core since getting to the middle is pretty dicey.