Mcnaughton Center saver users

Discussion in 'Woodturning Discussion Forum' started by chrisdaniels, May 2, 2016.

  1. john lucas

    john lucas

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    I have limited experience with my McNaughton. I simply don't do many large bowls and rarely have wood good enough to bother with saving the core. I did find that my main problem was the cutter getting below center as I got deeper. Clifton's experience is dead on in my book. I did have one cutter replaced by Mike Hunter and that tool cuts much easier. However if i let it get down at or below center it's the same fight. I do have some Walnut I may core pretty soon. It depends on whether I decide to make platters from it or bowls.
     
  2. robo hippy

    robo hippy

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    The getting below center is always a problem. If you have ever tried to remove the nub that is left after the core has popped off, by using the McNaughton blade, when it contacts, the tip can drop an inch or so. This is a bigger problem with bigger bowls. There is a considerable amount of 'flex' in the whole set up, which is planned because a rigid system that is suspended out that far off the rest might snap. I can 'feel' this now, and use the long handles and drop the handle to raise the tip. This is Master Level skill. You can raise the tool rest a bit, and mine is set so the tip is about 1/4 inch above the center if I am really lifting hard against the top bar. You can't raise it too much because you have a square peg in a round kerf, and it can only go so high without rubbing top and bottom.

    I have taken to putting my blades on a circle template and checking the curves. While they are considerably better than early versions, most of the time, the very last inch near the tip goes straight rather than following the curve. I have a couple of 5/8 inch bolts through hickory with about a 3/8 inch gap which I clamp down to the bench top, and put the blades in and tweak them to perfection. They no longer track to the outside of the cut.

    robo hippy
     
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  3. Bill Boehme

    Bill Boehme Administrator Staff Member

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    That is very good information to know. I recently bought a standard large replacement blade from CSUSA and the curve didn't look right when eyeballing it. I laid it on top of a template and I could clearly tell that there was a straight section about three inches long at about mid span in the curve.

    Your suggestion of making a hickory bending form is an outstanding idea. And, I think that your observation about the last couple inches of the blade being straight is a dead on accurate explanation of why the cut tracks to the outside.

    I guess that I shouldn't be surprised to hear about the amount of flex in the blades considering the overhang, but that is impressive.
     
  4. robo hippy

    robo hippy

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    I have argued that point with Kel for years, and he doesn't agree. My 'fixed' blades cut on a much truer arc. I did retip one of my blades with the tantung that I use on the Big Ugly tool, and think it cuts better than what ever Kel has on his blades. I did send him a piece and some silver solder to play with.

    Ideally for making the blades, I think I need to find a laser cutter for tubing as it would be easier to bent the tang flat than bend the curve to a perfect arc. For bending straight stock to an arc, you bend it a couple of inches longer, and snip off the flat parts. Some of Kel's old blades were cast stainless. Not sure what he is using now.

    robo hippy
     
  5. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I did a bit of playing around with a couple blades today to see how much flex I could see. With the largest blade from the large set (CSUSA calls it the Jumbo set) extended to its maximum out of the gate, I could only get the tip to deflect down about 1/16" below center when applying about fifty pounds of force downward at the tip and it appears that a good portion of that was due to free play in the tool post and the yoke/gate assembly. I repeated the test using the largest blade in the standard set and the deflection was a bit more, but still less than 1/8" judging by eye. I had the tip of the blade sitting about a half inch away from the center point of the tailstock live center. This led me to wondering about the source of the flexing. I have the new Mark 8 design and being new, everything is reasonably snug. Maybe if it had a lot of hours of use on it then there might be a lot more looseness allowing the blades to deflect downwards a lot more.

    Funny that you should mention tantung because I have been wondering about it as a better alternative to what I assume is just a piece of HSS brazed to the blade. I figured that the blade is probably carbon tool steel that has been tempered so that it doesn't bend too easily.

    The curvature of the bottom parts of my blades near the tip seem to be OK, but the top part that is flared out to make the wide kerf seems to be too straight. I'm thinking about using a stone to reshape that a bit on one of my blades, but I probably ought to use them for a while to get the feel for what they do before I go off redesigning it.
     
  6. Mike Johnson

    Mike Johnson

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    Can anyone identify this McNaughton tool gate, the post is .80" in diameter.
    I am assuming this is an older model/version.
    There are only 3-pins on top and (2) of them have a short riser base.

    McNaughton Post.jpg
     
  7. robo hippy

    robo hippy

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    That gate is probably the original, and my favorite to use. No idea about the narrow post though, I thought they were only 1 inch or a metric one to fit the Vickmark lathes. It will fit the standard and jumbo or large set of blades. On the newer Mark 8 blades, the jumbo set are a thinner gauge, and will wiggle a bit more.

    As for the blade and tool rest flexing, I have no idea how much downward pressure is on the blade when coring. I figure that there is a lot of torque on a 1 1/2 inch nub if you are trying to remove it with the coring blade. Exceeding 50 pounds, I would guess would be easy. I have lifted up the handle and applied at least that much pressure to see how far the tip would move down, and yes there is flex in the tool rest. Try to take the nub out and see what happens...

    robo hippy
     
  8. Mike Johnson

    Mike Johnson

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    Thank You Robo,

    The odd sized post was kind of throwing me off, I might get a 1x3/4" sleeve and drill it out or make a banjo with that
    size of opening fot the .80" post.

    If anyone has any knives for the McNaughton system that they are not using I would be interested in what you have.
    I will either forge some knives or purchase several new ones, but thought I would check here first.
     
  9. hockenbery

    hockenbery AAW Advisor Staff Member

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    Also some lathe beds and banjos flex too
     
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  10. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I agree that the gate looks like the original design that I have seen in several videos and that particular one is probably for the standard and small blade sets just guessing because of the smaller size tool post. According to the Kelton Industries website they have a number of tool post sizes available. The tool post on this one can be replaced with a inch diameter post, but you need to make certain that you get the one for the original gate and not the one for the newer M8. I believe that they are different.

    I watched Mahoney's DVD again today. I didn't see any noticeable flexing of the blades. However, he did mention in the tool tips section that he has bent a few blades in the past and the reason was because of overheating them due to rubbing.against the wood. That's one reason that he stressed frequent clearing of chips and shavings. He also suggested using a spray bottle to spritz water in the kerf to cool the blade and to keep the kerf clear of chips and shavings. I wouldn't be surprised if repeated overheating of a blade made it flex more than a new blade.

    The full load stall torque at the spindle of a 3 HP Robust AB in the low speed range (assuming it has three speed ranges like my model) is approximately 12 to 13 foot-pounds (I don't remember off the top of my head the exact pulley ratio). If we measure the force at different diameters just before stalling the motor, it would increase as the diameter gets smaller -- 13 lbs @ 1 ft diameter 2 foot diameter, 26 lbs @ 6 in diameter 12 inch diameter, 52 lbs @ 3 in diameter 6 inch diameter, 104 lbs @ 1½ in 3 inch diameter, etc.

    However, the thing that we're interested in would be the load torque and that can be divided into two components -- load torque created at the cutting edge and load torque due to friction of the blade rubbing in the kerf. Both of those components are somewhat dependent upon speed. The load torque at the cutting edge ought to be somewhat comparable to the torque load created when using a scraper the same width and taking the same size "bite" into the wood. Normally, the force feedback that you feel gets less as you work closer to the center. That is mostly because of the lower cutting rate near the center. The other component of load torque caused by rubbing friction in the kerf is highly variable. Kerf width, sharpness, the amount of force applied, chip and shavings clearing, wet or dry wood, species of wood, skill level, and "goodness" of blade curvature all make this an impossible number to quantify. However, we can try to minimize the friction load. I am still a few light years from the coring skill of Mike Mahoney or Dale Bonertz, but I think that identifying problem areas will help accelerate my progress ... that's the plan anyway :D

    EDIT:
    Corrections in math shown in red.
    updated 8-22-17
     
    Last edited: Aug 22, 2017
  11. Mike Johnson

    Mike Johnson

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    I have a metal lathe so I can turn a new 1" post to fit the banjos on my wood lathes.
    Just need to get a few knives to start working with.
    How thick and tall are the standard knives vs the large knives.
    I might pick up some tool steel if I can find the right sized pieces to make the knives with.
     
  12. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I'll make some CAD drawings. The basic blade material on the M8 system is ¼" thick for both the large and standard sizes.You should check to see what the pin spacing is for your older gate. It seems like I read somewhere that the large blades were thicker on the older system. You basically want the blades to glide easily through the guide pins neither binding nor rattling around. As a guess the clearance on mine is around 0.005". The height of the large blades is 1¼" and the standard blades are 1" tall. Unless you have a big lathe with a swing of 20" or more, you won't need the large blades.

    The radius of curvature of the two large blades are 9.5" and 6.5". On the three standard blades, the radius of curvature of the large blade is ~9.5" and 3.5" for the small blade. I don't have the medium standard blade yet ... it's been on back order for several weeks and isn't expected to be available until mid November at CSUSA. I would guess that it has a radius of around 6".

    Measure the height of the pins on your gate and that will tell you the correct blade height. The cutting end of the blade is the most difficult part to make because of the complex profile. It might be worth buying at lest one blade to study how they are made. Basically, the nose end looks a bit like the bow of a ship. I think that they use a welder to build up the profile and then use a grinder to shape it. The actual cutter is a thin piece of HSS welded to the nose of the blade, but you could create your own design ... maybe even using carbide cutters.

    The top and bottom and sides need to be smooth so that they won't drag or bind. When they are under load, it wouldn't take much to cause a rough spot on a blade to make it get stuck. In order to get a nice smooth core you need to be able to make nice smooth flowing cuts. Chamfering the edges also would be a good idea. I did a little file and stone work on my blades to make them slide as smoothly as possible. I also put a little Johnson's paste wax on everything ... it makes everything nice and slick.

    I'm not positive, but I think that the small (they use the word mini) blades are ¾" tall and probably 3/16" thick.
     
  13. Mike Johnson

    Mike Johnson

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    Thanks Bill,

    When I have the time to make bowls watching the floor fill up with shavings always seems like a waste
    of time and resources. I do enjoy the time practicing with different tools on the billets, but I have some
    body parts that get inflamed when I spend too much time with a roughing gouge or encounter tool catches.
    Has anyone done a time study to determine time wise which is quicker on a typical bowl roughing?
    With a sharp set of tools which method would be quicker to rough out the bowl if you did not care about the core?
    I run the risk of a tool catch using the McNaughton method the same as loosing focus on multiple cuts coring out
    a bowl with conventional tools. I would imagine the turners who make bowls every day can most likely core a bowl
    quicker with conventional tools then taking time to set up the jig and measure the bowl and determine the entry point.
    I have several lathes which allows me to dedicate each machine to do different tasks which speeds up the process and
    reduces the clutter around each machine. I plan on using this system on the billets that are highly figured and segmented
    billets mainly.
     
  14. robo hippy

    robo hippy

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    Following this on 2 forums....

    As for Mike saying that some blades have bent from heating due to friction, I have to scratch my head about that one.... Not sure how hot they have to get to bend due to heat/softening, but wouldn't think they could do that, though I have had some burn marks on the core and bowl, and I have burned my fingers more than once. For sure, with repeated use, and a catch or three, being curved and extending out a ways off the tool rest, the blades will twist, which is use and abuse, and will happen with or without heat. This is why we have the bent hollowing tools made so the straight part of the blade is on the tool rest, and the beginning and end of the arc are in line with each other so there is no torque with the cutting action. I put the blades in a vice and use a big adjustable or monkey wrench to twist them back up. The binding and friction is caused by the blades drifting, where you end up with two different arcs, the blade, and the actual kerf. This is why many open up or widen the kerf. Keeping the chips flowing is also a compounded problem because every stop/start you do leaves a ridge, which traps shavings. With a perfectly bent blade, the chips flow out a lot easier. With properly bent blades, I can remove an 5 or 6 inch radius core in one pass with out needing to remove the shavings.

    Now, out to the shop to measure the arcs, some thing I have needed to do for a long time.....

    robo hippy
     
  15. robo hippy

    robo hippy

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    Well, curiouser and curiouser...... I have several sets of large, standard, and small blades. I had always assumed that they were all bent to the same curves, but given the variance in the measured arcs, even considering the amount of use and abuse I have heaped on them, it appears that they differ from set to set. As near as I can tell:

    Shallow curve on large set about 11 1/2 to 12 inch radius, on standard set, about 9, on small set about 9.

    Standard/medium curve, about 9 on large set, 7 on standard set, and the small set, about 6

    Small curve, no available on large set, about 4 to 4 1/2 on standard and small set.

    robo hippy
     
  16. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Your large blades have a larger radius of curvature than mine. I was expecting the radius to be more like the radius of your blades on the large set. I made a PDF template (se attachment below) that you can printout on regular 8½ X 11 paper that makes it easy to check the radius of blades that have a radius of 5 inches and larger. I plan to make another template for smaller radius blades.
     

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  17. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Here is another PDF template to check the radius of smaller blades.
     

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  18. robo hippy

    robo hippy

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    Bill, I use one of those plastic templates with the different arcs drawn out on them. I was surprised at the variance, and will need to shape some of them, eventually. The variance could be from heavy use and abuse....

    Also, on the Mark 8 system, Kel switched on the large set of blades. As near as I can tell, thickness is metric. On old blades, the standard set appears to be 6mm, and the large set 7mm. On the newer ones, Mark 8, they appear to both be 6mm. I have heard a couple of people say the large sets of blades were bending with normal use, but I haven't tried them out.

    robo hippy
     
  19. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Using a carpenter's tape ruler, my calibrated measurement showed 1/4" thick.:D I suppose that I could whip out my fancy Harbor Freight digital caliper to see what it says.
     
  20. Mike Johnson

    Mike Johnson

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    I can only assume with a cold rolled steel tool the more you use the tool the quicker it will loose it's form
    from the heat and pressures/forces applied by the user and exerted by the piece being cut. I would consider
    using a harder steel and temper and anneal the tool so the tool will hold its curve without being too hard to
    where it would break on a hard catch. A knife maker using a forge can usually temper and anneal the steel
    and make the cutting edge hard and the other portion of tool somewhat softer to prevent breakage. The technique
    takes time to learn and understand how the different metals perform. This would certainly add to the expense of
    the tools being made which is the other part of the equation. By bringing the entire steel piece to the proper temperature
    and plunging just the cutting end of the tool into oil you can make one end of the tool hard and the remainder somewhat
    softer to allow flexibility in the tool. The tool is then reheated several times to a lower temperature to "temper" the steel
    and increase the flexibility of the tool. A Rockwell hardness tester can be used to determine the hardness along the entire
    length of the tool assuring you have a well "termpered" tool.
     

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