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problem with McNaughton height setting

N

Nate Hawkes

Joined
Jul 21, 2008
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Location
Ivy, VA
So, I'm having some issues......I've recently (today after coring several bowls in a row) become aware that when I'm using my McNaughton Center Saver, the height of the tip goes down as it travels in its arc towards the center, and ends up about 1/2" below where it starts. It seems to happen with at least two of the curved knives, and I'm relatively certain with the straight knife, although in honesty I didn't notice the problem until after using the straight knife, and didn't feel like putting it back on to check it. I had a couple serious catches that led me to check the height at the end of the cut, although I'd set it at the beginning. I had used the Mcnaughton on my old lathe a lot before getting my 3520B, but didn't ever notice the problem before now. I've cored probably 200 bowls with it, and love it, and really don't feel like buying a new one.I really doubt that I've somehow bent all the tangs on the knives without realizing it along the way. The odds of that are impossible. Something else is going on all the sudden.

I don't have a machinist's square to check it, but I'm thinking that the top of the banjo might have been milled at a little bit of a slope, which would explain the descending tip height. I came up with the hypothesis while sitting here on the computer, so honestly I haven't even looked at the banjo top to see if it looks out of square. Each time I used the McNaughton, the banjo was roughly perpendicular to the lathe bed, thus leading me to my suspicion. Something is wrong here. Has anyone else had problems that sound anything like this?




Side note, when is Craft Supplies going to get the jumbo curved knives in???!!! Theyve been backordered for months. I've been wanting a couple to complete my set for a while now (assuming I figure out what's up with the thing quickly)
 
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Nate, you have probably check it out already but might it have something to do with movement where the 'turret' fits onto the toolrest post, on the centre saver. Any small amount of movement here would be 'amplified' at the end of the cut. Only guessing. Also while you are at it, is the grub screw in the side of the 'turret' at the correct adjustment?
If your banjo was 'out' you could measure the height of your conventional toolrest (at the extreme ends) off the bed and compare. And/or test this at various positions, relative to the bed. A bit hard to explain, but I think you would get the idea.

I hope this helps.
 
Several things could be going on here. One, there is some play/flex in the tool rest as you core, especially with the longer blades. It isn't totally rigid which would amplify any catches or chattering that you can get with harder woods. There is also some flexing with the blade. If you want to see this, try removing the stub that is left in the bottom of the bowl after the core has popped off.

Another thing could be that your blades are bent. This happens over time if you core a lot of bowls, and can also happen if you have a serious catch or two. Lay the blade on your table saw table or other totally flat surface. If it rocks, it is bent. The bends are a toqueing or twisting of the blade. This will lower the point. They don't just bend straight down. This is normal. You can put the tang in a vise, and using a big monkey wrench or adjustable (crescent) wrench, bend/twist it back into place.

For setting the height, I extend the blade to its fullest and lift up against the top of the tool rest with a little pressure. I do prefer the cutter to be a bit above center when starting to core so that it is on center by the time I am at the bottom of the core.

Some times, especially on harder woods where there is a lot of chattering going on, the tool rest can vibrate lower in the banjo. I make an end grain tube of hardwood to put under the tool rest so I don't have to adjust the height every time, and to make sure that it doesn't vibrate lower.

robo hippy
 
GLENN ROBERTS said:
Nate, you have probably check it out already but might it have something to do with movement where the 'turret' fits onto the toolrest post, on the centre saver. Any small amount of movement here would be 'amplified' at the end of the cut. Only guessing. Also while you are at it, is the grub screw in the side of the 'turret' at the correct adjustment?
If your banjo was 'out' you could measure the height of your conventional toolrest (at the extreme ends) off the bed and compare. And/or test this at various positions, relative to the bed. A bit hard to explain, but I think you would get the idea.

I hope this helps.
Click to expand...



robo hippy said:
Several things could be going on here. One, there is some play/flex in the tool rest as you core, especially with the longer blades. It isn't totally rigid which would amplify any catches or chattering that you can get with harder woods. There is also some flexing with the blade. If you want to see this, try removing the stub that is left in the bottom of the bowl after the core has popped off.

Another thing could be that your blades are bent. This happens over time if you core a lot of bowls, and can also happen if you have a serious catch or two. Lay the blade on your table saw table or other totally flat surface. If it rocks, it is bent. The bends are a toqueing or twisting of the blade. This will lower the point. They don't just bend straight down. This is normal. You can put the tang in a vise, and using a big monkey wrench or adjustable (crescent) wrench, bend/twist it back into place.

For setting the height, I extend the blade to its fullest and lift up against the top of the tool rest with a little pressure. I do prefer the cutter to be a bit above center when starting to core so that it is on center by the time I am at the bottom of the core.

Some times, especially on harder woods where there is a lot of chattering going on, the tool rest can vibrate lower in the banjo. I make an end grain tube of hardwood to put under the tool rest so I don't have to adjust the height every time, and to make sure that it doesn't vibrate lower.

robo hippy
Click to expand...

Thanks Glenn, and robo hippy. I'll measure the straight tool rest when I go outside. I think the grub screw is in the right position--it has definitely vibrated loose a few times, but I generally check it before using the corer, as I've had a catch pop the turret guard off the top before. I'll check through its range of motion that it doesn't rise higher on one side than the other.

Reed, I think you may be right about the bending, unfortunately. I've definitely seen the flexing at the end of the cut that you're referring to!! It can move nearly an inch with really hard woods. I've had some major catches since I got the PM lathe, which doesn't give or slip at all compared to the step pulley 1.5HP motor I had on the other lathe. Even with the old lathe tensioned as tight as I could get it, the belt would slip when I took really heavy cuts. Keeps me honest and diligent with sharpening! 😀 The PM jolts much harder when I have a catch, which really didn't happen often at all before--I usually would just stall the lathe, and the built up shavings would sometimes bind the cutter as I tried to retract it to allow the shavings to exit. This is truly scary, and horribly noisy with the ribbed belt squealing. I've done a couple with my hand on the off switch just in case. As to the height of the tool rest, I put some 1" diameter schedule 40 PVC pipe around the post so I don't have to bother with adjusting the height too much--a couple cutters are a tad higher than others, but I start with them all slightly above center.


I'm going out to check things and I'll report back soon. Thanks for your advice guys.
 
Well, the answer was different than I suspected. The banjo is just fine, milled dead perpendicular to the lathe bed, and the top perfectly flat. All but one cutter is flat, and the other is only very slightly bent. I can't believe it isn't more bent, to be honest. The last couple catches were pretty violent. When I measured with the blade at the start of travel, and at the end, it was fully 5/8" lower at the fully extended position. I really am scratching my head, because as my memory serves, the turret and lock bar were always together, but I may be wrong here. I don't know what has caused my problem; bending of the over the blade lock bar is next to impossible. After measuring everything, and trying to put a spacer between the guide fingers, I realized the solution was to put a thin slice of PVC in between the guide finger "turret" piece and the pivoting over the blade lock bar. The effect of this is to bring the over the blade lock guard a bit lower, making the blade move straighter in its arc. I had to use a small sledgehammer--a 2lb rock splitting hammer, really, to loosen the pieces off the tool post after loosening the grub screw fully. I can't find my camera cord to upload pics, maybe later. I did put loc-tite on the threads to make sure the grub screw doesn't loosen up over time. I like it tight as well; I didn't at first, but I seem to be able to keep the cut straighter with it locked.

After putting the PVC spacer in, it moves only 1/8" from start to full extension with the largest of the standard length cutters. I don't have the jumbo set. I did not take the time to re-measure the other cutters in the set, but I imagine that the results are similar. I haven't actually tried it yet, as I don't have time today, but I will in the next few days to a week for certain. I'm a little worried that this slope was intentional to keep the cutter moving in the cut, but right now it sucks it in too fast, and catches too much.I will definitely be posting a follow-up with before & after info.

Let me say as a disclaimer, that I do not suggest anyone go out and do what I did; I have not tested it yet, and take no responsibility for your outcome.....😉



Thanks again everyone. I'll post an update soon.
 
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Nate, for what it is worth, there is a new version of your unit now available, Mark 8 which has a number of extra features. (as well as the smaller unit).
On the new model the height of the blades (to use different size blades) are compensated by small shims that fit between the 'fingers'. This might be an option for you?
Glenn
 
Dear Nate:
If all else fails I would contact Mike Mahoney through his web site. When I bought the McNaughton system, I spoke to him about some problems I was having and he was very helpful. He is a nice guy and easy to talk to.
 
Kel does have a new tool rest out. It will not take the large set of blades. He made new ones that are a bit thinner than the old ones, but the standard, mini and micro ones fit in it, and there is a bracket that goes on it for using his hollowing blades.
robo hippy
 
McNaughton catches.

Nate, I am probably not going to tell you something you already do know with your experience in these tools. One thing that will cause severe catches, is not having adequate tenons well seated in your chuck jaws. They need to be well seated on the upper ends of the jaws and almost the full length of the jaw depth, without touching the base of the jaws. The tenon diameter needs to be no smaller than 1/3 the overall diameter of the coring blank. Having tenons too small is one major cause of vibration and tool catch. I am partial to the vicmarc chuck jaws for coring but that is personal. Just my take.

Getting in touch with Mike Mahoney is an excellent suggestion. I thought I knew everything I needed to know about coring until my class with him. He is a master corer and does it so much easier and faster. Well worth the time to talk to him.

Bill
 
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