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gap between chuck jaws in wet wood

C

Craig Barton

Joined
Aug 28, 2021
Messages
16
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Location
Half Moon Bay, CA
I know the tenon should be sized so there is a very small gap (1/8 inch or less) between chuck jaws
when working with dry wood. I've had pieces fly off when I don't pay attention to this rule of thumb.
But what about wet wood? I want to leave a larger tenon to make up for the tenon warping as the wood dries.
But how large can I make it? Would a 1/4 inch gap (or larger) also cause the wood to turn into a UFO (unintended flying
object)?
 
standard jaws on my vicmark have a perfect circle. At 48 mm (1.9”)
with wet wood I turn a 2.5” tenon. This tenon has always dried for me with a 2” tenon inside.

the vicmark grips the 2.5” tenon extremely well
a oneway stronghold grips a 2.5” tenon really well too.

the nova bird beak jaws Have never held oversized tenons well for me.

dovetail jaws and ONEWAY profile jaws will hold oversized tenons extremely well.
the ONEWAY profile is designed to hold oversized tenons better than dovetail.
it is unlikely you or I will ever detect any holding deficiency using Dovetail or ONEWAY jaws on any tenon you can fit into the chuck.

When using the nova bird beak I stick close to the true circle diameter of the jaws.
 
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Not sure what caused pieces to fly out, but I don’t think it had anything to do with the gap between adjacent jaws. My response is assuming dovetail jaws. Proper angle cut for dovetail, proper mating between jaw face and blank, and a tenon sized appropriately for the size and weight of the blank are the important issues. I don’t think it’s ever wise to support 40 pounds of wood with a 2 inch grip, regardless of what one has gotten away with.

For my work, a 15 inch bowl blank is held with a 6 inch tenon. Even without a perfect circle, that piece will not go anywhere.
Im not worried about having the jaws open a bit, so that I can use those same jaws to final turn.

And don’t over tighten on the dovetail, especially a smaller one. You can break outer fibers, making it more likely to come loose.
Again, this applies to dovetailed jaws, only.
 
hockenbery said:
standard jaws on my vicmark have a perfect circle. At 48 mm (1.9”)
with wet wood I turn a 2.5” tenon. This tenon has always dried for me with a 2” tenon inside.

the vicmark grips the 2.5” tenon extremely well
a oneway stronghold grips a 2.5” tenon really well too.

the nova bird beak jaws Have never held oversized tenons well for me.

dovetail jaws and ONEWAY profile jaws will hold oversized tenons extremely well.
the ONEWAY profile is designed to hold oversized tenons better than dovetail.
it is unlikely you or I will ever detect any holding deficiency using Dovetail or ONEWAY jaws on any tenon you can fit into the chuck.

When using the nova bird beak I stick close to the true circle diameter of the jaws.
Click to expand...
This makes a lot of sense cause I was using a Nova chuck with the bird beak jaws. I even had a 4" bowl (dry wood) fly off with the Nova chuck (with a large jaw gap)! At the time
I thought I was taking too aggresive a cut. Might be time to upgrade my chuck...

Have you had any trouble gripping dry wood with a 2.5" tenon?
 
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At least with my Vicmarc jaws I've never had an issue with holding even very large blanks on even though I pay essentially no attention to trying to make the tenon as small as the chuck can grip. I've found the "8 point" grip to be very aggressive, even when coring 20+" blanks. So I use the entire gripping range of the chuck, as needed. I went through a phase of trying to make them close, observed no difference other than sometimes I could no longer make a round tenon I could grip with my smaller jaws after the rough bowl dried.
I do usually use a faceplate for the initial rounding up of logs, it just seems prudent, plus of course, you can attach a faceplate before you can make a tenon. Turning a half log between centers works and is sometiemes the thing to do to get the figure right-- it's easier to move the piece around, but the faceplate is easier.
I have broken off tenons, especially in the small 2 to 2-1/2 range. Punky wood and cracks are usually to blame. The tenon typically stays in the jaws in those failures.
 
Before you buy a new chuck (unless you want one. multiple chucks are nice). Try changing out the jaws. I use dovetail jaws on my nova chucks and rarely (can't think of the last time) have a blank come out unless I break the tenon.
 
Craig Barton said:
This makes a lot of sense cause I was using a Nova chuck with the bird beak jaws. I even had a 4" bowl (dry wood) fly off with the Nova chuck (with a large jaw gap)! At the time
I thought I was taking too aggresive a cut. Might be time to upgrade my chuck...

Have you had any trouble gripping dry wood with a 2.5" tenon?
Click to expand...
you can probably but real dovetail jaws for your nova.

i grip larger tenons and square stock with both Dovetail jaws and the ONEWAY stronghold. i see no difference in dry or wet wood.


i do a lot of 2.5” tenons. Actually 2 5/8”. Over the years I have gotten really good at guessing an inch.
I cut my tenons 1” out from my ONEWAY live center cup which is 5/8” so I get a 2.5” tenon +- an 1/8 every time with no marking or measuring.
dovetails hold these tenons really well in dry wood.
 
I turn mostly green wood and almost all mine are either 2 1/4 or 3 1/4 depending on the size of the piece. I don't use them as the foot for my pieces so just stick with a standard size. I've had a tenon break off the piece but never had the oneway jaws come loose from tenon. Like Roger I also use them on tenons of varying sizes if needed and don't fret much about the size or gap. I assume you're putting some torque on both sides of the chuck with the key. It's almost always the case that you can tighten one side, spin it 180 deg and get a good bit more tightening on the other side, then flip another 180 and check the first one.
 
Pretty much all the larger jaws for the nova chucks are dovetail. The only one that is the birds beak design I'm aware of is the standard 2" jaw that comes with the chucks. For almost all my green turning, I've moved up to the 100mm jaws (4"). Since doing so I don't believe I've had any losses from the tenon, which definitely happened for me using the 2" jaws. As much as anything, I think the significantly larger area of a 3" tenon vs a 2" tenon makes more of a difference than the dovetail vs. birds beak on the jaws.
 
I think Mac is correct about the tenon not made properly if the piece flys off. I had the Nova chucks and when I used the birds peak jaws I only used them on dry wood. Also I never made a cut for the birds peak, just a straight tenon. I know some people do make that cut, but IMO it lessons the holding/gripping power of the jaws especially if the recess is cut too deep. You just don’t need to cut that recess and Nova says not to cut that dovetail. I now have Axminster chucks and they have similar jaws called C jaws. Again I don’t make any recess for those. I did not use the birds peak jaws for wet wood. I use either my 4” dovetail jaws or my 6” gripper jaws.
 
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I have found in my turning journey that when a piece has become a UFO the reason it did so is not the fault of the chuck. In most cases it happens at the point where the tool tip meets the wood as in OOPS. As I probably have stated before with the 2" Nova chuck jaws I only have an 1/8" or less tenon and it is cut as a dovetail as the birds beak is a dovetail. The other thing I never do is put a death grip when tightening the jaws, tight is enough and a quick check for tightness during the process is all that's needed. I have the Oneway gripper jaws on just one of my Oneway chucks and those are the one I never use, don't like em and I feel a dovetail is better. That Oneway chuck is there in case a demonstrator prefers that combo (I think only one demonstrator here wanted to use that chuck out of the 20+ teaching here). In your turning journey you will find what works best for you, don't lock yourself into a closet.
 
The two main things that cause pieces to fly off the lathe, are usually a combination of too much speed and a catch. If you are getting catches, then you need to refine your tool technique. This can best be done with a mentoring session. With higher speeds, the accidents become more 'spectacular'.... I do have one video called Mounting things on the lathe. Might help.

robo hippy
 
Not mentioned above is the importance of making certain the surrounding base of the tenon - the part that is in contact with the top edge or face of the jaws - is flat and square to that surface. This contact surface adds a lot to the holding power of the jaws and prevents the blank from rocking if/when a serious catch occurs. The process David Ellsworth describes in his book shows this step and its importance in holding onto a blank.
 
While we are discussing the birds beak. Does anyone know if the other brands of chuck that interchange with Nova (Record Power, and Sorby I think) have 2" jaws with dovetails, or are the jaws exactly the same too?
 
Kirk Amidon said:
While we are discussing the birds beak. Does anyone know if the other brands of chuck that interchange with Nova (Record Power, and Sorby I think) have 2" jaws with dovetails, or are the jaws exactly the same too?
Click to expand...
The Record Power jaws, and the Sorby “Patriot” jaws fit the Novas. I have a set of Patriot jaws for my Novas.
 
For whatever it's worth... I've noticed that the Nova pin jaws and the Nova 25mm jaws both have an optimum recess diameter of 1". However, the 25mm jaws have more jaw surface contact against the recess wall thereby providing much more holding strength, particularly on wet wood.
 
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