Dovetail Nova jaws

[Gerald Lawrence]

Awhile back seems (i cannot find it) we had a discussion about dovetail jaws and I stated that nova was not dovetail. Well the 50mm is not doved in compression only in expansion. I just bought the 100mm and it dovetail on both compression and expansion. Just a little added info.

 

[Bill Boehme]

Thanks for the update. I am starting to like the dovetail jaws for their alignment repeatability. I still like the profiled jaws better for holding strength over a wide range of tenon diameters.

The demonstrator at our club this month was using a chuck that had dovetail jaws ..... and then, just before he knocked the piece out of the chuck, he said that he preferred the dovetail jaws for their superior holding ability over profiled jaws. 🙄

 

[Hal Taylor]

Although the 50mm jaws are not really dovetailed, the outermost portion of the jaws, away from the chuck, has a slight dovetail. I always cut a slight dovetail to accommodate this.

 

[robo hippy]

The little rim on those jaws is designed to bite into the wood, and is not intended for a precut dove tail/groove for it to fit into. Probably wouldn't make any difference in wet wood as it will easily push into the softer wood. In dry wood, especially if it is very hard, it might help. I do prefer the dove tail jaws.

robo hippy

 

[Bill Blasic]

Once again that little bit of steel at the inside top of the 2" jaws is a dovetail. That dovetail is between an 1/8" and 3/16" long. If you make a tenon 3/16 high and dovetail it it will hold as well as any dovetail jaws made. The mechanical advantage of dovetailed jaws is that they pull the piece down on top of the jaws so your holding not only in compression but your also pulling the wood down for a secure two point grip. I know what Nova says about these jaws but once you figure out that there is a dovetail on these jaws they work much better.

 

[hockenbery]

Once again that little bit of steel at the inside top of the 2" jaws is a dovetail. That dovetail is between an 1/8" and 3/16" long. If you make a tenon 3/16 high and dovetail it it will hold as well as any dovetail jaws made. The mechanical advantage of dovetailed jaws is that they pull the piece down on top of the jaws so your holding not only in compression but your also pulling the wood down for a secure two point grip. I know what Nova says about these jaws but once you figure out that there is a dovetail on these jaws they work much better.

Bill
I agree,
In my unscientific study of the holding power of jaws for beginning wood turners the winners are
Compression Dovetails number 1, compression ONEWAY profile #2, nova a distant 3rd, any expansion hold 5th place.

Turn a proper tenon for the nova as Bill describes and it holds fine,
The problem for beginners is turning a good tenon.

I prefer using a spindle gouge for turning tenons. It leaves a nice clean surface on both faces with no torn grain.
My spindle gouge can cut any jaw profile and its tip makes a nice little groove for the Nova Jaws.

Expecting the nova jaws to hold in a tenon with torn grain made by a dull scraping tool without the little dove tail groove is wishful thinking.
The sides of the tenon for the Nova and the ONEWAY profile need to be parallel to hold well.

The sides for the dovetail jaws should match the profile of the jaws,
However most of the time the dovetail jaws will hold a sloppy tenon with torn grain as long as the tenon is narrower at the base.


Al

 

[Dean Center]

I'm finding this discussion very interesting, and it may explain a lot. Like why I have to nag our high school turners to make really clean tenons.

One thing I'm still puzzled about is why folks in the Southern Hemisphere, maybe elsewhere, seem to like recess mounting so much. Any mates from down under want to chime in?

 

[Bill Boehme]

... One thing I'm still puzzled about is why folks in the Southern Hemisphere, maybe elsewhere, seem to like recess mounting so much....

Maybe it's because:

• They're not as wasteful of resources as we are.
• The connotation of the word "recess".
• It might be a mistaken perception if we think that everybody in Oz is Richard Raffan.
• Maybe it's from being upside down all the time that they do things the opposite way.

We should ask the AAW for an educational grant to take a junket ... er, fact finding mission to Oz to research this issue.

 

[Gretch Flo]

I'm finding this discussion very interesting, and it may explain a lot. Like why I have to nag our high school turners to make really clean tenons.

One thing I'm still puzzled about is why folks in the Southern Hemisphere, maybe elsewhere, seem to like recess mounting so much. Any mates from down under want to chime in?

I use a recess and leave in (embellish), and I am not upside down (I don't think!!!). I turn very few things over 14" and 6" deep. and use the tail stalk while hollowing out the inside til tail stalk interferes (a la Michael mouse). I think Robo uses some too. I have had a couple of people say they like my "bottoms". !!!!! . 🙂 Gretch

 

[hockenbery]

I have used the recess as a feature some pieces.
A few turners are closing the jaws and making the recess a snap fit so as to not leave marks.
They finish the inside of the recess before mounting. Works well looks nice, no revers finishing at the end

In most display situations the bottom is never seen.
Sometimes the recess works really well as an element.


For most pieces I don't like to see how it was mounted on the lathe.
A round bottom, small foot, larger foot.....

In my travels I see a lot of bowls that have feet the same diameter as the chuck tenon, glue bock, or faceplate.
When those are not the proportion that goes with the bowl, I think the turner has left the piece unfinished and has not done enough reverse turning to get a nice proportion.
1/3 of the rim diameter works nicely.

Al

 

[Hal Taylor]

Al, I didn't get the snap fit description. Sounds interesting, so could you explain it a bit more for the Luddite.

 

[hockenbery]

Al, I didn't get the snap fit description. Sounds interesting, so could you explain it a bit more for the Luddite.

It is interesting! I have only seen this done by Mike Mahoney. I think Tom Wirsing is doing it and some others.
You close the jaws of a chuck with dovetail jaws. Turn a shallow dovetailed recess with the opening a tiny bit less than the diameter of the closed jaws.
Then slide one side of the recess over the jaws and give it a little hit on the top and it pops into place. To get it off you give a tap from underneath and it pops off.
As I recall the recess is about an 1/8" deep.

If you are going to Pittsburgh, mike will be there and you can ask him about it.

It is last like making a snap fit box lid where you make little dove tails on the matching parts of the box and lid. The lid snaps on.

I do something quite similar when I make a ball in a ball. The small ball is a bit larger than the opening. Give it a tap and the small ball falls inside
Since no one can tap it out it stays in there.

Al

 

[Bill Boehme]

It is interesting! I have only seen this done by Mike Mahoney. I think Tom Wirsing is doing it and some others.
You close the jaws of a chuck with dovetail jaws. Turn a shallow dovetailed recess with the opening a tiny bit less than the diameter of the closed jaws.
Then slide one side of the recess over the jaws and give it a little hit on the top and it pops into place. To get it off you give a tap from underneath and it pops off.
As I recall the recess is about an 1/8" deep.

If you are going to Pittsburgh, mike will be there and you can ask him about it.

It is last like making a snap fit box lid where you make little dove tails on the matching parts of the box and lid. The lid snaps on.

I do something quite similar when I make a ball in a ball. The small ball is a bit larger than the opening. Give it a tap and the small ball falls inside
Since no one can tap it out it stays in there.

Al

Al, I don't know about Nova, but for Vicmarc and Oneway dovetail jaws, the perfect circle diameter is NOT the diameter with the jaws fully closed. For Vicmarc jaws, the perfect circle diameter is when the gap between adjacent jaws is 2 mm. The reason is that jaws start out as a solid circle that is cut into quadrants. So, if you want a perfect circle, go to the Vicmarc site to see what the range is for each jaw size where the perfect circle diameter is the stated jaw size. The bottom line is that the snap-in method can't be justified as the reason for obtaining a perfect circle fit. Besides, it sounds like a risk of getting chip out. Wouldn't it make more sense to go for a recess that has a loose fit about the closed jaws and then simply expand the jaws into the recess. Even better would be to go for a recess size that is a bit larger than the perfect circle diameter ... why? ... because that eliminates the chance of the corners of the jaws marking the recess. Do just the opposite with a tenon ... make it just a bit smaller than the perfect circle to prevent the corners of the jaws from marring the wood (assuming, of course, the you like to see a "tenon foot" on a vessel). 🙄

 

[hockenbery]

Al, I don't know about Nova, but for Vicmarc and Oneway dovetail jaws, the perfect circle diameter is NOT the diameter with the jaws fully closed.

Is that because the jaws are cut into four after being machined round as a unit?

 

[Bill Boehme]

Is that because the jaws are cut into four after being machined round as a unit?

Yes, I was editing my post to add additional information while you were asking the question. BTW, Oneway doesn't give perfect circle diameters for their jaws, but I measured a #4 dovetail jaw set for the Stronghold chuck and found that the jaws make a perfect circle when the gap is 3 mm. I don't know if 3 mm holds true for all Oneway dovetail jaws, but I will check out some of the profiled jaws to see what size gap results in a perfect expansion circle, but I'm not certain that the expansion profile is a perfect circle. It's a bit of a moot question for me because I'm not a fan of using the profiled jaws in expansion.

 

[Dean Center]

Once again that little bit of steel at the inside top of the 2" jaws is a dovetail. That dovetail is between an 1/8" and 3/16" long. If you make a tenon 3/16 high and dovetail it it will hold as well as any dovetail jaws made. The mechanical advantage of dovetailed jaws is that they pull the piece down on top of the jaws so your holding not only in compression but your also pulling the wood down for a secure two point grip. I know what Nova says about these jaws but once you figure out that there is a dovetail on these jaws they work much better.

I had to take a couple jaws off to investigate, but what I found was that the standard equipment 2" Nova jaws have a very slight dovetail on the inside jaw base, maybe 5 degrees, with an additional angled bump on outer 1/3 which adds up to about a 10 degree equivalent. The 100 mm bowl jaws have a typical 15 degree dovetail on the inside. I assume the other sizes in the bowl jaw series are the same.