Nova JS70N Question

[Lynn Dudenbostel]

I received a set of Nova JS70N jaws for Christmas and when I opened them was surprised to find the jaw profile different in the contracting mode. Normally I'd turn a tenon with the proper angle for the jaws. These jaws have the normal dovetail on the outside for expansion into a recess, but the inside of the jaws are straight with a "lip" that projects at the top edge. I'll attempt to post a photo.
My question is, do you turn a straight tenon and just let the lip bite into the wood, or do you cut it straight with a slight recess at the bottom of the tenon. I'm pretty sure the lip needs to bite into the wood some to hold the work piece securely.
Thanks in advance!
Lynn

 

[Rusty Nesmith]

My 50 mm jaws are like that. I cut a straight tenon. Has worked very well. Great hold and don’t have any problems.

 

[Denny Nebgen]

What Rusty said. I have several sets of Nova jaws like that.

 

[Lynn Dudenbostel]

I guess my 50mm jaws are old enough to be dovetailed. Nova doesn't give any instructions on the tenon required for these, but my gut feeling was to do it as you describe.
After reading some of the Nova literature, I get the feeling several jaws have been resigned like this. It must work better than the dovetail.
Thanks for the reply.
Lynn

 

[Gerald Lawrence]

On the regular Nova jaws which was pictured Nova says use a straight tenon and the birdsmouth will grip the wood.

 

[Bill Blasic]

I treat that lip as a dovetail and make my tenon 1/8" to 3/16" deep and have never lost a piece gripping that way. I spent a week with Richard Raffan and he showed how well an 1/8 tenon holds. I believe all my Nova 2" jaws are that way.

 

[hockenbery]

These jaws are more demanding of a good tenon than real dovetails or ONEWAY jaws.

What has worked best for me and students is a tenon close to the perfect circle diameter and then make a tiny notch for the birds beak.
These jaws will hold that near perfect tenon quite well. These jaws don’t hold oversized diameter tenons very well - those tend walk out of the Nova jaws with heavy cutting. A Tenon with a flat to rest on top of the jaws adds to the holding strength reducing the walkout.tendency.

I much prefer real dovetail jaws or the ONEWAY jaws. using the standard dovetail or oneway jaws I can turn a 2.5” tenon on a rough bowl for drying and then return that tenon to 2” for the final turning. The vicmarc has a perfect circle of 48mm which is 1.89”. Holds the 2.5” tenon extremely well.

Success with my nova jaws on a 2.5” tenon is iffy. With a 2” tenon they work well.
Nova was my first scroll chuck.
The jaws work well with proper tenons.

 

[William Rogers]

I don’t have any Nova chucks anymore. When I did, that profile is the same as their 2” jaws. Nova’s instructions are to cut a straight tenon for those. I think the intent is for the “birds beak” is to force the wood into the face. IMO it is unnecessary to cut the small the small notch. I am not saying cutting the notch doesn’t work as some do, but again IMO it can lesson the holding if cut too large and just isn’t necessary.

 

[Mark Jundanian]

I agree with most of the above. That's how Nova makes the jaws for the 50 and 70 mm sizes. I believe the 100 and 130 mm are dovetail in & out.
I generally make a straight tennon with a nice square junction to the flat surface for the top of the jaws. I have sometimes made a tiny groove in the base of the tennon for the bird's beak, but this probably doesn't make a difference except on a really hard exotic.

When you remove a tenon from the chuck you will see where the wood has been crushed. As to the perfect circle, my tenons are never perfect, always end up a tad large. I've never had a problem, but that's in my shop.

 

[Doug Freeman]

I guess my 50mm jaws are old enough to be dovetailed. Nova doesn't give any instructions on the tenon required for these, but my gut feeling was to do it as you describe.
After reading some of the Nova literature, I get the feeling several jaws have been resigned like this. It must work better than the dovetail.
Thanks for the reply.
Lynn

Interesting point of discussion. I do not know about early Nova jaws (‘88 thru ‘90’s), but at some point Nova developed the bird’s beak style, as for the past ~15 yrs they have been that way. With the PRO-TEK redesign a couple years ago the 50mm (and possibly others) were given a dovetail upper and serrated lower portion of the inner surface. Both styles are available as jaw sets and with a chuck body. The PRO-TEK chuck operation is opposite (same as other mfrs) Nova’s earlier chucks.

 

[Dean Center]

I appreciate you asking this question and other folks for responding. I have used the bird beak jaws for over 10 years and have pondered this question much of that time, without resolving it, in my own mind. One thing is very clear to me, however. If you make a dovetail tenon, and the angle of the dovetail is too great, it causes a very poor attachment. The tenon may split or break a chunk off and the piece may go flying. Lately, I have been making the tenon with a very subtle angle.

The dovetail upper/serated lower was used 7-8 years ago on the 100mm Power jaws, and also on a 35 mm set I've got (can't recall the name, but they're longer than the standard bowl jaws).

 

[Mark Jundanian]

Lately, I have been making the tenon with a very subtle angle.

Dean, it's your call, but I don't think that's worth the effort.

 

[Lynn Dudenbostel]

Interesting point of discussion. I do not know about early Nova jaws (‘88 thru ‘90’s), but at some point Nova developed the bird’s beak style, as for the past ~15 yrs they have been that way.

My first Nova chuck (still in regular use) was made in New Zealand, so it goes back a ways. The 2" jaws that came with it are dovetail. I have also seen a distinction between the 70mm jaws with some being listed as "old version". I assume those must be dovetail.

 

[Dean Center]

Dean, it's your call, but I don't think that's worth the effort.

For an endgrain mount, I agree, but for a face grain mount, I worry that the 'beak' will start a crack along the grain. In my mind, a very slight angle reduces the risk and isn't any more work than squaring it would be. I really had a lot of broken tenons in the old days.

 

[Gerald Lawrence]

The first two SN2 I bought were made in New Zealand and of late got a much older one from an estate and all have the birds beak on the inside.

 

[Lynn Dudenbostel]

Just a follow up, I turned a hollow form with the new jaws and they worked fine. The indentations left by the birds mouth make it easy to remove the piece from the chuck and put it back in so it registers just the same. I like them!