Straight tenons for Nova chuck jaws?

[Ken Hunter]

Most of my Nova chuck jaws have a dovetail shap on the inside of the jaws. Why does Nova recommend using a straight side to tenons.

 

[Paul Paukstelis]

I think this is only for the chucks jaws that have the additional threaded/serrated area below the dovetail, and if you plan on engaging that region. I asked myself this same question and couldn't figure out why my straight tenons never had my bowls running true when I flipped them around. I started dovetailing and keeping the tenons short and I had a much better experience.

 

[hockenbery]

Most of my Nova chuck jaws have a dovetail shap on the inside of the jaws. Why does Nova recommend using a straight side to tenon

If you have true dovetail jaws which Nova has the you want to turn a dovetail with a matching angle.
Their true dovetail jaws will also hold an oversized tenon

The nova jaws I have are not true dove tail. They are straight with a little bird’s beak at the top.
To work well these jaws demand a straight walled tenon at near perfect circle diameter.
I have found they hold best using a straight walled tenon of near perfect circle diameter. with a notch cut for the birds beak.

In many years of teaching and club workshops I have found these nova jaws to be the worst for beginners to use.
Beginners have trouble getting both the diameter and the straight wall.

ONEWAY and vicmarc Chuck’s with dove tail or profiled jaws excell at holding tenons larger than perfect circle.
I’ve also seen them hold god awful tenons that seemed to be intentionally designed by inattentive students to walk out of the chuck.

 

[Bill Blasic]

The 2" jaws from Nova have a little hook on top and that little thing to me is a small dovetail. from there down they are straight sided. Now Nova says that for these you do straight sided. I do not ever do that, I turn a 1/8" or 3/16" dovetail and then tighten the 2" jaws to this dovetail. I have never lost a piece doing it this way. When I spent a week with Richard Raffan he showed how using a 1/8 dovetail was very safe and I've been doing it that way almost 20 years.

 

[Paul Paukstelis]

At least for the jaws that gave me trouble, there is no discernible hook, and in profile it looks to me like a simple dovetail.

 

[Rusty Nesmith]

That would be for the Nova 50 mm jaws. The 50 mm jaws don’t have a dovetail and are straight.

 

[David Snodgrass]

That would be for the Nova 50 mm jaws. The 50 mm jaws don’t have a dovetail and are straight.

Santa was nice enough to have brought me a SuperNova2 Pro-Tek chuck set that included a set of 50mm jaws. Unlike the 50mm jaws that came with my SuperNova1 chuck, these do sport dovetailed inner and outer jaw faces. Nicer yet, the Pro-Tek chuck key tightens and loosens righty-tighty and lefty-loosey.

 

[hockenbery]

At least for the jaws that gave me trouble, there is no discernible hook, and in profile it looks to me like a simple dovetail.
View attachment 59940

I haven’t used these jaws. I think those are what Nova calls Powergrip.
They are not true dovetail. Looks like a combination serrated and dove tail like @Paul Paukstelis described.

I marked your photo. A dovetail tenon has to be short about 1/2-1/3 the jaw height.
A straight tenon should be longer than the bottom serration bit not bottom out.

With these style jaws, when a tenon close to the length of the bottom serration, the bottom serration can’t bite in and one jaw will often push over the top of the tenon letting the other 3 jaws bite. This cocks the piece slightly so it does not run true.
Also makes a space on that side if you turned a flat. So the piece can rock. Weakening the tenon.

 

[Bill Blasic]

The normal 2" or 50mm Nova jaws have what I call a 1/16 dovetail at the top then straight sided below that is what I was talking about above. Tomorrow I'll see if I can get a good photo of it.

 

[Rick Moreton]

Here is a screenshot from an online listing of the jaws in question:


I have these as well and haven't had any issues following the manufacturer's directions. I do smaller work on a mini lathe though and almost exclusively dry wood.

 

[Bill Blasic]

You can see that little bump out slanted inward. Never did I say Nova was wrong just said how I do it.

 

[William Rogers]

Unlike others when I had Nova chucks using the 50mm jaws with a “birds beak” I never included the small dovetail. I just turned a straight tenon as Nova recommends. I speculate that not turning the beak it make the jars push the wood to the face of the jaws for a tighter grip. If the small dovetail is turned too large/deep I believe you loose grip. However many turn this small dovetail and don’t seem to have a problem.

I never had the jaws with both dovetail and serration.