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Teknatool Nova G3 Recess: How hard to crank it in? (Read 617 times)
 
Chris Gunsolley
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Teknatool Nova G3 Recess: How hard to crank it in?
May 17th, 2016 at 4:13pm
 
I have a Nova G3 chuck, and fasten the bottoms of my bowls to the chuck using the common method of tightening the jaws within a recess. As I crank on the chuck key when tightening the jaws, I want to tighten it enough to hold the bowl securely, of course, but I'm also concerned about tightening it so much that I actually damage the wood, or split the bowl. This brings me to the question:

How tight should I make it?

If you're familiar with this chuck, you know that it has two different places to tighten the jaws. My current technique is to basically tighten it in the first hole until it's almost impossible to for me to get it any tighter, then, switch to the other hole and do the same, then go back to the first, tighten it a little more, switch back to the other hole and do the same, etc., until it is almost impossible for me to tighten either. I feel like I'm pushing this tightening the jaws thing a lot further than I need to, and perhaps further than is safe.

Wouldn't extreme pressure pushing on the walls of that recess pose added risk of the bowl actually splitting?
So, how do you determine what that point is at which it is tight enough, but not too tight?
Do you alternate between the holes a few times when you tighten it as I've described?
Do you have to make it super tight?

Fitting the jaws into the recess properly requires a dovetailed recess, and I would think as long as the bowl doesn't move and the highest part of that dovetailed wall of the recess is making contact with the jaws, that should be sufficient?
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« Last Edit: May 17th, 2016 at 4:28pm by Chris Gunsolley »  
 
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Ed Weber
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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #1 - May 17th, 2016 at 4:29pm
 
Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
How tight should I make it?

Just tight enough

Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
If you're familiar with this chuck, you know that it has two different places to tighten the jaws.


It actually has ONE method of tightening and TWO access ports which turn the same part, the scroll ring. There is no need to tighten from both spots.
Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
My current technique is to basically tighten it in the first hole until it's almost impossible to for me to get it any tighter, then, switch to the other hole and do the same, then go back to the first, tighten it a little more, switch back to the other hole and do the same, etc., until it is almost impossible for me to tighten either.

When you are going back and forth trying to get it a bit more snug, you may feel a bit more movement. Many times this is a small amount of slack withing the scroll ring and jaw slides, you may not actually be tightening the jaws at all.

Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
So, how do you determine what that point is at which it is tight enough, but not too tight?


Experience.
The Jaws only need to be snug, it's a dovetail connection, so even if it were to come loose a small amount it would stay on the chuck.
How tight varies with things like, how well you cut the recess, species and how wet or dry the wood is
If you're concerned, stop and check every once in a while until you get a feel for it.
If you need to use two hands to tighten it, it's probably too tight.
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Chris Gunsolley
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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #2 - May 19th, 2016 at 9:16am
 
Ed Weber wrote on May 17th, 2016 at 4:29pm:
Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
How tight should I make it?

Just tight enough

Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
If you're familiar with this chuck, you know that it has two different places to tighten the jaws.


It actually has ONE method of tightening and TWO access ports which turn the same part, the scroll ring. There is no need to tighten from both spots.
Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
My current technique is to basically tighten it in the first hole until it's almost impossible to for me to get it any tighter, then, switch to the other hole and do the same, then go back to the first, tighten it a little more, switch back to the other hole and do the same, etc., until it is almost impossible for me to tighten either.

When you are going back and forth trying to get it a bit more snug, you may feel a bit more movement. Many times this is a small amount of slack withing the scroll ring and jaw slides, you may not actually be tightening the jaws at all.

Chris Gunsolley wrote on May 17th, 2016 at 4:13pm:
So, how do you determine what that point is at which it is tight enough, but not too tight?


Experience.
The Jaws only need to be snug, it's a dovetail connection, so even if it were to come loose a small amount it would stay on the chuck.
How tight varies with things like, how well you cut the recess, species and how wet or dry the wood is
If you're concerned, stop and check every once in a while until you get a feel for it.
If you need to use two hands to tighten it, it's probably too tight.


Thanks, Ed. This is helpful. The part that put me at ease is when you pointed out that it is unnecessary to alternate between the two access points when tightening the chuck, and that the movement you can achieve in one after tightening the other doesn't necessarily mean that you're actually tightening the jaws more. I certainly didn't realize that.

Also, that's a good point on the effectiveness of the dovetail in keeping the bowl on the chuck. It would be physically impossible for the inner (deeper/larger-diameter) ring of the jaws to fit out of the smaller side of the recess.

I think now that as long as the jaws are flat in the recess as far as they can go, and the jaws are snug with no movement at all and I see that the walls of the jaws are in complete surface contact with the walls of the recess, I'll call that tight enough.
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Mark Putnam
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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #3 - May 19th, 2016 at 9:29am
 
Chris, I learned a lesson with the G3 recently, and that is when to make the call between mortise or tenon. I put a nice--but small--piece of Texas ebony on my G3 via the dovetail mortise method. But the bowl was small and the "wall" outside the dovetail was very thin, maybe a half inch. As soon as I applied a tool to the wood, it flew off. The stress on the thin outer wall caused it to crack and come off the chuck. In hindsight, I should have used the tenon method to grip around the bowl instead.

Depending on the type of wood you are using, I would suggest you carefully consider which gripping method to use.

To answer your original question, I typically tighten my G3 using medium pressure on the tightening handle until I feel the chuck come in to contact with the wall of the bowl. Then I give it 1/2 to one full additional turn. Be sure to test the grip by hand and give the piece a spin using the headstock wheel. And, as I read in a Richard Raffan book this weekend, stand clear of the lathe when turning it on for the first time!
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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #4 - May 19th, 2016 at 11:14am
 
I have a video up in the video section here, or on You Tube for 'Mounting things on the lathe'. It covers pretty much all of that. Simple and short, snug, but not tight, and use both key holes. Also, match angles of jaws and recess, and have plenty of shoulder on the outside of the jaws. Don't bottom it out as in deep recess so bottom of bowl sits on shoulders of chuck jaws. Yes, you can make it too tight, and green wood needs to be tightened up a time or two when turning because it compresses.

robo hippy
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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #5 - May 19th, 2016 at 11:37am
 
robo_hippy wrote on May 19th, 2016 at 11:14am:
and use both key holes


I thought we've been over this.
To clarify for those who don't know,
When you turn the chuck key, you are turning the scroll ring, which move all the jaws move simultaneously. It doesn't matter at what position on the ring you turn it from.
I didn't feel like opening up one of my own chucks to explain this again, so I grabbed some photos from the web.
These are of a 3 jaw chuck but the mechanical principle is exactly the same.

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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #6 - May 19th, 2016 at 11:41am
 
robo_hippy wrote on May 19th, 2016 at 11:14am:
I have a video up in the video section here, or on You Tube for 'Mounting things on the lathe'. It covers pretty much all of that. Simple and short, snug, but not tight, and use both key holes. Also, match angles of jaws and recess, and have plenty of shoulder on the outside of the jaws. Don't bottom it out as in deep recess so bottom of bowl sits on shoulders of chuck jaws. Yes, you can make it too tight, and green wood needs to be tightened up a time or two when turning because it compresses.

robo hippy


I'm going to watch your video right now. Thank you so many helpful contributions to other turners like me.
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Chris Gunsolley
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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #7 - May 19th, 2016 at 11:43am
 
Ed Weber wrote on May 19th, 2016 at 11:37am:
robo_hippy wrote on May 19th, 2016 at 11:14am:
and use both key holes


I thought we've been over this.
To clarify for those who don't know,
When you turn the chuck key, you are turning the scroll ring, which move all the jaws move simultaneously. It doesn't matter at what position on the ring you turn it from.
I didn't feel like opening up one of my own chucks to explain this again, so I grabbed some photos from the web.
These are of a 3 jaw chuck but the mechanical principle is exactly the same.



Very insightful, especially the second picture. And this means mounting my bowl is easier than I thought, so great!
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Re: Teknatool Nova G3 Recess: How hard to crank it in?
Reply #8 - May 23rd, 2016 at 7:59am
 
As other said, you do not need to make it "super tight".
Fitting as close as possible will give the best hold, for Nova the dovetail should be 15*. If you make a tool from an old flat screwdriver or other spend the time to make it as close to the 15* as possible.
Cut the diameter at the minimum to insert the jaws Fully Closed. The true circle for Nova has 2mm removed to split the jaw billet apart; this can expand within the recess. If turning twice it also allows the minimum opening (best fit) when re-trued.
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