chuck needed

[Bill Boehme]

... A metal to metal contact will seat chucks and faceplates as well as they can be seated.
I always tighten the chuck with a small force when I put it on.
Then it always comes off with the same force....

I agree fully. A piece of plastic might be very flat, but not as true as the machined register face of the spindle. It's not the threads ... it's that flat face that provides the correct alignment with the reference surface of the chuck. Anything inserted between them is going to make the alignment less accurate.

Yes when that happened on my Midi I was getting some nice catches. However remember that the surface of the plastic washer is slick and will allow easier removal even under normal circumstance. In my opinion even perfectly smooth metal will grip quite tightly in some circumstances as in turning wet wood and not removing the chuck right away. So I would rather err on the side of less work in the long run.

I guess that I've never turned wood wet enough to cause that sort of problem. Given that the washer is slick and reduces friction when removing the chuck, is it possible tht this reduced friction could allow you to overtighten the chuck? The only reason that I mentioned this is because it is something that Jimmy Clewes said during the class when somebody brought up this subject.

My guess is that the register on your lathe spindle could possibly be off from perfectly flat by a thousandth of an inch or even less ... not enough to be a problem other than causing the chuck to occasionally be too hard to remove without the plastic washer.

The plastic washer would only present a problem in a few situations such as:

• removing the chuck from the lathe (with the wood still held in the chuck) and then reinstalling the chuck to continue the work IF you are doing some very detailed work that can't tolerate any shift in alignment ... perhaps the type of work that Kelly does with detailed grooves and corners would be an example of this.
• It is also possible that using a plastic washer could cause the chuck to vibrate at high speed and this vibration could be a problem at high RPM's.
• If you have a very heavy piece of wood in the chuck and are using a plastic washer then it is important to recognize there is a flexible connection between the wood and the lathe. The amount of wiggle may be in the thousandths of an inch at the perimeter of a large piece, but who need vibration when not doing chatter work on purpose?

The fact that many woodturners use plastic washers is proof enough that they work as advertised and are only a potential problem in limited circumstances. But, my feeling is that if you don't need them then there is no compelling reason to use them.

 

[Gerald Lawrence]

I agree fully. A piece of plastic might be very flat, but not as true as the machined register face of the spindle. It's not the threads ... it's that flat face that provides the correct alignment with the reference surface of the chuck. Anything inserted between them is going to make the alignment less accurate.



I guess that I've never turned wood wet enough to cause that sort of problem. Given that the washer is slick and reduces friction when removing the chuck, is it possible tht this reduced friction could allow you to overtighten the chuck? The only reason that I mentioned this is because it is something that Jimmy Clewes said during the class when somebody brought up this subject.

My guess is that the register on your lathe spindle could possibly be off from perfectly flat by a thousandth of an inch or even less ... not enough to be a problem other than causing the chuck to occasionally be too hard to remove without the plastic washer.

The plastic washer would only present a problem in a few situations such as:

• removing the chuck from the lathe (with the wood still held in the chuck) and then reinstalling the chuck to continue the work IF you are doing some very detailed work that can't tolerate any shift in alignment ... perhaps the type of work that Kelly does with detailed grooves and corners would be an example of this.
• It is also possible that using a plastic washer could cause the chuck to vibrate at high speed and this vibration could be a problem at high RPM's.
• If you have a very heavy piece of wood in the chuck and are using a plastic washer then it is important to recognize there is a flexible connection between the wood and the lathe. The amount of wiggle may be in the thousandths of an inch at the perimeter of a large piece, but who need vibration when not doing chatter work on purpose?

The fact that many woodturners use plastic washers is proof enough that they work as advertised and are only a potential problem in limited circumstances. But, my feeling is that if you don't need them then there is no compelling reason to use them.

Bill, You have set off my curiosity. This possible vibration you speak of : have you seen or done any studies to confirm this happens? My thought was that the plastic (some types) only compresses a very small amount and that would be equal around the entire circumference. This compresson (if it exists) would then be equal all the way around the connection to lathe and chuck (or attachment).

 

[Bill Boehme]

Bill, You have set off my curiosity. This possible vibration you speak of : have you seen or done any studies to confirm this happens? My thought was that the plastic (some types) only compresses a very small amount and that would be equal around the entire circumference. This compresson (if it exists) would then be equal all the way around the connection to lathe and chuck (or attachment).

In my profession career, I was a controls system engineer, so this is a classic example of what is known as a "compliant" system. The term compliant means that some part of an overall dynamic system bends or flexes or has free play under load. The term dynamic refers to a moving or rotating system. In a closed-loop system, compliance typically leads to instability, so the design goal is to eliminate or reduce compliance to the point where it no longer is a problem.

Your thought that the flex would be equal around the whole circumference isn't the way that I would see it. Here are two different scenarios:

• An irregularly shaped chunk of wood is mounted in the chuck. It has not been statically balanced and because it is irregularly shaped, it has what are called cross products of inertia which simply means that it is not dynamically balanced. Because of this the forces acting at the compliant interface between the chuck and spindle aren't equal around the circumference, plus the following ...
• Whether a rough hunk of wood as described above or a well-balanced piece, the cutting tool is exerting a rotating asymmetrical force. If the force is exerted on thin wood or a flexible plastic washer, they will "comply" (or "move" in layman's terms).

As we all have experienced, turning something that is thin and large diameter can be a real challenge when even a very light cut sets up a vibration. We use all sorts of things to reduce the chatter such as steady rests, holding a hand on the back side of the cut, and checking to make certain that the piece is being firmly gripped in the chuck jaws. Imagine how much harder it would be to control the chatter if we loosened the chuck grip even just a tiny amount. Imagine if the chuck didn't have a hard metal to metal connection to the spindle. A compliant system doesn't have to be as limber as a wet noodle ... the flex or free play can be microscopic, but is unacceptable if it facilitates instability.

 

[Gerald Lawrence]

In my profession career, I was a controls system engineer, so this is a classic example of what is known as a "compliant" system. The term compliant means that some part of an overall dynamic system bends or flexes or has free play under load. The term dynamic refers to a moving or rotating system. In a closed-loop system, compliance typically leads to instability, so the design goal is to eliminate or reduce compliance to the point where it no longer is a problem.

Your thought that the flex would be equal around the whole circumference isn't the way that I would see it. Here are two different scenarios:

• An irregularly shaped chunk of wood is mounted in the chuck. It has not been statically balanced and because it is irregularly shaped, it has what are called cross products of inertia which simply means that it is not dynamically balanced. Because of this the forces acting at the compliant interface between the chuck and spindle aren't equal around the circumference, plus the following ...
• Whether a rough hunk of wood as described above or a well-balanced piece, the cutting tool is exerting a rotating asymmetrical force. If the force is exerted on thin wood or a flexible plastic washer, they will "comply" (or "move" in layman's terms).

As we all have experienced, turning something that is thin and large diameter can be a real challenge when even a very light cut sets up a vibration. We use all sorts of things to reduce the chatter such as steady rests, holding a hand on the back side of the cut, and checking to make certain that the piece is being firmly gripped in the chuck jaws. Imagine how much harder it would be to control the chatter if we loosened the chuck grip even just a tiny amount. Imagine if the chuck didn't have a hard metal to metal connection to the spindle. A compliant system doesn't have to be as limber as a wet noodle ... the flex or free play can be microscopic, but is unacceptable if it facilitates instability.

To continue the dynamics of you theory ( note all thoughts are just theory until proven in experimentation or use) this would also include the possibility of flex of metal in the lathe and chuck. Is that not correct? By the way this is very interesting reading. By the way the plastic washer is not metal so softer than that, but not a soft plastic.

 

[hockenbery]

To continue the dynamics of you theory ( note all thoughts are just theory until proven in experimentation or use) this would also include the possibility of flex of metal in the lathe and chuck. Is that not correct? By the way this is very interesting reading. By the way the plastic washer is not metal so softer than that, but not a soft plastic.

Don't forget that "solid ground" is only solid in a relative sense and moves too!
The big time laser work was done with the lasers on bedrock to minimize vibration and movement.

Wood turners just need to minimize vibration Work over the center post of the tool rest when you can
Mount things as close to the headstock as possible.

The washers and various adapted and extensions put things further out.

In the end we can accept a lot vibration adding components if they don't add up to much.

 

[Gerald Lawrence]

Don't forget that "solid ground" is only solid in a relative sense and moves too!
The big time laser work was done with the lasers on bedrock to minimize vibration and movement.

Wood turners just need to minimize vibration Work over the center post of the tool rest when you can
Mount things as close to the headstock as possible.

The washers and various adapted and extensions put things further out.

In the end we can accept a lot vibration adding components if they don't add up to much.

True point. Even skyscrapers and bridges flex, it is in the design. With a spindle extension I have see these inaccuracies and actually accommodated for it with masking tape for a longworth. To theory : would the flex of the washer (plastic) be steady and that created by the pressure of the tool against the wood which also flexes (or vibrates) not be equalized by the cutting action? That is once the vibration (which by the way exists in all items on earth due to atomic structure and other influences) not be equalized and therefore null when using sharp tools on a regular surface (that is surface of even hardness in full circcumfirence).
Is it not exciting working on theory?