Supernova Geared Chuck & tendon length

[cwearing]

Problem #1 is that I'm a beginner. I have a constant problem with "breakaway" from the chuck using both dry purchased turning squares and green wood turnings from maple.

Guess I don't know the proper accepted length of a tendon and/or the tightening force to be used during mounting. Lathe is a new Jet 1642 if that has any issues with the problem.

Thank God for the protective "cage" as I have no desire to include my dentist in woodturning.

 

[Wilford Bickel]

First, if you don't own and use a face shield - get one and wear it!! I never turn without mine!

Second, I try not to use my chuck in a recess holding the piece by opening out. There are cases where this is the only way to hold a peice but I make it the exception. I always try to use the largest diameter tenon that the chuck will hold. Open your chuck all the way and then close it just a small amount - measure the jaw distance and use that measurement for your tenon diameter. The reason to close the jaw a little before measurement is to give you a little leeway for error and allow you to open the jaw a little more if needed. Also it keeps my chuck from binding.

As to the length of the tenon, I want it as long as my jaws. Measure your jaws from the body of the chuck to their tip - this is max. length of the tenon. Look at the inside of your jaws, most will need you to angle the tendon some to allow full contact with the length of the jaw - this keeps your jaw from holding only at the point the tenon connects to the work.

I tighten my jaws tight!! I also make it a practice to bring my tailstock up to my work as a safety whenever possible.

Hope this helps - this is what works for me.

Wilford

 

[TEK]

Chuck Problems

Could you give us a little more information on what you are turning, bowl, platter, spindle or something else? What kind of tools you are using when this happens? It sounds like you are getting a catch or a dig in. Usually a tendon of 1/4" to 1/2" works. Some experienced turners make them even shorter. There are couple of things that help.
1. Use your tailstock whenever possible.
2. When cutting you tendon make sure you have a flat shoulder on the bottom of your work piece.
3. Make sure the ends of the chuck jaws are pressed against the flat shoulder on the bottom of the piece.
4. The chucks hold best on tendons close to the diameter of the point where the inside of the chuck jaws form a true circle.
5. As you work farther away from the chuck jaws. The leverage against them increases, so less force is required to pop the piece loose from the chuck.

I still chase some of my work across the floor. Good technique comes with experience. Do you have an AAW chapter in your area? I’ve learned a lot from the other turners in our club, The North Coast Wood Turners, in Cleveland.

 

[Jim Carroll]

I always work with a spigot as I find this to be a lot more secure than a recess, I have had timber fail on me when trying to tighten the jaws into a recess.

I only open the jaws 5mm from their closed size as this is when they are closest to a true circle, this gives me the greatest amount of grip on the spigot. If you open the jaws any further there is the chance if you have a catch it may pull out of the chuck,

To see how this works turn a peice to fit into the jaws and clamp down on the timber and take it out of the chuck and have a look at the marks the jaws have made. If the spigot was too large you will only see small indents where the jaws corners have gripped, if the spigot is closer to the right size you will see a groove going all the way around , this indicates a more positve grip on your peice.

If your work requires a larger spigot buy another set of larger jaws for your chuck they are not that expensive and it gives you greater peice of mind that you are holding the peice securley.

 

[Whit]

I agree with most of the previous comments. I just want to emphasize two things:

It is absolutely critical to have a square shoulder on the workpiece to ride solidly on the top of the chuck jaws. This is where nearly ALL of the energy transfer between the drive and the workpiece takes place.

It's a common misconception to think that the largest spigot size is best. As Jim pointed out the best holding power comes when the maximum amount of jaw is in contact with the workpiece. I know this is a little counter-intuitive, i.e., smaller being stronger, but it's true.

Whit

 

[Duane]

Tennon size

I agree with all that has been said. But this exception. After teaching alot of students and my own beginer experiences.
You could have the best chuck mony can buy holding the perfect tennon but if you still have DIG INS or CATCHES frequently your bowls are still going to fly off the lathe. I have had some students to knock bowls off face plates with 1 1/2 or 2" x 1/4 screws holding them.
The best advice is to LEARN GOOD TOOL CONTROL. When you do. the catches will disapear or at least be a lot less frequent.
When using a bowl gouge with a fingernail profile try using only the 1/8" to 1/4" at the very end of tool. Lower the end of the handle. Point the fluts in the direction you are going. Hold your arms still, against your body, and move the gouge with your body not your hands. Act as if you are dancing with your wife or girl friend. Hold her ( the gouge ) snugly to your body, and shift from one foot slowly to the other. Never allow the wings to come in contact with the wood. The wings are what causes dig-ins.
A dig-in with a fingernail profile. Because a bowl gouge is round the tool rest suports only a tiny area, and the wing is way off to the sides and unsuported. Still don't get it? Get a horse shoe. Stand it on a table top with the ends pointing up. The horse shoe represents a cross section of the gouge with wings pointing up. the table top is the fulcrum or tool rest. Now push down on one side of the horse shoe. This is the wood pushing down on the gouge wing. As you push down, the horse shoe or wing will rotate, and as it does it moves deeper and deeper into the wood. A DIG-IN.
Kind of windy but i hope this helps. Duane

 

[dkulze]

All of the above.

Tailstock, tailstock, tailstock! Even if a catch breaks the tenon, the tailstock will usually keep it from flying.

As to the face shield, I won't even turn on my lathe without mine on. Goggles will protect my eyes but I like my nose, teeth, forehead, cheeks, lips, etc. pretty much the way they are.

Rough the piece to approximate shape while between centers, then mount it on the chuck and bring the tailstock up to true it and support it before tightening all the way. Get as close to finished as you can in this position. Save the "chuck only" part of the job for the parts you can't get to with the tailstock in place. This will help alot with those breakaway tenons.

Finally, it sounds like you are getting some nasty catches, to break the tenon completely off. Hook up with your nearest turning club and get a little friendly coaching. I turned for several years before doing this and can't tell you how much it improved my skills when I finally did.

And, Duane, great description.

Good luck,
Dietrich

 

[Erwin Nistler]

First of all NEVER turn on the lathe without a face shield.
One more thing that has not been mentioned. Depending on the chuck you have you may not need to undercut the tennon in compression mode. With the Nova chuck be sure the spigot is square so the little ridge on the outer edge of the jaws will dig in to the spigot at it's base.

I have nothing but trouble using the expansion mode.

 

[TEK]

First of all NEVER turn on the lathe without a face shield.
One more thing that has not been mentioned. Depending on the chuck you have you may not need to undercut the tennon in compression mode. With the Nova chuck be sure the spigot is square so the little ridge on the outer edge of the jaws will dig in to the spigot at it's base.

I have nothing but trouble using the expansion mode.

I agree on keeping the spigot square. I have the Oneway Talon Chuck with the serrated jaws. It is very similar to the Nova. I’m surprised that no one likes the chucks in the expansion mode. It’s my favorite way of chucking platters. I think I waste less wood than when I cut a spigot. I mostly use this technique when I’m using 1†kiln dried stock I don’t want to make the platters much thinner than the wood I start with. I do use a spigot for bowls though.

 

[Captain Eddie]

make a template

CW, need a perfect socket or tendon for your chuck? Put that ruler away and make a template. Check www.bayouwoodturners.com's woodturning tips page for a sample. It takes the trouble out of perfection.
Makin' Shavin's
Capt. Eddie Castelin

 

[Jim Carroll]

One part i forgot to mention on my previous post was that when making the spigot I dovetail the same angle as the jaws, as you will notice that the jaws all have a dovetailed shape except for the spigot type jaws.

To make the dovetail shape I use my 30mm skew chisel laying on its side on the toolrest. I push the long point in with the long face square to the timber and this creates the correct angle for the dovetail. {this also depends on the angle you grind your skew chisel}
This way you are getting the full face of the jaw holding onto the spigot and not just the outer edge.

Tek one way to make spigots on thin platters is to glue a waste block onto the base of your platter then create your spigot on the waste peice. By doing this you do not waste any of your material and there is less chance of hollowing into your recess. To get rid of the waste peice you can use the cole jaws or bowl jaws to hold your platter then clean up the base or decorate it or whatever you do on the bottom of your platters.