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Thread: Tech Talk with Craft Supplies on Chuck Jaws update

  1. #1
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    Tech Talk with Craft Supplies on Chuck Jaws update

    Today i called Craft Supplies and talked with a technical rep and explained to him that i have a supernova-2 chuck with spigot jaws (pic below) that will hold a tennon up to 2 1/4. I explained to them i do put a dove tail in the tennon and the serrations seem to grip very well when i secure the tennon in the chuck. I explained to him about me tearing the tennons and he said the same thing as someone else in the previous thread - probably alot has to do with the wood im turning (some of which is douglas fur, pine,
    hemlock) but i also have some mesquite,and burls.
    So he suggested that a larger tennon would help alot with this (softer woods etc-).........and he suggested one of the following for the supernova-2chuck:
    1). Bowl Jaws - 4" with 3 1/16 - 3 3/4 opening
    2). Bowl Jaws - 5" with 4 3/16 - 5 opening
    3). Powergrip Jaws with 3 - 3 7/16 opening

    He said although they sell many different types of chucks etc - he personally uses a VicMarc with dovetail type jaws in expansion mode on recesses. He personally favored that way of turning. He strongly suggested either option 2 or 3 for the larger tennon and larger bowl turnings as i have the supernova.
    With kids using the lathe also i have favored the spigot jaws (shark jaws some call it i think) because the dovetail does not have to be exact and the serrations really grip into the wood hard (see pine bowl pic below)......the tech said that using a standard skew at the same grind angle it will create a perfect dovetail with no problem.....that option 2 has no serrations for gripping just a well made dovetail is all that is needed.......option 3 is meant to do both - a short tennon with a dove tail or you can make it a bit longer and the serrations in the back of the chuck would grip down into the wood like i was asking.
    My main concern is safety for the kids using the lathe and that i stop tearing out the tennons soft wood or not...........

    Thoughts? Wondering which one would be the best choice here....possibly the Powergrip ? anyone using it now??

    thanks Dan
    Attached Thumbnails Attached Thumbnails Jaws.jpg   Big Pine 2 (600 x 450).jpg  
    Last edited by Dan Mosley; 05-07-2009 at 03:56 AM.

  2. #2
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    Aha...I didn't realize you were using spigot jaws. You don't want a dovetail on the tenon with those jaws. I thought you were using the regular, non-serrated dovetail profile Nova jaws.

    Even though you're seeing lots of bite marks, the dovetail allows the piece to rock in the straight (serrated) jaws, causing the wood to fail. Still, the tenon you have on the big pine bowl in picture #2 looks real small for that size of bowl, especially in a soft wood like pine. The recommendations for bigger jaws sound good. I'd suggest getting the smooth dovetail jaws or the Powergrip jaws (which can be used with a dovetail). I have the Powergrips, but nearly always use them on relatively short dovetail tenons instead of longer ones that reach the serrations.

    Keep in mind that much of the stability of the turned piece comes from the shoulders of the tenon (where the front edge of the jaw touches the bottom of the piece), not just the sides of the tenons (where the jaws grab the piece). It's real important to make sure the jaws are seated well into the shoulder. That prevents the piece from slipping, which is the beginning of bad things happening. Also, with softer woods, it's possible to overtighten the jaws, crushing the fibers and weakening the tenon, which makes it more likely to break. You want them nice and firm, but not "Incredible Hulk" tight.

    I hope this helps -
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  3. #3
    Join Date
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    Dan,
    I use a Barracuda 2 with the same jaw pattern as yours. I don't cut dovetails, I like a straight walled tenon for better contact to the jaws and I like the tenon short enough that the jaws rest against the bottom of the bowl.. don't let the tenon hit the bottom of the chuck.. you'll get more stability that way. On the occasions where I have torn a tenon, I've almost always had it cut too long and resting against the bottom of the jaws with exposed wood between the edge of the jaws and the bottom of the bowl. The largest diameter I can grip on my chuck is about 2 7/8, but that's very near where the jaw slides(not proper name) will come off the chuck.
    Vaughn is right, once you break the threads/fibers of the grain on the softer woods, you are weakening the tenon enough that a strong catch can rip the tenon out.

    My plans are to get another set of jaws that will allow a somewhat larger tenon.. don't plan on going to a higher dollar chuck, even though would love to have one with a one hand key instead of the tommy bars.
    Chuck
    Tellico Plains, TN
    https://www.etsy.com/shop/TellicoTurnings
    My parents taught me to respect my elders, but it's getting harder and harder to find any.
    If you go looking for trouble, it will usually find you.

  4. #4
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    If you guys have some extra time, maybe you could put a few photos of some of these jaws and chucks. This is some good information but I just need to see what some of these things are. Thanks
    Aloha,

    What goes around, comes around.

  5. #5
    Join Date
    Dec 2006
    Location
    Boise, Idaho
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    I've moved up to big chucks. I've a Stronghold with #2 & #3 jaws and a Vicmarc 120 with #2 & #4 jaws. Since using the larger jaws, nothing has flown off the lathe and nothing has even budged on the Stronghold. I have a few problems with the Vicmarc as I'm not used to cutting dovetails. Things will improve as I get more familiar with the jaws.

    I recently finished turned a pine bowl that is about 3 years old. Sheared off the tenon as if it was cut with a laser. Went into the fire pile. That one had a very small tenon.

    Burt

  6. #6
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    Quote Originally Posted by Chuck Ellis View Post
    ...On the occasions where I have torn a tenon, I've almost always had it cut too long and resting against the bottom of the jaws with exposed wood between the edge of the jaws and the bottom of the bowl...
    Just to re-emphasize the point...a 1/4" tenon that's not touching the bottom of the jaws will provide a much stronger and more stable hold than a 3/4" tenon that is touching the bottom of the jaws. When the front edge of the jaw is making contact with the bottom of the bowl, you gain a LOT of resistance to the sideways forces that come from the turning process.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  7. #7
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    I would go with option #3. One thing to remember about chucks. You want to make your tenons for whatever chuck you are using so that the jaws are almost closed. With the chuck you show you are only actually gripping on 8 small points and not the whole chuck jaw. Mike Mahoney said if your chuck jaws closed are say 2 3/4" make your tenon 1/4" long and 2 7/8" to 3" at the most. If your chuck jaws closed measure 3" make your tenon 3 1/4" to no more than 3 1/2". You want as much jaw face on the tenon as you can. The more you open the jaws the less grip you have. Hope this helps.
    Bernie W.

    Retirement: Thats when you return from work one day
    and say, Hi, Honey, Im home forever.

    To succeed in life, you need three things: a wishbone, a backbone and a funnybone.

  8. #8
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    yes this all helps a great deal in my decision on the powergrip.......thanks to all for the comments

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