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Chuck loosening during turning - Help requested

Discussion in 'Getting Started' started by Don Armour, Feb 21, 2021.

  1. Don Armour

    Don Armour

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    new Turner, still learning so all help is appreciated.

    I have a Nova SuperNova 2 Chuck on a Laguna 1836 lathe. Am creating a tenon using guidance from Ken at turn a wood bowl. Tenon is about 2 Inches with shoulder 2.5" or so. Chuck seems to fit perfectly against shoulder and tenon is only about halfway down jaws. Dovetail on tenon looks good to me. There is space between the jaws and at 2" the jaws appear to be circular.

    Once seated I use the handle to tighten the pinions and twist on it pretty hard to make sure there is a good grip. Both pinions get tightened with about the same force. Prior to starting the lathe all seems tight and true.

    After turning for a bit, I check the pinions and they are loose.

    What am I doing wrong?
     
  2. hockenbery

    hockenbery AAW Advisor Staff Member

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    Can’t tell for sure without being there.

    you have described a near perfect tenon- this is in conflict with your results.
    If you do have a perfect then you just did not tighten the Chuck enough.

    more likely the tenon is not as good as you think.

    First I would check the tenon profile. Take a jaw off and hold it against the tenon.
    Tenon should be cleanly cut and free from tear-out. If you use a scraper to make the tenon it can lead to a lot of torn grain on the tenon unless it is extremely sharp. I cut my tenons with a spindle gouge.

    Second the tenon is too long and hitting the flat bottoms of the jaws which it should not
    Some foreign matter inside tour Chuck makes it seen tight when it is- this is really rare but open and close the Chuck

    do you have dove tail jaws?
    The nova I have has the little bird beak jaws
    For these I turn a 90 degree tenon and a tiny vee to register the beak on the jaws.
     
    Last edited: Feb 21, 2021
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  3. Timothy Allen

    Timothy Allen

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    The wood of your tenon could be shrinking due to drying and/or compression of the fibers due to the pressure from the chuck jaws.

    Try re-tightening your chuck after your first cuts.
     
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  4. Gary Beasley

    Gary Beasley

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    My experience the chuck will need several tightenings as you work. Always check the tightness every few minutes immediately after mounting it and every time you stop for anything retighten before restarting.
     
  5. Doug Freeman

    Doug Freeman

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    Yes, if you are using wet wood (and most purchased waxed blanks are still wet to some degree) check chuck tightness often. Being new you probably take a while cutting the form ( which is just fine), but this gives the wood more time to dry some, and it doesnt take much for the jaw grip to loosen.
     
  6. Bill Boehme

    Bill Boehme Administrator Staff Member

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    My experience with Nova chucks is very limited so this might be a three-sigma case. The Nova chuck that I was using in a class looked like it had suffered a lot of abuse and the jaws were continually backing off. The instructor even used a cheater bar to get more leverage to tighten the jaws, but even that didn't solve the problem. The wood was dry hard maple so wood movement wasn't the issue. Fortunately, we found another chuck (Grizzly) and everything was fine after that.
     
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  7. robo hippy

    robo hippy

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    From time to time, check the screws on your chuck jaws as they can, for reasons unknown, loosen up, and this can add to the need to retighten up your jaws. As said before, especially if you are taking a longer time to turn a green bowl, the green wood will compress more than dry wood.

    robo hippy
     
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  8. odie

    odie

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    I've had this problem occasionally with my Oneway Stronghold chucks while the Jumbo Jaws were installed. For me, this problem was solved by drilling and tapping the chuck body for a set screw.

    @Don Armour , if your jaws are backing off, and not some other issue, the set screw will solve the problem.

    -----odie-----
     
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  9. John Torchick

    John Torchick

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    I check the set screws on the chuck and adapter periodically while turning. I subscribe to Murphy's Law.
     
  10. Timothy Allen

    Timothy Allen

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    Odie, where exactly is this set screw located? Does it lock against the scroll? Presumably you have to unlock the set screw to adjust the chuck jaws?
     
  11. odie

    odie

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    Tim.....here's a pic:

    -----odie-----
    Stronghold chuck set screw installed_LI (2).jpg
     
  12. Mark Jundanian

    Mark Jundanian

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    From what Don described I think the loosening is most likely do to compression and shrinkage of drying green wood (as others have put forward). If that's the case, then frequent snugging up will be needed after the blank is initially mounted, but not so much after a while.
    In which case this add on set screw would be a hindrance. Maybe test the first theory before breaking out the drill and tap.
     
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  13. hockenbery

    hockenbery AAW Advisor Staff Member

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    I don’t think your problem is wood shrinkage from drying. It can happen but it takes a long time.
    If a “bit” is an hour then I would think shrinkage is possibly your problem.
    I’ve done dozens of club workshops and classes using chucks for bowls and retightening after the first few cuts is never needed.

    I assume a “bit” is 5 minutes and less than 10.
    Unlikely the wood will be drying that fast unless you were in Arizona where bread goes stale when exposed to the air.
    Last time I turned a NE bowl in Jacksonville I noticed no shrinkage while turning. In a demo I have the bowl in a Chuck for about 30 minutes.
     
    Last edited: Feb 22, 2021
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  14. odie

    odie

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    I think both Mark and Al have reasonable points worth considering. :D

    As for the set screw, I must mention that I only use those Jumbo Jaws for turning the foot.....no other application. When I do the foot, my bowls are dry, and the bulk of the second turn has been done. There is very little warpage or shrinking at this point. I use the set screw every time I turn a foot, but it's so long that I've had any trouble with jaws backing off, that I might be able to get away without using it. Since I first installed the set screw, I've evolved some, and I have much less troubles related to vibrations, or out of balance conditions. Even so, I'll continue to use the set screw, because it's there, and it does provide some sense of security, whether or not it's needed. :rolleyes:

    -----odie-----
     
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  15. John Torchick

    John Torchick

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    Misread the original thread. I still check the chuck jaws even on dry wood.
     
  16. hockenbery

    hockenbery AAW Advisor Staff Member

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    @Don Armour one other possibility is the quality of the wood.

    what wood are you turning? when was it cut?

    If it is punky and compressing that could cause the looseness,
    But it the wood is that soft the tenon is likely to break.

    if you are getting catches, that will often pull the tenon partly out of the Chuck which can make the tenon seem loose when the tenon gets pushed back into the Chuck.
     
    Last edited: Feb 22, 2021
  17. Bill Boehme

    Bill Boehme Administrator Staff Member

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    That is very interesting. Supposedly, the scroll plate and jaw teeth design is the laid-out-flat equivalent of a worm and pinion gear which is a no-back design (in other words, the worm can drive the pinion, but not the other way around).
     
  18. Russell Vance

    Russell Vance

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    If you are using Nova jaws, do NOT turn a dovetail tenon. You need a straight tenon with those jaws as Hockenbery mentioned. If you are cutting a dovetail, the jaws are not going to bite into the tenon properly. They will just be clamping against the outer edge of the dovetail and the beak won't be touching the wood. Turn a straight tenon and your troubles will disappear! I've watched lots of Kent's videos too. They are great, but he uses dovetail jaws, not the bird beak type that Nova has.

    Personally, I like the Nova jaws. I don't have to worry about getting just the right angle on the tenon. Just turn a straight 90 degree tenon, clamp it down, and get to work. As others have said, though, green wood can move, so it doesn't hurt to check it once in a while.

    Happy turning!
     
  19. Don Armour

    Don Armour

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    The wood was Magnolia and it was cut from the tree about 30 days ago and a blank prepared about 25 days ago. Ends were sealed with wax. Its wet, but not dripping wet.
     
  20. Don Armour

    Don Armour

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    Yes - i am turning a dovetail. I will turn straight tenons in the future and check pinion every time i stop. I am new so do tend to take time (about an hour) for outside and longer for inside a 7" bowl and I also stop frequently, so should have plenty of opportunity to check and tighten.

    Based on entire thread so far, it seems a few possible causes:

    1. Wet wood. I have several rough blanks from trees I cut down on a neighbors yard, so almost all of my wood will be wet to some degree. All were cut down in late Dec or early January. I have Magnolia and Catawba, both soft. Also have some hickory (from a different friends farm in SC) , but have not cut logs into rough blanks yet. Especially on something soft like magnolia, I can see how compression could occur on the wet wood. BTW - the outside of the turned bowl is just gorgeous. Very white wood, decent grain, but the bark for the live edge its incredible. On hold for the moment due to waiting on sharpening jigs and CBN wheels to arrive.
    2. Dovetail vs straight tenon - will do straight and will try to get a "V" moving forward.
    3. Some tear out. I have a little tear out on shoulder, but have been using a spindle gouge to get a smooth surface on tenon.
    4. Dirty jaws. My chuck has been sitting on a table near the lathe so could have gotten stuff in it. I will store in a nearby drawer and be sure to blow with compressed air before mounting.

    Thanks all, much appreciated.
     
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  21. hockenbery

    hockenbery AAW Advisor Staff Member

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    That wood should be solid enough if the tree was healthy.
     
  22. John Torchick

    John Torchick

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    Got some pecan boards. Fellow said it's a first cousin to hickory which is used for axe handles, etc. so it has to be hard. Have made some pens out of pecan.
     
  23. Don Armour

    Don Armour

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    agree and tree looked healthy to me.
     
  24. Gerald Lawrence

    Gerald Lawrence

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    I think the problem has been solved but just a little more on SN2 chucks. Not all the jaws are the same , 100mm jaws are dovetail in and out. The new Novas not only have threads to tighten and loosen like most of the other major brands but has dovetail jaws also. So when we talk Nova we might need to qualify in the future especially with new turners.

    One more thing not a problem here as it was clarified but Novas have a set screw to lock the chuck to spindle or adapter and adapter should also have a set screw to tighten to spindle.
     
  25. Don Armour

    Don Armour

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    Thanks Gerald. I will certainly check my jaws to verify whether they are straight or dovetail. I did just purchase it in the last 60 days. Might be a bit before all hear back on final resolution. Waiting on wheels and jigs for sharpening, tools are dull, and honey do list is growing by the day.
     
  26. Russell Vance

    Russell Vance

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    Interesting. I'll have to have a look at my 100mm jaws. I haven't used them yet. The 50mm jaws have the beak for a straight dovetail. I had seen videos and read information that said the Nova chucks tighten left hand, so that is what I was expecting. However, my G3 chuck tightens right and loosens left, so I assume this is the new version. I, for one, am glad they made that change.
     
  27. Doug Freeman

    Doug Freeman

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    The Nova ProTek G3/SN2 are the new versions with changed jaws and rotation. The old style are still in production. Have to use the “ProTek” branding to differentiate.
     
  28. Timothy White

    Timothy White

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    I own nearly all of the Nova jaws including the Infinity jaws. The 50 mm original jaws that come standard on all Nova chucks accept Infinity and the Titans, have dove tails on the outside and the bird beak on the inside. The new “ Pro Tek” jaws, as Doug pointed out are different. All other bowl jaws have inside and outside dove tails.
    This caused me more than a few problems when I first started out.
    The info that has been provided in the previous posts is right on the money.
    I don’t own a Titan chuck or jaws.
     
  29. Al Chavez

    Al Chavez

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    Yes, I don't like those bird beak jaws. I've been trying to find the Pro-Tek 2" improved jaws sold separately as an accessory but have not had any luck. I can only find them in a Nova SN2 ProTek bundle. I've got the bird beak jaws on a chuck for a smaller lathe and they are giving me problems too.
     
  30. Doug Freeman

    Doug Freeman

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    I think the bird beak works really well. Makes me wonder if your tenons are correct? Straight wall, no relief for the beak, slight slant on the shoulder toward the tenon. Use the tailstock to apply a bit of pressure when tightening the chuck. Or too small dia tenon for the work, but I’ve used them on undersized tenons and was surprised how well they held.
     
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  31. hockenbery

    hockenbery AAW Advisor Staff Member

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    the Bird beak is most demanding for a well made tenon.
    In teaching many classes when a tenon walks out of the Chuck a bit it is almost always with nova bird beak jaws.
    I stress making a clean corner on both straight and dove tail jaws. For the bird beak a straight tenon with a groove cut for the beak works really well.

    the dovetail @Doug Freeman describes works well too if the turner has the skill to cut the correct angle on the dovetail, cut the angle a couple of degrees off and the beak won’t contact the wood and the tenon walks out.

    When doing workshops, I do tenon inspection before the first bowl goes in a Chuck and they all hold well.
    Sometimes on a second or third bowl the students forget the details of making the first tenon and those show up mostly on the nova bird beak jaws.
     
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  32. Al Chavez

    Al Chavez

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    Definitely inexperience is a part of the issue for me. I have less than a dozen bowls under my belt. This particular piece is troublesome and I may need to chuck it up again to recut the tenon.

    I will try the techniques you both have described. I want to feel very comfortable with the basics before my new lathe arrives.

    I am looking forward to when clubs meet again in person as I can really see the added benefit of having meetings in persons with instructors/mentors.

    Meanwhile, for me, it will be more practice.
     
    Last edited: Feb 26, 2021 at 11:22 AM
  33. Doug Freeman

    Doug Freeman

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    Perhaps I was not clear - I do not advocate any slant or relief on the tenon. Straight wall perpendicular to the work, just as Nova recommends. The relief is on the shoulder. Err to having the OD of the shoulder slightly higher than the ID at the tenon (the jaw tops touch at OD) and the intersection of shoulder and tenon should be a distinct line, no radius. Have not had a piece walk out of the bird beak jaws unless I have a big catch, which will pull the tenon out a bit or break it, but the same happens with serrated and dovetail. It I do crank down when tightening to deform the wood with the beak, again as Nova recommends. Putting a relief for the beak weakens the holding strength. That and students not getting the chuck tight could lead to walk out.
     
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  34. Bill Boehme

    Bill Boehme Administrator Staff Member

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    The difference between a perfectly straight tenon and one that has a very slight taper the wrong way can be all but imperceptible. However, the difference can be quite significant as far as holding is concerned. I use Oneway Stronghold and Talon chucks with premium profiled jaws which, like the Nova jaws, call for a straight tenon. Instead of trying to get a perfectly straight tenon, I make the tenon with a slight dovetail (diameter at the end of the tenon is slightly greater than the diameter at the base where the tenon meets the shoulder).
     
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  35. Dave Landers

    Dave Landers

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    ...

    A new take on the "horse walks into the bar" jokes... but I was hoping for a better punch line.
     
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  36. Doug Freeman

    Doug Freeman

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    I also have a Stronghold with sets of profiled jaws, and as well prefer them to other jaw clamping designs. I got a great deal on the Nova G3 chuck. At the time I didnt know any better. One day it will be replaced with a Talon chuck.
     
  37. Dean Center

    Dean Center

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    These comments on bird beaks on some Nova jaws and regular dovetails on others explains a lot. I now strongly suspect that making too much dovetail for the unsuspected beak contour explains half of the flying bowls I've had. On the other half, the tenon broke off in the middle of the length, and that may very well have occurred due to the beak slipping, catching the wider part of the tenon, causing the tenon to break. Eureka! I haven't gotten many broken tenons in several years because I've reduced the angle on the tenon, and now I know why that has helped.
     
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  38. Russell Vance

    Russell Vance

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    I believe you are correct. I was fortunate to have watched a YouTube video, which I believe was made by Mike Peace, if my memory serves me correctly. It was before I had purchased a chuck, so I was in the research phase. It explained the different types of jaws and how to correctly cut the tenon for each type. When I finally bought my G3 chuck, I knew I needed a straight tenon for the 50mm jaws with the bird beak.

    I did have one tenon break when I was in the process of making a funnel, which I had originally thought was going to be a bowl. I have since constructed a depth gauge as I already have plenty of plastic and metal funnels and don't really need a wooden one. :oops: Not surprisingly, my tenons seem to hold on much better now. ;)
     
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