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Thread: Tennon Question again

  1. #1
    Join Date
    Jul 2008
    Palm Springs, Ca

    Tennon Question again

    I been still having tennon issues with them tearing out while turning.
    I did make the tennon shorter - not to short or the vessels/bowls with length wont hold - say about 1/4 inch or so ....but the spigot chuck has serrated teeth in it - i called Teknatool and talked to one of the guys that says the tennon "could" be longer if the wood were dry as the spigot chucks were designed to hold for vessels for hollowing without the tailstock support.
    I dont think im over tightening but i do snug it down or with large bowls will come off,,
    They said maybe my cuts are to aggressive - im using the Ci1 on the end grain hollowing so i dont think that is it.......

    Back Ground:
    I have some logs of Hemlock and Doug Fur - very green still, i have them cut and anchor spigot jaws will open to 2 1/4 inch at max, and i use the tail stock to hold the other end when turning.
    When the problem happens is always during the hollowing of the bowl. i cut around the tailstock and keep a tennon the inside as long as i can which helps alot but is kind of hard to work around but not impossible.....
    When i examine the bowl and tennon after it tears out - it looks like it just shreads it - leading me to think the wood may wet and weak but i see others not having this problem. Other thing i notice is the tool will get small type catches when hollowing the end grain which causes me to sharpen my gouge often in hopes this will reduce the tension put on the tennon. Still I tear the tennon often
    I have tried CA on the tennon prior to turning it but im not so sure that helps on wet wood....
    i have tried glue blocks with hot glue (letting the gun get dripping hot), CA, titebond III (over nite drying time), they dont hold and im sure its from the moisture migrating back and loosening up the bond.
    Proof was when i looked at the block after it came of - i noticed it comes off right at the glue line........

    I keep thinking there is something im not doing as correctly as i should be so im comming back for more thoughts on what others think ?????
    Last edited by Dan Mosley; 02-07-2009 at 03:20 PM.

  2. #2
    Join Date
    Feb 2007
    Inside the Beltway

    The picture's a little blurry, but it looks like those are expandable jaws? Maybe the glue area is too small? Have you thought of doing an "inside" tenon? In other words, take a wider block, and turn a depression in the center, just a bit smaller than the maximum expansion of the jaws, and maybe half an inch deep. That way, the block could be as big as the bottom of the piece, and you'd get a bigger glue area. The shearing forces on the glue line would be greatly reduced...



  3. #3
    Join Date
    Nov 2006
    Mountain Home, Arkansas
    Hemlock and fir are not very hard and being wet and green would/could make them quite weak. Probably kinda like trying to clamp jello. That's my guess. Get some dry hardwood and try same thing. I'll betcha you will have better luck.
    How big are the bowls you are trying to turn with that?

  4. #4
    Join Date
    Aug 2007
    Cotswolds, UK
    Quote Originally Posted by Dan Mosley View Post
    I,,,,,,,,,,,They said maybe my cuts are to aggressive - im using the Ci1 on the end grain hollowing so i dont think that is it...........
    Dan, In my experience I would say that loads when using the Ci1 can be quite high, especially on end grain, because it "cuts without the catch" so to speak it is easy to get carried away and load the piece quite high. It is the only tool I have used in the last 12 months with which I have destroyed a socket or spigot.
    (twice as it happens, it takes a while for things to sink in these days )
    Chas. just a traveller on the road of time.

    Bits & Pieces
    My Web Site

  5. #5
    Join Date
    Aug 2008
    Reno, Nv
    Try some harder wood Dan. I don't always like an inside chuck (sorry Bill ) but I use it on Peppermills and salt boxes. It's easy to get carried away with the tension of the jaws...more is better, right?...and split that mother wide open. I've never turned hemlock, but IMHO fir is no harder than pine and like Frank said...clamping jell-o. An off the wall idea...take lighter cuts. I have turning A.D.D., in other words, it must be done NOW!!!! The mill I'll post later today took 4 days and a lot of borrowed patience. Sounds like your tools are in good shape so take a little more time and a smaller bite and see what ya get...but first get some hardwood and enjoy!!
    Your Respiratory Therapist wears Combat boots

  6. #6
    Join Date
    Dec 2006
    Goodland, Kansas
    Dan how big are these blanks you are turning? Friend of mine has one of the Ci1 tools and he is always breaking off tenons. I don't like the tool myself because when you take a bite it puts a tremendous load on the wood in my opinion. With Hemlock, fir, pine, etc. they are soft woods and when green I would think you would be putting a awful strain on that tenon. My tenons are generally 1/4" or so but the diameter is fairly small. I was taught that the jaws of the chuck should have less than a 1/4" space between them so that when you clamp down on the tenon they are almost shut. If you don't you are only gripping on 8 points which doesn't give you much holding power. Try your Ci1 on something like maple or walnut chucked up to see if you have the same problem tearing off tenons. If you do I would say you might be getting to aggressive with the tool. Just my humble opinion. Give me my bowl gouge.
    Last edited by Bernie Weishapl; 02-07-2009 at 09:27 PM.
    Bernie W.

    Retirement: Thats when you return from work one day
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  7. #7
    Join Date
    Jan 2008
    Stow, OH
    I totally agree with Bernie. The Ci1 is very aggressive. The full 1/2" is engaging, that is why it is fast bulk removal. If you use the whole width of the side grind bowl gouge, you can stall a high horse power lathe. It sits on a 1/2" flat shaft and its stable, you just don't feel it.

    Besides what Bernie has mentioned, the shoulder is also an important factor. The drawing is not good. Of course the wood is spinning, the direction of the force and the counter resistance are changing as well.

    The dwg is for dovetail jaws; but the straight serrated jaw is the same. The holding power is not from the gripping force of the jaws alone. The shoulder also provides a counter leverage resistance. That why the 75 mm bowl jaw has a wide top area also.
    If the tenon material is very soft, you can drill some radial holes and glue some hard wood dowels. The end grain of the dowels would provide some resistance to the crushing force of your jaws.

  8. #8
    Join Date
    Jul 2008
    Palm Springs, Ca

    Responses to questions

    Jim - yeah i need to get some hard wood and let this stuff dry out for a bit and try again later. I perfer a compression grip over the expansion also but have used both. The wood: Hemlock, Pine and D.F. were given to me in log form and i have cut it down and anchor sealed it. The Pine after i tried to turn it just shreaded and wouldnt cut even with sharp tools so it is now in the firewood pile.

    Bernie : See the pic below, but guessing anywhere from 14" down, but my jet has as 16" swing. Yes, i think your right about the load (tension) the Ci1 puts as its cutting/hollowing. I think im going to take less aggressive cuts and try your idea of 1/4" space between the jaws of the tennon. Actually today i cut some Walnut and didnt have that problem but the wood was also much dryer than the DF,Hemlock stuff.
    I also have my favorite gouge and scrapper that i really like using. The Ci1 is great for roughing out but if you get to aggressive you can stall the lathe easily. With practice ive gotten used to using it and for teaching kids when they first start turning it is a safer tool to use (<-just my opinion) especailly in terms of catches and control it is easier.......but again i really like my HSS shallow and deep fluted gouges.......

    Chas - I now think that my cuts are to aggressive and the load is to high now that im reading what all of you have been saying about the cut etc....
    As much as i like the tool Ci1 - there is a learning curve to using it for sure . One thing you learn quick in my opinion is lathe speed enhances the cutting ability compared to using it at lower speeds - Safety first though ya know.

    Gordon - that is impressive drawing and it really anchors in the concept....Thanks and ill try this approach on my next turning . Also that is a good idea about drilling a hole and plugging it up with a dowel for additional resistance when securing the jaws......never thought of it but im going to try it..

    Thanks to everybody and the help..............Dan
    Last edited by Dan Mosley; 02-08-2009 at 04:38 AM.

  9. #9
    Join Date
    Dec 2007
    Tellico Plains, Tennessee
    I'm going to weigh in with a lot of your problem as being soft green wood.. I don't know about the tool as I don't use that cutter, but if it is really aggressive and combined with the soft green wood, you're putting a lot of torque on the tenon... I've used some pine as a waste block on a couple of small bowls... first catch has split my tenon/waste block every time.
    Tellico Plains, TN
    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.

  10. #10
    Join Date
    Feb 2008
    Grand Rapids, MI


    I have to throw in another vote for finding a harder species of wood.

    I have never had a tenon break on non-punky hardwoods (when green), and I take the most aggressive cuts I can when hollowing. Of course, I use dovetail tenons as well, which also add greater security. My lathe has a 2 hp motor, and I usually slow the motor with my roughing cuts. (Meaning that a tenon should be able to withstand lots of torque.) I think it's a combination of the soft wood and spigot jaws.

    Last edited by Matt Hutchinson; 02-09-2009 at 10:53 PM.

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