A little more info
When the bowl took off did the tenon stay with the bowl or is it stuck in the chuck. If stuck in the chuck jaws you probably "cut" into the tenon with the jaws. On occasion when I turn a soft wood that prone to split I put CA glue around the tenon to give it strength and stabilize it.
Not familiar with the Talon but does it have tapered or straight jaws? If tapered are you certain you did not kind of dig into the bottom of the tenon when you put the taper. Make the shoulder at the tenon base truly flat and wide enough to support the jaws?
Sometimes even before I start turning a piece of problematical wood I put a coat of lacquer or sanding sealer all around the bowl. Some woods just need more support then others. Finally I always keep my tail stock up tight until I must back it off to start hollowing. I generally shape the outside of a BE bowl close to finish before I attempt to holow and always keep the tail stock up until I have to move it out of the way.
First off, I found some information I didn't have before, the piece was too big and heavy for this lathe. Even as well dried as it was it was considerably thicker than they recommend and out of balance when I first started turning. Compounding this my old work bench was screwed together without glue twenty years ago and getting a bit wobbly. I have loosened the joints and added glue now but that had to add a little to the whip once the piece started moving. A new work bench is pretty high on my list of priorities. I have several in my shop but I think I am going to build a stand to support this lathe with good access, and add 300-400 pounds of concrete block ballast.
The tenon broke off and is beside me as I type. It was totally wood failure. Next time I won't tackle as large a piece and I will take many more steps to reinforce even slightly questionable wood. I was ignorant of some characteristics of this local cedar that makes it even worse than some to try to turn, especially after sitting drying for years. Pretty much a laundry list of all the things you can do wrong, I did, and finding a few more each day!
One issue is this lathe resembles the cast iron Jets and mustard lathes in the midsize and it doesn't seem to have near the strength and guts from what I read and see. Firmly mounting to a rigid bench would no doubt make it better, but I am coming to a better understanding of it's limitations. Coming from a metal lathe background I thought it was a little stouter.
I did tighten the chuck quite firmly but since the marks in the cedar are comparatively shallow that doesn't seem to have been a factor. The depth of the tenon was about 7/16", pretty much as deep as I could make it and still see that it wasn't bottomed out which I knew was bad.
With hindsight, this wood was something an experienced turner would have approached with caution. They wouldn't have put this big of a piece on this lathe, and they would have taken steps to reinforce both the tenon and overall piece if they did elect to turn this wood. Of course they would have shut down and found the wobble or threw away the piece when they didn't too. I did put a good bit of force on the piece looking for movement between it and the chuck with the lathe off just a few minutes before it broke so the crack was only apparent in the piece at turning speed then.
My jaws are the new design wave profiled jaws, it is a brand new Talon. It grips with wave shaped ridges in eight places around the tenon. Looking at the tenon again this morning, the tooth marks in the tenon are still very sharp and clean, the tenon did not move in the jaws before parting and the noses of the jaws were firmly against a shoulder.
My major issues were that I overloaded the lathe with an out of balance unsafe piece. I also had catches that a better turner wouldn't have had sending shocks through the piece. I suspect that someone with their ducks in a row could have turned this piece without problems but probably would have known better than to try.
A bunch of rookie mistakes. Fortunately I am used to turning metal on lathes and occasionally out of balance stuff so I mostly maintained good positions turning the piece. I am also being cautious positioning the tool rest so a piece can't get a good start in my direction whenever possible.
Thanks for your contribution to this thread. I'm learning from every post!
Well, I came into this one late. Cedar tends to split easily, Check! Tenon was the right diameter, Check! Chuck was snugged up, and not over tightened? Not sure about that one. Do snug it up in each key a couple of times, more important for big (12 inch and above diameter). Tenon might have been too long: from a class with Stuart Batty, he commented that almost bottoming out puts more stress on the tenon, and makes it more likely to crack: 1/4 to 3/16 inch deep is plenty. If it was wobbling while turning, some thing is loose. I have found the set screws on the chuck jaws can loosen up. I don't use locktite on them though, even though I have chucks with dedicated sets of jaws that I never change out. If it starts out spinning true, and then starts to wobble, that means some thing is loose, and loose things tend to go into orbit.
robo hippy
Much of my reply above answers yours also but to recap the list: Cedar splits easily: I knew this in theory. However I have no experience to understand what this really means in terms of what stresses and strains one wood can take and another can't. "Easily" can be as hard to define as snug if you don't have further reference points. No sugar coating it, I didn't.
The tenon and chucking questions I am going to lump together. These new design wave jaws fit a wide range of tenon sizes equally well and equally poorly. Unlike most jaws there is not an optimum diameter that offers significantly more contact than others. The tenon was 2-3/4" diameter. If I had it to do over after seeing the jaw prints this chuck leaves behind I would have made it bigger although I don't think that would have prevented this trainwreck, just better practice with these jaws. I don't want them almost fully extended fearing scroll thread failure but three to three and a quarter tenons will be gripped with pretty much the same strength as a smaller size in these wave jaws, maybe even more. I haven't really delved into the theoretical best size tenon for these wave jaws but at a quick guess it might well be bigger than the biggest opening they extend to.
I clearly overtightened the jaws if dealing with most wood. This wood was so hard that the jaws show little penetration nor does it appear that the crack could have started where a jaw bit in. A mistake, but probably not a factor here.
The tenon was too deep in the jaws according to Stuart Batty. To be honest, this doesn't jib with anrything I know about chucking from working with other materials, as long as the piece doesn't bottom out and the nose of the jaws rest solidly against the main body of the piece I'm just going to keep an open mind about this one until I learn why he said that. Not disagreeing or agreeing, I don't have enough info to understand why he made that statement.
The wobble: No getting around it, a dumb move ignoring it when I couldn't locate it. That is even something that I know better than from turning other things. This was flat a stupid mistake that I should have known better than. More than the "fools rush in" other errors I made this one galls me. I don't make many stupid mistakes that I know better than doing. I can't even plead ignorance here, carelessness, recklessness, thoughtlessness, none of the things I would like to admit to. I knew better and didn't think at that time.
A little information you might verify and give a try if you agree. Threads never make full contact in a threaded hole, varies with the hole and the fastener but you probably have 15% or more noncontact in those jaw screws. Putting the light duty blue Loctite, the original I believe, fills that void and usually prevents screws from loosening under shock and vibration. Because it also prevents corrosion and galling, it is often easier to loosen threads that have been together for a long time that were put together with Loctite than those with nothing. There are about a dozen Loctite thread compounds now, years ago when working in R&D I knew them all. I have slept a bunch of times since then though so I don't remember which is which. Put the wrong one on the threads and it takes a lot more heat than anyone wants to use on a chuck to free the threads. I think there is even a lighter duty one than the one I recommend too, little more than joint compound but that still gives more consistent tightening and prevents galling and corrosion in the threads.
The jaw screws were tight when this happened, I checked them three or four times during my early usage of the chuck and after this event too. I always suspect movement in new equipment.
Thank you for your contribution too! I do value every post and every one adds to my knowledge. I have to find out about that tenon depth deal now. It will bug me until I know why he says a short one is better than a long one.
Hu