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Knowledge You Can Build On — Est. 1998

So why did this happen?

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So why did this happen?

#1

So why did this happen?

Ron in Drums PA

>I rough turned a curly maple blank to about 11-3/4" round. Placed the tenon in a chuck as usual. When I turned on the lathe, the chuck of wood flew across the room.. Image my surprise, the tenon is still inside the chuck!

With nothing hurt or broken, I replaced the face plate on the wood and turned a new tenon. This time when I placed the wood into a chuck, I decided to use the tail stock and remove some wood. While I was doing this I thought it might be a good idea to turn a tenon on the inside, just in case.

I turned off the lathe, removed the tail stock, and as soon as I turn on the lathe, the tenon broke clean off and shot across the room. Again the piece of tenon is still in the chuck

Luckily, as I said before I had that tenon on the inside, so I reversed the bowl and made a new tenon. Reversed the bowl again.. This time I removed as much wood as humanly possible with the tailstock in place. This time when I removed the tailstock everything stayed in place.

Anyone have any idea why this happened?

Re: So why did this happen?

#2

Tony Reynolds

Re: So why did this happen?

Tony Reynolds

>Hi Ron,

Not sure how you're attaching the faceplate/tenon. If you're gluing it, are you gluing long grain to long grain? I've had this happen once when I mistakenly glued long grain to endgrain. That combo won't handle any stress before fracturing.

Tony

Re: So why did this happen?

#3

Re: So why did this happen?

Mark Mandell - Gone Round In Jersey

>From your description, you're cutting tenons into/from the original wood which then fracture.

If. so, I think

A) Too much compression pressure from the chuck or

B) Your wood has ring shake (bio-degraded lignin along the growth lines) or

C) Most likely, all of the above.

Mark

Re: So why did this happen?

#4

Re: So why did this happen?

Gary Evans, Tallassee, TN

>Ron,

I would think that the amount of curl in the blank could be the culprit. The reason the wood looks curly is because the cells were not laid down in nice, straight rows. Instead, the grain goes in all different directions. This results in your tenon containing a lot of short grain that might be weaker than the straight grain of a plain maple blank.

Also, if the blank is very green, the strength of the bond between the fibers is not as great as it will become as it dries.

Gary

Re: So why did this happen?

#5

Re: So why did this happen?

Ron in Drums PA

>You gave a few things to think about.

To much compression: I tighten this bowl about the same as I did other bowls, so I'm not sure about this.

Ring Shake: Could Be.

Curl in the Wood: Could be

When I look at the broken tenons, they are almost flat, which would make me think to tight a chuck. If the wood had ripples it would lead me to think ring shake or the wood's curl was the culprit.

The tree was cut sometime in August, I split the log and sealed the ends. The wood has been in my basement since. The wood lost allot of weight, but was still solid. I noticed a bit of gray color in the wood which tend to be the beginning of spalting.

(thinking out loud)

I'm wondering if my basement is too dry a place to store split logs, making the outer rings of the wood "brittle" compared to the inner "green" wood. Is it possible I tighten the chuck on the "brittle" wood causing the wood to shear off?

Re: So why did this happen?

#6

Dick Hines

Re: So why did this happen?

Dick Hines

>I agree with Mark. If you want to save the bowl sometime, sometime you can soak the tenon with CA and then reinstall the chuck. This may work but don't stand in the line of fire.

Re: So why did this happen?

#7

Re: So why did this happen?

Duane C.Leach

>Hi Ron

I have had this same thing to happen to me a few times untill I realy looked it over. Here is what I discovered. If the base of the wood where the top of the chuck jaws rests and the angle of the tennon are not formed correctly ( that is for your dove tail shaped jaws )then the jaws act like a wedge, and wedge the tonnon off. In other words the jaws grab the tennon and pull on it horizionaly wedging it off the bowl.

Or it could that sometimes bad stuff just happens.

Happy Turning

Duane

Re: So why did this happen?

#8

Re: So why did this happen?

woodspinner

>Ron

Anytime I am not sure of the stability of the tennon I run thin CA in to it prior to reversing.

I then re clean the tennon to be sure of its shape. I also agree you could be wedging the tennon off due to angle of the tennon.

Good turning and be safe

Bill

Re: So why did this happen?

#9

Re: So why did this happen?

Greg in Oshkosh

>When this has happened to me it was due to cutting the tenon in sapwood. The strength of the sapwood, especially when it's green or almost green, is lower than the heartwood. Also you are splitting the tenon off the bowl, just like splitting wood with the grain. This is the weakest spot for the wood to split.

Use the tailstock as you are already doing, Make the tenon as large as possible(more area is stronger) Don't undercut the tenon as it's like starting the split and LINE up the chuck jaws so they don't line up with the grain.