more advice please: green wood, tenon crumbled in chuck - Woodworking Talk - Woodworkers Forum
 
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post #1 of 7 Old 09-12-2011, 05:53 PM Thread Starter
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more advice please: green wood, tenon crumbled in chuck

Another problem I hope you can help me with ...

I'm trying to turn a fair sized piece of green wood (I believe it's ash), about 11" diameter, 8 or 9 inches head to tail.

With the blank on a face-plate, I rough-turned the shape of the bowl and turned a tenon to hold in my 4-jaw chuck so I could reverse it and hollow out the bowl. This technique has worked fine on a dozen or more blanks.

This time, the wood of the tenon simply crushed and broke away when I tightened the jaws of the chuck around it.

Suggestions please?

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post #2 of 7 Old 09-12-2011, 06:18 PM
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You most likely over tightened. Your chuck holds the strongest when the tenon is as close to the size of the chuck when the jaws are almost round (or when there is the max contact between jaws and wood. Don't over tighten. Bring your tailstock up to start (just turn as close as you can get...you can remove the nub later). Recheck your chuck every so often, but just snug it a little. Hope this helps.

That bowl was perfect right up until that last cut...
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post #3 of 7 Old 09-12-2011, 06:48 PM Thread Starter
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Quote:
Originally Posted by sawdustfactory View Post
You most likely over tightened.
Possible I suppose. The chuck is a "two-lever" model (not a single turnkey), I've always had to tighten it pretty good in the past.
Quote:
Your chuck holds the strongest when the tenon is as close to the size of the chuck when the jaws are almost round (or when there is the max contact between jaws and wood.
Yep, that's what I did.
Quote:
Bring your tailstock up to start (just turn as close as you can get...you can remove the nub later).
Didn't get that far -- the tenon came away before I even mounted the chuck onto the lathe. But I do use the tailstock for extra support once the piece is mounted.
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Recheck your chuck every so often, but just snug it a little. Hope this helps.
Thanks

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post #4 of 7 Old 09-12-2011, 07:49 PM
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Yikes!
First, take anything I say with a grain of salt. I am no where near a profession, just trying to help.
What chuck (name/size) do you have? What size/type jaws.
I have a Nova SN2 mounted with their PowerGrip jaws. Your blank size exceeds their capacity and for myself I would never even try it.
Are you trying to turn it end grain or side grain orientation?
With either I do not understand how the tendon can break. I can only assume you are turning side grain (normal bowl orientation) and the wood had a weak place. You said it is green so it should not be punky (rotten). Even with a proper fit to the tendon you are chucking up where the grain of the wood allows the tenon to break off.
With my SN2 and PG’s the rating is for end grain orientation up to 8” dia # 12” long. (like gripping a soft ball bat in the jaws and trying to break it). It does handle larger…up to 27” diameter I believe…BUT that is a max of 2-3” deep as in a table top or large platter.
Again, I am just trying to help so if I sound out of line excuse me. The president of our local turning club had an accident (last month or the month before). I didn’t hear all the details of what he was turning but a squished nose (broken in three places) and a broken cheek bone ain’t any fun.
I’m glad the tenon broke before you could mount it and bring it up to full rpm.
Be safe.

They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety. Benjamin Franklin
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post #5 of 7 Old 09-12-2011, 07:56 PM
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Good point there, the blank just may have been too heavy for the size of the tenon.

That bowl was perfect right up until that last cut...
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post #6 of 7 Old 09-12-2011, 09:35 PM
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Dunc,
You need a bigger set of jaws for your chuck for a green blank that big. I bought a set for my vicmark chuck recently just for that purpose. They allow for a tenon close to 5". Much better grip, especially on the softer wood.
Mike Hawkins
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post #7 of 7 Old 09-12-2011, 10:30 PM Thread Starter
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Ah ... that makes so much sense even I get it!

Time to place an order with Penn State ... #3 Large Round Jaw Gripping: External: 3-1/16" to 4-7/8" to add to my "Utility Grip 4-jaw chuck CUG3418CCX".

Thanks also for the safety reminder -- I'm also glad that the tenon broke off before I got it cranked up, don't like the thought of any projectiles ...

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