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View Karda's profile

tenon broke

by Karda
posted 03-09-2021 04:15 AM


24 replies so far

View Nubsnstubs's profile

Nubsnstubs

1774 posts in 2817 days


#1 posted 03-09-2021 02:14 PM

Mike, you know that pictures are worth thousands of words. Let us see what you did, then maybe we can steer you in the right direction. ......... Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

View Lazyman's profile

Lazyman

7018 posts in 2475 days


#2 posted 03-09-2021 02:30 PM

Pictures will help. Depending upon how deep you have gotten with your hollowing, one thing I have done is drill a hole on the hollowed side that is large enough for one of your jaws to sit in in expansion mode and use the tail stock for extra safety as you make a new tenon or recess. You can just put it between centers too but this approach may be a little more steady if you have a large enough Forstner bit or small enough jaws and you can find the center well enough to drill a well centered hole.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Axis39's profile

Axis39

483 posts in 684 days


#3 posted 03-09-2021 02:57 PM

I am a new turner, so so far from being an expert, but I watched a YT video a few weeks ago and the person suggested that making a dovetail recess instead of a tenon.

The logic was that a tenon lines up the grain across it’s width. This creates a weak spot (like you’ve experienced). Whereas a recess allows pressure on the grain in different directions.

Made sense to me.

Think you could turn a recess on the bottom and remount it that way?

-- John F. SoCal transplant, chewer uppper of good wood

View Davevand's profile

Davevand

268 posts in 1923 days


#4 posted 03-09-2021 03:02 PM

Can you cut the rest of the tenon off and glue a block on it?

View OSU55's profile

OSU55

2795 posts in 3077 days


#5 posted 03-09-2021 04:36 PM

Sometimes it just happens. It is helpful to look at the pieces to try to determine the root cause, and learn something about tenon shape or wood. Can be a hidden defect, especially if its spalted wood. Depending on the shape you have and the wood, a new tenon may be the answer, or a glue block. I’ll use a glue block before I use a recess. I may rechuck a piece for various reasons and recesses are not as reliable for getting back to the exact same position. Recesses are far more difficult to redress for twice turned items also.

View MrUnix's profile

MrUnix

8570 posts in 3286 days


#6 posted 03-09-2021 06:47 PM

Just turn another tenon if you can. Glue block would also be a good move, and you know me, I’d thread it first so I wouldn’t have to use a chuck :)

BTW: Like others here, I prefer tenons over recesses… tenons are held in compression and you can only compress wood to a point. Recesses hold under expansion, and it is possible to over expand the wood grain apart if you are not careful. I also like to keep my tailstock engaged with the piece for as long as possible for additional support on larger stuff, regardless of how it’s mounted.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View drsurfrat's profile

drsurfrat

604 posts in 274 days


#7 posted 03-09-2021 06:59 PM

another less-easy option is to flatten and screw on a faceplate, then after turning, make the screw hole square and fill with a different wood. it looks kind of Arts & Crafts-ish. i did it with a flat bowl and it looked nice

-- Mike (near Boston) ... Laziness is the mother of invention, necessity is the mother of exhaustion - me

View Karda's profile

Karda

3108 posts in 1641 days


#8 posted 03-09-2021 11:11 PM

here are the pics, it sheared clean and I don’t see any defects in the wood the tenon is about 2” my max is 2.5”
I uped the speed from 750 to 1100 that may have been to fast

View Woodmaster1's profile

Woodmaster1

1737 posts in 3674 days


#9 posted 03-09-2021 11:36 PM

Here’s what I use to prevent bowls losing tenons the dowel keeps pressure on the bowl so there is not as much stress on the tenon
.

View Karda's profile

Karda

3108 posts in 1641 days


#10 posted 03-10-2021 12:24 AM

thanks, I’ll turn a new tenon and keep the tail stock in place as long as I can i was wondering what other options there were

View Lazyman's profile

Lazyman

7018 posts in 2475 days


#11 posted 03-10-2021 03:18 AM

Karda, which part of the base was bottomed out against the chuck, the bottom of the tenon (in other words that part that broke off) or the bottom of the bowl around the tenon? The bottom of the tenon itself should not be against the chuck. If it was, that is probably why it broke off. Also, from the picture it looks to me that the area around the tenon that should be registered against the end of the jaws isn’t flat enough. The jaws need to make contact with the bottom of the bowl (not just the sides of the tenon) and it must be flush. Basically, it should fit like this:

It doesn’t have to have a step from the shoulder to the bowl like it shows, but the shoulder does need to be flat against the jaws and the tenon itself should not bottom out. Maybe yours was and it is just hard to tell from the picture.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Karda's profile

Karda

3108 posts in 1641 days


#12 posted 03-10-2021 04:13 AM

the chuck was installed properly I was looking at the broken tenon and it looks lop sided. I think one side of the tenon was too small

View Davevand's profile

Davevand

268 posts in 1923 days


#13 posted 03-10-2021 04:19 PM

I am a novice wood turner just starting out, I too have turned a few turning into frisbees from a broken tenon or a catch. Now if I am turning a larger plate or bowl I use a larger tenon with the larger jaws.

View Karda's profile

Karda

3108 posts in 1641 days


#14 posted 03-10-2021 04:32 PM

I don’t have larger jaws

View Lazyman's profile

Lazyman

7018 posts in 2475 days


#15 posted 03-10-2021 05:49 PM

I am not sure what you mean by lopsided?

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View LesB's profile

LesB

2993 posts in 4530 days


#16 posted 03-10-2021 06:45 PM

Karda,
So there must have been a crack or other defect in the wood for that to happen. Looking at the progress of the growth rings on the turned portion I would guess you chuck was holding right on a growth ring that split away under stress. I would suggest you go with the mortise method on this piece as it may happen again if you renew the tenon.

One alternative is to create a mortise in either the face side or the damaged tenon side. You can probably use the router method I described in a blog a while back. https://www.lumberjocks.com/LesB/blog

Or you could mount the face side on a face plate with screws (you will be removing the screw holes when you hollow the bowl out anyway) then create a new tenon or mortise on the bottom, turn the piece around and continue using the chuck.

-- Les B, Oregon

View Karda's profile

Karda

3108 posts in 1641 days


#17 posted 03-10-2021 06:59 PM

one part of the tenon was thick enough and the other side is to thin, just thick enough for the chuck to grab

View Leo Van Der Loo's profile

Leo Van Der Loo

56 posts in 1845 days


#18 posted 03-10-2021 07:05 PM

I would clean the tenon right off of the turning and glue a new block onto it.

If you can mount it first back on the top side it is easy to remove the tenon’s leftover, and also turn a shallow recess where the new to turn block will fit into, it centers the block that way and makes for a good glue face.

-- Have fun and take care

View Karda's profile

Karda

3108 posts in 1641 days


#19 posted 03-10-2021 07:45 PM

what is the point of a glue block if I can chuck anything bigger, the wood in the blabnk is solid

View Lazyman's profile

Lazyman

7018 posts in 2475 days


#20 posted 03-10-2021 08:22 PM

If you are going to use a glue block, why not simply glue it back on? As long as there are not any missing slivers and you can get a good glue contact, you should be able to get as good a joint as you would with a glue block.

In my experience, the main causes of a broken tenon are one or more of the the following:
  1. Fragile or cracked wood
  2. Tenon too small a diameter for the size and weight of the bowl
  3. Improperly formed tenon and shoulder making it impossibly to mount it correctly.

Just based upon where your tenon broke, I really think that it was not shaped correctly. If the corner formed by the tenon and shoulder is rounded, the dovetail is not the right angle or the shoulder is not flat, there will be gaps which allow the bowl to pivot slightly and the tenon may break or the bowl will simply come off especially if you get a catch.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Karda's profile

Karda

3108 posts in 1641 days


#21 posted 03-10-2021 08:42 PM

I am going to turn a new tenon, the shape was bad and the blank to big, I weighed it. 5 pounds. I’ll have to go slow

View OSU55's profile

OSU55

2795 posts in 3077 days


#22 posted 03-10-2021 09:52 PM

It appears the tenon sheared in the middle, which suggests to top of the jaws were NOT seated, as in the previous diagram. However, your comment about the end of the tenon being lopsided with uneven chuck engagement suggests the force against the taller tenon wall may have caused the shear to occur.

Always make the free end of the tenon flat at the OD, so the tenon wall is equal height all the way around, so the jaws grip the same amount of tenon wall. The middle part of the tenon can be sloped, no problem. When I have a blank between centers and the tenon side is sloped severely, I rough turn the tenon, and turn down the center to a small dowel size, remove the blank, cut that dowel off flush with the tenon end, remount between centers and finish the tenon. Gets the tenon flat and the tailstock center is not supported by a long skinny dowel.

View MrUnix's profile

MrUnix

8570 posts in 3286 days


#23 posted 03-10-2021 11:10 PM

what is the point of a glue block if I can chuck anything bigger, the wood in the blabnk is solid
- Karda

Thread it and you can make it as big as you like, without the need for a chuck. The glue bond is in theory stronger than the wood (as per all of those ‘glue tests’ I’ve seen), and you would not have to reduce the size or thickness of your bowl. Once you are finished turning, just part it off and clean up the foot.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View Karda's profile

Karda

3108 posts in 1641 days


#24 posted 03-10-2021 11:40 PM

I for got about threading thanks for reminding me

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