Thread: tenon and recess fail !!

Looks like it will be a great bowl when you manage to finish it, assuming it doesn't knock you out in the process

This is another reason I use a glue chuck, haven't had a failure since I started using them.

Jim

With your tenon try using some medium superglue. It prevents any minute movement when (if) you get a catch that loosens the grip, making the next catch the bad one. It also strengthens the tenon and prevents the catch from causing minute cracks. When you have finished turning opening the chuck will break the join on three jaws and a bump with the hand will loosen the 4th jaw. I use a Oneway chuck and use superglue whenever I turn a large bowl (300mm plus)

Forgot to add how in my earlier post. When yo have the tenon fitting well just add a bead of glue round the base and clamp the jaws closed. wait 10 min and turn. With the Oneway I clamp the jaws on the tenon and then run a bead down onto the tenon through the gap between jaws.
Works everytime for me

I find that with a mortice that you need a larger area of foot to prevent this happening and with the tenon you could have done with a flat area around the tenon for the jaws to sit against. Hope this works



and also

And maybe a set of 100mm dovetail jaws. That tennon is tiny and Camphor is a week wood. Phil

Just turn off the broke tennon, makeing the flat a bit bigger , then hotmelt glue on a new tennon . When the glue is set, true it up and away you go .
Ted

Originally Posted by powderpost

This is another reason I use a glue chuck, haven't had a failure since I started using them.


Jim

Hi jim, I will try a glue chuck and see how I go
I can feel a ....."told you so".... , moment !

Originally Posted by Richard Hodsdon

Forgot to add how in my earlier post. When yo have the tenon fitting well just add a bead of glue round the base and clamp the jaws closed. wait 10 min and turn. With the Oneway I clamp the jaws on the tenon and then run a bead down onto the tenon through the gap between jaws.
Works everytime for me

Originally Posted by Richard Hodsdon

With your tenon try using some medium superglue. It prevents any minute movement when (if) you get a catch that loosens the grip, making the next catch the bad one. It also strengthens the tenon and prevents the catch from causing minute cracks. When you have finished turning opening the chuck will break the join on three jaws and a bump with the hand will loosen the 4th jaw. I use a Oneway chuck and use superglue whenever I turn a large bowl (300mm plus)

Hi richard, I have never heard of that before , do you mean
using glue on the chuck jaws !

Originally Posted by Dalboy

I find that with a mortice that you need a larger area of foot to prevent this happening and with the tenon you could have done with a flat area around the tenon for the jaws to sit against. Hope this works



and also

Hi derek, yeah I think a bigger tenon might be needed
I will give a try on the weekend , thanks for your thoughts

Originally Posted by pommyphil

And maybe a set of 100mm dovetail jaws. That tennon is tiny and Camphor is a week wood. Phil

Hi phil , I don, t think I have ever had this problem
before, but I try bigger jaws , thanks mate!

Originally Posted by turnerted

Just turn off the broke tennon, makeing the flat a bit bigger , then hotmelt glue on a new tennon . When the glue is set, true it up and away you go .
Ted

Hi ted, thanks for your comments,i appreciate them

Hi Smiife
Yes effectively I glue the jaws to the tenon. I put the glue on the tenon then seat and close the jaws on the glue , or else if the gap between the jaws is big enough run a bead down on to the tenon. It fills up any minute gaps and any excess gets squeezed out, and locks the jaws to the tenon.
When you take the bowl off you have to clean/scratch the glue off the jaws , it takes about 30 secs to do this, I use an old pen knife, Acetone will work as well. We were shown this trick by Butch Smuts one of the turners featured in the book "New masters of Woodturning"

Originally Posted by Richard Hodsdon

Hi Smiife
Yes effectively I glue the jaws to the tenon. I put the glue on the tenon then seat and close the jaws on the glue , or else if the gap between the jaws is big enough run a bead down on to the tenon. It fills up any minute gaps and any excess gets squeezed out, and locks the jaws to the tenon.
When you take the bowl off you have to clean/scratch the glue off the jaws , it takes about 30 secs to do this, I use an old pen knife, Acetone will work as well. We were shown this trick by Butch Smuts one of the turners featured in the book "New masters of Woodturning"

A well formed and appropriately sized tenon should be strong enough. I won't be using super glue on my chuck jaws. I support the recommendations to follow Stuart Batty's tips, all sound well proven techniques.

Originally Posted by Mobyturns

A well formed and appropriately sized tenon should be strong enough. I won't be using super glue on my chuck jaws. I support the recommendations to follow Stuart Batty's tips, all sound well proven techniques.

Hi moby, I just went back to photo of the tenon and
thought that the fit was "well formed and appropriate sized tenon "
Could you tell me what Stuart Batty, s tips are please ?
Also not sure I want to glue my jaws up either !

Originally Posted by smiife

Hi moby, I just went back to photo of the tenon and
thought that the fit was "well formed and appropriate sized tenon "
Could you tell me what Stuart Batty, s tips are please ?
Also not sure I want to glue my jaws up either !

smiife, I had replied yesterday but some how I must not have posted the reply when I was disturbed by family.

I really can't comment on your tenon shape etc as I can't see it, only the sheared off portion. The tenon diameter is a good match to the lower end of the chuck jaws range of movement, which means that the jaws have maximum griping power and maximum surface contact.

My first thought when I saw the photos though was - its camphor laurel! The tenon size looks OK (depending on grain properties) for a bowl of that size and many turners get away with standard jaws on most woods for bowls of that size. However CL, at least the stuff we get up here, is notorious for being soft and for shearing easily, so a larger tenon diameter than normal is prudent.

When you look at photos 1 & 2 it is apparent that the bowl curvature carries right through to the start of the tenon, so there is no flat area on the base of the bowl to register against the flat front face of the chuck jaws. Stuart's videos go into quite a bit of detail about why the tenon profile must match the jaw profile, why it should not touch the bottom of the jaws, and how the small flat area on the bowl blank creates a register for the chuck.

Without the registration surface the bowl blank actually flexes and moves in the jaws while you are turning, plus if the tenon is not well matched the inner top lip of the jaws may crush into the grain starting a crack in the soft and easily sheared wood. The rest as they say is history.

A similar situation occurs when using a recess, match the jaw profile etc.

All woods can be classified as suitable for particular applications according to their varying mechanical properties, crush strength, shear strength etc, and grain features, straight, interlocking etc. Unfortunately a lot of CL is soft, has straight grain & shears easily, so if we want to use it we have to modify our techniques to make sure we have enough cross sectional area in the tenon or the donut around the mortise to resist the shear forces created when we tighten the chuck jaws.

Stuart illustrates & explains his views very well, & I go along with his school of though, so no need to repeat.

Smiife, give superglue a try. I was skeptical like you until I tried it. The glue leaves a very fine film on the top and inner edge of the jaws, which comes off very easily. In fact it is easier to clean off the superglue than than Sanding Sealer and/or wax polish which gums up everything. And sprays everywhere when you buff it.
Richard