Dealing with cracks??

[Regis Galbach]

I am cutting a small, about 4", natural edge bowl (holly). I've rounded it and see some cracks. At first, I put some fast CA on each crack and around the bark. Then I cut some more and they remain.
Question is: when is crack bad enough to just scrap the bowl? This one is small and probably not dangerous but, I still need to understand when to discard..

Appreciate helpful tips on cracks.
Thanks,
Regis

 

[hockenbery]

I reccomend using fresh cut wood that is crack free.

It is always an educated guess at best working with wood with cracks.

1. cracks extend beyond the visible - a 1" crack may be 2, 3, 5" long...
2. all the wood on one side of the crack may come off the blanks
3. Avoid any piece tha the has a compromised tenon or faceplate mount - the whole piece may come loose.
4. I have seen a piece smaller than yours cause severe facial injuries.
5. Turning cracked wood posses significant risks when a catch occurs.
6. Avoid turning cracked wood if you are getting any catches.

Here is a superficial look at your blank.

Red arrows : I would not turn a piece with the either red crack. As you hollow the bowl the wood on one side of the crack will likely break off. Worse it might break off before you begin hollowing. These both indicate the possibility of a compromised tenon and a structural issue for holding the bowl on the lathe.

Orange arrows: If this were the only crack I would watch it a lot for any indication that it extended into the base.
Before hollowing I would wrap the bowl with the strapping tape with nylon threads.

Green arrows: This one may be safer to turn than the others. It does not appear to be a structural issue for holding the bowl on the lathe.

With so many cracks this one is unsafe.

 

[hockenbery]

I should add that what you have are radial cracks that occur from the center of the log to the bark because the shrinkage if of wood around the growth rings is greater than the shrinkage across the growth rings and the woos has to crackmas it moves from shrinking.
Cutting through the pith allows each half log to move without having to crack.

With these cracks the wood is often only held together with a few fibers.
Not safe to turn.

 

[Regis Galbach]

hockenbery,
WOW! Now that is an education on cracks in wood for me. One of those cracks (marked red) does extend to the tenon. I thought about going ahead and finishing because of the small size. BUT, now that I've read your reply, I think that I will place your arrows on it and put it on a shelf as a reminder.
Glad I did post this and especially glad that you made such a thorough response.

Thank you,
Regis

 

[John Torchick]

hockenbery, yes! Thanks for the lesson in turning or why you should not turn cracked wood.

 

[Mike Johnson]

There are several methods that can be employed to turn a piece with cracks, but why waste
your time fooling with a wood blank that is full of cracks? If the wood is special or has some
characteristics that would be worth the extra effort, you can add supports to the wood blank
and carefully turn the outside and inside. You can also put the wood blank in a vacuum chamber
and saturate the wood with resin and cure the resin and then finish turning the piece. This method
is used on extremely spalted woods that are soft and punky, many pen turners will use this process
to harden soft woods to make into pens and other small turnings. Some turners will fill large cracks
with crushed rock and epoxy, or powdered metals and epoxy. This process is a lot of work and requires
numerous steps to turn the wood blank safely and fill the voids properly to allow turning the piece
and finishing it. There are a number articles and books written on this process.

 

[John Torchick]

Mike, thanks to you, also.

 

[john lucas]

Well there's dealing with cracks, and there is using cracks. Unfortunately cracks don't go away. The only real option is to highlight them. Al already covered all the dangers. We have all turned a piece with a crack and salvaged it by filling the crack in some way or another. By far the best thing is to learn what is causing the cracks and then avoid that. Usually it's poor storage of the wood or taking a day and half to turn a bowl and letting it sit on the lathe and dry. Ideally you turn a bowl fast enough that it doesn't have time to crack. I will often spray the outside with water to keep it from cracking if it's a wood that I have problems with.
Here is an example of taking it to the extreme. All the clear spaces are filled with clear epoxy and other areas filled with black epoxy. This is Brenden Stemp who is a full time turning I believe in Australia. This is a series he is doing from old Fence posts.

 

[Bill Boehme]

This is Brenden Stemp who is a full time turning I believe in Australia. This is a series he is doing from old Fence posts.

That bowl is certainly an extreme case. You could almost say that it is an epoxy bowl with a few wood particles embedded in it.