Cracked CA Finish---UPDATE

[Kevin M]

I turned an Osage Orange pen on the end grain and applied a BLO/CA finish. After 3 days in my case I found a crack all the way around the lower barrel. Today I disassembled the pen and it also had cracked around the upper barrel. I thought the CA only had cracked but after removing the finish I found the wood was also cracked just like cteaglesc had surmised. After sanding, reappling BLO/CA and a little polishing it looks as good as new, just more distinction. The sanding had deposited some Ebony in the cracks and when finished they showed up nicely. I still am at a loss for the the cracking, possibly from streses caused from end grain turning or absorbing some of the blo which was trapped under the ca?

 

[ryannmphs]

Nice save. I like the ebony accents.

Ryan

 

[Travlr7]

The pen looks great - good save.

A question that might answer why it cracked.

How much heat did your generate during finishing? I had one develop several cracks after finishing with CA. I got mine pretty hot.

Bruce[]

 

[Kevin M]

Bruce, during the initial finish, BLO/CA was applied, went on smooth and no additional sanding or polishing was done. The second time around I did polish the surface with mm and will look at this unit for the next several days to see if any cracks reappear. Still open to other ideas.

 

[JimGo]

Kevin,
It looks great! That's a heck of a save; the woods really compliment each other well, and it would have been a shame to lose those pieces!

The wood seems to be highly figured, and I wonder if your guess about the grain changes could be on the right track. I read somewhere that the growth rings represent differences in the density of the wood that occur throughout the season, as the tree gets more nutrients and water. So, I would imagine that the different densities will shrink/expand at different rates. However, that doesn't explain why yours cracked ACROSS the grain lines, rather than along them; I would have expected the areas of the same relative density to have expanded/contracted at the same rate, thus cracking along the growth rings. Were you able to figure out where the cracks started?

 

[Kevin M]

Originally posted by JimGo
<br />Kevin,
It looks great! That's a heck of a save; the woods really compliment each other well, and it would have been a shame to lose those pieces!

The wood seems to be highly figured, and I wonder if your guess about the grain changes could be on the right track. I read somewhere that the growth rings represent differences in the density of the wood that occur throughout the season, as the tree gets more nutrients and water. So, I would imagine that the different densities will shrink/expand at different rates. However, that doesn't explain why yours cracked ACROSS the grain lines, rather than along them; I would have expected the areas of the same relative density to have expanded/contracted at the same rate, thus cracking along the growth rings. Were you able to figure out where the cracks started?

Jim, sorry for the long wait on your reply. I have been waiting several days to see if any additional cracks developed. None, and I have given the pen away now and the new owner is tickled! As far as the cracks starting point, under close examination, there are old worm hole areas in the remaining block of wood that these came from, maybe this could be a suspect?

 

[JimGo]

Kevin,
Thaks for the update! I'm glad to hear that no additional cracks developed. Its interesting about the worm holes; maybe the worms contributed to the brittleness of the wood. Or, maybe the cracks were from wrinkles in the space-time continuum due to the wormholes. I guess we'll never know... (sorry, I'm a science fiction fan).

 

[leehljp]

Kevin,
I think I may know what caused the cracking - It is an end grain problem. One of the first rules of woodworking it to recognize that wood "moves". Surface stabilization is not necessarily enough. With humidity and heat / cold changes, most woods move (expand/shrink) along the horizontal or radial plane more than its length - considerably so. And this is where your fractures are.

Were your blanks vacuum stabilized?

Veneers do OK because they usually are thin, have good glue backing and usually have low moisture content when applied. The wood in pens can be similar to veneers, but if the thickness is much more or the wood not stabilized properly, <b>end grain</b> will certainly be prone to cracks with humidity or moisture changes.

I am not saying this from an experienced pen turner, but from my experiences with wood in general. Wood is going to move. One thing that I have noticed from 6 weeks of working with unstabilized blanks is that I can turn a slimline to the correct thickness, set the two pieces aside for several days; then get ready to finish by re-mounting it on the mandrel and notice that it is no longer the same thickness as when I took it off. Several had plenty of CA, but they just plain shrunk in diameter to the point that they were not the same thickness of the bushings like they were when I took them off.

 

[Kevin M]

Originally posted by leehljp
<br />Kevin,
I think I may know what caused the cracking - It is an end grain problem. One of the first rules of woodworking it to recognize that wood "moves". Surface stabilization is not necessarily enough. With humidity and heat / cold changes, most woods move (expand/shrink) along the horizontal or radial plane more than its length - considerably so. And this is where your fractures are.

Were your blanks vacuum stabilized?

Veneers do OK because they usually are thin, have good glue backing and usually have low moisture content when applied. The wood in pens can be similar to veneers, but if the thickness is much more or the wood not stabilized properly, <b>end grain</b> will certainly be prone to cracks with humidity or moisture changes.

I am not saying this from an experienced pen turner, but from my experiences with wood in general. Wood is going to move. One thing that I have noticed from 6 weeks of working with unstabilized blanks is that I can turn a slimline to the correct thickness, set the two pieces aside for several days; then get ready to finish by re-mounting it on the mandrel and notice that it is no longer the same thickness as when I took it off. Several had plenty of CA, but they just plain shrunk in diameter to the point that they were not the same thickness of the bushings like they were when I took them off.

Thanks Hank Lee for your thoughts on the subject. The next pen made of this type of wood I am going to set aside prior to fininshing to see if any cracks appear. My OO is cut right out of the fence post and not stabilized prior to turning and finishing. I am still thinking about Jim's space-time continuum thingy?

 

[leehljp]

My OO is cut right out of the fence post and not stabilized prior to turning and finishing.

Never underestimate the movement of undried or green wood. I have been bit too many times. Nature can be formidable on the molecular level too!

 

[btboone]

Jim might be onto something with the wormhole theory. And what was in those holes? Ebony. Black holes indeed. It definitely must have a space-time continuum connection.

 

[JimGo]

Well said Bruce!