My Hollow Form Cracked - Ideas Why?

[Glen Blanchard]

I turned a vase/hollow form today and about the time I was making some final passes on the lathe I noticed a crack maybe 1/2" long at the opening. I don't think it was there while I was turning. A bit later I noticed another crack (this one running perpendicular to the grain) near the neck. I can only speculate as to the cause, and was hoping to get some likely explanation. The blank was purchased at Woodcraft and was totally (all 6 sides) covered with wax at the time of purchase. The wax is intended to hold in moisture and prevent checking. As the wood began to dry, it cracked. Am I close?

Now I know about roughing out a bowl and coming back to it after it has dried to true it back up, but does one do the same thing with high moisture content wood and hollow forms? Is it inappropriate to make a hollow form with high moisture content wood?

Thanks.

[Rick Markham]

Glen, can you take a picture? It will be easier to tell. What type of wood was it?

Cracking can be caused by sanding the piece at too high an RPM (heat checks) or just normal checking from being wet wood drying unevenly. I've had normal checking occur in a cherry blank before I could get the hole drilled to hollow it. Sometimes it can be internal stresses in the wood, or wind shake damage from being from a large branch. I have Walnut that if you look at it wrong it cracks, some from the same tree that acts just fine.

Yes, you can rough turn hollow forms, allow them to dry (with what ever method you prefer, there are about as many ways as there are turners) and return to it later. The same 10% rule applies with hollowforms and bowls ;). I hope this helps you at least a little!

[Eric Gourieux]

I agree with Rick. Unfortunately, this is a part of our craft. Don't be discouraged. See it as an opportunity. You could probably fill or inlay in the cracks. A pic would help us give more detailed advice.

[Glen Blanchard]

Thanks Rick. Here's a photo of the larger of the two cracks. I think this is a maple burl.

Is it possible to find blanks that are already dried? If so (assuming that this was due to drying) I might be better off avoiding high moisture content blanks. Which I suppose leads me to my next question. Assuming dried blanks are not too difficult to find, why would one want to work with the wet stuff? It would seem that working with adequately dried blanks would be less fraught with problems.

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[Marc Himes]

Cracks part of turning, more in wet wood than dry, but can occur with both. Most of the wood I get is wet and I usually rough out, let dry and finish turn. Frequently I have to deal with cracks. I was at a demo by John Jordan and he said he uses almost all wet wood and finishes the piece in one setting other than some finish sanding. He had a lecture on "Why my wood don't crack" but I missed that one. As far as finding dry wood for hollow forms, I don't know of a source providing dry wood more than 4" thick so you would be limited by that dimension. Some turners us a spray bottle with water to keep the piece from drying too fast while they turn it, which may be useful this summer with all the hot weather across the US.

[Michelle Rich]

yes. dry wood is less prone to cracking, but at 3-4-10 in diameter it would take years & years to dry...1 inch per year plus a year is the standard

[Eric Gourieux]

Glen,
Most turners use wet wood for several reasons.
1) It takes a LONG time for thick blanks to dry
2) Wet wood is much easier to find in abundance and is often free
3) Wet wood turns much easier

Several years ago, I bought turning blanks from a guy who must have bought them from someone who was getting rid of his old turning blank stock. Most of it was VERY dry. When turned, the dry wood had a lot of tear out and still split occasionally.

The splits on your piece (nice looking form, by the way) are all too common for all of us. The common causes of splits have been outlined already. Sometimes the gap closes and the splits become practically invisible with time. As I mentioned, these provide an opportunity to ADD a dimension to your turning. It may not be planned, and may be a little (lot) frustrating, but we have to go with the flow.



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I filled these splits with jet black stone and ended up selling it at a local gallery.

Don't be discouraged by the splits. Set the piece aside for now and move on to the next one. You may decide what to do with it after it sits around for awhile.

[Reed Gray]

I can't really tell without seeing the piece in person. A lot of times there are minor cracks that we don't see until we are sanding or putting the finish on. Some times they appear as we remove wood, and the crack can move as there is less material to hold it still. It looks like there is a little color in the crack, which indicates it was there in the first place. While I don't do many hollow forms, I prefer green wood. Just so much more fun to work with, and I love warped shapes.

Half the art of being a master woodworker is being able to fix your mistakes. A crack, more so in an ornamental piece is a 'design opportunity'.

robo hippy

[Steve Schlumpf]

Glen - my first guess is that the piece started drying out as you were turning it. Its always a challenge to get something turned before it starts checking but I have had great success with using a spray bottle with water. Every time I see the piece starting to dry out a bit, spray it with water and keep turning. If I have to take a break from turning, I cover the wood with a plastic bag to keep it from drying out until I can get back to hollowing. Once I have the piece hollowed - I use the DNA method to assist in the drying, so a little extra water at that point makes no difference.

[Glen Blanchard]

Its always a challenge to get something turned before it starts checking but I have had great success with using a spray bottle with water.

Steve - Are you saying that if I can get it turned without it cracking, it is not likely to check afterward? Or are you merely stating that turning a cracked piece can create problems so it's best to get done turning it before it cracks?

[Steve Schlumpf]

My experience - when turning pieces that are not already cracked - is that if you can get the wood to dry evenly, then checking usually does not occur. The wood will dry evenly if it is of a consistent thickness. When you are turning, parts of it will be thicker than others... so it can start cracking if allowed to dry at that point.

[Faust M. Ruggiero]

To further what Steve told you abut the blank drying while you are hollowing, I usually wrap my hollow forms in stretch wrap immediately after shaping the exterior. That keeps the moisture in the wood and helps avoid cracks. If I must leave a partially completed hollow form over night, I either drop it in a pail of water and let it soak or totally wrap it in stretch wrap. I suggest you do nothing with the cracks until the form is completely dry. Throw it in a paper bag and leave it alone for a couple weeks. Occasionally, small cracks will close up on their own as the wood stabilizes. Be sure you wall thickness is thin and uniform.