Dealing with Radial Pith Checking in Hollow Forms

[Marty Tippin]

I'm working on a cremation urn that is turned from (fairly) green soft maple, in spindle orientation, centered on the pith (based on information from Peter McCrea and his demo for the Maine Woodturners in January, 2013 -- http://mainewoodturners.org/wp-conte...oHandout-1.pdf ) - dimensions are about 7.5" diameter by 10" tall, walls are around 3/8" thick.

After hollowing, I applied a coat of shellac to the outside in an effort to seal and slow drying on the outside, and stuffed a rag in the opening to further slow drying on the inside. I left the vessel sitting on my workbench in my shop, which may have been a critical mistake, as now that a few days have passed, I've got 2 or 3 fairly significant checks radiating out from the center at the top.

So far, I've put the vessel in a paper grocery sack to slow the drying process and I soaked the cracks with thin CA but doubt that will really slow or stop further checking.

What's a good way to keep the checking from getting worse as it dries and (more importantly) to "save" this piece and deal with the cracks once it's dry?

I can certainly fill the cracks with epoxy and coffee grounds as has been suggested here before, but I'm particularly worried that the checking may get worse over time and/or with seasonal movement of the wood, and given this vessel's purpose, I really can't have it cracking open at some point down the road.

[charlie knighton]

burn it, a cremation urn is of great importance to the family......you might try another blank and offset the pith, nothing is 100% when doing this type of form when you use the whole log with the pith.....could find blank from one side of pith.....7 - 8 wide can be found but

[Thom Sturgill]

Start over. Finish this 'urn' as an art/practice piece if you wish.

If you turn to final thickness (less than 1/4" - 1/8" is better) with the pith running side to side, then the walls can move without cracking, or at most a few small, fillable cracks. The form will not be round, but should survive uncracked. Turning green to finish also preserves the fresh color of the wood better. Of course the opening will not be round either, but that can be fixed to allow insertion of threaded piece for a screw on lid.

Best of course would be turn to final thickness from a large log so that the pith is not a concern, but that is not always possible.

[Kyle Iwamoto]

Curious as to why you shellaced the outside and not the inside. In my limited mind, that would create an imbalance in drying from the outside and inside, which is what I try to avoid. I would go no finish at this time or inside and outside.

Were you planning to finish turn? Depending on the severity of the checks (not cracks) and your closure device, it could remove enough wood to get rid of the checks, as long as they are not too severe. If they are severe, you could finish turn that into a vase. Start a new urn for all the reasons above.

[Marty Tippin]

I kind of figured the consensus response would be "start over" ... And I agree, given the importance of this item to the family. But it's also hard to have spent several hours so far working on a piece and being quite proud of how it's progressing only to have it turn into kindling...

The challenge, then, is finding a way to get an 8" diameter by 12" tall blank that either doesn't include the pith at all or where the pith runs horizontally but won't blow out when it dries. The maple I have on hand has a very spongy pith at the very center, maybe 3/4"" diameter or so, which would never work in a horizontal pith layout. I do have one log that I might be able to get close to 8" diameter from and avoid the pith altogether, but it will require some careful cutting and a bit of luck. That might be my project for this weekend.

As to why I shellaced the outside, the idea was to try to control the drying in the same way that some people coat the outside of a bowl blank, hopefully resulting in compressive force rather than expansive force as the drying progresses. May not be applicable to spindle-oriented pieces though.

I'm going to continue to monitor this piece as it dries and decide whether it can be salvaged or not, either for its intended purpose or as a vase. If the checking stops without getting too big, I may be able to make a larger lid for it and use a larger diameter piece of threaded ABS for the threaded portion - I've currently planned on 1-1/2" ABS but it seems like pouring ashes through a hole that small could be both messy and difficult, so maybe 2" would be better.

[Scott Hackler]

Marty, As soon as you get the urn roughed.... sit it on the bench and drip CA glue until it wont take any more in the inside...on the bottom. Then, flip it over and do the same thing to the outside bottom of the tenon and any small cracks around the top. Doesn't matter if the glue bubbles up right now, you will grind/part/carve/sand them off after it dries. Make sure you fill the cracks in the bottom after you remove the tenon as well. Dealing with the pith is almost always the same, it is GOING to crack. Turning it in one session will help in some ways (getting the bottom sealed up right away, but the form will likely oval and so will the opening. I usually do the large urns in the rough out / dry / return method. Darker wood helps hide CA filled cracks too.

[robert baccus]

I turn mostly vases ect and have stumbled accidently on a method for preventing pith cracks totally. I glue the base to a glueblock with thick CA, turn, finish and wax still on the glueblock. I do Endseal the outside as fast as It's roughshaped and hollow at my leisure. It is left barewood for compression drying as you mentioned. I may have minor cracking on 2-3 % done this way. Also CA glue is a great way to mount the wood--usually green and softwood as well and no screw length loss of wood. It is then parted off and bottom finished.

[Bill Bulloch]

I have never made an urn, but have made end grain hollow forms. With these, I always remove the pith and plug the bottom to prevent cracking. A little embellishment will hide the plug line and no one will ever know unless. of course, you tell.

[Marty Tippin]

The checking I'm referring to is at the top of the urn - 3 or 4 radial checks about 1" long each radiating from the opening which is about 1-1/2" diameter at the moment. The bottom I can deal with, either via super glue or a plug as suggested if it comes down to that.

The thin CA I applied to the cracks a few days ago seems to have slowed or stopped the progression. I also put the urn in a double paper grocery sack and hopefully that will slow down the drying process a little bit.

My original intention was to rough turn and then re-turn, but I'm pretty happy with the shape I've got so far and the wall thickness, at 1/4 to 3/8, is a little thick but unless it cracks, will be fine.

So fingers are crossed. But I'm also looking for another log I can use without the pith and will turn a second urn if I can come up with something that will work...

[Scott Hackler]

Marty, if your seeing radial cracks on the top, by the opening, then I suspect the log was too far gone to start with. The opening on an urn should remove all traces of the pith and should not develop cracks that easily, unless the cracks were already in that end of the log and you just didn't see them. It's a fun game, sometimes, battling the wood!

[Thom Sturgill]

+1 on Scott's statement. I recently turned an urn after cutting off 2" from the log, I turned it back another two inches. After hollowing part way I noticed cracking at the top and ended up removing the top and adding a large collar. When I checked the top against the pice I had removed I noticed that the cracks were in the same relative positions as the surface checking on the log end. So the cracks on the turned piece were the same checking I had originally seen in the log, I just had not been able to see them on the blank.

I know that I should have tested the end by sawing off a small circle and 'break testing' it, but I neglected that step. BTW for what its worth, I posted that urn as 'Eternal flame' due to a flame-like burl on the cap. The parents of the boy that was cremated loved the urn.

[Marty Tippin]

Thom and Scott are both right - there *were* radial checks in the log before I started, but I cut off a good 5 or 6 inches in 2 or 3 cuts and thought I was past the cracks but apparently not.

Thom, I really like how your urn came out and may consider removing the top and replacing it with a contrasting wood if I can't find a reasonable way to work with the cracks.

[Marty Tippin]

Well, the little cracks in the top of the urn are small potatoes now, the base split right through the pith, about 5" up the side of the urn (it's my fault, I took it out of the double paper sack to show my brother and forgot to put it away overnight....)

So I'll be starting over on a new one soon. I did manage to find a piece of maple that I could get an 8" diameter blank totally excluding the pith, so I'm hopeful I'll have better luck with it.

I cut the old one in half on the band saw and was happy to see that my wall thickness was generally consistent at a little over 1/4" - the Monster articulated system works pretty well once the laser is lined up.