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Sealing a crack in a bowl

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Forum topic by Llarian posted 12-14-2009 09:24 PM 1062 views 0 times favorited 7 replies Add to Favorites Watch
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Llarian

128 posts in 3075 days


12-14-2009 09:24 PM

I just finished turning a lovely bowl out of spalted siberan elm that I think turned out quite well, save for one little problem. There’s a small but expanding crack towards the lower section of the profile that’s clearly going to get larger as things shift.

The rest of it is solid, and its reached moisture equalibrium (for now), so it shouldn’t shift too much more.

I’m wondering if there’s any way to halt the advance of this crack before it gets any larger? I plan to use a poly finish, but I’m sure that wouldn’t be enough to hold the crack in place. Its barely open, but I might be able to work in some epoxy with a toothpick to the middle section or something.

I realize the best way is for cracks not to start at all, but I’d hate to send an otherwise nice bowl to the burn pile if I can avoid it.

Any suggestions?

-- Dylan Vanderhoof - General hobbiest and reluctant penmaker. http://llarian.etsy.com


7 replies so far

View Kindlingmaker's profile

Kindlingmaker

2656 posts in 2994 days


#1 posted 12-14-2009 11:09 PM

I am assuming that the wood is still green… Put a band on the bowl and tighten it and let it totally dry. Most of the stresses should be held at a minimum. Hardware stores sell VERY large hose clamps.

-- Never board, always knotty, lots of growth rings

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Llarian

128 posts in 3075 days


#2 posted 12-14-2009 11:13 PM

Not green anymore. I didn’t see any checking on the dried rough form when it finished seasoning, but one showed up after turning the wall thickness to 1/4”.

There’s just the one crack, I don’t see evidence of any others.

-- Dylan Vanderhoof - General hobbiest and reluctant penmaker. http://llarian.etsy.com

View jeffthewoodwacker's profile

jeffthewoodwacker

603 posts in 3272 days


#3 posted 12-15-2009 12:27 AM

You have a couple of options:
1. If you are able to get it back on the lathe you can sand it, create some sanding dust and shavings and work those into the crack with medium CA glue.

2. If you can’t get it back on the lathe you could use a black epoxy filler or inlace material – both of these can be sanded down and refinished and will add some character to the piece.

3. You could do some carving or use a dremel to decorate the piece.

-- Those that say it can't be done should not interrupt those who are doing it.

View dlmckirdy's profile

dlmckirdy

196 posts in 2601 days


#4 posted 12-15-2009 12:48 AM

Iv’e never done any turning, so this is just conjecture. In metals and plastics, you can “stop drill” the crack on each end to relieve the stress (drill a small hole at the END of the crack). Then fill it with a very thin glue or resinto seal the vod an equalize the stress within the cracked area ( as above, I would try mixing some sawdust into the glue/resin if the crack is wide enough). If it is a very fine crack, maybe just stop drill the ends and let the piece finish curing (the strab/band clamp sounds ideal).

Good luck.

-- Doug, Bakersfield, CA - I measured twice, cut it twice, and it is still too short!

View LesB's profile

LesB

1237 posts in 2911 days


#5 posted 12-15-2009 09:45 AM

I think Jeff gave the best repair answers.

I would work on one more thing before doing that. Put the bowl in a closed brown paper sack and then microwave it just long enough for it to feel quite warm. The more moisture that is in the wood the faster it will heat up and the hotter it will get so adjust your time accordingly. Leave it in the closed paper sack to cool. Take it out of the bag for a short while to let any surface moisture evaporate and then bag and microwave it again. This will in affect become a “steam” kiln in the bag and equalize the moisture relieving most of the stress in the wood. This works because the microwave heats from the inside out so the internal moisture is driven to the surface. The bag contains the moisture long enough for things to balance out by slowing the escape water vapor or steam.
You might have to repeat the procedure several times if the wood still has much moisture in it. After that let it stabilize outside the bag for a couple of days then use Jeff’s CA glue method if there still cracks of any size to repair. Note: Jeff said “medium” CA glue; I call it “thick” like syrup. It takes 30 plus seconds to set up so that gives it enough time to seep into the depths of the crack.

When I notice cracks forming while I’m turning I use the CA glue to stop them and in most cases it does and if the cracks is caused by moisture stress I stop and do the microwave drying process before continuing; usually I can then cut out those shallow “premature” cracks. If the cracking is not caused by a moisture problem the CA usually fills the crack and holds things together so I can finish the piece.

-- Les B, Oregon

View Llarian's profile

Llarian

128 posts in 3075 days


#6 posted 12-15-2009 04:59 PM

Thanks all, that gives me something to work with. I’m going to let it sit for a bit and stabilize while I wait for some stuff to be delivered to see if the crack expands any more than it has. I think the inlace/decorative fill idea is probably the best. I don’t have a moisture meter, but its pretty much dry based on weight change, so I doubt any of the methods for further drying it will do much useful other than shift things around a bit and widen the crack further.

I’ll see if I can carve it out a bit and get some sort of epoxy or CA filler with a decorative material to fill the crack and give it some character at the same time.

I definitely need to revisit my drying method, another formerly green rough turned blank is exhibiting some cracks on the sides now that its reached EMC. I suspect my garage is too dry and too cold (been near freezing lately), so I need to find someplace in the house where they can dry a little more slowly after being rough turned.

-- Dylan Vanderhoof - General hobbiest and reluctant penmaker. http://llarian.etsy.com

View reggiek's profile

reggiek

2240 posts in 2738 days


#7 posted 12-15-2009 05:47 PM

Llarian, take a look at lathe talk (I believe Steve is another LJ) he has some great info on green wood turning including a test on boiling the blanks – see this link: http://www.woodturningvideosplus.com/boiling-green-wood.html. You can subscribe to his newletter for updates and such….

-- Woodworking.....My small slice of heaven!

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