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Excessive warpage on small project! What happened?

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Forum topic by Joe Andrews posted 02-19-2020 05:01 PM 346 views 0 times favorited 6 replies Add to Favorites Watch
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Joe Andrews

78 posts in 2683 days


02-19-2020 05:01 PM

Back in December, I had a customer come to me with an idea for a CNC’d box to store vape supplies in. He stressed that he wanted it carved from a solid block of walnut. I was able to find a block the right size at my local supplier, but the grain ran all over the place. The dimensions of the box was about 9”x6”x2” total. Two internal pockets about 1” deep with 3/8” sides. After CNCing , I applied some danish oil just to see what it would look like. He left happy, and I didn’t think much more about it. This past weekend, he came back to get me to work on a new version and had the original box with him. To my surprise, it was SEVERELY warped! I’m talking at least 1/2” corner to corner. Almost looked like a bowl. The box had a sliding dovetail lid and everything was so warped, the lid wouldn’t fit anymore.

Needless to say, this was definitely a cause for concern, as he wants to mass produce this box for the high-end market. What could cause such drastic warping? I didn’t check the block for dryness, but it didn’t seem wet. Could it have been the varying grain direction? Removing all the material for the pockets releasing internal stress? Just trying to figure out what caused it so hopefully we can prevent it in the future.

Thanks!


6 replies so far

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ocean

205 posts in 1517 days


#1 posted 02-19-2020 05:18 PM

Sorry to hear about the wild warping. You hit the nail on the head when you said removing material from the inside caused a release of tension in the block. Figured wood is nice in some cases, but highly figured wood it not your friend in this case. Try again with a nice straight grain block and I don’t believe you will have as much of a problem again. Also make sure the new block has low moisture before starting.

-- Bob, FL Keys

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Phil32

998 posts in 587 days


#2 posted 02-19-2020 05:18 PM

Long, straight sections of trees are usually processed as lumber (boards). Everything else is cut into blocks or chips. That means the twisted, deformed forks and crotches are sold for woodturning or small projects. These blocks have internal stresses that make it impossible to predict warpage, cracking, etc. It is possible that CNC processes add some other unknowns to the situation.

-- Phil Allin - There are mountain climbers and people who talk about climbing mountains. The climbers have "selfies" at the summit!

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Aj2

2799 posts in 2482 days


#3 posted 02-19-2020 05:30 PM

Sounds normal to me. Your solution is to build up your blank from pieces. Not from solid

-- Aj

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Joe Andrews

78 posts in 2683 days


#4 posted 02-19-2020 06:45 PM

Thanks for the info. Building up the blanks might be a viable option. Will just have to make sure I keep the grain and coloration consistent so it isn’t too visible. The box has a sliding dovetail lid that I initially wanted to cut from the blank first so that when installed, it looked like a solid block of wood, However, this also releases stresses and the lid wants to warp.

My other idea was to just go with a built-up box with some fancy joinery so it looks high-end. Still researching that option. It would definitely be cheaper and less prone to waste if I happen to get a big blank with a knot or crack in it. I could just cut a new side and keep going without throwing the whole piece away.

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bondogaposis

5687 posts in 3035 days


#5 posted 02-19-2020 07:51 PM

For a project like this you will want to use straight grain, kiln dried lumber.

-- Bondo Gaposis

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Joe Andrews

78 posts in 2683 days


#6 posted 02-19-2020 08:08 PM



For a project like this you will want to use straight grain, kiln dried lumber.

- bondogaposis

Agree 100%, but unfortunately in this part of the country, access to good hardwood, especially in the thickness I would need, is very hard to come by. In order to cut the lid from the box like the customer wanted, I need to start with a block about 2.5” thick to have room for machining. Lucky if any of the suppliers within 100 miles even has 8/4 stock. The customer found a couple of blanks on eBay that were barely thick enough, and that’s what I used for the second try.

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