Wood "cups" after carving

[ljdm]

When I carve reliefs at a depth of .25" or more in plain sawn .75" oak, the wood tends to cup. Not sure if it's due to case hardening in the wood, releasing tension, or just a characteristic of carving in plain sawn oak. Not all projects allow cutting on the back side to relieve tension evenly. Pretty sure quarter sawn oak won't have this problem, but then you lose the more decorative grain patterns.
Wondering if I switch to other types of wood - does this occur in most woods?

[Brady Watson]

In my experience, oak moves around a lot while being carved, making hold-down a challenge. It is very frustrating spending hours carving a 3D relief into it, to find that the part lifts. The best way to overcome this is to use oversized material, and build in 3D tabs in the geometry of the relief to be carved. Then screw that puppy down every 6" or so. This will not prevent cupping after the part is removed, but I think that you can overcome a lot of the warp/cupping if you check the moisture content of the lumber before machining. If it is too dry, all kinds of ugly things happen...

-B

[knight_toolworks]

it could also be that the wood is not fully acclimated to your shop. this is something that is easy to check. but it is always a good idea to know your mc of your wood. it could also be because the wood was dried too fast. so it is full of tension.
changing woods can help. like European beech or purpleheart or most tropicals.

[srwtlc]

If this is a glued up blank, another thing that can help is to alternate the growth rings as you glue it up. Sometimes it's just not possible due to appearance, but if you can, alternating them can help to balance out the tendency to cup.

[ljdm]

Acclimation not the issue, nor MC. Glue-ups not the issue, even occurs with individual board carvings. Pretty sure it's either case hardening from improper kiln drying, and/or plain sawn wood behaving this way from tension being released, where quarter sawn wood expands differently. Was mainly wondering if other woods react the same as white oak when carved on one side.

[Gary Campbell]

Lou...
This will happen with most woods due to modern more efficiant kiln schedules. That was as nice as I can say it. You know what I really think!

The only thing that will "relax" the tension in hardwoods is to have consistant moisture thru the blank. Here is a 36w by 24hi blank that was carved and has been hanging by 2 screws for 2 years without noticable warping. The backside had exposed sapwood and was cauled from a job. The main thing is that is was glued up from all relaxed staves... and they live almost forever.

I learned these methods from an old woodworker in the eighties... and he learned them in the twenties... Dont fight the wood!
Gary

[srwtlc]

Just the nature of the beast (wood). I once saw a chart in some woodworking magazine that listed many species and their expansion/contraction rates.

[Gary Campbell]

Forgot the picture!

4791

You can see the 2 screws at the top... and also that the grain is no where near vertical!.
Gary

[phil_o]

I used to prepare stock for projects by running everything through a planer on both sides. Warping was an issue but not enough to cause real problems. A few years ago I started to prepare stock by face jointing one surface and then planing the other side. This has dramatically decreased warping issues.

[waynelocke]

Perhaps you can start with thicker wood and do a 3d roughing pass which should release a lot of the internal stresses. Then rejoint, resurface, and make the final 3d pass.

[chiloquinruss]

I did a small job for a local customer using his supplied piece of juniper. The piece was approx 3in x 6in x 60in. I made a table mount, did the carving (looked just great) and left it on the machine overnight. Came back next morning and released it from the table - WOW! I had only carved about 3/16ths depth and almost full surface into a single face - the whole piece at each end sprang up at least 2 inches! I had to fabricate an angle iron backer to pull it back into a close straight plane, what a surprise! And yes the wood was very dry and mostly straight of grain. Ouch! Russ