Warped Panel after carving

[lockeyone]

"any of you have any idea if 1 3/4" Mahogany will warp also??"

I have 2" African Mahogany for my bow pulpit on my 26ft boat. About 6 years old now without any warping. I would think if mine sits in the sun all summer yours would do fine. Just my thoughts.

[gravirozo]

capnl,
if you will make a carving of a board, and remove a larger amount of one side, then it will warp...
independently how long is it dry..... as humidity changing it will change it's shape...

gene crain the first (as i remember) on this forum, who pointed out, wood need to be dried down to 6-8 percent to keep stable... but after you pull out of the drier, it won't keep this percentage... and sealers, lacquers can not keep out the humidity...
before medieval people put large wrought iron hardware on woodpanels, keep them straight... since medieval, they started to use ""frame-panel"" structure, to keep wood straight...

close to you, i'm sure exist some ikea store... they sell shelves in ""vinylbag"" , as long as it is in the bag, it is straight... after you remove, it will warp, by humidity

try to rough it out, leaving a half centimeter on, and after a few day, finish it... might be working


thanks
viktor

[Rcnewcomb]

I've been thinking about trying carbon fiber rods as part of the glue-up. You can find 0.125" rods on e-bay for about $5 for 40" pieces. Imagine the rods inset into a backer board that is then glued on to the main glue-up. I'm thinking of trying this on a mantle piece carved from the Design & Carve series. The piece would be undergoing significant temperature and humidity extremes.

Thoughts?

[JCTalbert,LLC]

.125 doesn't give much of an area for gluing the rods to the panel. It may work but I have my doubts. creating the recesses as you have in the panel may be all that is needed. Much like wide plank flooring, recesses are placed on the underside to help prevent the warping, but as you know the panels are nailed to the subfloor further preventing the warping. Recesses with the grain should help. let us know as you proceed...thanks for posting

[darde]

Don't glue anything across the grain of the panel. It will warp worse or even cause it to crack if it can't warp. You could make some bread board ends (I think that is what they are called) and it would act like a raised panel. Raised panels were not really made because they looked good it was to overcome this exact problem of shrinking and expanding.

[woodturner550]

Another solution would be to glue 1/4 inch MDF to the back then plane then front to the thickness desired. The CNC machine. After machining seal the panel well 2 or three coats. The MDF will hold fairly well.

[Rcnewcomb]

I've been doing a bit more research on this the topic of warping. My greatest fear is doing a $1,000 mantle carving and then having it come back a month later because it developed a large split.

I've summarized some of my research here:
Sources:
http://sres-associated.anu.edu.au/fpt/d ... .case.html
http://www.woodweb.com/knowledge_base/W ... tches.html

Two important concepts of drying theory:
o Timber dries from the surface first
o Wood shrinks as it dries below 30% moisture content

Moisture is lost from the outside surface of a board first, and as the surface layers dry below 30% shrinkage occurs. The surface shrinkage is restrained by the inner part of the board which has not yet started to shrink. The surface fibres are thus held apart (in tension) and this imposes compression stresses on the rest of the cross section. If the tension forces in the surface layer become too large, surface checking can develop.

The drying proceeds to the inside of the board, which then shrinks but the inside shrinkage is restrained by the already dry and set outer layers. The centre of the board now becomes tensioned and the surface layers become compressed. The board is now in tension at the centre and the surface in compression, this is the stress state present at the end of drying.

Case Hardening
There are two types of casehardening - longitudinal (lengthwise), which causes pieces to warp lengthwise, and transverse (across the grain), which causes pieces to cup. Drying stresses are not visible but if a stressed piece of timber is deep ripped or heavily machined (such as deep relief carving), the balance of stress within the piece is disturbed and some distortion such as cup or spring, will occur. Also the high stresses developed during high temperature drying can cause significant internal checking if they are not relieved after drying.

How is stress relieved?
A high temperature, high humidity treatment period at the end of drying will relieve stress. According to Prof. Gene Wengert, "This is done by adding water back to the surface of the lumber at high temperatures (160 F or higher). In practice, usually the lumber is steamed for a few hours. Drying stress will not disappear with time. It cannot be relieved by letting the lumber sit around in a humid condition."

Wood Warp After Drying
Wood will warp (after drying) for only one reason and that reason is a change in moisture content. (One exception is drying stress or casehardening, mentioned above.) So, if you are experiencing warp a few hours to a few days later, then the wood was not at the correct moisture content when it was machined. Almost always, the wood is too wet for the air in which it is used. (Note: Tests made after the warp will always indicate dry moisture content. Measure the pieces before they warp to get the wet readings.)

In a few rare cases where the wood is stored poorly after drying, it can pick up moisture and then warp later. This event would be evidenced by having the core moisture content, measured with a pin meter, being lower than the shell.

Note: Do not wrap the lumber when you first get it as that will prevent the lumber from drying out to the correct moisture content. Keep your shop at about 35% RH in the wintertime. Once the pieces are run, do not wrap them, as they will potentially be too wet. If wrapped and then unwrapped at the customer's location, they will dry at that point and you will hear complaints. Let them dry in your shop so that you only ship good pieces.

Conclusion from Prof. Wengert
Basically, you need to either get your supplier to dry the wood properly, put in your own kiln, or change suppliers to one who is doing it correctly.

[tmerrill]

Randall,

I wasn't sure how technical you wanted to take this, but the accepted "bible" in this area is R. Bruce Hoadley's book "Understanding Wood" published by Taunton Press. If you don't have it, based on your research I think you would enjoy it.

Perhaps not too late to add it to your Christmas list

Tim

[Rcnewcomb]

Tim,
Thanks for the book recommendation.

FYI, this graphic seems to illustrate what I've seen in the shop from time to time. When a piece does move for me it seems to most often cup inward:


Working more on my faux finish for MDF seems to have some long term merits.

[tmerrill]

Yes, you are correct on how it will cup. One option is to put your carving on the opposite side so they work against each other and help balance out.

Some other thoughts:

Quartersawn is much more stable but sometimes hard to get. But if you can find a flatsawn piece that is taken from near the center of the log, the center will be flatsawn while the outer edges will be quartersawn. Rip this down the middle and re-glue to put the quartersawn edges in the center.

The thicker the better: 5/4 is better than 4/4 and 6/4 is better yet, but you start to run into weight issues.

The more uncarved material you can leave, the more stable the board. Try to reduce the overall size of the carving (WxL) and perhaps add some inlay detail (or v-carve) at each end to fill in the open area.

For the two large coat racks I did, there has been no wood movement. One was in 4/4 roughsawn maple and finished out at 1" thick. The other was in 13/16" hickory. I know the kiln where both were dryed and they have a good reputation for doing it right. For the carved window scene, where a lot of material was removed, it has cupped about 1/8" over 18" cross grain. This started out as 4/4 maple and ended up at 7/8" thick. Not a problem for something hanging on the wall but for the next one I'll start with 5/4 maple.

Tim

[Markm]

I do lots of deep carvings as a general rule Imake sure that whatever we are removing (lets say carving is 1") I have that much material left (so I would start with 2"). I now only carve with face glueing the peices. This has removed almost all warping from the peices. I had also seen that someone thought of putting braces on the back, just remember that the cross grain expands twice as much as the the other grain and can cause your peice to crack from that extra pressure.

Mark

[ckurak]

First of all, thanks to all of those who responded. Some of the answers I already knew, and some were new to me. What I was looking for was how to get myself out of this predicament first. Then, how to avoid it in the future. I learned all of that, and much more!

So, I am including some photos of the (almost) completed project. (The tile guy has to grout the hand-made Italian glass tile that makes up the top of this piece. He did not want to grout it until the top was firmly fastened. He wants to avoid stress cracks.)

There are four (4) carved panels in the project. I fastened the two end panels with screws from inside the cabinet box. The back screws were attached through enlarged holes with some washers to allow for seasonal expansion across the grain. So, any movement may be seen in the back of the piece (where folks usually don't look) and not in the front. The other two panels make up the front doors. I used battens on the inside of the doors to keep them flat.

The piece is actually a silver storage cabinet. The blue cloth on the interior is "silver cloth" that should prevent the sliver from tarnishing. There is a roll-out drawer for flatware and an adjustable shelf underneath for larger items.

Oh, the carvings! Thanks to James Booth for the magnificent job on creating this model for me. The model started out as a simple 2D image emailed to James. What he returned to me is nothing short of fantastic. And, thanks to Vectric for providing the software to let me do this. The "hand-carved" texture in the background helps make this piece a work of art. Finally, thanks to my designer who hand-painted the glaze on the carved models. I am sure I am forgetting some other folks who posted helpful tips on this forum that helped in this project. If you recognize something you shared, I say thank you.

[Phil]

Beautiful work. The panels make it very special.