Relief Project Question?

[pallin]

Kathy, I use the pipe-based cabinet clamps to squeeze the boards together, ordinary carpenter's glue. I clamp the oak strips on the back with C-clamps applied as deep as possible from each end.
Phil

[mark yundt]

If you do plan on putting strips on the back they should be floating,,,and use"walking screws" to allow movement. If you try to hold it fast the wood won't like that and will break itself apart.The grains are going two different directions and that's a no-no.

[Mottles]

Quote Put a few saw cuts along the back every inch or so,,,stopping it before it before the edge ( so you don't see it) and just deep enough that you don't cut through the surface. That's all you need to do,,works every time,,,no problem, end of story.The board will stay flat pretty much forever. Quote

Mark, regarding this part of your post....YES, I do have a table saw and a hubby who know how to use it. I pretty much stay with the bandsaw LOL. Irish, had mentioned using larger screws, so the wood can move too.

The 'few saw cuts along the back' you refer too. Do you mean across the whole back or just top and bottom and not in the middle? Just want to be sure....sounds to easy! LOL I don't mean to be questioning your expertise, because your work is fantastic and varied. I just want to be sure I understand where to cut!

Heinecke, has shipped my basswood boards as of the 19th....The relief will be in the ordered size of the boards, no additional laminating for width on this one.

Thank you, so much for your help too! We all have been brain storming and all ideas are most welcome. That is what so great about this site!

Kathy

[Mottles]

Thank you, Phil appreciate you getting back to me about securing the backing. I need to invest in some good strong C Clamps, but before that I think a raid on my hubbys clamps might be all I need. LOL

Thanks again,
Kathy

[mark yundt]

Hello Mottles,

Hey,,,question me all you like,,,I'm no "expert" ,,,I only know what I do,,what I've seen,,,and what has worked and what has not worked.The most glaring example of a 25 grand conference table a friend did,,,trying to control the movement with braces on the back. Not allowing the wood to move almost got to the point of destroying the table. Saying "I told you so" wouldn't have fixed it,,,but I ultimately did fix it.

Other than that,,between the furniture I have built...pieces I've done with others,,,and the size of some of the pieces you have seen me glue up here and being able to watch over time what happens to them gives me the general guidelines I tend to follow. Also,,if you research how others over time have solved these problems most of the methods and techniques remain the same.
Trying to mechanically hold and lock the wood in a certain position just seems to encourage it to do other things. Like forcing a 2 yr old to sit still,,,they're both going to continue moving somehow. Yrs ago table tops were held flat by the addition of a mortised and pegged board across both ends. They were not glued and screwed fast,,,the wood was allowed to float. Even the cleats to hold the legs were allowed to move. Well,,I could certainly keep going on,,but you get the point and I still need to answer your original question.

What I do,,,and I did it to the piece shown in the gallery ( the roses) was this. If I know the depth of the relief is going to be say a half inch in a one inch board I'll make parallel cuts the entire length of the board along the back every inch or so. To keep from cutting through the surface of the carving,,I'll zero out the blade,,count the number of turns of the crank it takes to get the blade up 1/4 inch from the surface of the saw. Lower the blade,,set the carving so the very edge is a short distance from the blade cut,,slowly raise the blade to the required height,,pass the board across the saw STOPPING short of the blade coming through the end of the piece.Then lower the blade.Move the fence over an inch or so and do it again. Dry run this a few times with a scrap piece,,making a mark on the fence where you should start the cut and end the cut then you don't have to guess where the starting and ending positions should be.

What this accomplishes is it removes the potential stress caused by the expansion and contraction of the cells across the back of the carving which causes cupping. Think of it this way,,you have removed the "stack" of cells across the front with their removal by carving..they can no longer expand and contract...but the cells are still lined up along the back. Now as the piece takes in moisture and releases it where is it going to start moving from. Right ,,across the back. So,,,if you provide these cuts you have effectively cut the stacks of cells from pushing against each other causing the piece to move. You've basically cut their legs off.If they do soak up water and expand,,,they'll expand into a cut out area...that's why the carved front won't move,,,they have all the freedom to move as much as they want and not bump into their neighbor. Now the board remains flat.In those areas where the carving isn't as deep you can also make deeper cuts with the saw blade set to a deeper depth. You could also use most anything to get wood off the back,,whatever is handy and does the trick.

If you care to,,look behind the large statues and many relief panels in many churches when you can. You'll either see large areas cut out behind them,,relief cuts made almost to the depth of the carving itself to relieve the back as well as the front. I've seen some that were almost to the point of being a shell,,,the backs were totally gone,,the piece is always flat and doesn't move. The original statues done out of one trunk of a tree are always hogged out this way for the same reasons,,,it eliminates or minimizes starshake splitting.
Neat huh? And it still follows Occams Razor,,,of course that usually is the best solution.

P.S,,,It's good to learn how to glue up pieces yourself,,with the tools you have,,there are easy ways to get perfect edges which are the key to a solid joint,,,and ways to check if the edges are perfect ,,,but that's another topic.

[pallin]

It is clear that Mark has a lot of experience putting together large "build-ups" of wood. All I can say is I have had no trouble with the approach I've used. The wood has not pulled itself apart. It is very likely that there are several (or many) workable methods.

[mark yundt]

Oh you're right Phil,,,there are many ways I'm sure,,and I don't know them all,,that's why I'm not an expert by any means. Certain methods do work. If they are confined to a relatively small area there usually isn't too much of a problem. What tends to happen though,,from what I've seen,,is the larger the expanse,,the greater the results. It only stands to reason,,the problems compound themselves almost geometrically as dimensions increase. A sixteenth of an inch increase over a foot isn't much to consider,,,but stretch that out to 10 ft and that sixteenth has now grown to almost three quarters of an inch,,,now that's something to account for.Same for cupping,,over a foot wide board it can and at times be noticeable,,now stretch it over a 6 ft wide table and you have the start of a boat hull.
I found though if you take the fight out of the board,,it becomes very docile and predictable in your hands...Take it to the limits and you can bend that very same board around a corner and it won't put up a fight any longer.It'll do what you want.

[xsailer]

This is a great great technical discussion. Rest assurd this will be a print out in my notebook. Thanks fellow carvers.

[Mottles]

Originally Posted by xsailer

This is a great great technical discussion. Rest assurd this will be a print out in my notebook. Thanks fellow carvers.

Thumbs Up YES, you are right and I truly want to thank everyone who is participating in this discussion. I think it's helping me and will help other carvers who plan to relief carve larger works.

Thanks again,
Kathy

[Mottles]

Hi All, FYI here is a link to my Kachina Three Panel WIP
Kachina Panels WIP
Kathy