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Plate warping while roughing out

 
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KenN
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Joined: 27 Mar 2007
Posts: 89
Location: Goodrich, MI

PostPosted: Sat Apr 07, 2007 5:45 pm    Post subject: Plate warping while roughing out Reply with quote

I've noticed that the plates warp. Most haven't been that bad but the last one I had to reglue. The plate ( spruce wedge, sawn almost all the way thru) had some twist that I had to plane away. I decided to rough some of the stock off (a trick I use when roughing steel) to get most of the future warp out of it before I glued it. It had about a 7mm wide strip to glue and I glued it with the bottom flat on the table with no clamps. After glueing I couldn't see any gaps. After I finished the inside and roughed the outside, I turned it over to file the edges closer to the line and I saw that the top and the bottom of the seam had a gap on the bottom of the plate all the way to the end of where the block will glue. After they opened up even more (to about 1-1.5mm) when I did some filing I decided to reglue them.
I had to plane some stock off because the joint was no longer square. The plate will be slightly narrow, but not too bad. Since the outside wasn't finished there is still stock on it.
Do plates always warp? Was the twist a good indication the plate would warp bad? Am I manhandling the plates too much? The original glue line looked kinda grey, the new one is yellow like the glue. Was there some graphite residue from a pencil on the original joint, making it weak?
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Chet Bishop
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Joined: 23 Mar 2007
Posts: 678
Location: Forest Grove, Oregon

PostPosted: Sun Apr 08, 2007 8:50 pm    Post subject: Reply with quote

The only time I have had anything similar happen it was because I began arching in Oregon and then went to Tucson or Los Angeles or some such place. One such plate ended up imitating a manta ray in flight-- but it clamped flat enough when I attached it to the ribs-- it is just a little odd-looking in places, as the arching shape is no longer quite as planned.

I expect that there are two levels to the problem:
(1) My wood may not have ever been fully dry when I began (I live in western Oregon--the humidity may never go low enough here to effect fully-dry status).

(2) Your wood may have some residual stresses which are simply being released as you carve-- this happens all the time, especially with sawn lumber, and particularly with non-radially-sawn lumber, because of the different shrink patterns for different grain configuration within the billet.

Anyway, all that to say: this is why the way the wood is produced matters, AND why it matters to actually get the wood fully dry at least once (humidity cycling helps too, I think).

Finally: I think you can go ahead and complete the fiddle; just know that it will do some rather fancy moving and changing, and may produce some rather strange humps and hollows in the final product. "Grin and bear it" would be my counsel, but I am sure the purists would say to junk it and get some decent wood. (On the other hand, the purists haven't answered yet, have they?) Smile
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ctvviolin
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Joined: 25 Mar 2007
Posts: 5

PostPosted: Fri Apr 13, 2007 7:09 pm    Post subject: Reply with quote

Between working on the plate, and gluing it to the rib assembly - keep it clamped flat.

1/4" masonite violin shaped board works well enough - with cheap plastic spring clamps.

Just like, until the rib assembly gets glued to the back, it must be clamped tight to the mold.
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KenN
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Joined: 27 Mar 2007
Posts: 89
Location: Goodrich, MI

PostPosted: Tue Apr 17, 2007 6:50 pm    Post subject: Reply with quote

I never heard of that before. I'll give it a try. Tried to post this a few days ago and it didn't work. This new board only seems to post half of my posts.
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