[zool]

Sign makers use V-carve bits to avoid the problems you are experiencing.

The V-carve bits cut wide, but cut shallow, thereby leaving more material than if the same cut was made with a straight bit.

[multiplex]

hey guys, thanks for the feedback. heres a picture of the piece i'm talking about, it will make more sense when you see it.

i've come to the conclusion too that its a cross between internal moisture and internal stress. you just gotta let the wood do what it wants to, and then go from there.

it was crazy watching the opening of my piece close up by .01" a day for a week. felt like it would never stop.

i milled the pieces with about .02" extra on the outside which was barely enough (not enough in most cases, but close enough)

moving forward, i'll leave more on these bigger units.

after letting the roughed pieces sit for over a week, i sanded the bottoms flat and then finished machined them. they seem to be holding the sizes just fine.

just figured i'd post all this up for anyone else down the line that might run into a similar situation

[keebler303]

You guys are using kiln dried lumber, right?

Matt

[multiplex]

yeah its kiln dried - to around 7% moisture, which matches the numbers i got.

[louieatienza]

Sometimes, even if your board is kiln dried, if your cutting and generating heat, the surface you are cutting will be drier than the rest of the wood, which may cause it to move. That, along with the internal stresses of wood as mentioned.

The opposite could also be true. The kiln was set too high, so the wood essentially is case-hardened, and wetter on the outside.

If you look at wide solid wood moldings, they'll often mill grooves or flutes on the back side to help alleviate this problem. If your piece won't be seen on the back, you can mill a relief to "balance" the piece, otherwise you might want to leave the piece thicker, and then mill the back side as well (flat)...