Black walnut or hardwood questions

[cowboy1296]

I started out with a true 2 inch thick piece of black walnut which i planned fairly flat. the black walnut was suppose to be dry and my depth of cut was 1 to 1.1 into the wood. almost over night the board started to warp. my thicker pieces that i have worked with in the past did not. I was told by someone locally that perhaps cutting slots on the back of the board could possibly take of the warping.

Anyone want to comment on how i can prevent the board from warping after cut. i do like working with black walnut and am about to venture into elm.

this is still a work in progress and i should be able to take the grainy-ness out of the project.

[srwtlc]

Rick,

When you take material off one side, you're relieving stress and exposing that surface to humidity changes, thus the cupping. You can cut a shallow relief pocket in the back side if the project permits. If the blank is of one solid piece of wood (not glued up narrower strips), it's almost inevitable that it's going to happen. The wider and thicker the piece along with the depth of cut, the more likely and pronounced it can be.

If you glue up a blank from 2" - 4" strips, try flipping every other board (heartwood/sapwood side up) while still maintaining a favorable grain/color match. That way, each boards movement will attempt to cancel out the other.

The other option, although not always available and more costly, is to try using quartersawn or riftsawn lumber.

While kerfing the back of the piece (with a tablesaw) may help, it may not be desirable to have kerf cuts showing on the edge of the piece. This is more often done on the back of a slab type cabinet door when a V-groove or bead is cut on the front of a panel. Cleats are generally added to the back then.

Scott

[cowboy1296]

i have been resisting getting a biscuit joiner but i do like working with hardwood.

i am about to have the opportunity to invest in as much black walnut and elm rough cut lumber as i want or can afford.

now correct me if i am wrong. but if i have a 2 inch thick piece that could be as wide as 18 inches then i should cut it into 2x4's and flip flop every other board and join them back together? does that make sense?

Sorry for being dense, I am still working on my first cup.

I did cut the Marine logo into MDF, man what a lot of machine time. I did chip out a few small pieces but after staining it, it is not noticeable.

thanks again

[mark_stief]

I never glue up anything wider than 3" when making panels and don't worry about the biscut joiner all I use is titebond III the last thing you need is a biscut showing up in you're carving

[cowboy1296]

I can buy a lot of glue for what buiscuit joiners cost.

[cowboy1296]

I am picking up 3 bar clamps tomorrow, thanks for the advise.

[waynelocke]

I would not cut an 18" wide board into 4" sections and glue it to prevent warping. If you flip a board every 3 or 4 inches the color and grain will not match. Most woodworkers I know match boards for glue up based on grain and color match.

If you have to do that then there is probably a problem with the board or the process. As mentioned above you need to remove equal amounts of material off of both sides of the board. If using a planer the board is usually flipped after every pass.

When someone tells you that the material is dry, what do they mean? They should be able to tell you and show you the moisture content which should be around 8% or 10% depending to some extent on where you are. A moisture meter is a good investment if you are going to work with hardwoods.

Also, how the wood is cut and where it was in the log can also affect the warping.

[myxpykalix]

Rick,
I have had the same issue with thick walnut and other woods however not that thick.

If you have a 2" thick piece and are carving out one inch leaving at least a 1" thick base it shouldn't cup.

Here are a couple untried ideas.

if you want to start with a 2" thick piece then why not take 2 one inch thick pieces and laminate them together (maybe cross grain?) then adjust your Z height of your model so as not to go lower then your top 1" then you have a solid uncut one inch base to keep the top from cupping.

Maybe someone can comment on the advisability of gluing cross grain, or just glue the 2 pieces regularly. The point is you have a sturdy "base" that is not subject to the forces of stress caused by the removal of all that material and the top layer because it is cut alot, if cut before it is laminated would cup severely but because it has the glue holding it to the base would not cup.

Another idea would be to simply adjust your Z height through experimentation to a point where it won't cause the cupping. Can you post some pictures of what you have now?

I would bet you could adjust your Z height at least .25 without a deterioration to quality.

[Gary Campbell]

Rick...
Along with what is mentioned above, I would add that you need to check the moisture content of the wood. Never, I mean NEVER, trust that an air dried piece of lumber is at a machinable moisture content (MC). Very seldom trust a kiln dried piece that has been stored in an area where the relative humidity is above 25%.

Every piece that I have machined at over 10% MC has curled, almost every one over 8%.

There are a good number of MC articles on the woodworkers forums that can help you gain insight into MC stability.

[cowboy1296]

the elk scene in the first post on here is what i cut. you cant tell from the picture about the warping. with a wall hanger the warping my not show that much.

i did two different elk plaques. the first and largest warped a lot and i broke the board trying to bend it, but it is not totally destroyed. one other black walnut plaque that i did was only v carved and i have been told by the vet group that i donated it to that it did not warp at all. it was about 17x32x2 so apparently its all of the cutting that i am doing.

its funny that you mentioned gluing. i did find a 1x11x40 inch scrap piece of black walnut. cut it half and glued it together matching the grain. and did a 3 d cut that went about half way in and i just checked it and its still flat but it is not nearly as big as the others being 10x18x1.6. its a work in progress and i still have a lot of burr removal to do. but you might be right about gluing.

here is a picture of the elk scene that warped. i reduced the quality too much but you can get the idea. the marine plaque is still flat