Due largely in part to cost of lumber and lack of experience I am using big box pine for practice projects.
What I am running into is boards that have a warp or cup if you will. My question is what is preferred method to flatten the stock.
Which side of stock should face up, the one with direction of the cup or the opposite side?
How do you keep the stock from wobbling to opposite corners?
Where would the Z - zero be set, should I touch it x - y and z in the lower left as I normally do?
Any insight would be appreciated.
Side note I have a whiteside 6210 flattening bit.
Thanks again in advance.
I believe you’ll find it easier to put the side with the positive arch up for the first pass and the negative (concave) side w/ raised edges along the edges of the board down — that way the stock won’t rock, then surface it, and then flip it over and remove an equal thickness from the other side, being able to place the stock flat and secure against the spoilboard.
What Will said, but keep in mind that the cup may not be consistent. If you put the cup side and there’s still wobble, you should put shims under the high spot to keep it from wobbling. The clamp and surface making sure you remove enough to make that surface flat.
That really depends on badly it’s cupped. If it’s not too bad, I’ll zero at the lowest point and do a cut 0.02" keeping in mind it will be cutting more than that at the high spots. If the cup is pretty bad, I start at the high spot and remove 0.06 until I get near the low spot. With a badly cupped board, you might just be better off throwing it in the wood stove because you will end up with a pretty thin piece of wood.
When I think of the “Cup side”, I think of the concave side…Is that what you guys are referring to? I would put the concave side down (hump up), so that I have four points (min) touching the board, and then shave off the hump (the convex portion). Then, Flip it over, it should now be laying flat, and remove the convex portions…
If you are looking for cheap wood to practice with, that is relatively “flat”. Go to Home Depot/Lowes and look near their shelving section. For a quick test cut, they sell simple woods like pine that are glued to make flat stock, and since it is used for shelving, its relatively flat.
Flat sawn pine that is cupped is likely to cup again. The growth rings are what cause the cup in the first place. The tree grows in rings annually. during the summer the tree grows fast and that part of the ring is soft. In the winter the tree still grows but that part of a ring is harder. The softer and harder parts dry at different rates. Fresh lumber from the box stores are kiln dried but are not really dry enough to use for many uses. It is hard but you should buy lumber for use in 6 months or more. I am sure you want to make stuff and not wait but wood movement is a by product of a natural material.
Search craigslist to see if you can find a local sawyer to buy from. Their prices will be competitive and they may have air dried lumber that is more stable. Some local sawers use solar kilns to dry lumber fast but that is not always as stable as air dried lumber. Big box stores are handy but not the best selection of species or quality. Find a good hardwood supplier if you can and support them. My closest hardwood supplier is 2 hours away but I get better products and cheaper than big box stores.
As Will suggested surface with the crown up, turn over and surface again on the bottom side. You may need to shim the wood on the first side because if your wood moves while surfacing you still have wood that is not flat. If your board is say 10" by 24" long draw a box that is 10.5 x 24.5 inches and keep your clamps below the surface. Draw pencil lines all over the surface and z zero on the lowest surface. Cut 0.010 inches per pass and cut one pass and see if your pencil lines are gone. If some are still visible then re zero and cut another pass. Repeat until all pencil lines are gone. Repeat on the second side until all pencil lines are gone. Suggest you use a 1" fly cutter. Using a 1/4 inch bit will take forever. Plus you need a fly cutter for flattening your waste board.
I usually put the “hump” up so that when I clamp the board down at the corners, it doesn’t warp. If necessary, I use shims to prevent the board from warping due to the clamps. Once the first side is done, then flip it over and do the other side. Clamping the second side shouldn’t be an issue because the board should lay flat
I had the same problem with 3mm Baltic Birch which would warp quite badly. I used a few magnets to solve the problem. I placed magnets three high so they were the same height as the rubber cutting mat and put them around the perimeter. When I put the warped 3mm Birch on the cutting bed I then placed some metal rods onto the magnets top and bottom. The magnets hold the rods tight against the material holding it flat against the rubber bed. If it is really warped I put a thin piece under the rod to give it extra pressure to hold it flat. I attached a couple of pics but not sure if they worked… Has worked for me, hope this helps.
Sorry, this solution was for my laser. For my CNC I just pin nail the material to the waste board and the bits will cut through them if they happen to hit…
