Planing using CNC question


(Stephen Taylor) #1

I am most likely over thinking this. I have a DeWalt planer which is amazing but my jointer is way out of level and I just don’t have time to fix the issue right now.

So my question is… I have a piece of Walnut glued up that is now twisted at two corners. So my thought was clamp down a piece of flat MDF and then use some hot glue to place the walnut on the CNC and level it.

I am correct shimming the corners that arent touching the MDF correct?

How do you go about flattering boards on the machine?


(William Adams) #2

I just use a set of hand planes and some aluminum angle for winding sticks.


(Stephen Gullage) #3

I do this a lot… I too have a jointer and a planer, but the CNC is so much better at getting a precise thickness. Of course, very few boards are dead flat, they can be cupped, bowed, or twisted. So i find the side with the least amount of movement when placed on a surface and put that side down. I use masking tape and CA glue to secure it to the wasteboard, making sure to get some contact between the board and the wasteboard. Hot glue works as well.

I use note papers to shim the corners or middle where it’s not laying perfectly flat on the table. Strips of note paper is nice because you can fold it in half, thirds, quarters, etc until you’ve got the board stable. It’s important to make sure the board can’t move vertically because it will get pushed by the bit and you’ll end up with a board that’s not flat. Take a pencil and put lines across your board every inch or so from edge to edge (closer for smaller pieces). Now run a leveling toolpath on the board. The pencil marks will make it easier to see your low spots.

Now, drop the endmill to the zero (+6mm) and then drop it to it’s actual zero. Then you can lower the endmill a little more (this is a guess, depending on how curved the surface is). Run the leveling program again, check your reference marks, maybe re-zero and run again (and again… and again) until there are no more reference marks.

Flip the material and you should have a board dead flat on one side, although most definitely not parallel to the other side. Attach it to the wasteboard, and mark your reference lines. I like to run the leveling toolpath again with the same zero because of the warp and shims, I’ve been surprised by the high points. Then repeat the lower zero - leveling toolpath until your reference lines are eliminated, and you have a board with parallel faces.

One thing I like to do when figuring out my initial zero is to zero off the wasteboard, then raise the endmill by a known amount, say 3/4" for regular 1" board, maybe a little more based on how much the board is warped. Then I take notes so I remember where I am and will have a record of the final thickness for setting up my jobs. For example, with a 0.02" leveling toolpath, I’d have notes like this:

Zero   Thickness
0.75        0.73
0.72        0.70
0.70        0.68

(Stephen Taylor) #4

Some damn good info. Thanks! Yea the shimming part was throwing me off last night because I wasn’t sure how much the machine would push down on the board.


(Stephen Gullage) #5

One thing I should bring your attention to is you’ll notice that instead of coming down the depth of my toolpath (0.02") for one pass I dropped it down 0.03". That’s a matter of getting a feel for it, depending on your material, and extra 100th is not going to affect things, and if it’s a rough pass, you can do more. I usually get an idea of how much I can drop it down my increasing the depth of pass in g-wizard until the numbers change considerable. I’ve done 0.1" cuts with a 0.02" toolpath just to speed things up without having to change my feeds and speeds.


(Stuart) #6

I have used this process too and it works a treat, my timber was about 2" thick, with a 1/4" - 3/8" cup.
i just lay it down, shimmed the gaps so it was supported most of the way around and roughly level (this doesn’t really matter, just means less wasted material) then found the highest point and took off 0.08" at a time. This depth of cut is completely dependent on material type, your experience and comfort etc… 0.02" is a great place to start until you get a feel for it


(Stephen Taylor) #7

Question, I dont have hand planes, which ones do you use?


(William Adams) #8

I use a #4 Stanley Jack Plane and block plane, and a tiny Bridge City Tool Works HP-8 Plane, and a Millers Falls smoother and jointer, and I need to get some older larger planes tuned up.

Unless you’re intrinsically interested in the idea of hand work, I wouldn’t bother — tuning up vintage tools can be messy, it’s hit or miss buying them used unless you buy from a dealer who can vet and fix them up in advance, and contemporary tools are really expensive for the nice ones.


(Stephen Taylor) #9

Yea I was watching something the other day about getting the level and whatnot. Was just interested, maybe one day ill get some.