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Thread: How do I make this cutting board curved joint?

  1. #1
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    How do I make this cutting board curved joint?

    Been going crazy trying to make a cutting board for a friend. Should be a very easy task. I've done it a ton of times on straight cutting boards.

    But for my friend I wanted to make one with a curvy connection between two of the boards in the middle. Not an inlay, but the two boards would be complimentary curves glued together.

    Sounds simple enough, but I can't get the boards to match snugly. I cut the curve on the first board, sanded it smooth, then made a template of it out of 1/2" MDF with a pattern bit on the router table. OK. Good so far. It's making the complimentary board and then using a pattern bit on the 2nd piece of wood that I can't get it right.

    What am I doing wrong, or how should I approach this differently? I've seen inlay techniques using a bushing and a handheld router. Is this a better approach?

    Here's the present joint between the two boards:
    Cutting board joint.jpg
    Last edited by Alan Lightstone; 06-12-2021 at 4:48 PM.
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  2. #2
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    After making it, did you use the pattern template on both boards?
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  3. #3
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    You need to make two templates by cutting on the line with the thinnest blade you can mange and then carefully working the two pieces until they mate cleanly...or have someone with a CNC make the matched templates for you. You need to do it this way so you can pattern route the mating edges and those routes have to be on each side of "the line" precisely.
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  4. #4
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    Quote Originally Posted by Julie Moriarty View Post
    After making it, did you use the pattern template on both boards?
    Yes. But strangely they didn't mate well. Perhaps need to play sexy music in the shop.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  5. #5
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    Quote Originally Posted by Derek Arita View Post
    Off the top of my head...make one pattern. Use it on one board, then flip it over for the mating board. It should come out the same, but opposite.
    That doesn't quite work. You need to make a parallel template to the first one. Can't flip it.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  6. #6
    Alan,
    Bosch makes what they call a "router inlay kit" which is intended to use a smaller bit size to do exactly what you are after, but on a smaller scale. If you look at how it works, you can use the same technique to achieve what you are after, only on a larger scale. The trick is to remove the cutter diameter from the equation, which isn't going to be easy, but should be possible. Hope this helps.

  7. #7
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    I have a pdf about cutting boards where a router with a 3/8" straight bit was used to create a curved dado maybe 1/4" deep, then that dado was split in the middle at the bandsaw, and the walls created by the router were used with a pattern bit to make mating curves. Haven't tried it myself but seems do-able. Alan, pm me your email and I'll send it to you. Might help.
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  8. #8
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    Can't you cut through both boards at the same time to get a tighter joint?

  9. #9
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    Quote Originally Posted by Bob Falk View Post
    Can't you cut through both boards at the same time to get a tighter joint?
    If that was a straight joint, absolutely.

    I could, I guess do one board under the other, with filler pieces diagonally. Thought about that originally. With a bandsaw that would make a perfectly mated joint, but a rough one.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  10. #10
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    Getting worse

    So I taped the boards next to each other, with filler pieces underneath with a gap and used a handheld router with a bushing and a 3/8" spiral downcut bit.
    Jig for Routing Cutting Board.jpg

    This went great until the middle of the board on the big curve when the grain changed on the board. The router jumped, and ruined the board.
    Cutting board router mistake.jpg

    So now I'll have to prep a new board (no big deal, I have one piece left), but still don't have a working approach.
    Last edited by Alan Lightstone; 06-12-2021 at 12:01 PM.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  11. #11
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    I think what you are missing is the radius difference between one side of the bit and the other -or- the bit offset if you are using a collar. If your templates fit fine and you use those edges independently to flush cut each blank specifically -AND- your flush bit is accurate (so many are not in this mixed imperial / metric world) things should fit. If you are not getting an exact flush cut I would look there. If you are using a collar you need to consider the offset. If you cut as shown in your previous post you have to account for the bit diameter.

    Template radii.jpg
    Example exaggerated for clarity.

    When you use the one piece for a template you are offsetting the mating piece by the diameter of your bit. This is why two templates are required.

    You can see here how the exact same arc used on opposing faces will not mate if one face is cut on one side of the bit and the other is cut on the opposite side. The diameter of the bit changes the radius by its size. A 12" radius on the "near" side of a 1/4" bit becomes a 12-1/4" radius on the far side.

    Template radii-2.jpg
    Here's another view of the same phenomena.

    Template radii-3.jpg

    If you filled the gap equal to the diameter of your bit with a third piece it would fit using your method.

    CB-Anthony (31).jpg
    Last edited by glenn bradley; 06-12-2021 at 12:25 PM.
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  12. #12
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    Thanks, Glenn. Makes more sense now.

    My first attempt was with two templates. I'll try that again, but using a 3rd piece to fill in is getting more tempting by the minute.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  13. #13
    Alan,
    I did a quick mock up to show how the Bosch "router inlay" system does it. It has a bearing which is removable from the router bushing after you have cut out pattern "A". After removing the bearing, you cut pattern "B" running on the router bushing. This beariing thickness is 1/8", so a 1/8" router bit is used for the cut. This leaves you with two patterns, one for each part to be joined.
    DSCN2417.jpgDSCN2418.jpgDSCN2419.jpgDSCN2420.jpgDSCN2422.jpg

    I used 1/4" MDF for the patterns which seems to work well for the 1/8" cutter to get through, and provide a good edge for the pattern bit. The mating is not perfect, but will match exceptionally well with light clamping. The wood shown is 3/4" thick walnut and white Oak.
    I'm sure there must be other similar choices available if you do not have a Bosch router. Best of luck.

  14. #14
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    Christopher, I'll have to seriously look at that. I don't have a Bosch router, and it may be specific to those. Infinity, amongst others has a similar piece. And I think I actually have that somewhere in a drawer. And thank you for doing that mock up. I am having trouble figuring out how to use that here. Basically the first template is made 1/8" larger than the wood size, and the second template is made the actual wood size? And could this be used with my first piece of wood already made?

    What I'm having trouble getting my head around is how to make the second template.

    Making the first is easy with a pattern router bit on my router table.
    Purple Heart Board.jpg You can't see it from the picture, but there is an MDF template underneath it that matches perfectly. The contour is traced in pencil on the Padauk piece, though it's hard to see.

    The question is how to make the second template. You can clearly trace the cutout needed by putting the first piece of wood or first template a piece of MDF. But how do you cut it with a router? Clearly a bandsaw cut is way too rough. And the dimensions would be wrong using a bushing, per Glenn's post.

    I can now see why people put in inlays. Seems much easier, even though more parts.
    Last edited by Alan Lightstone; 06-12-2021 at 4:47 PM.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  15. #15
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    This maybe a complete stupid suggestion, but this is the internet...could you overlay the boards and cut the curve on both at the same time with a band saw?

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