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  1. #1
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    Default How to cut curves that are parallel?

    I have ripped a board on a bandsaw, making an elongated S curve along the length of the board, and now want to make an identical cut 25 mm offset from the original, so that I end up with a snakelike flat piece of board 25 mm wide.

    Can anybody please advise on the most accurate way of doing this, in a manner that is consistent and reproducible without much sanding?
    regards,

    Dengy

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  3. #2
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    Quote Originally Posted by Dengue View Post
    I have ripped a board on a bandsaw, making an elongated S curve along the length of the board, and now want to make an identical cut 25 mm offset from the original, so that I end up with a snakelike flat piece of board 25 mm wide.

    Can anybody please advise on the most accurate way of doing this, in a manner that is consistent and reproducible without much sanding?
    Damn, its hard to explain but easy to do - you place a single point guide 25 mm from the blade fixed to the table so that you can keep the existing curve in contact with the point and it maintains your distance from the blade ensuring a parallel cut. you can clamp t to the table or make a way to fix it to the mitre slots.

    THink of a fence that is only a few mm wide but exactly parallel to the blade's cutting direction and offset by the width of the required piece. because the fence is so short you can still pivot the workpiece around the contact point

    It takes a little bit of practice. try a couple of pieces of Pinis Crapiata before you do it on the workpiece itself. It does not take long to get the hang of it

    Cheers

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  4. #3
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    Quote Originally Posted by Dengue View Post
    Can anybody please advise on the most accurate way of doing this, in a manner that is consistent and reproducible without much sanding?
    With a CNC router

    If you just HAVE to add cost-effective/cheap to your criteria, do what Doug said

  5. #4
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    If it has to be reproducible, you may be better off making a form and doing it on the router table?
    The world is a comedy to those that think, a tragedy to those that feel.

  6. #5
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    Quote Originally Posted by yowie View Post
    If it has to be reproducible, you may be better off making a form and doing it on the router table?
    Thanks yowie, the problem remains when using the router table and a flush trim bit - how to do a template that has parallel curved sides. Or have I misunderstood?
    regards,

    Dengy

  7. #6
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    Quote Originally Posted by Dengue View Post
    I have ripped a board on a bandsaw, making an elongated S curve along the length of the board, and now want to make an identical cut 25 mm offset from the original, so that I end up with a snakelike flat piece of board 25 mm wide.

    Can anybody please advise on the most accurate way of doing this, in a manner that is consistent and reproducible without much sanding?
    Simple!
    Place your already cut S curve over the next bit of wood you want and just mark with a pencil.
    Cut the curve out on the next bit of wood as close as you can on your bandsaw.
    You probably wont get it perfect but fear not. Glue the 2 curves together with 5 minute araldite then when the glue has set bandsaw straight down the glue line. The thickness of the bandsaw blade should remove any discrepancies in the joint. If it doesn't, repeat the process.
    The technique I believe is called "cutting together" as opposed to cutting apart which is the norm.

  8. #7
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    Use the curve you have cut as THE template and make 2 cuts on a new piece with a bearing router bit?
    a rock is an obsolete tool ......... until you don’t have a hammer!

  9. #8
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    New Zealand
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    Hi,
    I recently had need of a similar requirement and did the following steps :

    Draw a single curve (S shaped in your case) onto cardboard that can tidily be cut with sissors. (I used a long wire with a pencil to get a circular curve with large 7 meter radius on my workshop floor).

    Cut this curve out and transfer it onto thin 3-4mm mdf sheet with a pencil. Move it, 25mm in your case, away from the curve you first copied and remark.

    Cut outside of line with bandsaw and tidy up with sandpaper until you are happy with the accuracy. The thin mdf is thin enough to sand/shape easily but thick enough for a router bit with bearing to track on (provided the template is firmly tacked on to the wood you will finally be shaping)...

    Once you are happy with your template you can take it and trace it's shape onto the timber you wish to use for your project.

    Cut about 1mm away from marked curve with a band saw and then tack the template firmly back onto the work piece. Tidy up with a flush trim bit using a router (most easily done using a router table).

    Repeat the last step as often as required.

    Hope that helps )

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