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  1. #1
    Join Date
    Jul 1999
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    Glen Iris, Vic, Australia
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    Default Please help find a way to unravel the curved back on this mitre dust hood to cut

    Hi all,

    I've been following this gentlemans' techniques for designing a tight mitre saw dust hood for my Makita 1216 DCMS.
    https://www.youtube.com/channel/UCOk...F-qUO6C4Nh3lBA

    I've designed a curved back that has a curved top.

    I can't seem to find a way to unravel the back to layout a pattern to cut from 3mm flexible material.

    Any positive constructive help would be greatly appreciated.

    Thanks in advance.Untitled2.jpg Untitled.jpg
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  2. #2
    Join Date
    Jun 2010
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    Bundaberg
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    Default

    Is the cross sectional shape a semi circle; an arc or an oval? And is the bottom surface flat or is it a mirror image of the top surface?

    Basically though; you divide the length of the curved surface into a number of equal sections and calculate or extrapolate the lengths of each of the vertical sides.

  3. #3
    Join Date
    Oct 2014
    Location
    Caroline Springs, VIC
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    1,517

    Default

    I don't know how to flatten out a curved surface in sketchup, but I can work out how to draw the flattened panel easily enough.

    If the bottom curve is flat across the bottom, then when unraveled it will simply be a straight line. You can find out long the straight line will be by selecting the curve and opening "entity info". It will tell you the radius of the curve, but also the length of the arc.

    The top curve will have the same overall length as the bottom cord (in the x axis), but the curve "bulge" will be whatever the measurement is in the Z axis between the top point of the arc to the middle point.

    barryarclength.jpg

  4. #4
    Join Date
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    Glen Iris, Vic, Australia
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    Default

    Thanks Chief Tiff.
    Yeah was going to measure each of the panels on that curve and lay them out side by side.
    Didn't want to have to do that manually.
    Would get kinda tiresome after the second go.

    Thanks Kuffy.
    I think thats the way I'll have to do it unless someone comes up with an extension or an undiscovered built in tool.
    Much appreciated.
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  5. #5
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    Jul 1999
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    Glen Iris, Vic, Australia
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    Default

    I think this is it.

    Grrr.
    Had to calculate the length of the bottom curve by
    calculating the circumference from a diameter of 1060
    then divide by 2

    Not sure why I couldn't get sketchup to select the bottom curve (half circle / arc ).
    Might have been when I was using explode then intersect faces with selection.


    Untitled5.jpg
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  6. #6
    Join Date
    Oct 2014
    Location
    Caroline Springs, VIC
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    Default

    Quote Originally Posted by barrysumpter View Post

    Not sure why I couldn't get sketchup to select the bottom curve (half circle / arc ).
    Might have been when I was using explode then intersect faces with selection.

    Was the arc broken up into segments when you were trying to select the arc as a single item? I find this happens far too often in sketchup and is annoying. But like most things, I just work around the problem. I would have just drawn another arc wrapped around the curved face anywhere along its height. Just as if it was a real item, in the real world. I would wrap a string around it and measure the string, or just use the tape measure itself as the string.

    You also could have selected all of the arc segments and had sketchup spit out the overall length of all the selected items. But I have found sketchup to be very 'sketchy' with accuracy. So much so that I would NEVER use a sketchup file to produce accurate CNC cutting files. SketchUp seems to think that working within +/- 0.5mm is close enough...sketchup is great for illustration purposes though, and for drawings which have dimensions displayed even though the circles or arcs aren't drawn exactly perfect.

  7. #7
    Join Date
    May 2011
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    Murray Bridge SA
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    67
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    3,274

    Default

    Look up blocklayer.com he has a website that has a lot of different formula for different projects how to lay out cones etc. If you can't find it look in the Metalwork Forums right down the bottom CONVERSIONS & CALCULATIONS
    Kryn
    To grow old is mandatory, growing up is optional.

  8. #8
    Join Date
    Jul 1999
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    Glen Iris, Vic, Australia
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    Default

    Hi Kuffy,
    Yes I think thats what the Explode command does.
    12 segments is the "close enough" visual factor for Pi in sketchup.
    Its faster than plotting dots I guess.

    I'm sure I've seen faster circles in rastering or something like that.

    I'm in it for the accuracy of .5mm thats the best I can do with my current equipment and sight enhanced by a magnifying cap.

    I tried the tape measure and the string but left it in the workshop and returned to the computer for the math accuracy.

    I've had my eye on a DIY CNC machine but you need the accuracy of a CNC machine to build it. LOL
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  9. #9
    Join Date
    Jul 1999
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    Glen Iris, Vic, Australia
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    Default

    Hi KPs,
    Yes I've used the Blocklayer site for a number of projects.
    Thanks for the reminder.
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  10. #10
    Join Date
    Jun 2005
    Location
    Helensburgh
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    Default

    This may give you some ideas and it works well...Dust Hood For Bosch Glide Saw
    CHRIS

  11. #11
    Join Date
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    Glen Iris, Vic, Australia
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    Default

    Nice!
    Thanks Chris.

    Going now to Dandenong to see if 3mm clear plexiglass will bend around my 530mm radius arc.

    Unless someone can tell me if I should be using something else.

    I'd prefer NOT to have to pay $200 for a 2400 x 1200 sheet.
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  12. #12
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    Jun 2005
    Location
    Helensburgh
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    Default

    3mm MDF made the curved back easy and if you wreck the first version it does not hurt very much.
    CHRIS

  13. #13
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    Glen Iris, Vic, Australia
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    Default

    Excellent! Thanks for that.

    Just found 1mm clear perspex for $55 for 1200 x 2400 +$5 per cut
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

  14. #14
    Join Date
    Jun 2005
    Location
    Helensburgh
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    Default

    Why do you want the top sloping and curved and where does the air and extraction pipe go?
    CHRIS

  15. #15
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    Jul 1999
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    Default

    2hp extractor (not a 5hp)
    so need a tight fit

    4" extraction from the bottom
    and 35mm from the top
    is the current plan
    Thanks,
    Barry G. Sumpter
    May Yesterdays Tears Quench the Thirst for Tomorrows Revenge

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