Spoilboard Basics


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Thread: Spoilboard Basics

  1. #1

    Default Spoilboard Basics

    Hey Folks!

    I have a 6x12' router with a vacuum table. I do super long engraving cuts so it doesn't make sense to use the vacuum hold down (and have the vacuum on for 20+ hrs) so I usually just screw down. I'm not getting great Z accuracy because I'm using a spoilboard that's meant for vacuum use and only has screws around the outside, but lifts slightly from the vacuum table in the middle.

    I'm doing a full overhaul of my spoilboard situation and am looking for a couple of tips.

    First, is there a recommended distance between screws when using an MDF spoilboard? My current design has screws roughly every 24 inches, with a maximum distance between screws of 30 inches (so each of the 4x6' sections has 4 screws on each outside edge, then 4 screws through the middle area at that spacing). Would you think 24-32 inches between screws is ok for keeping Z tolerances tight-ish? Is there some sort of spec on this for MDF?

    Second, I plan to use counter sunk nylon screws on the middle work surfaces anchored by steel or brass threaded inserts. Are there any pro-tips for that sort of practice or is it pretty much straight forward?

    Any other pro-tips or wisdom for running this sort of "screw it down" setup (no T-track or bolted fixtures)?

    Thanks tons all.

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  2. #2
    Member routalot's Avatar
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    Default Re: Spoilboard Basics

    I suppose the thickness of the MDF would have considerable influence on the appropriate spacing of any screws.I've used 12mm,18mm and 25mm on different machines with only the 25mm used without vacuum hold down.For the kind of use described,would a really thick and substantial slab of MDF be useful?Something like 40mm would be unlikely to move too much,even though it is a real pain to lift around the workshop and 50mm really needs four people to lift a sheet.In either case you would get away with only installing it once and skimming it when say 1/2 inch has been consumed-at which point you glue on some more 12mm and give it a skim when the glue has cured.I suppose the concept I am laboriously describing would be that the fasteners are used to stop lateral movement and the stiffness of a thick slab of MDF resists vertical deflection.



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    Member ger21's Avatar
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    Default Re: Spoilboard Basics

    Any other pro-tips or wisdom for running this sort of "screw it down" setup (no T-track or bolted fixtures)?
    Turn on the vacuum. That's the only way it will be truly flat. Our 5x12 table moves up and down daily, and even throughout the day due to humidity changes. It's screwed down with nylon screws, but cups badly between the screws until the vacuum is turned on.

    Gerry

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  4. #4

    Default Re: Spoilboard Basics

    Quote Originally Posted by routalot View Post
    I suppose the thickness of the MDF would have considerable influence on the appropriate spacing of any screws.
    Very true, great thought. Man you can get a lot of MDF dimensions across the pond! The states seem to be limited to 1/4,1/2, and 3/4 inch without buying/shipping an entire unit. Will look into getting thicker MDF.

    Quote Originally Posted by ger21 View Post
    Turn on the vacuum. That's the only way it will be truly flat.
    Your comment made me realize that for these super long cuts accuracy is not important, it's only for shorter 10-15 min cuts that it's necessary because I'm cutting parts for boxes that must match one another for good fit. Easy to turn on the vacuum for 20 mins rather than 20 hrs. Thanks for commenting Gerry you're always helpful. Two Qs, do you have any estimation for how much the bed is cupping during these climate changes? Also what do you find your power consumption to be like for your vacuum for that size table? I have a multicam machine and their "TurboVac", I know what it's badged for but I'm finding what the badge says can be very different from actual consumption (My router is badged for 60 amps and draws probably half that at full load). The vacuum needs some work and I haven't yet fired it up. Just curious.

    With a plan to use the table both with and without the vacuum I suppose it still stands to reason to surface the spoilboard with the vacuum on.



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    Member ger21's Avatar
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    Default Re: Spoilboard Basics

    Two Qs, do you have any estimation for how much the bed is cupping during these climate changes?
    The biggest "fast" changes are in the summer, where it can be very dry for several days, and then become very hot and humid.

    It's still been cold here, and in the winter, we see gradual cupping and shrinking.
    We use 3/4" spoilboards, and usually surface then .005" at a time. Sometimes 2-3 times a day, sometimes one or twice a week. The machine has two spoilboards that are roughly 61" x 74", with 9 screws in each one, roughly 30" apart. Right now, the spoilboard is about 1/2" thick, and at the edges, between the screws, it's lifted almost 1/4" off the bed of the machine. The overall size of the spoilboard shrinks, too. When I put the spoilboards on the machine, they are tight together. Within 2 weeks, in the winter, there will be a gap between them close to 1/8" wide. So they shrink about 1/16" every 5-6 feet.

    Also what do you find your power consumption to be like for your vacuum for that size table?
    I don't really have any idea. The machine has two Busch pumps, which are probably 10HP each. They probably use a lot of power.

    Gerry

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    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

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    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Spoilboard Basics

    Quote Originally Posted by Parkgrr View Post
    Very true, great thought. Man you can get a lot of MDF dimensions across the pond! The states seem to be limited to 1/4,1/2, and 3/4 inch without buying/shipping an entire unit. Will look into getting thicker MDF.



    Your comment made me realize that for these super long cuts accuracy is not important, The vacuum needs some work and I haven't yet fired it up.
    I'm a bit puzzled by this,why does the cut take so long and yet accuracy isn't paramount?Tiny cutters for fine detail perhaps?I think you need to get the vacuum system working to better judge what the alternative could be compared to the way you are working at present.I do have some experience of long operations,my record is a 44 hour run on a 3D surfacing project which was sufficiently heavy that a few screws stopped it moving sideways and lifting was never on the cards.



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