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Thread: Slab Flattening Router Sled

  1. #1
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    Slab Flattening Router Sled

    Has anyone ever built a slab flattening router sled?

    I have some live edge slabs I need to flatten and I am planning on using a variation of Nick Offerman's router sled:


    Rather than use solid lumber for the rails, I thought laminating (3) 3/4"x6"x96" sanded plywood would be more stable. So I've got that done.

    (It's still too hot here to work outside so the kitchen has been hijacked )

    At the back of the plywood table is the sled that will go between the rails but I still need to make something like the boxes that lay on top of the rails as in the first photo. I have a number of thoughts but would love feedback for anyone who has ever built a sled such as this.

    Right now I'm thinking of using aluminum angle to rest the router plate on. This is the bottom view:

    I was thinking the open area will give me a better view of what I might have missed. But I'm wondering if the dust created by this process might be worse with the bottom being open. The parts are not glued together yet because I'm not sure how this will work.

    Thoughts?
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  2. #2
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    Yes it can be used for flattening slabs and it works just fine. The same principle is useful for turning columns including columns with entasis as long as the material is substantial enough. Many years ago a friend executed a contract for church columns (matching existing) including flutes. I've used the approach several times since.

    With your design you should be able to close down the bottom if you find the dust to be a problem. Perhaps the dust collection on the base of your router will be all that's needed.
    "the mechanic that would perfect his work must first sharpen his tools.” Confucius

  3. #3
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    I haven't built one...yet...but it's on "my list"!

    I like your ideas so far, including the lamination for the rails and the aluminum to support the router.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  4. #4
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    I've always just built whatever sled I needed for the slabs I wanted to flatten. Simple and cheap and nothing to store when the job is done. If I did slabs regularly I'd build something like you are making, Julie, or Nick's. If dust is an issue you will definitely want to implement some kind of control system. I built this sled twice as wide as the rails, with the router fixed in the center, so that the dust collection could be built around that point. I still had a lot of chips that didn't get collected but most of the fine dust was.



    I used some foam to help seal the area around the router bit to the wood, but I think the brushes you see on CNC routers would do a much better job but I couldn't readily find any low cost options. In any case, the sled has to sit above the slab, and that gap needs to be sealed around the bit so the airflow can be managed in order for the vacuum to capture a high percentage of the chips/dust.

    Joh

  5. #5
    I have done this a number of times. Making the sled slightly longer than the supporting rail width and running the router across the sled reduces the inertia of the whole affair. Wax it up well, eat your Wheaties and don't forget the dust mask.

    Now that I have a cnc router, I don't miss anything about the manual method.

  6. #6
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    I have some concern about riding the router base on aluminum angles. The aluminum router base made not slide very well on the aluminum angles. Aluminum on aluminum tends to create some galling. Maybe use some UHMW strips screwed to the routerbase.
    Good luck with your project

    Tim

  7. #7
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    One of the things I saw as being a necessity was creating clamping points for the rails. So I took the rails to the drill press...


    I placed the holes at 12", 24" and 36" from either end, figuring that would cover pretty much any slab I can now envision working on. The slabs I have now are between 84" and 96".

    John, I was thinking about CNC brushes as a possibility for containing the chips and dust. From what I have seen in videos, that can be pretty substantial. The slabs I'll be working on have been skipped-planed, both sides, so I shouldn't be seeing a fireworks display of chips flying.

    As for the cutter, I have the 1" mortising bit shown in the first post but it has seen a lot of work. I used it to radius dozens of fret boards and it's starting to show some wear. Plus it's only 1" wide. So I popped for an Amana 1-1/2 wide, bottom-cleaning, upshear bit.

    I still have to figure out what is the best route for the "wings" (that the sled attaches to that slide on the rails). I saw an Offerman video on YouTube where he extended the length of the wings to about three times what is shown in the first post. It gave him a lot of flexibility.
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  8. #8
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    Quote Originally Posted by Tim Janssen View Post
    I have some concern about riding the router base on aluminum angles. The aluminum router base made not slide very well on the aluminum angles. Aluminum on aluminum tends to create some galling. Maybe use some UHMW strips screwed to the routerbase.
    Good luck with your project

    Tim
    Tim, the router is attached to a 1/4" thick sheet of Plexiglas. I have run it across the aluminum rails and there is some drag. I plan to polish the AL rails and see how that goes but if there is still drag I will go the route of UHWM strips.

    Thanks!
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  9. #9
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    I managed to clear the saw horses and do a trial setup before making the wing boxes. I'm glad I did.

    I'm trying to figure out the best way to design the wing boxes so as to make the sled flexible for a number of different flattening jobs. Had I made what I drew up in CAD, I would have been disappointed.


    The sawhorses give me a lot of flexibility but... I'm thinking the boxes need to be at least 12" high. That would allow for most any thickness slab and with the adjustable legs, I should be able to flatten stumps.

    What do you think?
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  10. #10
    Very nice. I would make handles for the router carriage. This is fatiguing work. As such, it's easy to get lazy and move the carriage a little too much on the next pass, causing the router to run or skip. A good handle keeps the carriage under better control.

    I would also be leery of aluminum angle. In my experience, it has sagged.

    The hardest work, IMHO in this set up is leveling the rails. I used the string method for that.

  11. #11
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    How do you plan to hold the router? I can't see how you can get your hands down over those tall sides of the gantry to hold it, and with that design you have to hold the router. Even if you can I think it's going to be awkward and tiring to do so. This is another advantage of the router being fixed at the center of a gantry twice as wide as the distance between the rails. The router stays fixed, and you hold the gantry anywhere that's convenient. With that design you can make the sides of the gantry any height you want, and the bottom of the gantry can be a solid sheet of plywood with a hole cut in it.

    FWIW, I found a 1/2" diameter straight bit to work best. A bowl bottoming bit takes a wide cut, but you can't cut very deeply, and it still leaves ridges. A 1/2" straight bit takes a narrow cut, but you can cut more deeply and the ridges are no worse. 1/2" straight bits are HF cheap, so you can afford to replace them more frequently.

    John

  12. #12
    20171015_141144.jpg
    I've been flattening a bunch of wide oak planks lately using a freud 2" straight bit. Bit works well, but it can get a little hairy when it catches a knot. Something that I have noticed is that it seems easier to make my passes going with the grain rather than across. It cuts easier, and the ridges are almost non-existent. I still have a lot more to do, and I am not looking forward to it. It is hard work, and makes a huge mess. I wish I had a friend with a wide jointer.

  13. #13
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    Quote Originally Posted by Prashun Patel View Post
    Very nice. I would make handles for the router carriage. This is fatiguing work. As such, it's easy to get lazy and move the carriage a little too much on the next pass, causing the router to run or skip. A good handle keeps the carriage under better control.

    I would also be leery of aluminum angle. In my experience, it has sagged.

    The hardest work, IMHO in this set up is leveling the rails. I used the string method for that.
    Prashun, I was playing with it last night, after I temped the wing boxes together, and the sled slid fairly easily using 3/4"x3/4" UHMW on the bottom of the wing boxes. In my mind's eye I was seeing taking thin-cut passes rather than trying to take it all at once. More passes but hopefully less fatiguing. When I get to making cuts, I'll see how handles can fit into the design.

    Quote Originally Posted by John TenEyck View Post
    How do you plan to hold the router? I can't see how you can get your hands down over those tall sides of the gantry to hold it, and with that design you have to hold the router. Even if you can I think it's going to be awkward and tiring to do so. This is another advantage of the router being fixed at the center of a gantry twice as wide as the distance between the rails. The router stays fixed, and you hold the gantry anywhere that's convenient. With that design you can make the sides of the gantry any height you want, and the bottom of the gantry can be a solid sheet of plywood with a hole cut in it.

    FWIW, I found a 1/2" diameter straight bit to work best. A bowl bottoming bit takes a wide cut, but you can't cut very deeply, and it still leaves ridges. A 1/2" straight bit takes a narrow cut, but you can cut more deeply and the ridges are no worse. 1/2" straight bits are HF cheap, so you can afford to replace them more frequently.

    John
    John, the Offerman videos show him holding the top of the router and applying pressure that way. And he takes some pretty deep cuts. The problem with the wide gantry design is you have to adjust the slab up or down, rather than adjusting the sled. The sawhorses have adjustable legs and with the travel between the wing boxes and the sled I'll have a lot more flexibility. But this is still a work in progress. I may find I'm wrong.

    Quote Originally Posted by Jake Elkins View Post
    I've been flattening a bunch of wide oak planks lately using a freud 2" straight bit. Bit works well, but it can get a little hairy when it catches a knot. Something that I have noticed is that it seems easier to make my passes going with the grain rather than across. It cuts easier, and the ridges are almost non-existent. I still have a lot more to do, and I am not looking forward to it. It is hard work, and makes a huge mess. I wish I had a friend with a wide jointer.
    From what I've seen, Jake, the mess can be substantial! I saw one video where the waste piled from the floor up to the slab that was being flattened, and the slab was about 3' off the floor. That's why I plan to take this outside when I actually do the work.

    Thanks for the great input, guys!
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  14. #14
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    So yesterday I cut up the wing boxes and clamped them together to see how they might work.

    They look pretty bulky but after I sat them on UHMW pieces the whole unit slid pretty effortlessly.

    I marked for an angle cut on the side of the boxes. I plan on routing two slots in both the box and the end of the sled to allow for T-bolts and knobs.


    This is a bottom shot of the UHMW strip I temped in. The strip will be permanently attached to the sides, where the recess is.


    I've got the sides cut and strips of the UHMW installed on the bottom of one of the box sides. I'm trying to anticipate what it will be like adjusting the sled up and down. I've been thinking about using miter track and miter bar to keep the whole thing square. I ordered some from Rockler. We'll see how that works...
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  15. #15
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    Julie, you don't have to adjust the slab up or down with the double wide gantry. No different than any other design. You adjust the router bit in the base of the router, whether using a fixed or plunge base type.

    I would not want to try holding the router only by the top, whether Offerman does it that way or not. That would be tiring and there's just too much chance for a dangerous situation if the bit catches (and it will). I would cut down those sides, at least on one side, so I could hold the router as it was intended to be. If you make the lower side twice as thick you will get back most of it's stiffness.

    If you put a solid plywood bottom on your wing boxes you wouldn't need any UHMW. A little wax and they will slide nicely on the rails. If they don't because your rails are rough, then just glue or tack some face grain plywood to the top of them.

    John

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