Roughing Slab before Flattening - Router Forums

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post #1 of 7 (permalink) Old 12-13-2016, 02:54 PM Thread Starter
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Roughing Slab before Flattening

I didn't want to high-jack the post by @sunnybob about wide router bits for flattening a panel so thought that I would start this.

I had just finished cutting a couple of half lap joints in 2x4's for a shop project when I read the post, and it occurred to me that it would be possible to "rough out" a badly warped or twisted slab using the same method that I'd just used to cut the half lap joints - ie using a circular saw to cut closely spaced kerfs across the parts and then knocking out the strips with a hammer.

If you had the type of set-up that uses fixed rails that run alongside the slab combined with a router mounted on a bridge that spans the rails, it should be fairly simple to make a second fixture with side rails to contain the base of the CS and an open bottom that the blade projects through. Set the depth cut so that the blade tips just miss the surface at the lowest point and go ahead and kerf across the high area. Knock out the thin projections, replace the CS with the router and proceed with flattening.

It's two set-ups, but the initial roughing phase should be way quicker than nibbling away at the high spots with the router.

I don't have a project in mind - my buddy's slabs are still drying and they looked pretty flat when I was over visiting the other week - but it seemed like a good idea. What do you think?
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post #2 of 7 (permalink) Old 12-13-2016, 04:42 PM
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I think you are onto something Tom.
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post #3 of 7 (permalink) Old 12-13-2016, 05:04 PM
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Oliver's jig...

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post #4 of 7 (permalink) Old 12-13-2016, 07:50 PM Thread Starter
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That's the idea Stick. The saw carriage would have to be longer and sit on rails parallel to and up off the slab - I'd make the opening in the carriage wider so you could get a better look at where you're cutting and adjust the length based on where it's cutting. Thinking that it wouldn't take too long to do a slab as you'd probably only be doing opposing corners and not the full width or length. Slice it up and knock off the fins with a 2lb maul and you'd be good to go.

Almost makes me want to go looking for a nice warped slab..............
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post #5 of 7 (permalink) Old 12-13-2016, 08:11 PM
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Tom; I've been cutting relieved portions out of framing lumber with a circ. saw for decades. I just slide the saw sideways (once I've removed the scrap bits) to flatten out the bottom of the cutout portion.
Having a rest front and back gives you pretty much a perfectly flat bottom. I have to say I've never tried it in the context of fine woodworking, in Hardwood.
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post #6 of 7 (permalink) Old 12-13-2016, 09:15 PM
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Quote:
Originally Posted by DaninVan View Post
Tom; I've been cutting relieved portions out of framing lumber with a circ. saw for decades. I just slide the saw sideways (once I've removed the scrap bits) to flatten out the bottom of the cutout portion.
Having a rest front and back gives you pretty much a perfectly flat bottom. I have to say I've never tried it in the context of fine woodworking, in Hardwood.
I have done the same, Dan, I didn't want to mention it as some might think it unsafe.
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post #7 of 7 (permalink) Old 12-13-2016, 11:28 PM Thread Starter
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@DaninVan & @Herb Stoops

I've cut a good many half laps in framing lumber but always finished the job off with a sharp chisel and a Surform block plane. I've seen videos where they've fed a part like that on a TS to clean up to a flat surface - never had the nerve to try something like that either. For making door frames or shelving units, that's always worked OK for me. As far a finishing a slab, I would think that you would still be finishing it up with a router, just doing most of the work with the CS.
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