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Hi all. Looking to start my table project. Got a nice slab of Walnut. I am looking to start evening out the surface. However, I am unsure of the right approach. I have seen alot of folks posting videos in regards to using router sled jigs. I guess my one concern or question is. Should I take this approach as my slab of wood has some nice sized knots in it? Given I have not attempted this before I was just wondering if there was a better tool for the job here. My main concern is the router skipping or kicking once I hit the knot. Or is this the generally preferred method and you need to just go extra slow over the knot areas / expect some kick or skipping.
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A flattening sled is the easiest, cheapest & most practical. I haven’t done a ton of it, but I did flatten a couple workbench tops and here are my take aways:

1. Router - this is a very taxing job so you need at least a 2HP router. Even with my 3 1/4HP router I had to let it cool off periodically.

2. Bit - Buy the best you can afford. I used a Magnate planer bit which was ok. Size the bit to your router. I uses a 1.5” bit and as mentioned, things got hot.

3. Shallow passes decreases load and increase quality if cut. Be patient. Start by looking for twist and high spots, shim the slab to even them out.

4. Carriage - for that span you need a very stout carriage. I would use 2 layers of 3/4 plywood for the sides. A sturdy base to ride on that has been made planar using a level and strings.

5. Process - slabs are notorious for misbehaving. Very subject to moisture imbalance and internal stress, particularly if kiln dried (look up case hardening). Do both sides per session, take equal amounts off each side, and do the milling in several steps, allowing it to acclimate for up to a week in between. It does not hurt to hold it in cauls and clamps while it reacclimates.

Marc Spagnolo (Wood Whisperer) has a good demonstration of setting up a sled on YT.
 

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welcome to the forum.
tell us what you intend to do with the slab once it is finished.
also - about your woodworking experience and tools available.
 

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Knots are always trouble, but a router handles them fairly well.

Hand planes and powered hand planes take a little skill and sharpening ability but are also an option.
 

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You'll be fine with a router sled. How thick is your top? Is it cupped, etc?
 

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You'll be fine with a router sled. How thick is your top? Is it cupped, etc?
That slab looks pretty "smooth" already. A router may flatten but makes for a rough surface so lots of sanding. If it's flat, having a shop run it through a wide belt sander would be a major time saver. The crack will need a bow tie or some other kind of reinforcing. Others here are more capable of explaining the process that I am.
 

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That slab looks pretty "smooth" already. A router may flatten but makes for a rough surface so lots of sanding. If it's flat, having a shop run it through a wide belt sander would be a major time saver. The crack will need a bow tie or some other kind of reinforcing. Others here are more capable of explaining the process that I am.
At least in my area most places that sell slabs will also offer shop services for flattening. Not cheap but definetly helpful.

-T
 

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That slab looks pretty "smooth" already. A router may flatten but makes for a rough surface so lots of sanding. If it's flat, having a shop run it through a wide belt sander would be a major time saver. The crack will need a bow tie or some other kind of reinforcing. Others here are more capable of explaining the process that I am.

Many shops won't even touch that. It takes too many passes if it's not flat., We had a planer Sander but still has to flipped several times to find a base flat...
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I agree, build a router sled and use a router. You won't have issues with knots and such, IMO. It'll be good experience for you, also. Your subsequent sanding to a smooth finish shouldn't be that bad, either.
I routed, flattened these 3.5" walnut root ball slabs for table legs. It was good experience, and easy enough, for my first time routing slabs flat. Lots of burl in the root ball and my finish hand sanding was tedious because of the burl.
https://flic.kr/p/ndguvr https://flic.kr/p/ydXHvL
Wear a good dust mask when routing.

Sonny
 
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