large surface flattening jig - router setup - question

[Dennis Peacock]

Has anyone here ever built a sled / rail system for running a router with a large bit over the surface of a large wooden slab to flatten the surface of the slab with? I'd love to see/hear about your setup.

[James Zhu]

http://www.infinitytools.com/shop-es...ing-router-jig

[Kevin Jenness]

Shim your blank level on a flat surface and clamped between two parallel blocks taller than your blank. Put some spacers between the blank and the parallels. Make a sled for the router of 3/4" melamine or ply covered with p-lam just wider than the router base and long enough to span the parallels plus a few inches, with side rails to capture the router and stiffen the sled vertically. Add guides on the bottom of the sled to run along the parallels and stops on the top to confine the router travel within the parallels. Plunge through the sled to make a slot between the stops. Now run the router side to side and the sled along the parallels until the blank is flat. Plan for bushels of shavings.

James Zhu's link shows the essentials clearly.

That's how I did it before I had a cnc router. If you have one close by it will save considerable aggravation.

[Bryan Lisowski]

Marc Spagnolo did this when he built his Roubo bench and posted a video on his free site as well. The other would be the Samauri Carpenter did the same to flatten a 60" wide piece. Router planning sled should give you options in Google.

[Ken Kortge]

Eurekazone.com - the company that makes an excellent guide rail system that uses your circular saw - also makes what they call a Super Smart Routing System (SSRK) that connects to just about any router and accurately guides it along two dimensions.

Though they don't list it on their web site, their SSRK User Instruction Guide (a pdf file) shows what they call a "Dual Routing Kit" for exactly what you want to do - flattening large slabs.

Eurekazone.com is a relatively small U.S. company that is based out of Ocala, Florida (I've used their guide rail system since 2008), and they seem happy to take product related calls. Give them a call and I think they'll help you find with your needs.

[John TenEyck]

It's pretty darned simple. Two parallel rails, and a bridge that's twice as wide as your slab.



I did this with a 1/2" straight bit.

John

[Mike O'Keefe]

Volume 38 of The Woodsmith magazine has a article on building a flattening jig. Mike O'Keefe

[Dennis Peacock]

Thank you everyone!!!! I now have all kinds of ideas running through my head.

[David Eisenhauer]

Dang Dennis. The crew knocked that one on the head right now. I think we need to get up a little earlier in the morning to stump this crew.

[Rick Moyer]

It's pretty darned simple. Two parallel rails, and a bridge that's twice as wide as your slab.



I did this with a 1/2" straight bit.

John

Two questions:
1> why does the bridge need to be twice as wide? As the router reaches the outside seems sufficient to me.
2> how long did that take with a 1/2" bit and why not use a larger bit?

[Prashun Patel]

It doesn't need to be twice as wide. It just needs to have a slot that extends the length of the slab.

All this is to say, a wider bit doesn't always translate to less work in this application.

You CAN use a wider bit, but 'planing' with such a 1 1/4" ish 'bottom cleaning' bit is tricky. The bit can be prone to running away and it requires good power on the router to handle. Any abrupt changes like skipping can cause a larger bit to alter depth ever so slightly. Enough to make more work for you. So, I find with a large bit, you end up having to take very shallow passes. The process for me is less like 'planing' (using the bottom of the bit) as it is a series of flush trimming cuts (using the side of the bit). A 1/2" or 3/4" bit gives IMHO better control.

Whatever bit you use, this planing process requires careful smoothing after.

[John TenEyck]

You can put a slot in the sled that is only as wide as the rails, as Prashun said, and slide the router side to side. Or you can screw the router in the middle of a sled that's twice as wide, as I did, and then slide the sled side to side. I found it easier to do the later, personal preference.

My experience with big wide bits is similar to Prashun's, so I typically use a 1/2" bit. I think it took me about 45 minutes to flatten each side of the slab. I had to make a couple of passes, changing the depth of the bit in between, because the slab was pretty warped. You can see in the photo above where the bit isn't even hitting the slab at the ends and is cutting almost 1/4" deep in other places.

John

[Prashun Patel]

One more tip on holding the slab down:

You should make a series of 12" x 1" thick tapered wedges. It is critical that the slab not rock as you do the first side. These wedges can be slid underneath the slab.

Next, you will have to position your rails far enough away from the widest point of the slab such that your router doesn't hit the rails. You really want the 'stroke' of the router to begin and end off the slab, or you will get burning at the turnaround point. Like John says, if parts of the slab are cutting as deep as 1/4", you will generate significant force on moderately sized slabs, so you need to prevent the board from moving laterally as well. To do this, use wider tapered wedges between the slab sides and the rails. You can use a set of opposing wedges on each side to basically clamp the slab to the rails this way. Just don't do it so hard that the rails bow.

Personally I've always used the slot/slide the router method, but I am thinking to build a sled now like John suggests. I would also screw handles into the side of the sled so it can be 'rowed' back and forth ergonomically. I find that this repetitive motion can get very tiring. Gripping the handle of the router for so long is fatiguing for me. Also, with my method, you have to hold the sled with one hand, and the router with the other. It's hard coordinating both independently which means I tend to skip and move with the direction of the cut every now and then. This causes skipping. Securing the router to the sled and doing as John does gives more leverage over the tool, and allows you to use both hands to control one dimension of movement. Like.

Ok, John, have you solved the room-full-of-dust problem with this method? BTW, I'm using that same Bosch 1617.

[Rick Moyer]

Thanks guys, great advice. I have a friend doing slabs right now but he's just getting started and thought I could give him some better ideas than what he's doing now. Appreciated.

[Dennis Peacock]

Well, to build John's version of the sled? I'd have to have build a sled to mount the router to that would be 120" long in order to go across the 56" kitchen island top to cut down on the time and effort of sanding it all flat.
I'm just looking to do this for this island top I'm building.....56" wide by 10' long by 2.5" thick