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33K views 9 replies 8 participants last post by  Randy_ATX 
#1 ·
Flattening slab with router sled

I started a post about a wood gloat about a month ago. I found some nice walnut slabs at a sawmill for some projects. The first one up is a coffee table. I thought I would start a blog about the process of preparing the slab. I may follow this with more about adding a base to the table as it progresses.

I've done a fair number of projects in the past, but nothing involving a big slab like this. I have been excited about getting this project started, but Christmas was approaching fast and I had to finish some gifts to send to the east coast before it was too late. In the end, it was too late when I sent them, so they didn't arrive until after Christmas. Luckily, the recipients are forgiving, and really loved the lamps that I made.

Now that I had shop time for my own purposes, I was able to get started on the coffee table. The first thing I had to do was build a jig for the router to flatten the faces. I created a sled like the one described in Fine Woodworking (issue 222, I think). It is basically a bridge over the work piece which allows the router to ride across a level plane above the piece. It took me a couple of nights in the shop after work assembling and flattening everything I needed to get the jig set up.

When the jig was ready, it was time to rearrange my shop. I had to wheel the table saw out of the middle, and drag my bench out so that I had access all around it. It didn't take long to shim the legs of the bench to get it all level. Leveling the bench is important because you will use the level on top of your work piece to determine the plane to which you want to flatten the slab. For the slab I was working on, it had a twist from one corner to the other, and it was thicker on one end. I was pleasantly surprised at how quickly I was able to get it shimmed to where I was happy with it. I have to admit, it is a bit stressful, at least the first time doing this, because you really just take a good guess about what it the best position. If you proceed cautiously, you can adjust as you make progress. I had to make a small change. More on that later.

Here is the initial setup on the workbench:


You can see the stretchers that the slab is sitting on. These will hold the rails for the jig. There are about a half dozen shims and a strip of 1/2" ply between the slab and the stretchers to get it leveled the way I wanted it.

I built my jig around my new Triton router. I've heard a lot of good things about the Tritons, and a few bad things as well. In short, I can say it is far and away better than the dewalt 621 that I've had for a long time. The Dewalt is dying a slow death, so I went with the Triton. As a bonus, it comes with an "extended base plate". That meant that I didn't have to buy a router table plate. The router is on its base plate and the trough is just big enough to allow the router/plate to slide across it.

With the jig all set up it was time to start up the router and see how this thing works:



Basically, I needed to find the highest spots and start lowering them. The first couple of passes were pretty quick because there were a few high spots that came down quickly. I lowered the router some more, and adjusted the jig down, too, to work more of the slab.



I was really excited with how fast and easily this operation was progressing. I got a little farther than in the last photo and decided it was time to assess how the slab was looking, more closely. In doing so I realized that the low spot on the left if the previous photo was about 3/8" lower than the spot across from it on the other edge of the slab. I didn't want to have to remove that much wood to get it down to that level, and I wanted to keep the slab as thick as possible. That meant it was time to re-level it. I lifted up the left edge with some shims, and used the lower edge of the router sled to determine when the low spots on each side were in the same plane. This was only a 10 minute operation to get it adjusted. Then it was back to making more sawdust.

By the way, leveling a slab this way is a good thing to do when your shop is really dirty and in need of a good cleaning. You are going to get wood chips EVERYWHERE! I filled 2 garbage cans with chips, and I'm not close to done.

Back to flattening, this is where I had to stop for the night:


It was shaping up very nicely. You can see the track marks that the router leaves striping their way across the slab. They are very shallow and will come out easily when the time comes. I still had a few low spots, but this was very close to being done. It took me about 2 1/2 hours to get this far.

The next day, I couldn't wait to get back to the shop and continue this project. Now that the top was basically flat, flipping it over to level the bottom becomes easy. I stood the slab on edge, removed all of the shims, and laid it top side down. It didn't wobble at all.

At this point, it started to go faster. I was confident that the top side was flat, and I was happy with the way it looked. Now it was just about making the bottom side parallel to the top side. I reset the router and sled to hit the high spots and started working again.

After 2 or 3 passes the highest spot started coming down:


In another 20 minutes, I was getting pretty close to done:



I was amazed at the incredible figure in this slab. It seemed every time I flattened out more of it, the figure just kept getting better.

I took a break for a while to ponder how much I wanted to work the bottom and the top, then came back to finish up the routing. The bottom isn't totally flat, but the low spots are in places that will still allow a base to support it well. I went back to the top side and finished leveling it out a little better.

The router left some tearout in a few places. I think that is because I was taking a fairly wide (but shallow) cut. The angle of the cut near the edge was not supported, causing the tearout. I guess that will be a test for my finishing skills.

Overall, if you want to work with a slab like this, the jig and router method is well worth it. I bought a 3/4" sheet of birch ply, 2 straight 2×4s and a 10' 2×6 from the BORG for this project. That totalled about $60, and I have half a sheet of ply left for other jigs. I think it was about 4 hours total to get the slab flattened. It was my first time, and I was being cautious, and enjoying the process so it took longer than it needed to. I enjoy using hand tools for most things but I would have never attempted this project with a couple of hand planes and winding sticks!

I plan to add another entry about finishing the rest of this project. I am hoping go make progress on it soon, so I have something to add here. I need to get to Woodcraft to get some epoxy to fill the knots/splits in the slab. The store is about 10 minutes from where I work, but about 50 minutes from my home. I'm not going to make a special trip out there this weekend to get it, although I would love to make some more progress in it this weekend!
 
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#2 ·
Thanks for sharing. I'm hoping to use this method for planing large slabs as other traditional power tools are quite expensive. I'm sure that you must have had knots in your stomach most of the process (The fear of ruining fine wood both worries and excites me each and every time). I'll be tuning in for this series. Have an amazing New Years.
 
#4 ·
Hi Lumber2sawdust,

I am planning to make a similar coffee table from a slab for the top. I could not find any other posting from you regarding how you finished the table, specifically how you designed and attached the legs to the slab.

Could you share how you completed the project and the leg construction?

Thanks,
Ken
 
#5 ·
Hi Lumber,
I'd have to agree, i'd love to see how you went about the legs as well. I just picked up a 4' round of maple to make a few tables out of. But most of all I'd love to see some details on how you built your jig. the round being 4' wide i won't be able to go to my buddy's mill, his has a max of 28"...so it looks like a chain saw as careful as i can, and then i need to construct the same type of jig you used here to smooth the face. any photo's?
-FrankMoney
Seattle
 
#6 ·
Hey Frank,

The jig I made came from Fine Woodworking #222. You can the plans from there and will be way better than I could repeat here. I added a second blog post in this series which shows what I did for the base. I ended up not using wood on the base because my wife really wanted a metal base.
 
#7 ·
Finishing and the final result

I started this blog with a post about flattening the odd-shaped slab of walnut over a year ago. A lumberjock recently requested that I follow up on that post as I had intended to. I don't have as many photos of the rest of the process but will describe what I can.

The router sled was awesome for making the slab flat and it was smooth enough that I could spend some time with hand planes and a card scraper to get it smooth without too much difficulty. It was still challenging because of all of the figure in the slab.

Before I could smooth the slab completely I had some other work to do: epoxy. The mill started cutting a slice from this slab and hit a piece of metal so they backed out the blade and didn't finish the cut. You can see a dark streak in the surface, and see where the hole is. I hit that metal with the router! I never got the metal out. I just used a nail set to force it below the surface then filled the void. That was from the cut end of the slab. I decided I wanted to stabilize the slab by filling the slice by gluing in some strips of walnut were I could, then fill the rest with epoxy. There were also several voids in the crotch section of the slab on the top that I wanted to fill. I bought some epoxy from Woodcraft and some black dye for it, too.

That slice (from a band mill) swallowed up a tremendous amount of epoxy! It took me at least 5 sessions of adding more epoxy to the openings. I had to use (many) layers of masking tape to resist the hydraulic pressure of the epoxy on the edges so it wouldn't just flow out the sides. In the end, I'm happy with the result, and you don't even notice it in the finished piece. It would have been wise to use an epoxy that set faster. I just didn't know which one to use.

When filling the voids in the surface I had a lot of troubles with air bubbles in the epoxy, too. I would use a plastic cup to mix the epoxy and then pour it into the voids. I have read advice that you should avoid over-agitating the epoxy when mixing it so you don't trap too much air. I guess I'm not able to stir it thoroughly without whipping in a lot of air. The epoxy would take its time descending into the bottom of the voids. Some must have been pretty deep. It seemed that the epoxy would drain into the void for a while and then stop, as if it were full. Then just before it set, it would flow some more and I would still have a void to fill again. I used a lot of masking tape to prevent the epoxy from going too far, or possibly staining the surrounding surface. Here is a shot of the top while I was in the process of filling voids:



After the epoxy set, I would use a block plane and card scraper to remove the excess. That is when I would find that the bubbles in the epoxy were now visible at the surface level, so it was time to mix another batch of epoxy and start the process again. I would love to find a better way to do the epoxy so that it doesn't take quite as long but the result was worth the hassle. After all of the filling was done, this is when it was ready to finish:


The figure in this crotch slab is amazing so I really wanted a finish that would highlight the beauty of the piece. I chose Watch Danish Oil. In spite of this being walnut, I didn't use the walnut-colored oil, just the clear version. I followed (roughly) the steps outlined in this web site. Basically, the process is to apply the danish oil using sandpaper. I believe I started with 400 grit. The slab was already pretty smooth from planing and scraping it first. The 400 grit might have been more than I needed. I probably could have started at 800. I spent a lot of time on that first application though. The walnut absorbed a lot of oil on the first few coats, especially in the sap wood.

The process has you just stepping up to higher and higher grits. You are polishing the surface by wet sanding with the danish oil. After the first application, it starts going much faster. I'm not sure if that means I was less uptight about it, or if things start to progress more easily. It can be hard to really see any defects while the finish is wet, so I kept working the surface, probably well beyond what I needed to because it seemed easier than having to deal with finding an imperfection later.

This is the bottom side of the slab. I didn't smooth it out to the same degree as the top, so you can see some of the imperfections. I flooded the area with danish oil to see how it would look:


The instructions I linked to say to you can stop at 1000 grit. It depends on how fine you want the finish to be. I kept looking from a low angle across the surface of the slab and could see scratches. They kept getting smaller and smaller after every grit, but I could see them. I don't remember if I stopped at 1500, or went to 2000. In the end, you can drive yourself mad trying to get it that smooth. The table has been in our living room for a year now and nobody has put their eye down at the level of the table and looked for scratches from the sanding! In fact, I don't notice them in daily life. It looks just fine. I wouldn't go any higher than 1500. Once all of the polishing was done:


My wife was adamant that she wanted a metal base for this piece. I would have preferred to build something from wood (I'm a woodworker after all!) probably inspired by Nakashima, but we went for the metal base. We spent a lot of time looking at various catalogs to find styles we liked, and possibly to buy something and just replace the top with this slab, if the price was right. We never found the right fit from anything commercial.

My wife found a local business that mostly builds custom signs. The guy has a forge and the ability to work a lot of metal for custom hangers for signs and other cool stuff. We took the slab to his office on snowy Saturday morning and we spent quite a bit of time with him deciding what we liked, and sketching out some things I had envisioned. We settled on a 4-legged design with each leg arched toward the center. The opposing legs were joined by a thinner arched piece to provide some room beneath the table. (I'm tall, and hate sitting somewhere when I can't stretch my legs). It took him a couple of weeks to get the base done but it was well worth it. The base has a small metal circle on the top of each leg with holes to screw it to the top. Actually I never added screws. It is just gravity and inertia holding it in place! I may screw it down eventually though. Here is a shot of the final piece:


I can say that the base is exactly what my wife and I asked for but after getting it all together, I left me feelling … unsatisfied. I think the scale of the base and the slab don't work together. If I ever complete all the other projects on my list, I might build a different top to use with this base and build a Nakashima-inspired base for this slab. I think it will just look better.

That said, when a friend saw it, she sat down on the couch in front of it and said "I've been trying to find a coffee table I like for 5 years. This is what I want." I've gotten a lot of compliments about it, but that one takes the prize. I have a customer wanting a coffee table if I ever have time to build things for others.

I really like the look of the danish oil finish. You have probably already heard that danish oil isn't great for protecting wood, especially for high-use pieces. I was willing to take the chance. Since we don't have kids, the coffee table won't get a lot of abuse. I did sit a coffee cup on it and there is a slight ring as a result. Use a coaster! Putting a more durable finish over the top might be wise, but I'm going to leave it for now. If you anticipate more use, I suggest a different finish, or a topcoat over the danish oil.

I've already used the router sled to build a desk from 2 bookmatched pieces of walnut, too. I think that one came out even better than this table did. I encourage you to take the time to build a sled like this. I really enjoy working with slabs.

Thanks for reading.
 
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