Welcome to the World of Large Slab Woodworking.
The Incredibly Beautiful Woodwork of George Nakashima
Flattening anything that is too big for your Jointer and Thicknesser is a daunting task.... but those large waney edge slabs of exquisitely figured timber are just waiting for you to turn them into magnificent coffee tables, side tables, sofa tables and dining tables. You can do this easily with your own Cradle Jig, or like a growing band of enthusiasts, you can enjoy going off-grid with your Scrub Planes, Jointer and Fore Planes. Jack Planes, Smoothers and Cabinet Scrapers, saving a fortune on Gym Fees!
The above image is of a single large Bubinga slab.
The patterning is known as "Waterfall"
What do you do with the cracks that inevitably come with large slabs of figured timber, how do you get the slab flat enough to finish it beautifully and what do you need to achieve your dream waney edged table?
Exquisite Walnut Slab!
Slab work is actually extremely easy, although it does take patience and time. The challenging part is setting up and jigging up for the process. Slabs are too big and heavy to manhandle with confidence, safety and ease, so this is definitely a case of "take the tool to the wood, and not the wood to the tool".
The only machine you will need to preliminarily flatten any size of wood slab is most probably already in your workshop.... Drum roll please.......Your Router!
Any router will do, as long as it has a 1/2" collet. Without doubt, the bigger and heavier and more powerful your router is, the better. In my workshop, I use an ancient 3HP deWalt 625. It is very basic, and does the job admirably. I also use my Triton TRA-001 3HP now and then for this kind of task and it is extremely well suited to the job.
This article also applies to woodworkers who build their own workbenches, either flattening them with hand planes, or using the same router setup that you would use for large slabs.
Basically, you will be building a jig for your router that has available horizontal travel in two axes, namely with the grain and across the grain. The jig functions very much like an X-Y table that is found on top-end mortising machines, but a lot simpler and bigger.
Let us use an example slab for the building of the jig. Say we are wanting to flatten a live edge slab of 2 metres long by a maximum of 1 metre wide. First we would need to support the slab on a few cross braces and place this on a stable and flat surface, your workbench for example.
(Note: A quick, easy and dirt-cheap reference base surface for this kind of work is a standard hollow core door. They work like a charm for assembly tables, and a have a myriad of other uses around your woodwork shop. When one side gets too gunky to use, simply flip it over and you have a fresh, flat surface!)
The cross braces need not be very big in cross section, but would need to extend at least 100mm further than the slab on either side. So, for a 1 metre wide by 2 metres long slab, you would need at least five cross braces of at least 70mm x 38mm in diameter, at a length of 1,2 metres each (100mm wider than the slab on either side).
You will also need two rails about 2,2 metres long, with the same cross section dimensions as your cross braces. These jig parts can be cut from any cheap timber, as long as they are straight and stable. The cross braces are placed on their 38mm wide edges underneath the slab, spaced equally apart.
Once you have got your cross beams in place & evenly spaced below your slab, then attach the long rails with screws to these braces, making an effective frame for the slab to lie on. Remember to assemble the base frame on a known flat surface!
The next step is to cut a pile of small wedges on your bandsaw and wedge them between the slab and your cross braces, wherever you can, so that the slab in completely stable and does not wobble at all. Don't miss this step!
Next, you need to attach two rails. Make dead sure that they are absolutely level and parallel in relation to each other, along both long edges of your slab. Now you have also framed and stabilised your slab on your lower cradle.
With the lower cradle frame assembled and your slab wedged to be as level as possible to your lower frame reference, you are now ready to build your router cradle.
The cradle can be made from solid timber, but I usually use MDF. The cradle can be assembled with Kreg Pocket Hole Joinery, or simply glued and screwed together.
The most important part of building the router cradle, is to make the base of your router captive between the side panels of the cradle. This must ensure that the router can slide easily along the base of the cradle, but not have any noticeable side to side movement within it. Note that your router bit must be able to travel a little further on each side than the full width of the slab, so cut your access slot accordingly.
Your cradle must overlap the slab sufficiently to enable it to travel along your lower cradle frame. Attach two hardwood runners underneath the router cradle base on either end of the cradle. These will slide on your lower frame's rails. Note that the dimensions of the runner must be sufficient in height, so that the cradle completely clears the slab everywhere, but is as close as possible to it. The runners should also each extend at least 130mm away from the cradle on either side. The longer they are, the easier it will be to track the cradle along your base rails.
Once you have assembled your router cradle firmly and accurately, it is time to test the jig by using the upper cradle to cut your router cutter access slot.
I suggest that you use the Dimar #1600059 Six Wing Router Cutter to level the surface of your slab. This bit is very well suited to the job and is great value for money. With its 1/2" shank, and using reasonably shallow passes, your slab will soon be flat enough to sand, plane or scrape.
The process of flattening a slab is as follows:
- Position the Upper Cradle at the extreme end of your slab with your plunge router set to cut about 4-5mm in a pass.
- Clamp the Upper Cradle in Position.
- Router your first pass making sure that you cut the full width of the slab.
- Loosen the clamps, move the Upper Cradle over into the next cutting position, overlapping the previous cut by 5-10mm.
- Clamp the cradle and make the pass.
- Continue in this way until you have cut the entire slab.
Safety Notes to bear in mind:
- Always switch the router off, let it come to a stop, then retract it before unclamping and moving the Upper Cradle to your next overlapping cutting position.
- Make sure that you router's power cable is kept clear of the cradle at all times. If you can, try and suspend the cable from above, allowing sufficient travel for the router.
- Do not get lazy and try to cut without firmly clamping the Upper Cradle to the Lower Cradle!
- Keep debris clear of your cutting area at all times.( I simply use compressed air and blow the area clean each time, after I have moved the Upper Cradle to it's new position.)
- This router bit is a big cutter, so pay attention to the rotational speed recommendations for it, accidents happen very quickly!
- This is a job for a big router. We suggest the Triton 2400W
When you have complete one side of your slab to your satisfaction, it is time to turn it over and surface the other side.
With regard to tension cracks in you slab, these are quite often unavoidable, but can be controlled to varying degrees by the use of "Butterfly Keys".
Keys are basically strong long grain hardwood pieces that are inlaid across your cracks and can be made to look really good and quite artistic when cut from a contrasting hardwood. The Keys are a "Double Dovetail Loose Tenon" design and they function exactly the same way as dovetails do in traditional joinery.
Beautiful and creative use of Butterfly Keys.
I hope that I have managed to wet your appetite for slab work, and that you will add yet another string to your woodworking bow, so to speak. Writing from the perspective of one who attempts to reproduce furniture pieces of the 18th and 19th centuries, I can truly appreciate the art of Live Edge woodworking and the remarkable natural creative beauty and tactility that it offers.
Until next time, let's keep making shavings, not dust!