Several years ago my workplace had to chop down a large tree, a horse chestnut which was threatening the building. Once it had been felled the workmen roughly chainsawed it into sections ready to be disposed of.
A couple of pieces somehow ended up in my possession, the largest one being a cross section from near the base which was too heavy to lift. After many years of it laying around the garage getting in the way I decided to do something with it.
Luckily it hadn't cracked during this time, though the flat edge it'd been stood on had deteriorated a little.
This is how I flattened and polished that slice, and prepared it for being an outdoor table.
Step 1: Starting Point
This is the slice I started with, roughly cut on both sides, some bark missing, and a chunk sliced off the back so it's not a full section unfortunately.
But still too good to chop up for firewood, so something had to be done with it.
Heaving the thing up onto a workmate was the first challenge - once it was on there it stayed in place until finished. The one benefit of such a heavy lump of wood is it didn't need clamping down.
Step 2: Removing the Bark
Unfortunately a lot of the bark had already been knocked off, so I had to remove the rest. This turned out to be a lot trickier than expected as the intricate knots and knurls meant a lot of surface area was obscured or folded back on it's self.
The easiest way I found to do this was using a blunt wood chisel and a mallet - to get into the gaps and gently prise the bark away from the wood - hopefully without leaving too many marks.
One surprise was the number of spikes protruding from the trunk into the bark - these were mostly hidden until the thick bark was knocked off. I am guessing they were branches that hadn't formed. Whatever they were, they were sharp and a menace to peoples legs. So I carefully rounded them all over to form bumps rather than spikes.
Hopefully this is unique to this species of tree, if I do it again I'll try and pick a more uniform section without spikes.
Step 3: Making the Router Plane Jig
I had no idea how to flatten the surface, a chainsaw would work but I'd probably make even more of a mess. The wood was far too tough to consider planing or sanding it.
Then I saw a youtube video of somebody flattening a home made work bench with a router running on fixed rails, something that'd work perfectly on this tree section too. I'd been wanting to buy a router for a while, and this was the excuse, so a trip to Screwfix and I came back with a plunge router and a 22mm straight bit.
The challenge was to screw two rails to the log at the same angle, in the end I used a spirit level to get them as close as possible
Step 4: Making the Router Plane Jig, Continued
To make the sled for the router to slide back and forth in, I used a piece of laminate floorboard as a base - thinking it was just the right width, thin enough not to get in the way too much, and smooth enough for the router to slide back and forth easily.
To stop it bowing in the middle, a frame was made out of cheap pine timber, a couple of mm wider than the router base.
To cut the channel for the first time, simply plunge the router through the laminate, and slowly work along the length of the sled to cut the slot.
On reflection, I should have used a router collar rather than trying to guide it with the sides of the sled - but this worked well enough.
Step 5: The First Cut Is the Shallowest
Now everything is ready, it's time to put on the dust mask, goggles, earmuffs and whatever else is available. This stage is long, messy and noisy.
- Find the highest point of the surface using the sled and a ruler, and set the router plunge depth to be a little below that. I settled on taking off about 5mm deep at a time.
- Start slowly, don't overheat the bit or it'll blunt and cuts will get more and more ragged as you progress.
- Take off about half the bit's width on each pass, don't try and plough straight into it at full width, it'll just lead to slower cutting and more heat.
- Once you have chosen a height, lock the router depth. I found setting the depth stop and plunging each time lead to fractionally different depths every time. This gets more important (more visible) as you approach the final stages.
- Shavings may build up underneath - it's important to either turn off and clear these, or keep moving - staying still with the router running can cause them to get hot and start smouldering (Yes, I did that)
- The side rails are sacrificial, to get near the edges of the trunk you'll probably need to cut into them a little.
I collected all the shavings and gave them to a friend who wanted hardwood chippings for something, there was nearly a bin-bag full by the time I'd finished.
Step 6: Levelling Off
In my case the height difference of the surface exceeded the depth my router could adjust to - so after getting everything as flat as possible - I removed the two rails and reattached them lower down. Again, taking care to level them both as accurately as possible.
Then start again, find the high point - set the depth and cut....
On the final pass, take it as slowly as you can, and take off as little material as possible for the smoothest cut.
The time you spend on this step will make up for sanding time later.
Step 7: Sanding
Now the aggressive cutting is done, remove the boards and break out the sanding gear.
I started by hand, with a roll of 80 grit paper wrapped around a block of wood - but quickly got tired of that. I borrowed a random orbital sander and that seemed to be the best solution. With a pack of sanding discs I worked through 60 to about 400 I think - until the surface was smooth enough to reflect light.
There were some voids where the tree had grown and left gaps - the smaller ones of these I filled with some sawdust (from the sanding, to match the colour) and woodglue mixed. The larger voids I left open.
Keep on sanding until all the tool marks from the router are gone - I was careless and one of the router passes was a fraction lower than the rest - so that took a lot of sanding out.
If you screwed the rails for the router sled straight into the wood - now is the time to repair them with a bit of filler
Step 8: Applying a Finish
Now all the hard work is done, it's time to apply some finish. I chose Danish oil because it's food safe (this table may have food on it at some point in the future) and I like the shine it gives natural wood.
I'd been a bit disappointed with the colour of the wood up till now, with some dark grey stains showing through in patches - presumably that's the natural colour of the mature wood in the middle of an old tree through. The oil really made a difference, and applying three coats and polishing transformed the surface.
Step 9: Current Status
Due to a impending house move I've had to postpone this project - as it was so heavy though I didn't want it to get damaged being transported. So I mounted it on the base of an old office chair for easy transportation. If it weren't such an ugly plastic base then I'd probably keep it like this, as it rolls around so easily.
It's still rather wedge shaped, but I'm not going to try and flatten the other side too - so it's mounted with some shims on the low side to make the surface level.
To hide the ugly cut off side, I used a bit of pallet wood to make a rough shelf on the back. This got a coat of Danish oil too, though if I can find a place to position this up against a wall, that shelf can go.