project, woodturning

Turning a burr

Burrs are very interesting bits of wood. They are odd growths that occur on the surface of tree trunks. I'm fascinated by what causes them to occur, since they are basically a mass of knots. Wikipedia on burrs Burrs typically have all sort of faults within the wood. But the wood is so dense both physically and visually in terms of grain patterns, that you can turn something quite beautiful, faults and all.

At the Hampshire woodturners meetings I go to, I've seen a number of examples of really great burr pieces. Of all shapes and sizes, which have often inspired me to consider trying myself. But I rarely justify buying myself more wood pieces when I have so much that I could do with what I already have.

burrOnLathe.jpg

However, recently Kat took a trip to turners retreat, and among the things she brought me back was a piece of burr. I have no idea what tree it's from, there was no label to say, and I guess it doesn't really matter. It's a fantastically odd looking thing:

My first reaction was 'where do I start?'

I decided I wanted to make a bowl, but attempt to leave a cross section of the original exterior just beneath the rim of the bowl. I've seen examples of this approach, and I like the way you get a feel of the original burr exterior cross cut through the smooth sleek finished bowl.

BurrOnLathe2.jpg

To mount between centres I first used a forstner bit to drill a hole in the face side, roughly central, and just a little wider than my drive centre. This was so the drive centre would be locked in place and there is now way this thing would fly off once the tailstock pinned it in position. I brought the tailstock up to try to have the bulk of the burr fairly central. Obviously I wanted the most material centred as possible to get the biggest bowl I could in the shape. Regardless there was a large growth off on side of the bottom that I just had to turn away.

I turned the rough shape of the bowl at the bottom, leaving enough left to be able to shape a little top 'rim' for the bowl and keep a sliced cross section. This was fairly tricky, To begin with the whole thing is quite out of balance, and once you are preserving the cross section your turning without constant contact to the wood, so it's very difficult to get a good cut.

After quite a lot of time, and a few catches that could have been disastrous but were ok, I wound up with the outside profile done.

BurrOnLathe3.jpg

Unfortunately, or perhaps fortunately, the most centred position for the bowl meant not such a central cross cut of the original exterior, and so it is rather one sided. I'll kid myself that this is part of the natural effect I was going for.

BurrOnLathe4.jpg

You can just about see here that one side of the bowl wall is actually the original exterior, I could have tried to turn it away, but again most of the point of these shapes is to preserve the interesting faults.

Having shaped the outside I sanded and finished, before turning to re-chuck on the spigot that I turned on the base.

I didn't take any pictures of the hollowing process. I used my spindle gouge to do most of the hollowing, but then used a small bowl gouge to get the final cuts on the inside. I also used a scraper to finish under the rim. This was a last minute decision, as I was hollowing I decided to leave the rim a little wide and give an undercut. As I hollowed I found one of the faults ran from the outside to the centre, leaving me with a hole in the side. But I'm ok with that.

BurrOnLathe5.jpg

It's not easy to see, but I tried to leave a downward curve on the cross section. It ended up being quite a subtle effect, mostly because it's quite hard, and partly because as I did it I was aware that if I took away much more material I'd weaken some of the smaller sticking out bits too much, and either risk snapping them, or be forced to turn even further to remove them completely.

I spent quite a lot of time sanding down grades, and trying to get a good surface. The 'wing' on the cross section in particular I spent some time with a sanding arbour in my drill working down grades to smooth out the fairly rubbish surface I'd left with my not so great tool skills. Ultimately I did quite of lot of hand sanding to try to lose any scratches and avoid just rings left by sanding with the lathe on. I also spent a fair amount of time applying wood wax, and trying to get a streak free finish. This mostly involved giving it time to cure a little, and going around with my lamp shining to show off the surface, and using a buffing pad to work away to a smooth surface.

Having satisfied myself with that finish, I removed the bowl from the chuck and put it to one side. Whilst I turned a jam chuck to remount the bowl so that I could turn away the spigot. At this point I have enough bits of scrap around that I happened to have an off-cut of oak with a spigot already on, that was just about right. I turned a domed end on it, and then put 4 or 5 layers of kitchen roll in the bowl to protect the surface as I remounted it. Again bringing the tailstock up to it's original mark at the base of the spigot.

I was pretty pleased that it turned pretty much right back on centre. Which made life much easier as I very gentle turned away the spigot, being careful to take small cuts. I did cause the lathe to stop a couple of times, but mostly my cuts were light enough to not be a problem.

I turned the spigot down to a small pin of wood, then worked on finishing the base. I turned a slight recess curve to ensure the bowl will sit flat on it's rim. I also refined the curve at the base of the bowl to turn into base a little, which I hope gives it a slightly 'lifted' effect when finished.

The last step was off the lathe, slicing the last pin of spigot away with a sharp chisel. I was very careful here, really didn't want to slip and gouge finished surface. Once it was pared down as much as possible with the chisel, I sanded by hand the bottom, from 120 grit in all steps down to 1200 grit. Then a very small amount of wax on the base.

BurrBowlBase.jpg

And finally it's finished!

BurrBowlFin1.jpg
BurrBowlFin2.jpg

Ultimately, despite the time I put into finish, I'm still not that happy with it. I obviously need to learn more about applying wax finishes. I suspect I need much more patience between stages for a start. But with limited time that can be difficult.

That said, I am pleased with how the overall process went. I didn't have any real frustrating slips, and it came out as planned, without me having to adjust to cover up mistakes.

Kat took some better pictures of the bowl