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Hampshire woodturners – September

September 3, 2008

This month’s wood turning group was a pretty good one, both for the demo and for my ‘haul’.
Harry and Bill were once again kind enough to provide me a critique on my door stops, which were last month’s project.
And Harry had brought a project for next month, this time a candle snuffer. But not just the design and instructions. He also brought the wood needed to make it. Plus some other bits of nice dried wood. And co-incidentally Bill had brought a couple of nice lumps of wood for the novices also. As it happens I was the only novice there, or certainly the only one that showed much interest, and as I result I came away with all the wood :-) So many thanks to Harry and Bill.

Each month there is a raffle, and for the second month running I won a prize! So last month I won some wood wax. And this month I won an Axminster drum sander kit. So I’m pretty much quids in for my raffle ticket investments so far.

But enough of that, I thought I would write about the demo we were given. I did make a load of notes about it at the time. Unfortunately I elected to make notes in this blogging app on my n770, which has no auto save. And I ran out of power on the way home :-(

So here is what I can remember. The demo was of off-centre turning by Colin Simpson. Harry said that Colin used to edit the woodturners magazine that I have a subscription for (courtesy of Kat).
So Colin started by showing how to make a three sided ‘box. The important part of this was how the measuring out works. Having roughed a cylinder out of a block, he drew two circles on the ends, at something like one third and two thirds the diameter. The 3 sided nature means you need marks at 120 degrees from each other, and to measure this he used a simple technique. First setting a pair of dividers to the radius between centre and outer circle, then stepping the dividers around the outer circle marking each point stepped to. This yields 6 evenly spaced marks. And every other one gives you 3 marks at 120 degrees apart.
Transposing these marks out to the edge of the cylinder it was then possible to use the tool rest to mark the line alone the length of the cylinder and from there transpose the same three marks onto the outer circle at the other end. The point of all this is to accurately mark out three ‘centres’ that can be used to turn between. Providing the off-centre turning points that gives the three sides. So first mount at any one of the three points, and spin (fairly slowly because it’s off centre) Now using a rouging gouge cut back until the path of the cut runs just between the nearest 2 horizontal lines. These lines are basically the ‘corners’ of the box, so you want to cut up to, but not over, too far and you’ll have sides that are different sizes. Not far enough and you’ll have flat spots between the sides. Repeat this process for each of the three points you marked, and you have a three sided box. You’ll need to do a lot of the sanding and finishing off the lathe. In particular sanding on the lathe will tend towards ‘dulling’ the corners, and it is still hard to sand that way.
Re-mounting on true centre it’s possible to cut a spigot for mounting in a chuck. Then do much as you would for any other box.

At this point Colin gave us the option of him finishing the box, or moving on to demonstrate more off-centre techniques. Unsurprisingly we opted to see more techniques.

He talked a little about skew chisels, the bane of many wood turners. Specifically different things people say about correct angles and shapes. Mostly amounted to, what ever angle works for you is best, and new ‘oval’ section skews are a bit of a gimmick, potentially easier to make a planing cut, but considering the versatility of the skew, other cuts, and sharpening, become much harder.

The next thing he demonstrated a ‘pseudo-cabriolet’ leg. These are traditional legs for chairs and such, the real kind tend to be formed into paw/claw shape at the base, and have a leg which tapers in at an angle.
For this he kept a section of 40mm or so of square section at the chuck end, and maybe 30mm at the ‘foot end’ also square section to a pummel, but in this case the pummel is the top of a ‘foot’, and he used the skew chisel to turn a large bead, which forms the outer profile of a foot sections, resting on top of a small remaining piece of square section. Each end has diagonal lines drawn from corner to corner which is how you find a centre point. Then marking at the foot end a point about half way between the centre and one corner. And at the other end a mark about a quarter the way from the centre to the opposite corner. Mounting between these centre points the idea is that the ‘ghosting’ caused by the off-centre rotation should stop at about the base of the pummel. As this is where we want the ‘true centre’ and the new axis of rotation to meet. If it’s not there, then adjust the centre point at the top end until it does.

Spinning in this position you can turn away all the ‘ghosting’ between the top pummel and the foot which creates a tapered cylinder for the leg.
Also turning a little off of the foot section just to give the front of the foot a different profile shape.
Finally returning to true centre you can part off the remaining square section at the base down to a small pad under the foot.

The last demonstration was a paper knife. Though he didn’t say what it was going to be at first. The idea of being able to make something like a paper knife on a lathe is pretty interesting. It’s not immediately obvious how to do such a thing.
Basically in a square section of wood, he turned what looked like one of those tools gardeners use to poke holds in the ground, a ‘dibbler’. This is turned leaving a chunk of square section at either end. Then this is taken off the lathe and a cheap piece of square section, probably just spruce, is put on the lathe heavily off centre. This is down so you can screw the piece to the side closest to the centre of spin. This creates an overall piece which is slightly off-centre, and where the whole of the ‘main’ block is rotating outside of the central axis. This allows you to make parallel cuts along what will be the blade, to cut down to just above half way. Then unscrewing the block, and screwing it back the other way up. You can do the other side. Then remounting the main piece on it’s original centre, a skew is used to clean up around the base of the handle.
Apparently if you were doing a ‘production’ run of these you’d make up 4 and screw one to each side of the carrier block. And it would be mounted on its centre not off to one side.


This was pretty cool, and gave some nice ideas about what is possible.

I’m looking forward to having a go at the candle snuffer project, and I’ll try to find some time to put some pictures up to go with this post. I have some of the things others brought to show this month, so I may put some of those here.

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