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Frank&Earnest
21st Sep 2009, 08:05 PM
Did you pardon the pun (well, the alliteration)? The chucks do not have to be made in China, the point is that they are now relatively inexpensive and available everywhere, so they make almost obsolete other ways to mount a piece on a lathe. I always liked mounting, this is a good way of enjoying it in my old age. :D

The point about Australian timbers is that very many of them are tough enough to withstand without damage ( that is, no marks that a pass with 150 grit won't fix) the pressure required to mount them safely using the chuck, both in compression and expansion mode, which gives great versatility.

The scale most used here to measure timber hardness, the Janka test, measures in kilo Newtons the force required to push a steel ball (read a chuck jaw) into the timber. No need to enter into technicalities, suffices to say that the timbers prized for carving require less than 2 kN, gidgee and a few other arid climate timbers get close to 20 kN.

The first time I fully exploited this insight was when I had a short piece of gidgee and used the cavities of the two parts of a box (a salt shaker) instead of cutting spigots (pic1 and 2).

But then I found another thing: if the final diametre is smaller than the 110mm jaws, another trick is possible. The time honoured way of turning a box is to mount a cylinder between centres to cut a spigot at both ends, then to cut the cylinder in two pieces and chuck them by compressing the spigots (pic 3). If there is a way to mount them separately, then it is possible to start with two pieces.

Slabbed a small log and been left with a first and last slab that is virtually waste? Waste no more, a small round bottom handbag box is there. (pic 4)

It does not matter if the slab is not perfectly square, it only means that the circumference obtainable will be a bit smaller. For what we want to make a diameter of about 70mm is best anyway. The timber is plum, not very hard and not a native but quite adequate for this mount. The blank is about 25mm thick at the centre, where the spigot is cut. (pic 5)

The same is repeated with the second similar blank: this one is square and sits well inside the 110mm diameter of the jaws. (pic 6)

The spigots can now be grabbed by smaller jaws and a recess cut on the flat side. (pic 7 and 8)

This achieves the same result as starting from a cylinder and cutting spigots at both ends. The process for finishing the box is exactly the same.

At this point the spigot could also become the foot of a bowl, and, if the timber is a tough Aussie, the spigot/foot can be grabbed by the jaws without damage and the bowl finished. This one (diameter 95mm, thickness 3mm tapering to 1mm) is made of Western Myall, a mere 14 kN Janka. (pic 9 and 10)
Next post after dinner: mounting the wierd and wonderful.

artme
21st Sep 2009, 09:27 PM
Thanks for that F&E. A really interestng read.:2tsup::2tsup:

One thing I note with the standard jaws on my SN2 chuck is that they have a slight chamfer on the outside. Do you think this effects expansion grip?

Frank&Earnest
21st Sep 2009, 10:00 PM
Thanks for that F&E. A really interestng read.:2tsup::2tsup:

One thing I note with the standard jaws on my SN2 chuck is that they have a slight chamfer on the outside. Do you think this effects expansion grip?

Yes, but I found that if the rim is against the shoulder of the jaws the pressure on a thin circumference is enough for light work like this and not enough to mark the timber (as in the picture. Note the shape of the small jaws in the previous post). It is something to be aware of, though, I agree with you. Thanks for bringing this up.

Frank&Earnest
21st Sep 2009, 10:16 PM
Second instalment.

I love the stark contrast of the acacias and stocked up on Western Myall at the last Woodgroup SA get together (in case you are lurking, excellent function guys :2tsup:).
The small and gnarled logs do not yield much, though, and it took a bit of thinking to work out how to get anything decent out of this leftover. After the problems in the previous post (pic 1 and 3 are meant to be figure 1 and 2) I am not attempting to number the pictures. The only comment is that the lid piece is held with double sided tape and when it slipped due to the action of the tailstock point I took the point off, gently flattened an area in the centre, repositioned the piece and held it against the tailstock with a timber spacer taking the point.

Harry72
21st Sep 2009, 11:15 PM
Is that some of the broughton willow/sally wattle?

Ed Reiss
21st Sep 2009, 11:20 PM
Good post F&E....very informative. :2tsup:

Ozkaban
22nd Sep 2009, 09:31 AM
Interesting technique. Thanks for posting :2tsup:

Cheers,
Dave

wheelinround
22nd Sep 2009, 09:35 AM
all I can say FE is well done very nice

Frank&Earnest
22nd Sep 2009, 10:08 AM
Is that some of the broughton willow/sally wattle?

No Harry, your pieces were good to start with, thanks! :U

Here is a couple made with your A salicina.

The first is 167mm diametre and 42mm high, the second 135d 54h.

Harry72
26th Sep 2009, 06:21 PM
They look good Frank, nice work mate:)