On Nov 3, 8:28*am, Matty F wrote:
Since I don't have a wood lathe, I propose making a tool about two
inches wide that is curved to the shape of the knob and just wind it
straight in.
That's a form tool. Effectively a shaped scraper, sharpened as a
scraper edge (80 degrees or so - a right angle with no rake and a bit
of front relief). Works OK (not well), but only in mahogany (or
similar) and you need to use a form tool lathe to work it. Absolutely
_massive_ things. The forces involved in shoving such a form tool into
the timber need a thick slab of HSS to make the tool from (otherwise
it chatters) and you need a guide slot on the lathe, not just a tool
rest. It's HSS because you don't want to have to re-sharpen it
frequently, but it's thicker than power hacksaw blade. You can grind
these out of other lathe tools (a cheap source of HSS bar with a
handle on it) or go traditional and rework old files. NB - files need
to be softened before use, their teeth taken off (angle grinder!) and
their tangs checked for robustness. Use a lathe tool handle (bigger,
stronger), as file handles on lathe chisels have been known to break.
The re-hardening and tempering is in any school metalwork textboook of
the 1950s - I assume we've all got such a useful thing.
I use form tool scrapers a fair bit, but none more than 1/2" wide and
I don't have a lathe solid enough to be useful with one more than 1/4"
wide. They're a good way to make beads (semi-circular raised ridges)
where you want repeatable consistency between many, without being a
virtuoso of the skew chisel. They'll also make pairs of adjacent
beads, something that's hard with a skew.
Form tools were never used like this for your handles. They don't like
squared or newly split timber and the forces were too big. Production
work like this was instead done on a back-knife lathe. These were (and
still are) very widely used for staircase spindles etc. They use a
chisel-edged knife, not a scraper.
http://commons.wikimedia.org/wiki/Fi...k-knife_lathe_
%28Carpentry_and_Joinery,_1925%29.jpg
What I would suggest is that you build yourself a wood lathe
conversion. Read some stuff on wood turning and see what the tools
ought to look like, then emulate. Find a medium sized metalworking
lathe - Colchester Student or similar, but an ML7 just doesn't have
the space. Kit it out with a woodworking drive centre in the
headstock (buy a drive centre, or re-grind a spade bit). Put a dead
centre in the tailstock, or a live centre if you want less of a divot
left behind (dead is easier on wayward chisels). Build yourself a
woodturner's slide rest - Either fit a real one with lashed up clamps,
weld one up from heavy steel angle, or just clamp a hefty bar in the
four-way toolpost, if that's the best you can do. Really you want
something that's supported from beneath, not in the way at the sides
(why the toolpost cantilever doesn't work well) and is also height
adjustable. Cutting angle in woodturning is controlled by the chisel
position, not the tool grind, so it's crucial to adjust this by
adjusting the toolrest height. If you can't do that, you might even
want to stand on a box to adjust yourself to the right height! It's
that important.
You need some chisels (4 minimum). Basic set is a Big U Gouge, used
for turning random split billets into well-behaved, balanced
cylinders. Then a small gouge, with a fingernail grind (you have to
put this onto cheap sets yourself, but it's worth it as it's so much
easier to use). Then a skew chisel that's either oval or with well-
rounded corners. Also a scraper. You'll use the gouge to make things
about the right size (nothing else works), then probably use the
scraper to make the shape you want, because it's easier than the
gouge. Don't even pick the skew up until you've read something like
Keith Rowley's "Woodturning foundation course" book, or at least a
website that explains about "rubbing the bevel" and "lifting the
chisel to cut".
Best starter chisel set around is Axminster's
http://www.axminster.co.uk/axminster...set-prod822073
Add a square ended scraper to it as well, and maybe another big gouge
if you're doing bowls. Then re-sharpen two of the gouges with
fingernails and keep one big one for bowls.
Then ignore the beast, and go find a woodworker with a proper lathe.
Get them to teach you how to do it right, under optimum conditions. If
you're now slightly skilled in the way of doing it right, then you'll
be able to cope in extremis far better. You might even just borrow
their lathe for a while, or get them to turn it for you. Woodturners
_love_ an excuse to turn wood, especially if it's not just more
fecking bowls to clutter the house up with.
I'd also consider just getting a wood lathe. They're cheap - a decent
cheapie is less than the price of the full set of chisels and gubbenry
to go with it. If you have the space and the recurrent need, then it
might be a sensible approach. There's not much woodturning in a tram
or steam train, but there's an awful lot in station fittings of that
period.