Re: [CAD_CAM_EDM_DRO] CNC lathe retrofit and phase converter

Hi,

I'll just add a little to this thread. The only way to cut sharp file teeth
is with a chisel as Bill says and this is still done but by automatic
machines which usually use carbide chisels and hammers which are sprung
towards the work but repeatedly pulled away and released by snail cams. It
is essential that the work has a film of oil on its surface and some studies
have suggested that it is this oil which actually raises the tooth by
hydraulic forming. If you want to do it by hand it is perfectly possible and
I have made many files this way using antique tools (it was a common trade
in this area and so I learned from some of the last hand cutters still
working). The technique is to hold the blank firmly down - this can be by
clamping it in a vise but was originally by holding it down onto a lead
block fixed onto a stone 'anvil' using a leather strap which was fixed to
the stone at one end and had a 'stirrup' into which you put your foot at the
other end. The chisel is just a piece of tool steel wider than the workpiece
and was usually triangular in shape with one edge sharpened from both sides
to about a 30 degree included angle. This chisel is placed on the work at an
angle across it and at what will become the front end of the file and is
angled away from the worker at about 45 degrees. It is given one hard blow
with a hammer (the originals had their heads angled towards the worker so it
was easier to hit the chisel cleanly) and the chisel is then withdrawn from
the cut so made and placed back on the work closer to the worker. It is now
slid along the work until it rests against the back of the first tooth and
is struck again. This is repeated until the whole length of the file is cut.
It is usual for a second set of teeth to be cut on the 'opposite' angle (a
double-cut file) in exactly the same way. If anyone is really interested I
can post some pictures of the original tools I have on my website although
it may take a day or two to get it organised.
For small files like 'needle' files there is also a technique called
'etching' which has nothing at all to do with acids and resists. In this
method a triangular bar of tool steel is file cut on the corners with a
special type of teeth. In use, the corner of the bar is rubbed across the
workpiece so that these teeth effectively cut grooves which become the
teeth. Files made this way are not as sharp as chisel cut ones but are far
more controllable on small work. The needle files made by Stubbs, Vallorbe,
Spear and Jackson etc. using this technique are far superior to the modern
chisel-cut needle files from India and China.
Whenever you buy a new file it is a good idea to stone the safe edge smooth
before you use it as the ragged ends of the cut teeth can otherwise tear
your good work to pieces.

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk

----- Original Message -----
From: "Smoke" <smoke@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: 09 January 2002 15:46
Subject: Re: [CAD_CAM_EDM_DRO] CNC lathe retrofit and phase converter


> I'm really surprised to see this info here! It was told to us by the
> instructor (now retired) at the college. We had to make a lot of tools
but
> fortunately making a file wasn't one of them!
>
> Smoke
>
> > >Question #3: (OT)
> > >How are file teeth formed?
> >
> > With a hot chisel and a hammer, allways remembering to chill the chisel
> > frequently by dunking it in a bucket of water, so it won't lose it's
> hardness.
> > When you have enough teeth, let the file blank cool. Press refractory