[TheForge] Hammering blades (Was: Spring steel...)

[Mike Spencer]

Larry Ruebush wrote:

> At old farm show I have seen large saw mill blades hammered. I never
> have really understood what the man was doing, but he runs his hand
> over the blade, makes some chauk marks and then starts hammering. He
> uses special looking hammers.
>
> I am guessing that this is to staighten the blade and maybe put a
> dish in it, but a dish doesn't make sense.

I've been told by Old Timer [1] sawyers that this hammering dishes
the rotary mill saw blade.  The skilled guy knows from experience just
how much to dish it and where to kit it to get the effect
uniform. When the blade gets up to speed, centrifugal force [2]
flattens it out or very nearly does so.  If the blade were perfectly flat,
it would tend to ripple and oscillate out of the plane and cause
problems such as binding or fatiguing.

I've never had that confirmed by a mechanical engineer who knew about
sawmills. 

"Bob Ehrenberger" <eforge at centurytel.net> wrote:

> After hammering the [scythe blade] edge was he done, or did he still
> have to work it over with a stone?

I think he was done except possibly (he didn't say explicitly) for
very light dressing with a hand stone.

Another demonstrator who was teaching novices to mow said that the
whetstone carried by mowers and used to dress the blade was solely for
putting a fine tooth on the edge.  To that end, he said, you use the
corner of the stone and dress lightly.

However: I have two old stones -- fine-grained natural stone -- that
clearly show years of wear on the flats.  I saw another like them on a
workbench while I was at the do. So I'm guessing that the the second
demonstrator was, at least to some degree, misinformed , possibly
by an Old Timer. [3]

I read somewhere, long ago, about sharpening knives (and maybe
swords?) with a hammer. Never understood that. Now I see some sense to
it but only for thin blades,  not for blades expected to hit, say,
plate armor or a steel-bossed shield.


Oh yeah, another little item:  I've had for years a stake tool that I
think is forshaping up the rib on th eback edge of a hand forged
scythe blade.  Only one I've ever seen.


FWIW,
- Mike


[1] That is, people who, in the late 60s, were the age I am now.

[2] Please don't lets have a bunfight along the lines of, "There's no
    such thing as centrifugal force; there's only centrepital force" or
    the like.  You know what I'm talking about, eh?

[3] Not everything one learns from an authentic Old Timer is true.
    Guys get old automatically but not all of us acquire god-like
    wisdom in the process. :-)

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^