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

[Jerry Frost]

Dishing the blade does as Mike describes, it stiffens the blade so it 
doesn't warble in use. Warble is the term a sawmill guy used, it's a 
combination of wobble and describes the sound it makes just before the stuff 
hits the fan. A neighbor on my Uncle Fred was a millwright who specialized 
in saws and his explanation is pretty much the same.

My personal experience with the effect is from Father's metal spinning shop. 
It was often necessary to put a little backward (toward the sailstock) dish 
in the blank's edge before spinning proper. We used a lubricated stick with 
a slit cut and later worn in the end, slipped it over the edge of the 
spinning blank and using a little english bent a little bit like a pizza pan 
rim. Without the rim bend the blank would go nuts when you tried moving it 
with a spinning tool and that's a BAD thing. The bend put structure to the 
blank so it had to go through a compound bend to warble. Yeah, it warbled at 
the start of the failure, if you're fast enough you can control it or back 
off and not lose the part. You can't just release the tool pressure either 
or really bad things happened.

Anyhow, the old millwright was surprised I knew what he was talking about 
till Uncle Fred told him I used to be a metal spinner. some couple years 
later I got word from Uncle Fred he'd passed away but left word that if I 
wanted the blacksmithing tools he'd collected I could have them at a 
discount. I have a number in my shop now but not the sawyers anvil, hammers 
or the little bitty benchtop power hammer in his garage shop. <sigh>

Sorry about the long winded story, the question brought back a bunch of 
memories. Thanks Larry.

Jer
----- Original Message ----- 
From: "Mike Spencer" <mspencer at tallships.ca>
To: <theforge at mailman.qth.net>
Sent: Sunday, August 28, 2011 2:49 AM
Subject: [TheForge] Hammering blades (Was: Spring steel...)


>
> 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.
>