Pancake/RT dies, continued
Below I’ve copied and pasted three consecutive posts I made to the
Bonny Doon forum a couple of months ago regarding the tool steel used
to make blanking dies. They cover my opinions and some factual basis
to support those opinions, the facts provided by the manufacturers of
the steel, so from my perspective there’s no debating the fact that
some steel comes harder than other steel. The issues of exactly why
are not so mething I’ve researched, but I have a mountain of
firsthand experience working with the steel, that can offer insight
into the whole process.
One of the first things I did when I started sawing dies back in
1986 was to try to make it as easy as I could. The two obvious ways
were to a) only use steel that was thick enough for the specific job
(while also considering that I’m selling tools that I intend to last
a long time, so I actually use thicker steel than is absolutely
required), and b) use as big of a sawblade as I can get away with.
Two main factors determine what blad e size that is : first and most
important is the degree of sharpness of the turns in a given design,
and second is the fineness of detail, such as in a hand with
articulated fingers. With such a hand, a smaller blade may be
desirable because
a) it will take less steel away from the fingers and the spaces
between them (leaving more mass behind for strenth), and
b) the cutting angle will be less acute (which will also functionally
achieve what “a” does.
So, bigger, simpler designs can be sawed with bigger blades, and I
usually use size 1 for all but the biggest, toughest jobs. It becomes
physically more difficult to propel bigger blades, so size 1 may be
too hard for some to use. Size 2 is hard for me, and approaches the
oint of diminishing returns as far as effort put in to speed of
sawing resulting.
Earlier I said “easy”, and I should have included “faster” , because
that’s really why I use bigger blades. I only use size 4/0 on
designs with the most detail/sharp turns, and go up in blade size
accordingly for different degrees of complexity.
Recently a client asked for a small design, only an inch across, but
very detailed, that she said took her four hours to saw herself. I
understand people’s frustration, because I can imagine sawing such a
design with a 4/0 blade in a harder-than-average piece of steel.
Well, it’s routine for me, and even though it is no picnic, I
actually can’t imagine taking that long sawing any die, so I do
sympathize. I did have to saw this die for her, but I used size 2/0
because all the critical turns were rounded, and it saved a lot of
time. Really, just the difference between 4/0 and 2/0 is very
significant, as is the jump from 2/0 to size 1.
Another thing I did recently, to try and deal with what seems to be
a trend of even more harder-than-average steel (maybe I’m just
getting older, but I am also stronger than when I started dies, so I
doubt that I’m the ‘problem’, yet), is to find the best possible
blades. The brand (Swisss) that I’d been mostly using for almost 20
years just wasn’t working as well as I was used to (was it the
blades or the steel ?.. see below for part of the answer) so I tried
some Scies and some Pikes (also Swiss) again. Only marginally better,
but there was a significant improvement when I got a hold of some
Pike Platinum blades. They made sawing the hard-hard steel tolerable
and went through the softer steel like… well, certainly not like
butter, but like softer steel, which can be a lot. By feel and
experience, I’d say that some steel is up to twice as hard to saw as
other steel, even though they may only be a few points apart on the
scale (see below).
posts to the BD forum, in sequence:
"I always knew it wasn't my imagination, and it wasn't just the
sawblades. It's right there in the stated variance range
provided by the manufacturers. Brief research this weekend turned
up numbers of Brinell 179-212 as the range from Sheffield, and a
max of 229 from one American company. I'm going to try and get
info from Starret and Precision Marshall this week. But let's
look at the Sheffield numbers, which corresponds to about RC
16-19. Four points on the Rockwell C scale, call it three,
conservatively. Looking at the tempering chart for Starrett
--just as a way of correlating the numbers to some sort of
meaningful,real-life situation -- 3 points corresponds to about
200 degrees F difference in temper. Three points is still the
real phenomenon, the real difference in hardness, the 200 deg is
just my way of giving it functional meaning. So what does 200 deg
difference in tempering make ?. In a nutshell, 'ALL' the
difference. Temper a die to 500 F and it will not respond to
peening blows for realignment, but at 700 F it will. 550F and the
steel will barely start to take marks and move a little bit, but
at 750 F it readily moves, and takes significant marks. 600F and
it becomes a bit more responsive, and 200F more, at 800F, the
steel seems downright soft under the ball peen.
So, 3 points is, to me, a significant difference, and even if
the raw steel only has 1/2 of this variance, it is still going
to be noticeable, all other factors being equal. I have no doubt
that the makers of the tool steel adhere to their stated
standards strictly. My point is that, within that stated range,
I can tell the difference when sawing dies with a jewelers saw,
between "harder" and "softer" plates. Case closed. I've sawed a
few miles in that material over about 20 years, so I know what
I'm talking about. "
"I got the Starrett numbers today, which are Rockwell B 88-95,
or Brinnell 175-212, which translates to (depending where I look)
to Rockwell C 7-15 or 9-19, even more of a range on that scale
than I had estimated. I can't say that I can consistently tell
the difference when I'm cutting the large pieces up into die
plates on the bandsaw, but with a jewelers saw in hand, it's a
whole other story. Yes, there can be a lot of variation in
sawblades, between brands, and grosses, dozens, and single
blades of the same brand, but it's generally less, because
manufacturers ARE aiming for a specific hardness. What has never
been a question (not really) is that there is some difference in
saw-ability between batches of steel, and I have heard from a
person, who heard from a person who is a metallurgist that there
can even be variation in areas of one plate. That isn't
something I can say I've noticed for sure, but I have seen some
funky steel. Every once in a while I'll get one where, when I
harden the dies, they won't stay flat no matter how I do it, and
all it usually takes for 'normal' steel is to quench vertically.
The worst piece of steel I've seen was so defective that I could
break of corners with a pair of pliers and see an abnormally
large grain structure.
The normal difference in saw-ability I've encountered has made
life frustrating now and then, but this looking at the numbers
is something of a relief, and I've found that buying the most
expensive blades helps a little. So, again, the steel is
consistent within it's stated range of specs, except for a rare,
rogue plate, like the 'crumbly' one I got 20 years ago, but not
so perfectly consistent that an experienced hand, with a
delicate feel, and a precision tool (small sawblade) can't
notice variations.Truthfully, I doubt that it takes experience
to tell the diffference, just one bunch of blades and two pieces
of steel that are of different hardness. "
"I just talked to Precision Marshall, and the guy there said that
when the steel is annealed in large batches, they are simply
following a prescribed cycle, not aiming for a specific pinpoint
end-hardness that the entire batch must adhere to. Obviously,
this leaves the door open for slight variations in the condition
of the end product. All they want is to provide the steel in an
annealed, machinable state, and they do that. The guy also agreed
that the range of composition specs (tiny differences in the %'s
of other metals alloyed in ) might also affect resulting
hardness."
Dar Shelton