On Cerro Alloys.
Here is a website
http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=384
McMaster Carr also has other Cerro Alloys.
http://www.midwayusa.com/MediaSvr.dll/TechNoteStream?saleitemid=462291
Material:
Proprietary Alloy (exact mixture unavailable)
Basic Instructions:
Plug the bore immediately ahead of the throat of the chamber using a small
cleaning patch.
Pour the alloy directly into the chamber until full and allow it to cool, it
will turn a shiny silver color. As soon as it has cooled enough that it is no
longer a liquid (and doesn't present a burn hazard), remove it from the
chamber. Take care not to overfill the chamber as the alloy will then run into
the locking lug area, making removal extremely difficult.
During the first 30 minutes of cooling cerrosafe shrinks. At the end of one
hour it should be "exactly" chamber size.
Notes
Melts between 158 and 190 degrees Fahrenheit
Should be melted in a clean iron ladle without direct flame on the product.
The chamber being cast should be cleaned thoroughly and a thin coat of oil or
graphite applied.
Reusable
Contraction - expansion factor versus time, measured in inches per square inch:
2 minutes -.0004"
6 minutes -.0007"
30 minutes -.0009"
1 hour +-.0000"
2 hours +.0016"
5 hours +.0018"
7 hours +.0019"
10 hours +.0019"
24 hours +.0022"
96 hours +.0025"
200 hours +.0025"
500 hours +.0025"
Dale
Dale Ertley <[EMAIL PROTECTED]> wrote:
Have you tried to use a Cerro Alloy to reproduce a screw from a nut? It is
a very low temp alloy ( about 200 F ) that has a near 0% shrinage after
solidification. I stay away from the alloys that contain Cadmium.
Dale
Gene Heskett <[EMAIL PROTECTED]> wrote:
On Friday 22 February 2008, Ian W. Wright wrote:
>Thanks, In a way I'm glad that I won't have to dabble in the realms of
>servos yet...
>
>Gene, I do usually have to measure the hole as it is most often the
>screw which is missing - or broken in the hole. I can usually get a
>pretty close measurement by screwing a wooden cocktail stick or skewer
>into the hole and measuring it as soon as it is unscrewed or by using
>Plastimorph (Jett Sett) - neither is exact as the wood usually expands a
>fraction when it comes free of the hole while the Plastimorph contracts
>slightly as it cools but I have always got 'good enough' measurements so
>far..
I'd expect the Plastimorph has a pretty well characterized shrinkage that
could be well compensated for on a % per inch basis though. That however is
a bulk shrinkage so don't forget to adjust the tpi as well as the diameter.
The wood would be the more WAG in the 'SWAG' of the two methods by quite a
bit but probably pretty accurate for tpi right out of the hole as its crush
is all radial, not axial.
One of the better definitions of good I ever heard came from an ex
brother-in-law, who was fond of saying that 'its good enough for the girls I
go with.' :-)
>I usually measure them with a travelling microscope over several
>threads.
Oohhhkayy. I had in mind some sort of a dial indicator with a v-tip ground on
its probe, using the dial to see when you were sitting in the bottom of the
groove, and an optical scale of some sort to read the intergroove spacing.
The microscope is obviously an even better tool.
>Oh, and you can add at least a hundred years onto the age of
>the screws - not 75 years but 150 - 250 years and some of the screws
>probably haven't been moved in all that time until their heads have
>corroded off... fortunately, most are blued steel screws in brass plates
>and so they will 'disappear' in an Alum solution after a few days.
Presumably with no damage to the brass? And whats a few days if its 200+
years old now. :)
I'm not a chemistry major except in the photographic darkroom, where I have
for many years concocted my own color print paper developer cuz the
commercial stuff is so hot it fades by the minute and you can't mix up a pint
because no two prints developed 20 minutes apart will be developed alike.
With my method, I can make 8 identically exposed 8x10's give me 8 identical
prints with that pint of mix and a few hours of rolling a uni-drum. But now
that things are going digital its easier, but I cannot say the quality is the
same as the optical is/was. Digital has a ways to go yet.
Sounds like an even better solution (pun intended) than using edm to remove
the remains, edm is not fussy what it takes with it if the electrode aim is
poor. I would certainly feel like I had violated some sort of a priceless
artifact of a lost art if I actually damaged the big stuff.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
The linuX Files -- The Source is Out There.
-- Sent in by Craig S. Bell, [EMAIL PROTECTED]
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