DIYbanter - to cast or to machine from the solid?

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to cast or to machine from the solid?

Hi,
Back in December I inquired about making a ball vise. I have been
practicing some simpler machining since, and now would like to begin.

I never did have any luck finding 7-10" diameter steel balls or even
solid rod at scrap yards.

I can buy 6" rod stock from the campus machine shop for ~$60, or
$1.10/lb I believe it was (although my calculator is predicting that it
should be $48, so it might have been more...), and machine it into one
hemisphere and one clipped-off cone shape. The hemisphere is doable; I
have access to a CNC lathe. Off campus, inquiring about 8" diameter
rod stock, they wanted $1.75/lb!

Alternatively, I can cast. I asked a local club, and they'll help
me cast it for $1.20/lb if I provide the steel. I can find random
scrap steel for $.10/lb. This at first had great appeal when I learned
of the low cost of scrap steel, but it makes me recoil some to think
that I'll end up paying more per pound because of casting costs! AND,
coming out of the cupola, it will be cast iron, which while quite
functional, is inferior to steel for this application.
The two benefits of this would be that a sphere is 2/3 the volume of
the smallest cylinder that will contain that sphere, so even though
it's $1.30/lb and not $1.10/lb, it costs $.23/lb less to cast in a
sphere than to purchase a solid cylinder and machine off 1/3 of its
weight in making it a sphere. Also, while I still want to program the
lathe to machine a sphere, it will have to machine off far less
material, saving not an insignificant amount of work.

What do you advise? Cast an iron sphere, or machine from a solid
steel cylinder, assuming the former to cost 23cents/lb less? I want a
100-lb vise (trust that I do intend to make a 4.5" vise from all scrap
first, before investing in this), so this is expensive for me :-(
Is it possible that, if I shop around, I may be able to have it cast
for less than the $1.20/lb quoted me, or is that a bargain...?

thanks!
-Bernard
Arnest

to cast or to machine from the solid?

Oh, another factor-- this foundry is 1.5 hrs out of the way, a
disincentive to save the $.23/lb in casting it. But if larger rod
stock is more like $1.75/lb, and it seemed to be if I can't find it as
scrap, casting in fact saves $.58/lb compared to that. And there is
the coolness factor, since as this is a college club, I will be able to
participate in the process :-) I hate intangibles, they make
rational decisions more ambiguous....

I have no idea if their $1.00/lb fee (I said 1.20, because I'm
supplying the 100 lbs of fire clay for the mold, so all together this
is costing me $1.30/lb after I buy the clay and the scrap steel) just
covers their costs in fuel and sand, as they are a college club and not
a commercial foundry, or if they are making much of a profit at that
fee.

to cast or to machine from the solid?

Geeez...a bean counter. Look, if you want ot make the thing, do it in a
way that excersizes your abilities and produces the result you want. The
nicklels and dimes approach will spoil the project.
JR
Dweller in the cellar

Bernard Arnest wrote:
Hi,
Back in December I inquired about making a ball vise. I have been
practicing some simpler machining since, and now would like to begin.

I never did have any luck finding 7-10" diameter steel balls or even
solid rod at scrap yards.

I can buy 6" rod stock from the campus machine shop for ~$60, or
$1.10/lb I believe it was (although my calculator is predicting that it
should be $48, so it might have been more...), and machine it into one
hemisphere and one clipped-off cone shape. The hemisphere is doable; I
have access to a CNC lathe. Off campus, inquiring about 8" diameter
rod stock, they wanted $1.75/lb!

Alternatively, I can cast. I asked a local club, and they'll help
me cast it for $1.20/lb if I provide the steel. I can find random
scrap steel for $.10/lb. This at first had great appeal when I learned
of the low cost of scrap steel, but it makes me recoil some to think
that I'll end up paying more per pound because of casting costs! AND,
coming out of the cupola, it will be cast iron, which while quite
functional, is inferior to steel for this application.
The two benefits of this would be that a sphere is 2/3 the volume of
the smallest cylinder that will contain that sphere, so even though
it's $1.30/lb and not $1.10/lb, it costs $.23/lb less to cast in a
sphere than to purchase a solid cylinder and machine off 1/3 of its
weight in making it a sphere. Also, while I still want to program the
lathe to machine a sphere, it will have to machine off far less
material, saving not an insignificant amount of work.

What do you advise? Cast an iron sphere, or machine from a solid
steel cylinder, assuming the former to cost 23cents/lb less? I want a
100-lb vise (trust that I do intend to make a 4.5" vise from all scrap
first, before investing in this), so this is expensive for me :-(
Is it possible that, if I shop around, I may be able to have it cast
for less than the $1.20/lb quoted me, or is that a bargain...?

thanks!
-Bernard
Arnest

--
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If you're not the lead dog, the view never changes
Doubt yourself, and the real world will eat you alive
The world doesn't revolve around you, it revolves around me
No skeletons in the closet; just decomposing corpses
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to cast or to machine from the solid?

"Bernard Arnest" wrote in message
ups.com...
Hi,
Back in December I inquired about making a ball vise. I have been
practicing some simpler machining since, and now would like to begin.

I never did have any luck finding 7-10" diameter steel balls or even
solid rod at scrap yards.

I can buy 6" rod stock from the campus machine shop for ~$60, or
$1.10/lb I believe it was (although my calculator is predicting that it
should be $48, so it might have been more...), and machine it into one
hemisphere and one clipped-off cone shape. The hemisphere is doable; I
have access to a CNC lathe. Off campus, inquiring about 8" diameter
rod stock, they wanted $1.75/lb!

Alternatively, I can cast. I asked a local club, and they'll help
me cast it for $1.20/lb if I provide the steel. I can find random
scrap steel for $.10/lb. This at first had great appeal when I learned
of the low cost of scrap steel, but it makes me recoil some to think
that I'll end up paying more per pound because of casting costs! AND,
coming out of the cupola, it will be cast iron, which while quite
functional, is inferior to steel for this application.
The two benefits of this would be that a sphere is 2/3 the volume of
the smallest cylinder that will contain that sphere, so even though
it's $1.30/lb and not $1.10/lb, it costs $.23/lb less to cast in a
sphere than to purchase a solid cylinder and machine off 1/3 of its
weight in making it a sphere. Also, while I still want to program the
lathe to machine a sphere, it will have to machine off far less
material, saving not an insignificant amount of work.

What do you advise? Cast an iron sphere, or machine from a solid
steel cylinder, assuming the former to cost 23cents/lb less? I want a
100-lb vise (trust that I do intend to make a 4.5" vise from all scrap
first, before investing in this), so this is expensive for me :-(
Is it possible that, if I shop around, I may be able to have it cast
for less than the $1.20/lb quoted me, or is that a bargain...?

If you have hollow spots in the casting which is almost guaranteed on this
project. What have you saved if you need it cast several times. I would go
with solid stock, since you already know the quality if the material before
you start.

to cast or to machine from the solid?

I can buy 6" rod stock from the campus machine shop for ~$60, or
$1.10/lb I believe it was (although my calculator is predicting that it
should be $48, so it might have been more...), and machine it into one
hemisphere and one clipped-off cone shape. The hemisphere is doable; I
have access to a CNC lathe. Off campus, inquiring about 8" diameter
rod stock, they wanted $1.75/lb!

Hey Bernard, it's Zack. What CNC late do you have access to that I
don't know of? The one in the MIT Hobby Shop can't swing something that
big, so unless you have something off campus or can get it done at
Central Machine that doesn't look like much of an option. I'm not sure
of the size of the manual lathes in Edgerton shop but you might be able
to turn it with a set of outside jaws. There are a few options for
turning the sphere on a manual lathe, none of them very appealing, but
it can be done.

to cast or to machine from the solid?