Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old June 17th 15, 02:25 AM posted to rec.crafts.metalworking
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Default Materials for making a mold

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that I
could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Old June 17th 15, 03:20 AM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Tue, 16 Jun 2015 19:25:47 -0500, Tim Wescott
wrote:

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that I
could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?

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Old June 17th 15, 03:41 AM posted to rec.crafts.metalworking
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Posts: 12,540
Default Materials for making a mold

On Tue, 16 Jun 2015 19:25:47 -0500, Tim Wescott
wrote:

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that I
could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?


There is a polymer-modified, machinable gypsum that is made for CNC
test-cutting, which has been used for molds. Compared to aluminum,
it's dirt cheap. And there is another one, which I haven't seen for 10
years and the name of which I forget, that is made for casting
highly-finished molds for fiberglass molding. Maybe someone else here
knows brand names.

I'm sorry I can remember the product names. One thing to watch for
with polymer-modified gypsum cements: they don't dry very well. The
trick to using them to make a polished mold is to wipe them with
acetone and then to spray them quickly with lacquer before water
migrates back to the surface. They can take months to dry completely
but you can use them the next day with the acetone trick.

With the kinds of work you do, you should have the Freeman catalog:

https://www.freemansupply.com/catalo...manCatalog.pdf

I love plaster because I'm a real cheapskate. g And I like
styrofoam. I have made models from ordinary pink styrofoam insulation
board, glued together with a thin coat of white glue; painted it with
three coats of house paint; and then sanded them, buttered them with
bondo (screeding it on is tricky), sanded it, coated it with one-part
polyurethane paint, waxed the hell out of it, shot it with PVA, and
then pulled a fiberglass part off of it.

If you're a little less cheap than me, use high-density polyurethane
foam. It takes less finishing and you don't need the housepaint.
Polyester won't dissolve it. You probably won't need the bondo,
either. Just spray on some external gel coat, which you probably know
well.

In fact, you probably know all of these processes well. So why are you
asking us? g

BTW, the machinable plaster is pretty shiny after it's machined. Did I
mention that it's cheap? Just like me...

--
Ed Huntress
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Old June 17th 15, 03:46 AM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Tue, 16 Jun 2015 19:25:47 -0500, Tim Wescott
wrote:

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that I
could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?


That's almost twice what I'd expect the shop to pay for that piece.

If you're cutting a large cavity in one side of a piece of 6061 plate
it's not going to stay flat. Cast tooling plate (e.g. Alcoa MIC6) is
stable, but is relatively gummy, so will be more difficult to machine
and finish to a polish. Also more expensive.

--
Ned Simmons
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Old June 17th 15, 04:02 AM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Tue, 16 Jun 2015 19:25:47 -0500, Tim Wescott
wrote:

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that I
could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?


Eh, I forgot about Rayite MDM:

www.chavant.com/new_site/files/pdf/rayite.pdf

I don't think you can machine it, but it makes really good molds, with
extremely high accuracy. It may not be for this project but it's
something to remember for inexpensive fiberlass molding.

--
Ed Huntress


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Old June 17th 15, 06:27 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Tue, 16 Jun 2015 21:41:25 -0400, Ed Huntress wrote:

On Tue, 16 Jun 2015 19:25:47 -0500, Tim Wescott
wrote:

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that
I could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?


There is a polymer-modified, machinable gypsum that is made for CNC
test-cutting, which has been used for molds. Compared to aluminum, it's
dirt cheap. And there is another one, which I haven't seen for 10 years
and the name of which I forget, that is made for casting highly-finished
molds for fiberglass molding. Maybe someone else here knows brand names.

I'm sorry I can remember the product names. One thing to watch for with
polymer-modified gypsum cements: they don't dry very well. The trick to
using them to make a polished mold is to wipe them with acetone and then
to spray them quickly with lacquer before water migrates back to the
surface. They can take months to dry completely but you can use them the
next day with the acetone trick.

With the kinds of work you do, you should have the Freeman catalog:

https://www.freemansupply.com/catalo...manCatalog.pdf

I love plaster because I'm a real cheapskate. g And I like styrofoam.
I have made models from ordinary pink styrofoam insulation board, glued
together with a thin coat of white glue; painted it with three coats of
house paint; and then sanded them, buttered them with bondo (screeding
it on is tricky), sanded it, coated it with one-part polyurethane paint,
waxed the hell out of it, shot it with PVA, and then pulled a fiberglass
part off of it.

If you're a little less cheap than me, use high-density polyurethane
foam. It takes less finishing and you don't need the housepaint.
Polyester won't dissolve it. You probably won't need the bondo, either.
Just spray on some external gel coat, which you probably know well.

In fact, you probably know all of these processes well. So why are you
asking us? g

BTW, the machinable plaster is pretty shiny after it's machined. Did I
mention that it's cheap? Just like me...


I know one process for making molds. It starts with a high-quality plug
(which is often an original Ford body part that's been modified for the
purpose) and makes a fiberglass mold around it.

I'm working on a project with my brother that starts with a 3D model and
ends up with a part. Rather than having him make a high-quality plug,
then a mold, I'm thinking that it would be nice to send a 3D model to a
machine shop and get back a hunk of aluminum or whatever, polish the snot
out of it, and make parts.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Old June 17th 15, 06:30 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Tue, 16 Jun 2015 21:46:30 -0400, Ned Simmons wrote:

On Tue, 16 Jun 2015 19:25:47 -0500, Tim Wescott
wrote:

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that
I could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?


That's almost twice what I'd expect the shop to pay for that piece.

If you're cutting a large cavity in one side of a piece of 6061 plate
it's not going to stay flat. Cast tooling plate (e.g. Alcoa MIC6) is
stable, but is relatively gummy, so will be more difficult to machine
and finish to a polish. Also more expensive.


I knew about the issue with 6061 -- that's part of the reason that I'm
asking questions here!

I wonder if one could just pour a couple of gallons of epoxy casting
resin into a box, then send that off to the machine shop -- if you can do
it without bubbles you certainly have something that you can polish to a
high shine.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Old June 17th 15, 07:34 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

"Tim Wescott" wrote in message
...
I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that I
could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com



Depending on desired finish quality and tolerances you could machine a
fiberglass mold out of any of a number of things, coat it with something to
seal it and use a good mold release. I imagine you could make it out of
wood if it was stable enough (which in general it is not - although there
are tricks).

There are guys who mold hot plastisol (350F) in plaster of paris molds
sealed with Elmers glue, and I have seen guys mold molten lead for a few
pours before it burns out in Bondo.

Silicone mold material is used for plastisol and lead casting all the time,
although you do need a master to pour a silicone mold from. I am sure if it
was left in a rigid form box to prevent distortion it would work fine for
your fiberglass part. All kinds of things are done quick and dirty with
silicone molds, and you might not even need a mold release. (you probably
want one on your master)

If you are just vacuum bagging then any materials that will managed the
temperature of your catalyst reaction will do. If you are going to
autoclave your parts then it needs to stand the temps in your autoclave.

The price for the piece of aluminum sounds a little high, but then price has
usually stopped me from buy from Speedy Metals or On Line Metals in the
past. I have gotten better prices on large orders from on-line metals by
having them submit a quote, but for me freight is usually a killer. I found
a local metal vendor finally for the the aluminum I use to make molds.

The real questions a How many of these fiberglass boxes do you need to
make? Would a hand made mold do? (wood frame, plywood box, hand filleted
inside corners. Maybe glassed sanded and gelcoated?) Do you have a machine
shop in mind that can make a 48" mold in a reasonable amount of time? Will
they do it for a reasonable price? Will they do it in one setup or multiple
setups? If multiple setups how accurately can they align one setup with the
next? Does it matter?

Something to note: A piece of aluminum that big might hold your mold
cavity, but I've found if you have large areas of thin web from large
cavities or multiple cavities to close together the total work piece can
start to distort from clamping force. It can be tricky to hold the piece
and hold tolerance. I personally don't do anything over about 18-20 inches.
If the piece is longer than the table it can sag causing some distortion.

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Old June 17th 15, 07:40 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

"Tim Wescott" wrote in message
...
On Tue, 16 Jun 2015 21:46:30 -0400, Ned Simmons wrote:

On Tue, 16 Jun 2015 19:25:47 -0500, Tim Wescott
wrote:

I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that
I could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?


That's almost twice what I'd expect the shop to pay for that piece.

If you're cutting a large cavity in one side of a piece of 6061 plate
it's not going to stay flat. Cast tooling plate (e.g. Alcoa MIC6) is
stable, but is relatively gummy, so will be more difficult to machine
and finish to a polish. Also more expensive.


I knew about the issue with 6061 -- that's part of the reason that I'm
asking questions here!

I wonder if one could just pour a couple of gallons of epoxy casting
resin into a box, then send that off to the machine shop -- if you can do
it without bubbles you certainly have something that you can polish to a
high shine.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com



One trick for pouring resins with few bubbles is to pour a long thin stream
from a long distance above the forms. However I am not sure if epoxy would
work well for what you are doing. I've found epoxy pours thicker than about
1/2" tend to scorch from their own reaction heat. Even 1/2" is pushing it.
I've had the small amount left in a mixing cup scorch once or twice if it
was still fairly thick. I've read that you can get past the issue with
epoxy by making multiple pours, but I seem to recall that you either need to
have your timing just right, or you need to let it fully cure and then prep
the surface before making the next pour. Sounds like a long tedious
process. There are other casting resins that might work better for thick
pours, but I really don't have any first hand experience with them.





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Old June 17th 15, 07:44 PM posted to rec.crafts.metalworking
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Default Materials for making a mold


"Bob La Londe" wrote in message
...
"Tim Wescott" wrote in message
...
I'm working on a project that may well end up having a case made of
fiberglass. As I'm working on a 3D model that will use mostly to make
pretty PDFs for my fiberglass guy and my customer, It occurs to me that I
could just make a 3D model of a mold and send it to a machine shop.

A 1.25 x 12 x 48 inch piece of 6061 costs $430 from Online Metals. Is
that pretty much what I would expect to pay for materials from a machine
shop? Is there any material that's significantly cheaper, that can be
tossed into a CNC mill and made into something mold like, and then hand-
polished to a high shine?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com



Depending on desired finish quality and tolerances you could machine a
fiberglass mold out of any of a number of things, coat it with something
to seal it and use a good mold release. I imagine you could make it out
of wood if it was stable enough (which in general it is not - although
there are tricks).

There are guys who mold hot plastisol (350F) in plaster of paris molds
sealed with Elmers glue, and I have seen guys mold molten lead for a few
pours before it burns out in Bondo.

Silicone mold material is used for plastisol and lead casting all the
time, although you do need a master to pour a silicone mold from. I am
sure if it was left in a rigid form box to prevent distortion it would
work fine for your fiberglass part. All kinds of things are done quick
and dirty with silicone molds, and you might not even need a mold release.
(you probably want one on your master)

If you are just vacuum bagging then any materials that will managed the
temperature of your catalyst reaction will do. If you are going to
autoclave your parts then it needs to stand the temps in your autoclave.

The price for the piece of aluminum sounds a little high, but then price
has usually stopped me from buy from Speedy Metals or On Line Metals in
the past. I have gotten better prices on large orders from on-line metals
by having them submit a quote, but for me freight is usually a killer. I
found a local metal vendor finally for the the aluminum I use to make
molds.

The real questions a How many of these fiberglass boxes do you need to
make? Would a hand made mold do? (wood frame, plywood box, hand filleted
inside corners. Maybe glassed sanded and gelcoated?) Do you have a
machine shop in mind that can make a 48" mold in a reasonable amount of
time? Will they do it for a reasonable price? Will they do it in one
setup or multiple setups? If multiple setups how accurately can they
align one setup with the next? Does it matter?

Something to note: A piece of aluminum that big might hold your mold
cavity, but I've found if you have large areas of thin web from large
cavities or multiple cavities to close together the total work piece can
start to distort from clamping force. It can be tricky to hold the piece
and hold tolerance. I personally don't do anything over about 18-20
inches. If the piece is longer than the table it can sag causing some
distortion.


If you go an with aluminum mold clamping/bolting it to a heavy backing plate
can help it retain its correct shape.




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