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, 06:48 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 21:41:25 -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
================================================== ===========================

I've never done it, but seems to me you could glue together sheets of the
thickest MDF you can buy to get up to say double the height of your piece,
find someone with a cnc router to cut the mold cavity, sand it, then paint
with epoxy resin. Now you have the same surface you would if you were
pulling a mold off of a body part, so sand and polish like you do those. If
12x48" is big enough, buy a 4x8' sheet and cut that into up to 8 strips to
glue together to get plenty of thickness so it won't warp. I think you said
that this is for the carrying case. If so, you could even put in a line or
divot pattern and logo with the router and not sand at all, to get a nice
surface texture that would hide future dings and scratches. Have to keep
the sealing coat very thin and uniform. Anyway, just a suggestion from up
here in the cheap seats :-).

-----
Regards,
Carl Ijames



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Old June 17th 15, 07:06 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

"Carl Ijames" wrote in message
...
"Tim Wescott" wrote in message
...

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
================================================== ===========================

I've never done it, but seems to me you could glue together sheets of the
thickest MDF you can buy to get up to say double the height of your piece,
find someone with a cnc router to cut the mold cavity, sand it, then paint
with epoxy resin. Now you have the same surface you would if you were
pulling a mold off of a body part, so sand and polish like you do those.
If 12x48" is big enough, buy a 4x8' sheet and cut that into up to 8 strips
to glue together to get plenty of thickness so it won't warp. I think you
said that this is for the carrying case. If so, you could even put in a
line or divot pattern and logo with the router and not sand at all, to get
a nice surface texture that would hide future dings and scratches. Have
to keep the sealing coat very thin and uniform. Anyway, just a suggestion
from up here in the cheap seats :-).

-----
Regards,
Carl Ijames


I LIKED IT!

You an actually machine a pretty decent surface finish in MDF, although I
don't use it much except as glued backers for special projects.




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Old June 17th 15, 07:15 PM posted to rec.crafts.metalworking
jim jim is offline
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Posts: 100
Default Materials for making a mold

Tim Wescott wrote:


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.


You could pour your own. But I think it would be
cheaper to buy something ready made. The patternmaker
suppliers have a number of products designed for CNC
machiningto make patterns, plugs or molds.

https://www.freemansupply.com/RenShape5179Foundr.htm
http://www.alro.com/divplastics/plas...ct_lab850.aspx

https://www.toolchemical.com/showcat...lanks&SiteID=5



A pattern shop in your area would probably be
your best bet for the machining and help in
getting type of finish you need.

  #14   Report Post  
Old June 18th 15, 03:41 AM posted to rec.crafts.metalworking
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Posts: 897
Default Materials for making a mold

On Wed, 17 Jun 2015 11:30:09 -0500, Tim Wescott
wrote:

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.


But why aluminum? Nearly all fiberglass boats, for example, are made
using a fiberglass mold. Nearly always a female mold.
--
cheers,

John B.

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Old June 18th 15, 05:33 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Thu, 18 Jun 2015 09:41:37 +0700, John B. wrote:

On Wed, 17 Jun 2015 11:30:09 -0500, Tim Wescott
wrote:

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.


But why aluminum? Nearly all fiberglass boats, for example, are made
using a fiberglass mold. Nearly always a female mold.


Because machined fiberglass takes a huge amount of hand work to polish
up. To date, I know of no 3D printing technology that'll lay down
polished gel-coat.

--

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


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Old June 18th 15, 05:34 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Wed, 17 Jun 2015 13:15:02 -0500, jim wrote:

Tim Wescott wrote:


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.


You could pour your own. But I think it would be cheaper to buy
something ready made. The patternmaker suppliers have a number of
products designed for CNC machiningto make patterns, plugs or molds.

https://www.freemansupply.com/RenShape5179Foundr.htm
http://www.alro.com/divplastics/plas...ct_lab850.aspx

https://www.toolchemical.com/showcategory.aspx?

CategoryID=590&SEName=tcc-tooling-planks&SiteID=5



A pattern shop in your area would probably be your best bet for the
machining and help in getting type of finish you need.


The one quote that I got (from Freeman) was more than the cast aluminum
slab!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Old June 18th 15, 06:56 PM 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?

========================
After reading the replies to this post, I have some
questions:

(1) What is your projected volume?

(2) Why fiberglass? How about alternatives such as vacuum
formed thermoplastic?

(3) Did you get quotes from enclosure/case vendors? The
size/shape appears close to a gun case.


--
Unka' George

"Gold is the money of kings,
silver is the money of gentlemen,
barter is the money of peasants,
but debt is the money of slaves"

-Norm Franz, "Money and Wealth in the New Millenium"
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Old June 18th 15, 07:03 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Thu, 18 Jun 2015 12:56:52 -0500, F. George McDuffee 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?

========================
After reading the replies to this post, I have some questions:

(1) What is your projected volume?


A few dozen a year.

(2) Why fiberglass? How about alternatives such as vacuum formed
thermoplastic?


First, it's the devil I know, and I know it'll be strong enough (I want
the thing to easily survive a drop from table height onto concrete).
Second, I have a strong personal tie with the vendor.

Vacuum-formed thermoplastic is certainly a contender, but I think that by
the time I get all the other properties I want, given my anticipated
production volumes, that I wouldn't be happy.

(3) Did you get quotes from enclosure/case vendors? The size/shape
appears close to a gun case.


A hinged case isn't a good starting point, I don't think. I've been down
this sort of road before, and I just don't see finding a case that'll
meet my needs that isn't custom-made.

(Enclosures are a bitch. With the exception of PC builds I have yet to
do an electronics project where the cost of a nice-looking case didn't
exceed the cost of the stuff inside it.)

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Old June 19th 15, 02:36 PM posted to rec.crafts.metalworking
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Default Materials for making a mold

On Thu, 18 Jun 2015 13:03:46 -0500, Tim Wescott
wrote:

(Enclosures are a bitch. With the exception of PC builds I have yet to
do an electronics project where the cost of a nice-looking case didn't
exceed the cost of the stuff inside it.)


+1. Isn't that just f'n CRAZY? And it's not just for electronics.
Carry cases in general are gawdawful overpriced, too.

--
Find out what people will submit to, and you have found out the
exact amount of injustice and wrong which will be imposed on them.
--Frederick Douglass


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