Making Hard-shell molds

[John Spencer]

Hi Everyone

This is a bit of a followup to a conversation I had with Dave Chanter
about possible ways to make lightweight futuristic nerf guns, but I
suspect others might be curious.

Make recently ran an article that was basically a repeat of one in Make 24:
http://blog.makezine.com/2012/10/10/making-hard-shell-molds-with-adam-savage/

That covers making a resin mold of an existing prop, not exactly what we
were discussing, but similar and still interesting.

The current edition of make (32) has an article about some guys who made
full Warhammer 40k space marine outfits using vacuum forming. This is
pretty much what my suggested direction was, with cnc cut parts to make
the molds.

Anyway, enjoy :)

John S

[Dave Chanter]

FYI: More Background, Some friends and I will be attempting to make props of weapons & other costume items from the Mass Effect Series of video games. Hopefully in preparation for a good showing at the Penny Arcade Expo next year.

Expect to see me in the space working away on guns and armour if all goes well. If this interests anyone else then let me know, the more the merrier.

Thanks for the reference John.

[samotage]

What you should do is use polystyrene foam for the shaped mould, easy to carve etc.

Then use the 3M #77 spread adhesive (safe for polystyrene) to spray the surface and apply box tape (use heat gun on curves) to act as a release film.

After than, laminate with glass fibre!

Fill, sand, finish and paint. The "mold" will either pop off, or can be dissolved out with acetone.

I've made many RC plane fuselages and moulds using these techniques, and its easy and fast. Have a look on some of my threads on rcgroups.com for more info.

The only thing is an appreciation for sand papering :)

Sam, @samotage

[samotage]

[John Spencer]

I like the idea of using foam. I've heard of people routing it, but I'll have to do more research.

With the hard coating is the mold reusable?

John S

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[Keith Franks]

Hey, I was looking into this a while back and found this link:

http://blog.makezine.com/2009/08/24/how-to-lost-foam-metal-casting/

Some more exploration around how this guy did things (you should be able to find his website) shows some very cool hits and misses and great ideas for different ways to do this...

Hope this helps.

[Zac Watts]

There is a whole heap of interesting videos on the http://www.youtube.com/user/jamesbruton youtube channel, he is currently building an iron-man costume. Starting from expanded foam based on papercraft models which he seals, then paints, to give an ok costume, He then created molds from those and casted / fibreglassed to give the current one.

[John Spencer]

I just thought I should post a follow up.  I had a go machining blue foam yesterday and for my first go it went surprisingly well!

Here's a pic of the finished product : https://twitter.com/i/#!/mage0r/media/slideshow?url=pic.twitter.com%2FD03YH0Nh

The texture there actually looks worse than it is.  There are a few problems with it caused by my meshcam paths (and the difference between climb and conventional milling).  This particular foam is slightly rubbery, which may mean I have the wrong stuff.

The piece of foam is 80mm deep but the model is only 40mm, so there's a fair bit of wasted depth.  I machined this at a maximum speed of 2400mm/minute, but in reality it rarely got over about 600mm/minute due to acceleration.  I used a 1/4" 4 flute upspiral bit that was 3" long with 1" of blades.  Most of it was machined at 6500-7000rpm, however without the dust extractor running the blue foam electrostatically stuck to the sensor and it would occasional spin up to 32000rpm.  I ran the dust extractor for the first half of the machine, but realised it was making a lot of noise for not a lot of benefit as foam still ended up almost everywhere.

It also took about an hour and a half.  Definitely have to work on the toolpaths.

I also took a video.  It's very dark and loud.  you've been warned.

http://www.youtube.com/watch?v=wpMGt8RuSSY&feature=plcp

Anyway, I'll bring it in Tuesday and people can have a look.

John S

[Dave Chanter]

Thats just awesome!

I need to get off my ass and into CAD to make the ME guns.

John S

Hope this helps.

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[John Bosua]

Awesome !!!!!!!

JB

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[Clifford Heath]

On 22/10/2012, at 11:32 AM, John Spencer <john.spe...@gmail.com> wrote:
> I just thought I should post a follow up. I had a go machining blue foam yesterday and for my first go it went surprisingly well!

> ...This particular foam is slightly rubbery, which may mean I have the wrong stuff.

It's not unknown to machine rubber - but it's usually done after freezing in LN2.
Not sure how well your foam would freeze due to being a good thermal insulator,
but OTOH that could help - immerse the foam overnight so it freezes hard and
you could machine it to a good surface before it defrosts.

Just a thought anyhow...

Clifford Heath.

[samotage]

Did you get blue snot?

[John Spencer]

Lol, no.  I have a powered 0.3 micron dust mask :)

On Tue, Oct 23, 2012 at 5:16 PM, samotage <sam....@esskware.com.au> wrote:

Did you get blue snot?

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[Luke Weston]

Check out this link. There's a wealth of interesting stuff to read here, across a range of different areas.

http://lcamtuf.coredump.cx/gcnc/

[John Spencer]

What an excellent find!

It's a good read for anyone interested in CNC milling.

John S

On Wed, Nov 7, 2012 at 2:40 AM, Luke Weston <reindeer...@gmail.com> wrote:

Check out this link. There's a wealth of interesting stuff to read here, across a range of different areas.

http://lcamtuf.coredump.cx/gcnc/

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[April Staines]

Awesome,  thanks for sharing this.

On Nov 7, 2012 2:40 AM, "Luke Weston" <reindeer...@gmail.com> wrote:

Check out this link. There's a wealth of interesting stuff to read here, across a range of different areas.

http://lcamtuf.coredump.cx/gcnc/

--

[Dave Chanter]

http://lcamtuf.coredump.cx/gcnc/ 

This is an amazing find, so much information aimed at Hobbyist level with actual Science & Engineering based assessments of materials.

Of course, now I want to buy a desktop CNC mill...

On Wednesday, 7 November 2012 08:13:58 UTC+11, April Staines wrote:

Awesome,  thanks for sharing this.

On Nov 7, 2012 2:40 AM, "Luke Weston" <reindeer...@gmail.com> wrote:

Check out this link. There's a wealth of interesting stuff to read here, across a range of different areas.

http://lcamtuf.coredump.cx/gcnc/

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[John Spencer]

Wait a bit for the hackCNC version 2.0 (name pending) John McNamara and Shane Rogers are working on.

Should have comparative performance to a ShapeOko and use the same drivers as the hackCNC. :)

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