TWINE Uranium Core Hemisphere

Gadget Meister

Looking for a little help here guys, I'm hoping to make my first foray into the world of casting from moulds. I looked around for a fairly easy project to start with and came up with the TWINE Core hemispheres which lock together to form a full sphere. It is all smooth surfaces and not too much detail but intricate enough to provide a good learning experience. I'm looking to use Smooth-On products throughout even though they are expensive, they get good write ups. What I need help with is the dimensions of the original prop, all I need is the diameter, I can extrapolate the locking lugs from there. Any help gratefully accepted.

minigeff

hi mate, i'm a bit busy at work right now, but i'm gonna post you some help later on how to do this, and a better place to go than shmoooove-off.

MG -{

Gadget Meister

Thanks Jeff, appreciate that {[]

minigeff

Right, sorry its taken so long in getting this sorted.

If anyone wants to add anything, or correct me anywhere then please feel free, we can all learn from this hopefully.

Just so we all know what the prop in question is, here's a shot of it in the nimble little sophie's mitts;



Time for business then.

First up, is this really the easiest prop to start taking moulds from? Although the dome shape is nice and simple, the addition of the hemispherical bumps and holes make it somewhat tricky. To take a mould of this form in its entirety would be a bit problematic in my humble opinion.

So you have 3 options;

1) Make the pattern 100% complete and try to take a mould off it

2) Make the pattern as a simple hemisphere and add the bumps and holes after casting

3) Make the prop 100% complete and don't bother with the moulding part.

With a simple 1 part mould, you need a surface that you can use to create an opening in the mould to pour the resin in. This area is traditionally called the 'feed' area. With the hemisphere shape, the form would be placed into a box. Then silicone rubber is poured over the dome. When the silicone cures, it can be removed from the box.

Heres an example of a small component i've recently taken a mould off.




here's the pattern in the mould box, the feed area will be the bottom of the white gear as its a nice flat surface and there are no overhangs above it, meaning the cast will be removed from the mould without any hassle.



the silicone rubber is poured over and left to cure



when its cured, the box can be dismantled



and the silicone rubber mould is removed, showing the negative of the pattern.




OK, so lets take;

Option 1. Make the pattern 100% complete and try to take a mould off it.

To make the pattern, I'd take a block of material and turn it on a lathe to make a cylinder the right diameter of the hemisphere.

Then saw the cylinder off the lathe and place it flat face down on a rotary table on a milling machine. Skim off the top uneven surface (where you sawed it off the lathe) and then drill and tap a blind hole in the centre, tap it to something substantial like M12.

Then using the rotary table, use a ballnose milling cutter to drill the holes. Say you choose to go for 10mm diameter bumps and holes, use a 10mm ballnose cutter and drill half the cutter diameter (5mm) down, every 60 degrees.

Now you can put the cylinder back on the lathe, but instead of holding it in the chuck, use some M12 threaded bar and using the M12 tapped hole in the cylinder's centre, you can 'screw' the cylinder onto the threaded bar in the lathe chuck.

Now you can turn the profile of half a ball into the cylinder, et voila, you'll have a hemisphere with 6 equ-spaced round bottom blind holes on the flat side. Fill the M12 tapped hole in the centre with car body filler and sand flush.

Now in every other hole you can glue in a 10mm ball bearing et voila, your pattern is complete.

To take a mould off this is gonna be tricky.

My advice would be to use the bottom of the dome, not the flat side, the curved surface, and the mould is gonna be very large. Imagine an upturned wine glass, with the resin flowing in where the stem of the glass would be. Make sense? The overhang is huge, its like a miniature underground bell shaped cave, so you'll need a firm silicone to avoid any sagging in the silicone and thus a deformed casting.



Option 2 would be a similar operation to Option 1, but minus the drilling of the blind holes. The mould making part will be easier as you can now use the flat surface as the feed area, but you'll need to drill the blind holes in the flat surface after the casts have been made. Holding an upturned dome will be tricky and could lead to inaccuracies.



Option 3 is now looking more interesting now isnt it? )



As for a simple 1 piece mould, you have 2 options here.

1) Put item in box, pour over silicone and you have your mould.
Plus side - its easy.
Minus side - It uses loads of silicone in a job like this hemisphere

2) Use a jacket mould. Place item on a flat surface, cover it with silicone mixed with something called 'thixotropic' to make the silicone go gooey like buttercream. Brush on the silicone and leave until it sets. Then cover the silicone with fibreglass to make a supportive jacket. When the fibreglass cures, remove it, then the silicone from the pattern, and re assemble the silicone liner into the fibreglass jacket. Now you can pour in the resin.
Plus side - Less silisone is used.
Minus side - Can be tricky for a novice, air bubbles can get caught in the silicone, resulting in 'warts' on the resin casts, and locating the silicone liner back into the fibreglass jacket can be tricky, resulting in possible distorted casts.


As for material supplies, Smooth on is ok, but pricy. Try a company called Tomps. They're not amazingly quick, but their stuff is pretty good and cheaper than smooth on. You'll need patience with the customer service though.


Hope this all makes sense and helps you out mate, any questions just post them here so others can gain more info as well.

MG -{

danjaq_0ff

Are you any good at baking cakes Singe

minigeff

danjaq_0ff wrote:

Are you any good at baking cakes Singe

im not bad at baking your buns sweetheart ;%

Gadget Meister

Wow, thanks Jeff. It's going to take me a while to digest all the info. I'll come back to you with my plan.

MANDY1

Going slightly off the topic as usual, but MG really knows his onions and his passion to make stuff is amazing - ya know it pal

There's not enough words to praise he and his team, but i sure am lucky to know this talent n skill :x

thespyboys11

Here’s the interior detail (all imagined as we never see it onscreen) I “cobbled” together for mine. See, there IS a use for all your broken VCR’s, radios, toys, etc…

I placed a series of earth magnets along the edge so the top flat cover with bumps could be removed. For inspection of the interior.





Looking forward to seeing your take on it.

Higgins

wow, very impressive Ed.

I guess that's why we call you "The Master" and Jeff "Singe"

danjaq_0ff

) ) )

Bondtoys wrote:

wow, very impressive Ed.

I guess that's why we call you "The Master" and Jeff "Singe"

minigeff

Bondtoys wrote:

wow, very impressive Ed.

I guess that's why we call you "The Master" and Jeff "Singe"

I'd say what people call you, but this is a family friendly forum apparently, so ill refrain from saying.

As for Teppo's comments, thanks mate that's very kind of you to say. Although I only consider 'how to make it' as half of the puzzle, the other half being obtaining the information in the project. We all have our areas of expertise mate. -{

I like ed's ad-hoc internal details, a great example of kit bashing and part robbing, great work mate. I'd always thought that the hemisphere was a solid lump of uranium, so it's interesting to see other people's interpretation of something.

MG -{

minigeff

Just a bit of an after-thought;

Instead of turning and casting the hemisphere, why not buy an acrylic dome? If you can get one in the right size, for the sake of a few quid you can save a huge amount of resin and silicone.

Therefore, scrub the casting the dome idea. Buy a dome in acrylic, and concentrate on making the flat surface to fit onto the dome.

MG -{

Gadget Meister

Yeah I'd already come up with that one Jeff, but was going to use it for the blank and still go for the casting. Prob a two part interlocking mould with the pour spout being at the apex of the dome and the mould split point being at the circumference, just awaiting the exact measurement for the acrylic dome from one who knows the original.

minigeff

Well my guess would be about 100mm in diameter.

An indication of if I'm close would be good

Gadget Meister

That was my guess too

minigeff

Gadget Meister wrote:

That was my guess too

Let me know if this is confirmed pal -{

CJ007Goldeneye

As Minijeff said earlier the best way is to use as little as silicone rubber as possible only covering what you need to be cast. I find pouring plaster in the remaining space to give it the rigidity needed is best. Imagine it like this fill a sock with plaster (without a case) and leave it on the floor once set it will be flat, deformed and squashed. With a casing you will have a perfect shape of the object your casting. The hemispheres you are referring to I believe are know as positive and negative nipples (I know haha) this is what I was told when I was at college anyway. They are achieved simply by getting a clay tool spinning around to make hemisphere then when cast the negatives become the positive (raised hemisphere) and positives become negative (sunken hemisphere) the basic rule in moulding is whatever is positive is negative and neg is posi. Alec tirantis is an excellent supplier for all this material. It is located in London, 27 Warren street a short walk from the tube station. Tirantis.co.uk

Gadget Meister

Cheers Craig, all input welcome.

minigeff

In addition to CJ's supplier (tiranti's) I can say that although good, they can be a little expensive.

When it comes to resins, there are load of suppliers out there who all do good deals, but with certain types of resin.

If its a bulky cast and I need it cheap, I use tomps, for clear resin I use Ambaseal, for other resins I got elsewhere.

Also, what craig says is true, try and use as little silicone as possible. However, sometimes you will need some flexibility in your mould to aid releasing the cast part, so a plaster or fibreglass jacket is not always suitable.

In the case of a hemisphere you should be ok as theres no details and its a nice smooth shape. Casting something like a miniature car seat however could prove problematic with a plaster jacket.

As its nice and simple I might have a play with this myself, just for shits and giggles. I'll post the progress as and when or if it happens.

minigeff

Right then, I thought about this for a second and decided to give it a try myself. Hope you don't mind Andy, hopefully this might help you.

Ok, to get started, parts. Acrylic dome, sheet of acrylic and some acrylic balls. I'm not stating sizes here as its not important. Andy, after guessing and you confirming them, I went with the sizes you suggested.

I cut the acrylic sheet into squares just bigger than the diameter of the dome. Then I drilled a 2mm hole in the centre to use as a datum.

Mounted the square of acrylic on a rotary table and bored 6 equi-spaced holes using a ballnose cutter the same diameter as the acrylic balls, boring the holes to half the diameter deep.

Then I took the squares and roughly cut then circular, then using a secret trick, made them perfectly round. The square has now been made round, and sits inside the dome tight when flush with the edge of the dome.

I then applied some plastic adhesive to the inside edge of the dome and sat it over the disc on a flat surface. This results in a disc inside the dome, but a gap needs filling afterwards. I used P38.

I also filled the 2mm hole in the centre and sanded it back flat after it'd set. Then the acrylic balls were stuck in the recesses with more adhesive.

Then the lot was sprayed in satin black, et voila, one prop.

For a base I cut a square of wood, chamfered the edges and removed any splinters before drilling a blind hole in the centre for the dome to sit in. Then I laser cut a plaque, and a piece of light gathering Perspex to add a nuclear glow in the dark effect.

The total time spent on this was 6hrs.

Gadget Meister

Don't mind at all Jeff, in fact now I know where to come for a mount I've started to do a write up as I go but will not be able to crack on to this project as I'm about to go out to the States. Hope you had a great time today at the C&C, I've got to wait till Tuesday
I have got myself a frame though and a new hot glue gun. I'll take photos as I go and post them up on here.

Top marks as always on yours though. {[]

minigeff

Gadget Meister wrote:

Don't mind at all Jeff, in fact now I know where to come for a mount I've started to do a write up as I go but will not be able to crack on to this project as I'm about to go out to the States. Hope you had a great time today at the C&C, I've got to wait till Tuesday
I have got myself a frame though and a new hot glue gun. I'll take photos as I go and post them up on here.

Top marks as always on yours though. {[]

Thanks very much mate, good luck with yours. I chose to keep mine cheap and quick, but the downside is the very light weight.

Just in case you were wondering, I made a set of 4 in the 6hrs stated. 1 is mine, 2 are gifts to friends who deserve a thank you and the 4th (pictured here) is going to another friend if he's interested and replies to his bloody email )

Gadget Meister

But I haven't had an email ?:)

Higgins

Hey nanojeff,

Aren't these halfballs parts of the MR camera? :v

thespyboys11

I love your
base (and replica) Nice job, Jeff!!!

ics

Very nice Jeff -{

minigeff

Thank you guys.

I'm looking forward to seeing Andy's attempts at casting this.

Like I said earlier, mine are hollow so light weight. Andy's being cast will weigh a good amount so they should be better than mine.

MG -{

Gadget Meister

Mmmm now I have to live up to the anticipation

As I said it won't be till after I get back from the States though.

minigeff

Gadget Meister wrote:

Mmmm now I have to live up to the anticipation

But it's not about 'outdoing' or competing mate. It's about enjoying researching, designing and producing these things.

The second I loose interest and don't enjoy doing it, I'll stop. But my interest and knowledge has evolved since being a member here, so I think me stopping making stuff for my collection will probably never happen.

The thing I find is that things never go to plan. Even this simple project didn't go as I hoped. The domes I bought were not as described so I had a little more work to do than I thought. Just about every project I've ever worked on has gone... well, not wrong, but not as planned. You inevitably come up against some hurdle, but that's what makes it interesting for me, overcoming the problems and finding solutions to the mistakes.

Anyone can make mistakes, the clever ones work out the solutions

CJ007Goldeneye

God damn mini geff you are a prop god and to make 4 in 6 hours. That base is kick ass love the way you incorprated the bond 50 emblem and that yellow perspex. The plywood base is so simple but yet so effective. Did you laser engrave them plates yourself? Just a suggestion i would of put a layer of ally over the base and some bolts plugged into it resembling the inside of a submarine.