View Full Version : Spin Cast Moulds

Mark Gruninger
03-12-2007, 12:26 AM
I need information on using my Laser to create moulds for metal spin casting. I need to learn about the best material to use as well as the best procedure to follow. Any help would be greatly appreciated.

Rodne Gold
03-12-2007, 12:58 AM
I do 100's of these. Perspex works well , but is destroyed in the mould vulcanising process , the cavity is however perfect. Essentially you make the master on your laser.
We make multiple masters to fill a mould.

Mitchell Andrus
03-12-2007, 8:43 AM
Wow. First time I've heard this. Please elaborate/post a few shots of the molds and finished pieces.

I'm looking for ways to add small escutcheons to my wooden furniture.


Karin Voorhis
03-12-2007, 8:47 AM
I too would love to hear more about this

Rodne Gold
03-12-2007, 11:24 AM
Well spin casting involves making a master , this master is encased between rubber or silicon discs are that are soft. These rubber discs are vulacanised at about 150 odd degrees C and is split forming a cavity mould of 2 halves. The rubber is Able to withstand low melting point metals like zink and pewter. The Pancakes are put into a centrifuge and molten metal is poured in while they spin , the metal fills the cavity you made using a master.
Now you can make the master very easily on a laser as well as using hand tools to finish it off if the laser cant do the job by itself. In fact you can make like 25 masters with the laser.
Now let me tell you why this is so good. cos traditionally you would have had a single master made. You would have spun 25 copies of this single master to get enough masters to fill a panckae.
Problem is in production you are using a copy of an original for a batch of masters , so your production isnt a spin of an original , but a spin off a copy , which has lost detial and has shrunk
With a laser you can easily make 25 masters real quick. and then production is a spin off a master , much crisper , less shrinkage.
the other issue is moulds wear out , and being able to present another 25 or so masters quick , theres no disruption.
Perspex comes in carious thickneses and works well for flat masters like custom keytags.
Spin casting is a very cheap way to make stuff in metal.
Very complex coins , momentos , industrial parts can be made this way and if you can supply your spincaster with multiple masters , it makes life easy and you will save a ton , but more importantly know exactly what the finished object will be like
You can produce all manner of things for your business , pins , coins , medallions , plaque stands , customised trim , bases etc. Applications are endless.

We have a good relationship with a few spincasters and get very good pricing on stuff , for example a good quality 43mm diameter 3mm thick medal either antiqued or plated costs us around 20c to cast in 1000+ qtys
The medal sells for about $2 and we sell a lot of them a year !!

Now you can either choose to develop stuff for yourself and for sale or make masters for other people.
Making masters for others is pretty much an excercise in frustration as you are dealing with onesies and heavy development to get the onsie spot on. You can never really charge enough to justify the time you gonna spend doing someone elses masters. You need to understand the limitiations of what you can do and the limitation of the moulds.

The best way to be good with masters for this process is to work with a spin caster till you get the requirements and compensations you have to perform on the laser to get him being able to make durable and easy to cast moulds with your masters.

We dont do masters for others , just myself and one other big customer (we do a lot more than that for them) as we don't want to make life easy for our competition.
Were made that way , however tomorrow at work will take some more comprehensive shots of masters and ther resultant products,

Bill King
03-12-2007, 1:29 PM

I've enjoyed reading your experience in spin casting(and the pictures too). 2 years ago, I had money in hand ready to purchase a tekcast system. The reason I didn't was that they mention that is was essential that the master part be made of metal or anything that can take the high heat of the vulcanization process(couple hours at 300 degrees). I was ok with the warped masters afterwards...I was concerned with the master mold cavity being true to the orginals.

You have gave me hope that the process is viable.

Now all I need to do is figure out what perspex is? Is it cast acrylic or extruded acrylic?


Mitchell Andrus
03-12-2007, 2:51 PM
Thanks, Rodne. I never thought that these kinds of items started life in a laser.

Mitchell Andrus
03-12-2007, 2:56 PM
A side question. Perhaps you know of a resin that looks like the old "Tortoise Shell" plastic from the 30's and 40's? I have had a request to mold a few radios face plates. I can make the closed silicone mold alright, I'm stumped for the material. It looks like a clear resin with a molasses/amber sworl running through it.

Allan Wright
03-12-2007, 3:49 PM
Can you put brown pigment in Allumalite?

Dave Jones
03-12-2007, 4:40 PM
Now all I need to do is figure out what perspex is?

Perspex is a brand name of acrylic made by Lucite. In many parts of the world people call all acrylic sheets by that name, just as in the US we might call it plexiglass. (Plexiglas is a brand name of acrylic from Atoglas)

Larry Bratton
03-12-2007, 9:05 PM
Are the examples you posted one sided or two? What I mean is, do they have the same design on the opposite side or are they smooth? I am a senior citizen and this is my first encounter with this process. It appears that a relatively small investment is involved to acquire equipment to do spin casting. I have always been involved with wood and related products and it just never occurred to me to question how items like this were made. :)

Craig Hogarth
03-12-2007, 9:27 PM
I find this very interesting (and information, thanks Rodne). I googled this site and can see how the molds work.


Rodne, I'm just getting started, but I've had a lot of requests to make challenge coins for a military base. I've looked at a couple companies that can make them for me, but at about 10x the cost you mentioned. Do you have any companies you can recommend to make the coins if I provide the mold?

Rodne Gold
03-12-2007, 9:34 PM
We do a lot of double sided items , we have found a method to engrave and cut from one side and then flip the item and get very good registration on the other.
There is another option too , using various materials like dental wax , faux wood and acrylic , you can build up complex masters that DONT have to withstand heat. You can use whats called RTV silicon to make a mould , this is a 2 part liquid that "vulcanises" at Room temp (RTV = room temp vulcanising)
So you make your OWN mould using your laser , carving , cnc machine etc to make the master. This rubber can ALSO withstand low melting point metals.

Now you can use this mould to make an intermediary master out of resin that the spin caster can use as the resin will withstand heat or you can cast your own "faux" metal items from it. (or real metal if you wish)

If you get brass , copper or aluminum powder and mix it with casting resin and cast that , you get an object that has used the "cold cast" metal process.
The object feels like metal , looks like metal , can be polished or patina'd just like metal due to the high % of the metal powder in it.

We actually work with a co that does stuff in metal for the tourist trade , they use us for 2 items , their masters and our domed full colour printing.

We supply em , lets say , a master in the shape of Africa with a cavity in that master that a sticker can be put into , we also supply em the sticker domed with a flexible resin as we have a machine that prints full colour and die cuts the decal to shape.

So they cast an africa shape in various configurations , fridge magnet , keytag , on the top of a cork bottle stopper , as tablecloth weights etc. all of these take a sticker thats shaped like the map of africa with various pictures. For example in Cape town , its marketed at tourist destinations with pictures of Table Mountain , in Zimbabwe , with pictures of the Victoria falls etc.

We do marvellous business together cos we both come up with new items and cos we can do masters in a day or so , time to get the ideas launched is extremely quick.

the africa keytag thing is exactly what I was talking about. The image inside it is the flag of South Africa.
as I said , will post some more pics later today if I get the chance

Rodne Gold
03-12-2007, 9:42 PM
Craig , most high volume spin casters will work in weights , IE charge you according to weight.
Be aware however that spun cast medallions are rather "rustic" in look and a better way to do high definition upmarket products is to die cast or die stamp them.
I would shop around for a caster that does higher quality work and that has a plating plant in house and ask them to give your masters a try. Ask em to use your masters in a combined sample mould so you dont pay for a full mould for sampling.

BTW the laser can engrave DIRECTLY into the vulcanised moulding rubber , its like engraving stamps. You could for example engrave a logo into an existing cavity in the rubber.
PS one of the biggest problems in engraving masters for medals is the fact that the areas that are engraved away into the acrylic dont have a very good surface finish , often having lines and striations , we either give a "polishing" pass to these areas or engrave a pattern into them after they have had the main engraving done , so the surfaces look better.

Mark Gruninger
03-12-2007, 10:57 PM
I need to make a master mould for some metal tags - 2 sided. I have a 75 watt laser and have heard I can use delron plastic to reverse engrave into to create a master. What process is used to do this. What is the best power and speed to use to get the best definition and sharp lines. Is it like rubber stamp engraving? Please let me know where I can read about or get additional information regarding this subject. Thanks so much for any help.

Mike Null
03-13-2007, 7:17 AM
Re: Rodne's last post

We used the post script fill tool in CorelDraw to do the designs/patterns on the open areas of the masters to avoid the striations of the laser.

Rodne Gold
03-13-2007, 10:10 AM
Ideally using stamp mode on masters is first prize , cos the stamp mode creates "shoulders" , Ie the sides of a raised letter dont go straight down , they angle outwards. This places a LOT less stress on the mould rubber and aids demoulding the cast piece , often if you have straight sides and items close to each other , the tiny piece of rubber in the mould gets torn away between them and subsequent castings arent good.
Casters also want to minimize their metal usage and deeper engraving is better for this , however too deep and you put a lot of heat into the piece , warping it , especially double sided stuff.
Another tip is to use a very fine brass brush with some abraisive household cleaner and scrub the master thoroughly , this dislodges the crusty bits and de burrs the sharp edges.
After that , rub the face of the master on very fine wet and dry sandpaper to "polish" put any marks or scratches.
Another tip is to use a rotating de burring tool and try put a very slight chamfer on the edges of the pex where you cut it , often the laser can leave a very fine ridge there or its very sharp.
Hand sanding the edges to remove striations is also advised if you can. When doing angular stuff like squares , put a VERY fine fillet on them , ie round the corners EVER so slightly. Sharp and pointy dont work well with rubber moulds.
Cavities work best if you dont have to engrave them but can "build" them.
For example if you needed a 4mm thick 2" x 2" square with a 1.5" x 1.5" 1mm deep cavity then cut a 3mm thick 2" x 2" solid and cut a 1mm thick frame of 2" x2" with a square cut out in the middle of 1.5" x 1.5"

Glue em, together and you hasve a perfect cavity with a smooth bottom and its precisely 1mm thick and takes like 1/10th of the time to do.

like this pic