wax prototype solutions?

[lbstyling]

hello! 1st post, so go easy on me!

im looking to make a master mold out of machinable wax (as i need a top quality finish) for a product that im working on (end product will be a resin casting)

the cnc router i have access to cant machine to the required 130mm depth for the whole unit in one piece and the final product cant have a join line that Im concerned will be visable if I make it in 2 pieces.

so I have 3 questions-

1) is it possible to join machining wax layers perfectly?

2) if not, is there a alternative product that gives a practically perfect finish easily that can be joined?

3) if its not likely that 1) or 2) are going to get the results - what options are there out there?

thankyou all!

[RomanLini]

If you want a really top quality surface finish i would rule out any ideas of joining 2 mold halves, you will get a line even if you can machine each half perfectly. It's amazine how a misalignment of even a fraction of a thou will make visible lines and ridges that you can feel with a fingertip.

My suggestion would be to make the master as a positive, finish it with some high gloss (or whatever) clear coat to give you absolute control over the surface finish and then make the mold in silicone. People making statue heads etc regularly do this high gloss finish molding, you could check the art forums for resin casting statue techniques or check some of the resin suppliers have online tutorials on making high quality molds and casts.

[lbstyling]

hello romanlini,

I should have said, this is for a positive mould. and im planning to make a silicone negative that I make the casts with as you suggest.

I still cant machine the required depth of 120mm and I understand that you cant join machining wax together with glue etc.

is there a suitable alternative material that will glue together easily? I could attempt it with the wax by drilling and tapping the 2 halves, but its going to cost $200 for the priviledge of finding out!

even then - as you say, theres a good chance that the join would be visable.... hmm.

[RomanLini]

Ok, so you *are* making a positive (master).

It's going to depend on your shape really. You can make the master in 2 halves, then join them and finish by sanding or surface prep, varnish etc to remove the join. This is a common technique. It would be easier if you said what it is that you are making, or at least what the shape is and why the finish is important ie; does the outer surface need to be flat to attach to something or does it need to be attractive as the visible face surface of a product, does it need tobe dimensionally accurate to mate with something, etc etc.

[lbstyling]

The unit is a hi end hifi component that has a simple shape that is almost a standard AV box shape, but with a open face on the bottom (for a aluminium plate containing the electronics)
The walls will be approx 20mm thick, and made of a clear cast plastic.

similar sise and layout to a typical dvd player- 550x350x120. I can machine 60mm deep. The finish needs to be as close to perfect as possible.
example-
Saffire II

the electronics are (finally!) finished after 10 years, now I need to make a case worthy of it.

[RomanLini]

Sounds like a very interesting project. I'd like to see the finished amp.

Do you know someone who does good finishing ie paint? That maybe does custom paint jobs on motorcycles etc. You could machine it in 2 halves, then join them, then a finishing process like clear lacquer with sanding etc as needed to remove any evidence of a join line.

That will add a little thickness too, so you would need a design that is not thickness critical just surface finish critical. A good paint guy could probably fix that seam and add very little thickness, but I would still allow for thickness especially if you are including detail like embossed logo etc. One of the benefits of paint finishing is that you can choose a texture from high gloss to satin and matte finishes.

Also bear in mind that you may only get 10 casts from a silicone mold before the surface finish changes due to deterioration of the silicone. And that's going to be a real expensive mold with such a large size.

If you want a high gloss like the Saffire you can also do some post-finishing polishing on the cast acrylic.

[lbstyling]

I could make the mould in layers of mdf and finish in paint myself If I had to, but what paint needs to be used if Im making a negative in silicone? I cant use anything that would react with the silicone, and idealy I could make many silicone moulds from the one master if needs be, so I would presumably want the master to be made from a material that is resistant to wear?

In all honesty, I think the design has moved beyond my machining capabilities at this point. It looks like some of the features I want will require a 5 axis machine anyway so i will need to send it to a machine shop. God knows what this is going to cost me!

Variation in the finished size is no issue within reason. Every measurement conforms to the golden ratio, and this has a little flexability so no probs. The silicone mould longevity isnt ideal, but still preferable to the competitions finish - solid billit aluminium is outragious to be working with when trying to offer value to the end user, and Im determined to do just that.

ps- while Im here, how would I go about screen printing on the flat serface on the top?