Hi all,

I have a 3D CAD model of a fuselage (roughly 4ft x 1ft x 2ft) for which I'd like to create a mold. I'm considering using a CNC service like quickparts.com or firstcut.com. My questions are:

1) should I have a CNC-created plug and then make a composite mold myself, or just have a CNC-created female mold?

2) has anyone here used one of these cnc services, and if so would you mind sharing some ballpark costs?

You can have the master/plug cut from cheap and easy to cut materails like MDF. This can be sealed/painted to prep it for molding.

You can also have a mold directly cut but the material choices can be expensive if you are trying to pull more than a few parts. If you want a high grade surface on your parts then you need a material that can be cutt and polished. Your options will be aluminum, tooling boards, and glued stacks of Corian. If the surface isn't super important then you can cut a mold from MDF or syntactic foams, seal it with resin, and pull your parts. This type of mold doesn't produce very many parts.

An aluminum mold set (fuse, stab, wing, joiner) for a 60" plane can easily cost $10,000.

Yow - $10k is certainly steep.

I assume an aluminum plug would be similarly priced as an aluminum mold?

An aluminum plug isn't any cheaper. Many people will mill aluminum masters and then pull multiple composite molds off them for large production runs.

In today's economy you will find a shop that will cut for less. Many shops are looking for work so they are more competative with their rates. Most charge a per hour fee for machine time plus a set-up/tool path fee.

Hi Caplan

You can maybe visit our thread on the Radiance Pattern Plane to see the moulding work we have doen there.
We also do cnc work for outside companies.

http://www.rcuniverse.com/forum/m_10..._3/key_/tm.htm

Thanks
Tommie Prinsloo
Pretoria
South Africa

If you are going to get it CNC'd from Aluminum, why bother with the extra step of going from plug to mold. Go direct to mold. I think you could get something for like a 2m pattern fuse for less than 10k, but it will definitely be in mid to high four figures. I design, and have had built, female vacuum form molds from aluminum, and we pull thousands of parts from them, so the cost gets spread out.

If you think you will sell a thousand, that's $10/unit for a $10k mold. I fly pattern, and would be hesitant to invest that much. A successful design may sell one to two thousand units over it's market life, but most sell less than that. The materials and labor to carve a plug and pull a resin mold can be less than $1k, if the builder is a pro. A beginner risk loosing his arse if there are snags (been there, done that)

Is the cost of CNC machining foam tooling board any lower than aluminum? I'm guessing that if most of the cost is labor then it won't make much of a difference...

Cutting foam is cheaper than cutting aluminum simply because it can be cut much faster. The less time that the blank is on the CNC table the cheaper it will be.

True, and the material is much less expensive. It is so easy to work that it could just as easily be carved by hand. Factor in how much work it is to build the computer model needed to program the CNC, I would carve it by hand if using foam. Aluminum is the most economical for production tooling for producing hundreds, or thousands of parts. As a hobbiest, it would be prohibitively expensive, unless you have money oozing out of your pores.