The length of time it takes to design a product always depends on a few factors.
I have had people come to me with ideas that are just thoughts in their head while other times I have had people come to me with sketches and even prototypes.
If you do your homework and try to develop the idea yourself so it can be handed over to someone else will reduce the time it takes to design the final product.
Basically you have come up with a concept on how you part will look and perform and now need someone to design it in 3D.
If you don’t have the ability or time to sketch your ideas down then the designer will charge more as the concept design needs to be started from scratch therefore taking longer.
Size funnily enough doesn’t matter when designing in 3D. Something can be 6 feet long or 6 inches, it doesn’t make a difference. The thing that makes the difference in the amount of detail and parts that you are trying to fit in the design.
If you have a product that has 10 parts it is going to take considerably longer than a product that has 2 parts. This is where you need to sit down and try and simplify things and be clever in your design. By being clever i mean take two parts and try and make them one.
When dealing with inventions and concept there are sometimes parts of the design that will require testing and development.
For instance if you want to see if you can reduce the material thickness but not sure if it will break. (This is where Finite Element Analysis comes handy). The more the designer needs to run simulations in FEA the longer it will take due to long simulation times. This cost and time should be incorporated in your original quote from the designer if initially he voiced his concerns.
Having to deal with electrical or electronic items will increase the design time. It may be a case that the designer needs to source the item to take dimensions so they can model it in the assembly correctly.
The reason why this is important is to ensure there is sufficient room in the design to fit these parts in. Some suppliers may take up to a week to respond to requests for dimensions or they have to send out a catalogue to the designer. If you have already done your homework you might have sourced the parts and saved the designer a lot of time.