Dave,
The nice thing about computer modeling is that you can find all your errors before anything is actually built.
Theoretically.
The tedious part is modelling all the off-the-shelf pieces first so that you can create pieces that match and mount properly.
Laying out geometry for the setup was fairly easy because there's not much compliance, and each arm has essentially one function. Just a matter of checking things through the full range of motion to corroborate my basic "feel" of the layout, and make sure there are no places of interference.
- Do some stress calulations on all the pieces to determine thicknesses, etc.
Then you just give $3000 to the pattern maker, commit to a few thousand dollars of laser cut parts, an initial run of castings, new machine tools and a short initial run of machined parts. Oh yeah - a welding jig.
No problem - unless you screw up.
I was lucky. Since the initial run, I have only made a couple of changes - mostly to make the parts easier to assemble.