Hi again M. Roberts:
You wrote:
" Some of the parts that is in manufacturing are roughly 27" square x 4" thick, with features on all four edges, and both faces"
"Does anyone make a sinker with an indexer that would accommodate a part of this size?"
No, a 27" x 27" x 4" plate of just about any metal is going to be a beast for weight, and you'll have a very hard time finding an EDM indexer for something that huge.
You'd also need enough dielectric oil to fill a big tank, and that stuff is EXPENSIVE!
However, the beauty of CNC sinkers is that you do not need to flip the part to orient it to the Z axis of the machine...you can burn in any orientation.
So you could just make your electrode kind of like a Renishaw star probe and use it to burn your threads on the top and all four sides without ever moving the block.
Since EDM is a non contact process, you don't even need to clamp the block down...its own weight will hold it just fine.
You can also index the trode at will with the C axis so you have a roughing trode and a finishing trode simply by saving one trode for only the finishing burns and indexing it into working position when you need it.
If the pitches are all the same you can make a single diameter trode that drops into the smallest hole and just orbit it out to whatever thread diameter you want...just like a threadmill.
27" x 27" x 4" is still a pretty big block and needs a big machine, but it's not impossible big.
I would do a simple test:
Contact Reliable EDM in Texas and get them to burn one for you.
They specialize in big stuff and can do a block like this no sweat.
Find out how expensive it will be and how well it works for the threads you want to make.
Now you can make an informed decision about whether to continue to farm them out, whether to invest in the goodies you need to do it yourself with EDM, or whether to find another way (like accepting one threaded hole per tap and just chucking lots of taps and billing the customer)
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com