Design a Special Purpose CNC Cylindrical Grinding?

A CNC machine that fabricates only one item. That idea is wrong in so many ways.

I also see no advantage at all in grinding inside and outside at the same time. This seems more likely a method to quickly make thermal stress fractures than expedite production.

Congratulations! Good Luck!

I was a machine designer for 15 years, designing precision grinding machines. I can tell you from experience that this sounds like a bad idea, and very impractical. Making your own, one-off machine is VERY expensive if you want something that actually works and requires any kind of precision. Grinding machines are designed as ID or OD grinders for a reason. My advice is to skip this idea. There are good, relatively inexpensive CNC ID grinders and CNC OD grinders on the market by companies who have years or research and experience in grinding.

I should clarify my response. There are combination ID/OD grinders available. My main point is that designing your own machine is likely a bad idea if you only have one product application in mind.

my critical requirement is concentricity and that is the reason why i opted to design a grinding machine capable of grinding machine capable of grinding both internal and external grinding in a single setup.i mean first internal grinding then external grinding without disturbing the setup.

"bullet shape dia 350, length 700 where does the 6mm thickness come in?"
An internal diameter of 338 maybe.

Why???

Considering the fact that you don't know anything about the specific grinding energy, unit power required, cutting wheel speed, work speed, feed and depth of cut, nor how to decide the shape, diameter and width of grinding wheel when cylindrical grinding sintered silicon nitride I think you are in the wrong business and are wasting everyone's time.

Try a different line of work.

As others have said the idea doesn't really make sense and is going to be very expensive to design and run. It almost sounds like you are thinking of reshaping and repurposing scrap you may be able to obtain.

Perhaps there is a better way. What are you trying to fabricate exactly, what size and shape is the raw stock and the object and how many are you trying to make?

Is this scrap sintered silicon nitride you are trying to re-machine?