Hi updatedsecurity:
In addition to what Dan said in post #2, be sure to look closely at the surface finish callout for the bottom of the groove if there is one.
Especially in high vacuum situations it matters a lot and not always in an obvious way.
If you are going to mill the groove, you MUST achieve a better surface finish than if you trepan or turn it.
The reason is that the lay of the toolmarks has a major impact on the sealing performance, and the orientation of those toolmarks is unfavourable for sealing if they are milled, especially if the oring has a high durometer.
If it's not called out at all on the drawing it is not safe to assume it doesn't matter, even though you may be legally covered if there is no callout and the assembly fails.
Moving on to how to do it...I always helical mill them down and use a vertical entry and exit radius so the cutter never clonks down onto the finished surface and does not dwell down there either.
I want to avoid a scar on the bottom face at all costs.
This is also not a place to get greedy about making time on the job... ease the cutter in gently and don't beat the shit out of it.
A nice shallow ramp at a modest entry angle and a nice gentle feedrate is the ticket here...also chuck up your cutter as short as you can, and use a stubby if you can.
However, if the sidewalls are dovetailed you cannot do it this way...obviously at some point you have to drop straight down with the cutter and then feed it sideways to dovetail the walls.
I like to mill the whole groove including the bottom first with a regular endmill and then run the dovetail cutter up a thou or so so that critical bottom face doesn't get scarfed up.
So that's it...hopefully it all works out brilliantly for you.
Cheers
Marcus
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Vancouver Wire EDM -- Wire EDM Machining
