Work holding and planning

[Jonathans]

At the risk of appearing minimally exceptional here, I have a noob question to ask.
I am working with a BP Series 1 Boss CNC 3 axis mill.
Lets assume I need to make a carburetor spacer that is shaped to the same profile as the bottom of the carb.
Lets assume it is .5" thick.
If I start with .5" material I won't be able to hold it in my vice and still be able to run an end mill around the perimeter.
So........ do I start with .625 material, machine what I need to, flip it and face mill off the extra material until its down to the .5" I need?
Or, do I start with .625 material, machine off .125 leaving a center protrusion for the vise to hold on to, and machine that off later?
Or, double stick tape the material to a sacrificial plate held in the vise?
Or, should I only cut half depth around the perimeter, flip the piece and cut the other side halfway? This could get complicated if the part is not symmetrical.

Am I missing another option that is preferred more? I thought I would ask before doing something dumb for a year or so.

 

[Bob Korves]

Sacrificial plate, can be something as simple as MDF. Use multiple hold downs and remove one at a time as you go around the work, replacing them when you are done in that area. Er, that would not work if using the mill in CNC mode unless you have pauses in your program at intervals to change the clamps.

 

[Wreck™Wreck]

Drill the mounting holes first then bolt to a suitable fixture plate and mill away, cut into the fixture plate to get to full depth.

 

[Jonathans]

Thanks. So once any holes are drilled they are used to hold the piece to the fixture plate. Got it!

 

[Wreck™Wreck]

Thanks. So once any holes are drilled they are used to hold the piece to the fixture plate. Got it!

Exactly, if making many parts use more then 1 fixture, bolt the next part down while the current one is running. Also construction holes are a perfectly good way of holding parts when they are in positions that do not effect the performance of the product, consumers may find this unsightly however if appearance is more important then function and cost.