Aluminum molds - RA level and hand finishing?

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#1

I am trying to get some aluminum molds done on a budget. Can someone with experience hand finishing aluminum molds suggest a maximum RA value I can get away with and still be able to block sand + polish to a fine finish? The surfaces are curvalinear so there is a mix of vertical and horizontal milling.

Also, I have read to include a proud edge at join lines to protect the corners during hand sanding. Should I plan for that to extend up from the parting line in addition to inwards? Suggestions on how big I should make it? (thinking about 1.5mm?)

#2

How complicated of a shape is your mould? do you have tight tolerance requirements? We usually aim for 1.6-3.2Ra (depending on the mould). Sanding isnt too difficult, but takes time. If your mould is very complicated(lots of corners and small nooks and crannies)it can be difficult to sand smooth. If you have a tight tolerance than you should aim for a finer CNC finish as hand sanding can knock it out of tolerance potentially.

#3

The part doesn’t have any critical fit dimensions and the only corners are at the parting line- there is about 2mm of space around it in all directions:

Those numbers are super useful, thanks. The machinist I am planning to use said they usually take parts to ~.5 RA on the mill so that RA range ought to be no trouble for them.

#4

Probably once you start sanding you will wish you paid extra to get it down to 0.5Ra haha, but if you’re on a tight budget then its good enough. You’ll have to start with a pretty aggressive sand paper to remove the machining marks. Good luck