Draft Angle

Being a mold maker (small niche market) this may sound funny, but its something I rarely think about. Most of the stuff I make is rounded
and/or organic with a flat plane parting line. Ocassionally I'll make a mold for a mold and the draft angle of the master mold is just exaggerated. The cast mold just falls out of the master mold, cavity details not withstanding.
I watched the series The Tool & Die Guy started on YouTube about mold making, but he was mostly working with plastic injection molds with ejector pins. He talked about draft angles of around 1 degree. Usually done in setup rather than with a tapered mill.
I just started (in 5 or 6 weeks I'll cut it) a job to make a "blank" master mold for somebody. They plan to use the master to mold their own molds when they use them so they have to come out and go back in pretty easily. Its really just a box. He had not even considered draft angle so I asked him... we agreed that it needed some. Do to usage he asked that I use the least draft angle I thought was practical. The easiest way to do it is to rough it out of a solid piece of stock and finish with a tapered mill. Only one setup then. When I was looking at end mill options from MSC 3 degrees seemed to be the most common tapered end mill.
Is 3 degrees common for some particular reason? Not necessarily just mold draft angle, but for any reason.
When I print or machine master molds I usually go with 5 degrees. I use the resulting cast molds (usually silicone) with a backer plate and a clamp.
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Am Samstag, 16. Mai 2020 18:47:32 UTC+2 schrieb Bob La Londe:

What material goes into the master mould? I don't know a lot about this myself, but I'd be interested to hear the answers.
Chris
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On 5/17/2020 4:29 AM, Christopher Tidy wrote:

I do not know what intermediate materials he is using, but based on his final product I'd probably use a medium to high durometer silicone.
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