In laymen terms someone please explain what the datum line is
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Datum line
- Thread starter crystalgayleguy
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There are multiple uses of the term. In reloading it's usually referencing a point on the case shoulder where the case head to shoulder dimension is calculated when using a shoulder bump comparator. It can also be the point where dimensions or a features characteristics are measured from.
What Are Datums? | GD&T Overview | GD&T Fundamentals | KEYENCE America
This page explains the different types of datums and the drawing indications of datum features. “Learning GD&T From Scratch,” provided by KEYENCE, walks you through the basics of geometric dimensioning and tolerancing, datums, and measurements by coordinate measuring machines. It also introduces...
www.keyence.com
^^^
This. It's a reference point used to measure/determine headspace on rimless cartridges that extends from the boltface to the stopping point of the cartridge- which is a circle of a specified diameter on the shoulder of the cartridge. Common ones-
.330, .350, .375, .400, .420.
Aside from their use in manufacturing headspace gages for rimless (or rebated rim- any cartridge that headspaces off the shoulder), their practical use for us is as mentioned above- using a comparator that has a ring of the appropriate diameter for the cartridge to set full-length sizing dies for minimal shoulder bump to extend brass life.
This. It's a reference point used to measure/determine headspace on rimless cartridges that extends from the boltface to the stopping point of the cartridge- which is a circle of a specified diameter on the shoulder of the cartridge. Common ones-
.330, .350, .375, .400, .420.
Aside from their use in manufacturing headspace gages for rimless (or rebated rim- any cartridge that headspaces off the shoulder), their practical use for us is as mentioned above- using a comparator that has a ring of the appropriate diameter for the cartridge to set full-length sizing dies for minimal shoulder bump to extend brass life.
FireFlyFishing
Well-Known Member
You can find the Datum Line's location and measurements for each caliber on the SAAMI spec sheets listed on their site.
59FLH
Well-Known Member
When creating a mechanical or engineering drawing, they are the surface or feature where the other features are referenced from.
You got to start/measure from somewhere.
Edit: Oops, you asked about datum "line" that's slightly different. Its a line of reference typically used for tooling or gauging
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