How to specify a cone as a datum
How to specify a cone as a datum
(OP)
How would I call out the centerline of a cone as a datum??
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How to specify a cone as a datum
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RE: How to specify a cone as a datum
Attach the datum to the cone surface, and the centerline will be used as the reference for certain calouts (location, runout, concentricity).
RE: How to specify a cone as a datum
One way would be to estabish 3 datum points at 2 different elevations A and B on the cone. These could then be used to establish axis A-B. Then you could use the surface at the base as C. A-B would be the primary and C the secondary. Tiertary could be added if needed.
RE: How to specify a cone as a datum
I've seen datum axises called out as the only datum for a part. You see this especially on shafts with concentricity and perpendicularity callouts in reference to the datum axis A. An example is shown in ASME Y14.5M-1994 5.12.2.
Theedudenator,
Grab or draw the dimension of the smallest or largest cross-section of the cone, either end will do. Insert your datum inline with the dimension arrows.
Failure is a prerequisite of successful design
RE: How to specify a cone as a datum
FinTom:
In the figure you mention above, is the datum flag placed on a centerline or on a surface?
RE: How to specify a cone as a datum
That reference isn't using the "axis" or centerline as the datum. The datum is the cylinder which has a cylindrical tolerance zone about an axis, but the centerline is not in fact the datum. A datum must be an instpectable feature, centerlines do not qualify as features.
The rest of your advice however is sound.
David
RE: How to specify a cone as a datum
RE: How to specify a cone as a datum
RE: How to specify a cone as a datum
Yes, you can specify a specific distance and area to use for datum. This is a datum target.
RE: How to specify a cone as a datum
RE: How to specify a cone as a datum
RE: How to specify a cone as a datum
So, yes the cone geometry defines the centerline of feature, which is the datum axis.
So I could call out the edge diameter as the surface to define the datum axis?
Or maybe I should call-out datum A-B that is defined by the top and bottom diameter...
RE: How to specify a cone as a datum
David
RE: How to specify a cone as a datum
I had a contract job designing gearboxes for machine tools. All gears and spindles got bell centers for consistent location.
RE: How to specify a cone as a datum
Tunalover
RE: How to specify a cone as a datum
We establish the centerline of the cone using a special chuck, then create the hole on this centerline.
So there is no easy way to call out a datum based on the centerline of a cone?
RE: How to specify a cone as a datum
Now, for the part that most people tend to miss. If the cone is used to generate the Primary Datum, it actually generates all three mutually perpendicular datum planes. The first two, as expected, are through the axis of the cone. The third is at the apex of the cone. The problem there is that this typically is not a real location, or one that is easily used. So, if you are using the cone to generate the Primary Datum, but you don't want to use the apex to generate that third plane, you will need to indicate that in a note.
Jim Sykes, P.Eng, GDTP-S
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RE: How to specify a cone as a datum
This limits how far the cone is pushed into the chuck.
The chuck adjusts to clamp down on the cone (at any position)