Keyway/slot on shaft

Yes. This covers the symmetry about the derived median line of the part. It does not locate the slot along it though.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

It will ONLY cover symmetry (but rather position) wrt axis, because axis is the only datum you actually have.

ah, so add a c datum on the end face and add that to the frame?

Beat me to it, powerhound

doesn't the 1.625 give the position along the shaft?

It can't, because it isn't a dimension to either A or B and the FCF only includes the mutual A-B axis.

Datum A and datum B are the points at which the conical elements of the feature converge. One might argue that the cone has an axis, but then the two axes can be mis-aligned and how is that reconcilled?

So, either add a datum at the end of the part or add a point representing the convergence of one of the cones to dimension to.

If the shaft won't be mounted on the cones in the next assembly, use the outer surface of the shaft as the primary datum feature and one end as the secondary.

No,
Problems:
1) Most here, and ASME, do not like locating Radii with a position tolerance.
2) A & B do not appear to be functional datums, but mfg datums
3) Without "C" referenced in the framework you are instructed to ignore it, it does not apply, therefore you have an incomplete definition. You would be better with a 1.625 non-basic dim.
Frank

Powerhound: so if it covers the symmetry, is the best way to control the position along the shaft with a basic dim and to add a C datum? (see slot qu added c.jpg)

fsincox: I'm assuming you'd prefer to use the OD and end face as A & B. The orientation of the slot around the part is not important here only that it is symmetric about the axis (centreline of B datum). If that were done the 1.625 could be basic and the FCF would just be true position to A and B

You better replace 1.625 with dimension pointing to the center of slot.

OK, so add the C datum to the original and have the basic dim going to the centre of the slot? see attached.
Is the FCF valid as depicted? i.e. A-B then C

Does the shaft seat on A & B in the assembly?
Frank

@pedrof:
I dropped in picture related to dimensioning slots. There are several rules out there related to dimensioning and I suggest you get yourself familiar with them.

fsincox said:

Does the shaft seat on A & B in the assembly?

Click to expand...

No and neither is this shaft, which didn't stop ASME Y14 committee from including this picture into the standard:

@fsincox: The shaft doesn't sit on the cones, they are centers for tooling so I guess they are manufacturing datums.

@Checkerhater: I'll dim the slot as per the examples, I was really asking about the datum scheme and how best to control the symmetry and the position along the shaft with the correct use of basic dims and a correct control frame.

@fsincox: I think this is what you are getting at?

The ASME picture is an example of 'targeting' of a casting. That is, back-driving the locations of the machined features which are used as datums in order to find a condition that the rest of the casting simultaneously meets. Essentially one finds the part you want to end up with inside the cast material and create datum features that record its position.

The give-away is that the crank surfaces the piston rods will ride on are given an LMC modifier, ensuring that enough material will be available to machined the final shaft surfaces.

It's a way to satisfy a number of conditions simultaneously that would be difficult to otherwise handle, while at the same time effectively recording the particular orientation and location of the solution to the the question - where do the datums need to be to make the callouts true.

Once the pre-machining solution is found, the center cones are machined to record that solution. If the solution was incorrect the machining process would either leave unmachined casting surfaces or encounter unexpectedly large amounts of material to remove.

It's a way of using the standard to control a manufacturing process with a drawing. One could have skipped the step entirely and just applied control requirements to the finished part.

CH,
I did not say it was illegal or anything like it, I just pointed out it may be a problem as, I suspected and was right, it is not functional. Therefore, you can't take proper advantage of MMC which the mating part will most likely do.
Frank

@fsincox: So the other datum scheme (symmetry from the OD, and position from the end face) would be your preference) I posted that earlier but here it is again. I may go this route, saves ink.