Keyway/slot on shaft
Keyway/slot on shaft
(OP)
Just seeking opinion on using a true position on a key way slot on a round shaft. Datums are A and B in the centres at each end.
Does this cover symmetry of the slot about the part axis?
Does this cover symmetry of the slot about the part axis?





RE: Keyway/slot on shaft
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Keyway/slot on shaft
RE: Keyway/slot on shaft
RE: Keyway/slot on shaft
RE: Keyway/slot on shaft
RE: Keyway/slot on shaft
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.
RE: Keyway/slot on shaft
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
RE: Keyway/slot on shaft
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
RE: Keyway/slot on shaft
RE: Keyway/slot on shaft
Is the FCF valid as depicted? i.e. A-B then C
RE: Keyway/slot on shaft
Frank
RE: Keyway/slot on shaft
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.
RE: Keyway/slot on shaft
No and neither is this shaft, which didn't stop ASME Y14 committee from including this picture into the standard:
RE: Keyway/slot on shaft
@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.
RE: Keyway/slot on shaft
RE: Keyway/slot on shaft
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.
RE: Keyway/slot on shaft
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
RE: Keyway/slot on shaft