Angular orientation of two hexagonal drive features

[CoryPad]

I am joining a hexagonal hub to a shaft with a hexagonal drive feature. These two hexagons need to have an angular misalignment of 10 degrees maximum. What is a good way to specify that according to ASME Y14.5M-1994? An image is attached. Thanks.

 

[powerhound]

Dimension the hexes with basic dimensions, tolerance the hexes using profile of a surface, and call them out to the same datum refernce frame. Simultaneous requirements will ensure that they are clocked to each other but you have to establish the value that will ensure they are always within 10 degrees of each other.

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

 

[CoryPad]

Thanks

 

[pmarc]

I agree with powerhound that the hexes could be dimensioned with basic dimensions and toleranced with profile all around, however in my opinion this should be done on single part drawings. Then, on the assembly drawing I would just assign one width of one of the hexes as datum feature, and tolerance one of the widths of the other hex relative to it with a loose orientation tolerance. The value of the orientation tolerance should ensure that no more than 10 degrees of actual orientation error between hexes will happen.

If you just apply loose profile of surface tolerances relative to the same datum reference frame to both hexes on assembly level drawing, you will probably have to add additional profile tolerances without datum feature references to control form of the hexes tightly. Without this additional profile controls actual form of both hexes could become quite crazy.

 

[CoryPad]

Thanks for the further advice. I forgot to mention that each individual part has its own drawing (with GD&T for a hexagon), while the assembly drawing requires the orientation of the hexagons to each other. I will use profile on the assembly, and I have done the trigonometry to convert the 10 degree angle into the required profile height.

 

[pmarc]

And which feature the profile tolerance will be applied to on assembly drawing? Which feature(s) will serve as datum feature(s)?

 

[CoryPad]

I thought I would use the bottom surface of each hexagon on the assembly drawing. I am relying on a pocket guide from ETI (Alex Krulikowski) that shows profile of coplanar surfaces and implied self-datum. That should work fine to determine if the parts are misaligned. Each individual part drawing will have profile tolerances to control the 3 pairs of surfaces for the hexagons.

 

[pmarc]

Sounds like good idea. As long as both hexes are shown on the drawing aligned, the concept should indeed work fine.

Just keep in mind that the coplanarity-controlled-by-profile concept controls locational relationship of considered surfaces too. This means that in some extreme cases the actual assembly will meet the requirement of 10deg MAX between the surfaces, but the assembly may be rejected during inspection. Imagine actual part having these two controlled surfaces very close to 10 degrees to each other, but in addition there is a radial misalignment of the hexes due to (for example) certain positional error between hex portion of the shaft on the left and cylindrical portion of the shaft on the right. Assembly meets design intent, but the surfaces won't fit into profile tolerance zone. Do you see my point?

 

[powerhound]

I didn't notice that this was an assembly. It looks like you're on the right path.

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

 

[CoryPad]

This all makes sense, thanks guys.