Allowance for Stepped Alignment Pin

[TryingToHelp]

I would like to create a dimensional scheme that would allow a machinist to create a stepped alignment pin based on the hole diameter. While the protruding portion of the pin would be controlled to tighter diameter tolerance, the interference fit portion of the pin would be allowed to have a greater diameter tolerance. I am facing the following issues with this idea.

1. If the hole is within the allowable diameter range of the alignment pin protrusion, then the pin could be created without a step making the existence of the step conditional.
2. If the hole is larger than the allowable diameter range of the alignment pin protrusion, then the step on the alignment pin should be located below the surface of the hole.
3. If the hole is smaller than the allowable diameter range of the alignment pin protrusion, then the step on the alignment pin should be located above the surface of the hole.

Has anyone seen this kind of allowance for stepped pins before and if so, how was this allowance achieved.

 

[ctopher]

Allowing the machinist to come up with the final design is open for errors.
I suggest dimensioning the pin how you need it. You can add a table on the dwg with configurations.

Chris, CSWP
SolidWorks
ctophers home

 

[3DDave]

There is nothing wrong with creating a procedural document and referencing that on the drawing. This is often done for adaptable items such as shims. I've done so for a case where the fundamental operation of a CMM was unable to resolve the geometry given on the drawing and the procedure was essentially to perform the math the CMM software could not manage.

What you are missing from the description is the amount of interference you want the pin to have with the hole. This will require in-process inspection steps and a related inspection record for both the pin and the hole.

Usually the cost of the additional steps exceed the cost of a more careful setup for producing the hole with the suitable tolerance. Custom fitting would not be recommended.

A more typical approach is to thread the plate and use a threaded step pin and use locking compound to retain it.

 

[Eric Gushiken]

Can you design it so that there's an undercut groove at the junction where press-fit portion and the protruding portion meet? This way there won't be any interference with the diameters regardless of the tolerances.

 

[TryingToHelp]

Thank you all for the replies. The parts that this question relates to are low volume and at a cost that leans toward fixing issues verse remaking parts. It is easier to make a pin fit the hole verse remaking the parts due to a hole being slightly out of tolerance. The dimensional scheme for the stepped pin would have a note that states that a specified amount of interference is required.

I agree that this may be an issue that can be resolved in words verse using a dimensional scheme.

The idea of using a undercut would allow the step to be located within the undercut region, thereby eliminating potential issues during assembly. The first problem remains in that there may be instances, hopefully more often than not, that a stepped pin would not be needed which could lead to issues for the quality department as the step would not exist for inspections.