Interference Fit D-shaft 1

[Mandrill22]

Is there a standard, perhaps ISO, for oversizing a D-profile shaft and mating hole? It's going to be a softer aluminum part (not a shaft, but a small length piece with a D flat), 8mm OD, going into 7075-T6. It needs to have 0 room for unwanted movement, so a small interference is required.

 

[Mandrill22]

Alternatively, I could really use any shape with a flat or flats.

 

[mxv]

I do not know of any ISO standard for this, but i would just measure the widest part of the shaft and use a standard shaft and hole fit call out as if it was just a normal round shaft. When making the drawings for both the shaft and mating part, instead of calling out a diameter with the fit class, I would call out the shaft profile nominal dimensions and use a profile of a surface geometric callout and the corresponding tolerances from the shaft fit you chose previously. Also, I highly recommend adding circular cut reliefs to the female D shape so the whole part can be machined without a wire EDM or custom broach.

Hope that helps! Also anybody that knows better than me feel free to chime in if you know a better way. I'm curious as well.

 

[tbuelna]

I've used these rotary broach tools. They are precise, work extremely well in materials like aluminum, and can be used on any mill or lathe. They come in standard shapes like square and hex, or you can special order a double D profile. Bore the specified diameter hole and chamfer in your part, broach the profile, measure the distance between flats, adjust for your interference fit, and machine the shaft accordingly. Make sure to relieve the profile corners on your shaft so that there is only contact along the flats with clearance at the internal profile corner fillets.

The rotary broach cutters are inexpensive, but the basic tool holder is $425. Worth the cost for a dozen or more pieces. But for just a few pieces the cheapest method is probably to CNC mill the internal profile with the smallest diameter end mill practical for the hole length (ie. L/D < 8.0).

If you are feeling ambitious, you can even purchase a $50 parts kit to make your own rotary broach tool holder.

Hope that helps.
Terry