DFM Guidelines

=DFM Guidelines= In order for manufacturing to effectively do its job we need the mechanical teams to have a healthy understanding of what is and isn't possible to make and have an idea for how their part will be made in their head when they publish a drawing file. To this end we have created the following DFM guidelines for quick reference from design teams:

Primary DFM Presentation
During the Fall 2021 onboarding cycle the team was given a presentation on design for machining, it was designed to be readable without a speaker, and is a good first resource for reviewing DFM principles.

Bad DFM Examples
Other than lecture material, we're also hoping to maintain a running list of bad DFM examples, explaining what not to do and why, so designers can learn from their mistakes. We don't meant to put any designers on blast by doing this, these are simple mistakes to make that nobody taught you how to avoid, the goal here is to learn by doing.

Press fit on a waterjet part


This part submitted from Arm depicts a plate that's supposed to have a press-fit with a bearing. Press-fits are very specific tolerances, but the exact tolerance zone will vary depending on the manufacturer. Labeling the dimension as "bearing press fit" doesn't contain any helpful information for the machinist, as someone reading the drawing file would have no way of knowing what tolerances the specific bearing will need. Additionally, in the bottom-right we see that this part was designed to be machined on the waterjet, a machine that doesn't get tolerances any smaller than 0.01". This means that a press fit tolerance is unattainable from this drawing file alone, both due to the lack of available information, and due to the limitations of the machine.

Instead, the designer should look at the data sheet for the bearing they have ordered to determine what the tolerance zone for this specific bearing is, and placed that information in the drawing file so the manufacturer could tell what they wanted. They also should've kept in mind that this part wouldn't be make-able on the waterjet alone due to the tight tolerances. Instead this part will be made by taking a flat piece of metal and super-gluing it to a flat piece of sacrificial material, had all the profiles machined out, and then removed from the plate with acetone.