Better precision with PCB stand-offs.
These are the default stand-offs that came with our MDC pick and place machine.
While assembling a medium-sized PCB panel, we found a problem with the stand-offs. The larger the PCB, the more flexible it is, and without proper support underneath, the PCB would move up and down as much as 0.5-1.5mm when the machine was placing components. This was enough to make some of the previously placed parts to bounce off the PCB and become unaligned.
After measuring, we saw that the PCB is located about 38.0 mm above the base plate of the machine. The height of the stand-offs is set by the securing the nut against the base of the stand-off. It is quite tricky to get the correct height, and a difference of only 0.5 mm can be quite substantial on a large panel.
To get our stand-offs better aligned, we prepped them with more bolts and washers. This makes it easier to come as close to 38 mm as possible. You can see the results in the picture below: