Trimming printed parts gently with a custom sanding block.
Many of the plastic pieces in my Mostly Printed CNC are meant to fit very snugly around a piece of steel pipe. When I was test fitting parts and pipe together, I noticed some problems with the fit. This issue appeared to have two causes. First, there were little blemishes on the parts – mostly hard bits of plastic stringing, especially near the edges. Second, the curves were not completely symmetric. This caused the part to rub against the pipe in some places, but leave a gap in other spots. This was probably due to a slight mis-calibration in my printer.
So, what to do? It is possible to scrape away plastic surface blemishes, but I wanted a gentle approach that kept a good curve. The fit was close but not good enough. Minor trimming printed parts was needed, not wholesale surgery.
Then, I hit on the idea of trimming printed parts using a custom-printed sanding block, shown on the left. The outer diameter of my pipe was 23.5 millimeters, and the thickness of the sanding paper was around 0.3 millimeters. So I designed a one inch long plastic cylinder with an outer diameter of 23.2 millimeters. This left space to wrap sand paper around the cylinder and then slide the device along the curve of the plastic part.
Trimming printed parts only in the right places
As shown in the right picture, this gentle approach to trimming plastic parts worked like a charm. You can see the places which had plastic removed (shown in grey) and the places that the sanding block left alone (still the original blue color.) The bulk of the smooth curve was left alone. The places which were most effected by the poor calibration (the edges of the curve that fits around the pipe) were reduced in size. The parts now fit snugly and properly around the outer diameter of the pipes.
I suspect there are many opportunities to custom make little “helpers” or jigs to support project construction. This sanding cylinder was a good place to start.