Climbing holds

When my kids got interested in rock climbing my natural first thought was to build them a climbing wall. Okay, I like climbing as much as they do, probably more, but the kids always make a good excuse. "But sweetie, I bought the cnc vertical mill for the kids." As an avid 3d printer I thought why not 3d print some climbing holds?

At first blush 3d printing seems ideal for the job, but on closer investigation it presents some problems. The first is strength. 3d printed parts can be weak especially when stressed across the layer lines. They can be made stronger by making them denser up to the point that they are 100% solid, but this adds dramatically to the cost and print time. A fist sized climbing hold printed at 100% infill would take between 12 and 24 hours to print. This is compounded by the tendency of large solid prints to fail by peeling off the build plate as they are being printed. It typically wastes a lot of material which brings us to another problem. 3d "ink" is expensive. Most of my machines use plastic filament which costs a minimum of $20-30 per kilo. So we are looking at $5-$10 a shot to try to print something which probably won't work and may not be strong enough if it does. Given that climbing wall requires hundreds of holds this was beginning to look like a real non-starter.