I’m starting the 5th version of the Prairie Grass prototype. I’ve taken into the studio all five of the previous prototype stalks and taking them apart. Most of the pieces can be reused: the 5, 1/2″ conduit pipes, all the stainless rods and the seedpod-wire assembly. The plugs and the sheaths will need to be relaced.

When reassembled, prototype number 5 will be permanently installed about 50 feet to the south of the current location. Both locations are outside our studio windows.

We have learned from each prototype. Version 4 revealed a few weaknesses that we intend to address in version 5. We will be redesigning and reprinting the Plugs and the Sheaths in ASA filament. This page will track our progress.

The Sheath

The sheath slides down over the stainless steel rods and holds the 1/16 inch diameter wires. It is 6.5 inches tall. The wall thickness is 1/8 inch.

The tricky part is getting the right inside diameter so that it fits perfectly on each of the 3 different diameter rods. This can vary with type of filament used, and the printer parameter’s.

ASA: 3/8″ rod = ID = .375″ (.378)

ASA: 5/16″ rod = ID = .3125″ (.3155)

ASA: 1/4″ rod = ID = .25″ (.26)

ASA: 3/16″ rod = ID = .1875″ (.197)

ASA: 5/32″ rod = ID = .15625″ (.166)

The diameter in brackets is the inside diameter used to allow the rod to slide into the sheath naturally with just hand force. The ASA filament used is 1.75mm (0.75kg) Fillamentum (Metallic Grey). $43.21

The plugs had two issues. They were too shallow. In high winds, they could shimmer their way up and out of the top of the conduit. So the new plugs will be 3 inches tall instead of 2 inches. And the bottom of the plug will have a threaded hole for two apposing flathead 5/32″ bolts. See drawing.

The bolts have two functions: they make it impossible to shimmer out of the conduit; and they create a mechanical joint that does not require epoxy.

This make maintenance and/or replacement as simple as unscrewing two bolts.

The other issue is that, with a lot of movement they began to widen the hole in the PLA. We will address this issue by using a harder filament and printing them solid (zero infill). Plus they will be epoxied into the plugs.

The Plug

The plug is the 3d printed part that slides into the conduit. It has a lip at the top to keep it from sliding past the top of the pipe. It has several holes to hold the stainless steel rods.

Conduit Diameters…
ID = .61, OD = .72 (ID = .63)
Perfect fit for conduit.

1/4″ holes + .015 (.02)

3/16″ holes +.015

5/32″ holes +.015

1/8″ holes +.015

+.015 is snug, and .02 is slightly loose. We are using .02 because they will be epoxied.

There are a few more issues that we might consider at this point to make maintenance easier.

Thinking About Maintenance

I definitely like the carter pin idea and think I’ll test it. I’ll make the ID smaller so it goes in easier and will com out easier.

Adjustments coming…