Pipes and Nails

Our first idea to mount a bicycle rim to the ghatta's grinding stone was to use a length of plumbing pipe with two nails welded to the end. Feeding the pipe through the stone's center hole, the nails would grip the sides of the key as the ghatta rotated. The top of the pipe had a cap placed on it. A hole was drilled through the cap, and a bicycle wheel bolted to it. The pipe is available in several different diameters and lengths. We hoped that the variability in grinding stone height and center hole diameter could be accommodated by using different pipes.

Domodar Karki of CRT gave us directions to our first water mill located about an hour south of Banepa (two hours south-east of Kathmandu). After several precarious motorcycle river-crossings, we spotted a ghatta 50 feet down, off the left side of the road. Although we found the ghatta in use, the owner (ghattera) had no problem postponing the grinding to help us test our system. (Although he did want money for raksi - a strong native rice wine - afterwards...) The basket holding the grain was quickly emptied and conveniently hooked up on the wall, well out of the way for our test.

We spent some time examining the ghatta in detail - this was the first operating one we had been able to closely examine. The runner (turbine and vertical shaft) was completely made of wood. The stone was much thicker than we expected - 10 inches thick with a 26 inch diameter. We could see no obvious place on the floor to mount a generator to, although there were several old grinding stones, which could in theory be used for support.

We were surprised to find that we could not even get our smallest pipe to fit into the top of the stone. The stones are hand-chiseled and we discovered that the center of the inner diameter varied significantly; although the cross-sectional diameter was a good 2-3 inches, it was hardly straight! The only way we were able to get our pipe into the hole was to lift the stone off the key and run it through upside down (the bottom was wider than the top, and could accommodate the extra width of the welded nails).

In order to lift this stone up and off the key, the ghattera and his son raised the stone by wedging pieces of wood under the lever connecting to the beam below the runner. This was the first time we had seen a grinding stone actually raised (even if it was less than an inch) and the mechanism seemed to work well. With a little effort, they were able to fit pieces of wood underneath the stone and pry it up and off the key. We ran our pipe through the bottom and then returned the stone back into position on the key. The stone was left in a raised position (i.e. the wedges of wood were left underneath the lever) so that the mill stone could freely spin without scraping the bottom stone.

We then attached the bike wheel and turned on the water. The belt exerted a great deal of force on the bike wheel; our mounting job failed immediately and the wheel became free-spinning. We were not able to tighten the nut down hard enough to keep the bike rim from unscrewing itself. It quickly became obvious to us that we needed to have something welded directly on to the rim itself.

Testing our device revealed a second key observation about ghattas: grinding stones do not rotate about a centered point. Having these stones off-center meant that we could not mount to anything to the stone itself. Our bike wheel - free-spinning though it was - followed a rather elliptical path, as it was wedged into the stone's center hole and in constant contact with the stone. It was questionable whether the pipe had even fit around the key, or was just turning because it was wedged into the grinding hole.

Key Lessons from this Test:

• Ghatta stones are hand-carved; features can vary considerably

• Ghatta stones can rotate off-axis and create a very irregular motion when turning

• The shaft mounting bike wheel to ghatta needs to be as skinny as possible to fit into central grinding hole

• Forces on bike wheel can be greater than expected; system needs to be robust