Grinding and Buffing Wheel for the Great Machine
Now that I have created the motor, or the tread-wheel portion of “The Great Machine”, I am working on a brake to control it, the main drive shaft, and something for it to run. One of the simplest useful tools I can think of is a grinding and buffing wheel machine.
Theophlis (from about 1100 AD) talks about smoothing file blanks on a grinder before cutting the teeth1. Earlier grinders seemed to be hand cranked like the example pictured in the Luttell Psalter, Fig 12. Note the large size of the wheel. I have seen some pictured as if they were twice this size where the grind man worked from the top of a large frame. Perhaps they were adapted from used mill stones. Leonardo da Vinci drew a pedal powered lathe in the late 1400’s3 and we see a similar adaptation to the grinding wheel in 1570 fig 24. Pedal power seems to be a later adaptation perhaps contemporary with attaching these machines to water and tread wheels. I can’t say for sure weather pedal power existed earlier than Da Vinci or not. Agricola in 1556 had woodcuts for pedal powered bellows along with many manual, water, and tread-wheel powered versions.5 I built a pedal powered grinder of old pedal grinder parts, see Fig 3.6 It is “fixed up” with modern hardware but designed to be in form and function like the one in Fig.2. The original parts were beyond restoration and I was not interested in rebuilding the entire framework and bucket of wood. I wanted the experience and capability of using a pedal powered machine and thus discovered it is difficult to hold a part steady while pedaling at the same time. I wanted both hands and both feet free to control the part and more power!
Leonardo da Vinci lists knife grinding and sharpening, as well as burnishing arms, among the things that water power could be used for if the Arno River could be rectified.7 The grinders and polishers Leonardo had in mind were probably similar to the ones pictured 100 years later shown in Fig. 4.8 and Fig.5.9. A smaller system of this design would be perfect for The Great Machine. Note the large size of the wheels in Fig. 4 & 5. They look to be about 3 or more feet in diameter. The polishing wheels in Fig.5 appear to have some sort of applied surface such as a thick felt or leather belt to hold polishing compound. Contrast these to a modern buffer as shown in Fig. 610 which has only a 6 inch wheel (See soda can for scale.) and is made of pieces stitched together Although some modern buffing wheels are a bit larger than the one shown, they go on motors that are designed to run slower.
The large wheel size was important for the medieval grinders to work properly. Modern machinist will talk of “sfm” meaning “surface feet per minute”. This number can be calculated by multiplying the circumference in feet of a cutting tool (buffing and grinding wheels are considered cutting tools) by the revolutions per minute that its motor turns. Each type of tool and material has an ideal sfm that it machines best at. For grinding and polishing wheels, it represents how much grinding surface goes past the object being ground or polished in a given amount of time. Too much speed heats up and or burns the metal while too little is simply slower and less efficient. The 6 in. modern wheel above runs at 1725 RPM on its ¼ Hp motor or at about 2700 sfm. My dogs run their wheel about 20 RPM and I plan on gearing that up to 60 RPM on the main drive shaft. I originally planed on making a 28 in. buffing wheel from material sewed together from old blue jeans. (The 28 inches is about as big as the material will allow.) The 60 RPM gives a sfm of 440 fm or only 1/6 the sfm of the modern wheel. A 3 foot diameter wheel would bring the sfm up to 565 sfm. If the water wheel turning the toothed gear in the period picture goes about the same speed as my dogs then I would estimate from the gear diameters that the shaft rpm would be about 100 RPM and the biggest wheel at about 2/3 the height of the workers. Figuring the workers at 5.5 feet tall gives an estimate for the largest wheel of a sfm of about 1150. Running my 28 in. buffing wheel at two and a half times the mane shaft speed would put my sfm at about 1100, or similar to the large sized wheels in the picture. If I made my wheel 3.5 ft in diameter then the sfm for 60 RPM is 659 and 1320 if it were doubled. The sfm would be 565 or 1130 for a wheel only 3 ft in diameter The bottom line is that doubling the speed from main shaft to grinder should make my machine run at about the same sfm as the medieval one. It is worth noting that there are wheels of different sizes in both medieval pictures. It is unknown weather this is because some of the wheels are partly worn or weather it to make allowances for different sfm applications. The sfm works out to be about 40% of the modern version. For comparison sake I timed myself as if I was hand buffing with a 6 inch stroke at 165 strokes per minute. That’s about 330 sfm figuring as if both stroke directions would be equally effective. This would be a pace that would be impossible to keep up more than a few minutes especially when a little more pressure is used. It is only about 12% of the modern buffer and 30% of the period machine. So the period power buffer would be 3 times faster and far more sustainable than hand buffing. It would be a very effective tool even if not up to modern standards. I have the option of gearing up the buffer to go faster and I may try that eventually but there is a limit to how much speed or RPM the period bearings can handle before heating up with friction or getting wobbly due to balancing issues. Large wheels running at slower speeds were the medieval solution.
By careful design I can use the same framework for grinding and buffing, or to rotate a wine barrel for tumbling and polishing chain mail or by adding a rail, head, and tail stock to create a lathe. My system is small enough that it probably won’t be able to power as many wheels as is shown in figures 4 and 5. I therefore will only set it up to run a few.. I plan on designing it so that pulleys are interchangeable as well as the grinding and buffing wheels. Eventually I hope to be able to have several buffing wheels with different grits and abrasives. I have collected several large grinding wheels from broken peddle grinders which I wish to use. See Fig. 7. See Figs. 8 and 9 for some undimentioned but roughly to scale drawings of what I plan for the grinder-buffer and the barrel-tumbler and lathe attachments. Fig 10 is an 18th century hand cranked barrel tumbler simular to the one I have in mind.11 It was used in processing leather, but such a tumbler has many uses.
1 Theophilus 1979, 93
2 Backhouse 2000, 37 909 9 (F.78 verso of Luttrell Ssalter)
3 Reti and Dibner. 1969, 51 Originally From Codice Atlantico di Leonardo da Vinci (C.A.,fol. 38LR)
5 Agricola 1950, 211
6 Authors Photo
7 Reti and Dibner. 1969, 90 Originally From Codice Atlantico di Leonardo da Vinci (C.A.,fol. 38LR)
8 Stradanus, (1580's)http://posner.library.cmu.edu/Posner/boo
9 Price 2000, 264 (From Hausbuch der Mendelschen c.1571)
10 Authors Photo
11 Diderot 2002, pl vi
Citations For Grinder
Agricola, Georg, Herbert Hoover, and Lou Henry Hoover. 1950. De re metallica. New York: Dover Publications.
ISBN0-486-60006-8 LCCCN A51-8994
Price, Brian R., David Edge, and Alan Williams. 2000. Techniques of medieval armour reproduction: the 14th century. Boulder, Colo: Paladin Press.
Recueil de planches sur les sciences, les arts libéraux, et les arts méchaniques, avec leur explication Arts du cuir. 2002. [Paris]: Inter-Livres.
Reti, Ladislao, and Bern Dibner. 1969. Leonardo Da Vinci, technologist: three essays on some designs and projects of the Florentine master in adapting machinery and technology to the problems in art, industry and war. Norwalk, Connecticut: Burndy
Originally From Codice Atlantico di Leonardo da Vinci (C.A.,fol. 38LR)
Stradanus, (1580's by Stradanus., Straet, Jan van der, 1523-1605) http://posner.library.cmu.edu/Posner/boo
See web page above for picture.
Still working on proper form of documentation but I think I'm getting better. If you can't track where something came from, let me know.