Pottery in Australia Vol 17 No 1 Autumn 1978

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1 \I~c-uum (;.\lAt"n!!>F.9.. .... PUCsMILL rwo:rrAGE BARREL PUGMILL SINGLE-BARREL PUGMll.L shredded clay falls to the lower level, keeping the vacuum chamber from becoming blocked with clay. The problem with this design is not one of performance but the cost of manufacture. A new machine of this design is far beyond the average potter's budget. The single-barrel design is simpler to make with less engineering, thus a lower final cost. Harry Davis, a potter well known to most in the pottery world, produced a plan several years ago which went a long way towards reducing the problem of the vacuum pulling clay into the vacuum chamber. He overcame this by using a single shaft with blades set at differential pitches and what he termed a breather valve in the vacuum chamber. A number of potters built these machines and they have given good service, except for two problems: the mild steel blades pit and corrode badly over a period of time, and the hinged breather valve needs constant maintenance. During 1975 Geoff Hill, who manufactures Yenco wheels, approached Harry Davis to enquire if he could use Harry's design with some modifications. This was agreed upon, so Geoff set about re-designing the original pugmill and it is now available on the market. The main modifications were the use of a split aluminium barrel (easier to clean) , a stainless steel shaft and blades (less resistance so a smaller motor needed to power the pug) , a plunger on the hopper, which makes the machine safer and also enables turnings and slops to be more easily fed into the pug, a high-capacity piston vacuum pump with water trap and a vacuum reading of 26 in-28 in mercury. One notices an appreciable difference when the vacuum reads above 22 in mercury. Milking machine vacuum pumps are not very suitable because they are designed to operate at 15 in mercury. ln theory and practice, the higher the vacuum the better quality clay produced. There are 28
other minor innovations on the Venco pug, such as a heavy perspex cover on top of the vacuum chamber, which is quickly removed for cleaning. But the most innovative and important feature is the solution for maintaining the vacuum to the shredded clay in the vacuum chamber, and inhibiting the action of tbe vacuum in drawing the clay towards the source of vacuum. This solution eliminates the moving parts involved with Harry Davis's breather valve. In the Venco design one blade on the shaft scrapes an opening slit to the vacuum source each revolution; it's foolproof. When considering the size and capacity of a pugmill, it's wise to go neither too small nor too large. Most of the small pugrnills with 4 in barrels and 2 in extrusions are only toys to the serious potter. One could knead more clay per hour by hand than these small pugs produce and very few of them are de-airing models, though some have an application in the re-cycling of scraps. Large pugmills above 8 in diameter barrels are usually designed to be fed by a primary mixer, not by hand, so one could have problems keeping up the feed to these machines; also the barrel could hold a massive quantity of clay before the machine started pugging, a problem if one wanted to run a new body through the machine. So my recommendation would be a pugmill with a barrel diameter of 8 in and extrusion diameter of 4 in; this size would have the capacity to produce one-half to three-quarters tonne per hour, depending on the rate of feed and whether the screens were clean or partially blocked. The logic behind the choice is that one would normally only use 100 kg of clay per throwing day, unless very large pots were made. This 100 kg of clay could be put out and run through the pugmill in about ten minutes. If cutting harps were used instead of weighing out, the kneading and balling up time would be reduced by 90% . One bas the choice of building a pugmill, buying a second-band unit, or buying a new one. Harry Davis's plans are still available; if you are either a good welder or have access to cheap engineering, building your own is still a proposition. Some good second-hand machines appear occasionally, both two-stage and single barrels. Try to purchase these at auction or privately as they are usually bargains. Some small commercial potteries are currently going to the wall, so keep your eyes open and ears to the ground. If buying new I would recommend the Venco Mark IT de-airing pugrnill for a number of reasons : its good design, impeccable engineering, the geared motor drive (less maintenance), the performance, and the man who makes it donates $50 for every machine sold to Harry Davis's Peru project, and provides one of the best back-up services in Australia. Should I say it? Yes, I will: Geoff Hill listens to potters' problems and tries to design to suit their needs, a rare situation in Australia, and his machine is less than half the price of its imported equivalents. Finally f will offer some bard-learned hints on how to get the best out of your de-airing pugrnill. Given one accepts that the pugmill is not a primary mixer, and does not try to feed in dry clay and water, expecting perfect plastic clay at the other end, there are few problems to be encountered. The screens can block up and slow the flow of clay, especially if one uses heavily grogged clay. We clean the screens periodically, usually when the rate of extrusion and capacity of feed considerably slow down. It's amazing what is found on the screens-hair, lost sponges, pot stamps, ciggy butts-you name it, if you have lost it, it's in there. Vacuum leaks are sometimes a problem. if the gauge is not giving a high enough reading, turn the motor off and listen for leaks. Once traced, the leak can be sealed with heavy-duty, waterproof grease or thick 29
Page 2 and 3: EDITORIAL COMMITTEE Editor Janet Ma
Page 4 and 5: EDITORIAL The publication date of t
Page 6 and 7: statement, even the repetition of o
Page 8 and 9: 6
Page 10: FAENZA 1977 The 35th International
Page 13 and 14: CERAMIC FIBRE KILNS THE DAWN OF
Page 15 and 16: A NEW ENERGY - SAVING KILN FOR POTT
Page 17 and 18: efractory fire-brick structure of t
Page 19 and 20: I UO:::!*- I , 70
Page 21 and 22: should enable potters to be more im
Page 23 and 24: CHERYL SMALL: "Peter the hot bread
Page 25 and 26: L YREBIRD RIDGE POTTERY A BEGINNI
Page 27 and 28: Martin Kelly was the first trainee
Page 29: AN AIRING ABOUT DE-AIRING PUGMILLS
Page 33 and 34: ---------------- A CLAY MIXER Leona
Page 35 and 36: WARREN PALMER : Shino glaze, cone 1
Page 37 and 38: RECENT WORK (continued) FREDERIC CH
Page 39 and 40: RECENT WORK (continued) IAN WfNTER:
Page 41 and 42: RECENT WORK (continued) GREG DALY :
Page 43 and 44: The material that worked beautifull
Page 45 and 46: POTTERY IN CRETE Penny Riley In Apr
Page 47 and 48: "'"eT c.. L4P ~"'T F I"-'-' TO fJ.
Page 49 and 50: SOME THOUGHTS ON CRACKS AND TEXTURE
Page 51: College Courses Col h~lIe Coursels)
Page 54 and 55: 51
Page 56 and 57: ticles act as constant irritants to
Page 58 and 59: glaze mixing, should be isolated as
Page 60 and 61: serving as an excellent guide to po
Page 62 and 63: on view in state galleries. It also
Page 64 and 65: EXHIBITION REVIEWS H1ROESWEN Pastor
Page 66 and 67: Copacabana beach (near Gosford), is
Page 68 and 69: DULCE HERD At Potters' Cottage, War
Page 70 and 71: Adele Hollywood, Prahran College of
Page 72 and 73: section of some of the ceramic scul
Page 74 and 75: MEMBERSHIP : There are three catego
Page 76 and 77: SA Studio Potters' Club Jolanta Jan
Page 78 and 79: NEWCASTLE CERAMIC GROUP continues t
Page 80 and 81:
"... a true museum-piece, too good
Page 82 and 83:
HEAVY WEIGHTS OR BANTAMS WHEN IT
Page 84 and 85:
RUSSELL COWAN's for RUSSELL COWAN,
Page 86 and 87:
KRAUS R. C. ELECTRIC WH EEL MOTOR:
Page 88 and 89:
WALKER CERAMICS Factory and Showroo
Page 90 and 91:
POTTERS EQUIPMENT by DOALL THE "DOA
Page 92 and 93:
DIAMOND CIRAMIC SUPPLIES IN.S.WJ Pl
Page 94 and 95:
TALISMAN POTIERS' EQUIPMENT Manufac
Page 96 and 97:
POTTERS EQUIPMENT 14 PITT STREET RI
Page 98 and 99:
DESIGNED & BUILT IN AUSTRALIA FOR A
Page 100 and 101:
POTTERS' EQUIPMENT 74 WILSON STREET
Page 102 and 103:
terrapotta stoneware by anne alexan
Page 104 and 105:
VENCD ELECTRIC POTTERS WHEELS, PUG
Page 106 and 107:
VENCO ELECTRIC POTTERS WHEELS, PUG
Page 108 and 109:
KI LNS. FURNACES. POTTERY WHE ELS.
Page 110 and 111:
12A George Street, Blackburn, 3130
Page 112 and 113:
KILN SERVICES STATEWIDE REPAIRS Re-
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Pottery in Australia Vol 17 No 1 Autumn 1978

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