ot being a production papermaker but an artist who uses sheets of paper and pulp for my art work, I had always found that my vacuum table press, which pulls up to 25 psi (pounds per square inch), was sufficient for my needs. The pressure is consistent through the 4' x 6' surface, it works quite well for molding and forming but does not lend itself well to the younger children's classes because of the number of students. The simple technique of placing the post between two boards and then treading out the water was an inexpensive and extremely practical method that had always served well with the large art classes until that fateful day just described.
Actually I guess I owe a lot to that young man because his "slide" galvanized me into action to consider how I could get a press designed and built to fit my needs. The project was put on hold when I left to study Japanese papermaking on Asao Shimura's washi tour in April of 1987. I had the great opportunity to see several varieties of old screw presses while in the Japanese workshops. The simplicity of their design was attractive and there seemed to be few parts to break, which is always important for me when I use equipment in classes. I soon gave up the idea of a screw press, however, no matter how much I liked the look, when I saw what strength it took to lower the pressing board the final distance. Since I often work alone, I need a press that is easy for me to use.
I talked over the idea with my husband, Don, a landscape architect, who would design and build the press. We sat down and went over all of my particular requirements. I wanted a press that would allow variable pressure, press at an even rate throughout the surface of the sheet, and have the capacity to handle a variety of sheet sizes. Also I wanted to be able to store and use the press outside my studio to eliminate water flowing on the studio floor. I wanted the press to be reasonably portable without my having to resort to a crane and I wanted the pressing boards to be as light as practical so I could change them around quickly and easily to fit the project. I also wanted the press to be safe to use and as unbreakable as possible and, lastly, I did not want it to be too expensive to build. And, yes, I had to admit, I wanted it to look as good as those charming Japanese screw presses.
Luckily Don is well equipped to design papermaking equipment as well as landscapes and the whole idea seemed like a good challenge to him. His first idea was to use a hydraulic jack. He discarded this idea because using the jack upright, pressing up, would mean I would have to move the 65 pound jack everytime I loaded the press. He could not mount the jack upside down pressing down because the jacks he looked at were all marked with words saying they could not be used upside down. He finally came up with the idea of using a scissor jack and this works just fine. It is also as lovely to look at as it is functional to use.
Don showed me one way to control the pressure, by varying the surface of paper to be pressed. A range of 6 to almost 100 psi was possible, depending on the size of the surface area of the paper in contact with the press board chosen for that size of paper. This lower pressure works very well for me since I work mostly with tree barks and other plant fibers for thin sheets of paper. The accompanying chart of calculations shows how to determine psi on various sheet sizes with one or more jacks mounted on the press.
Pressure at an even rate was solved by the pyramid pattern of the design and the boards were cut in several sizes to hold the paper sizes most used. Equal height stacks of the smaller sized sheets could be laid side-by-side. (Remember when figuring psi on these stacks to go by the square inches of the total surface area of all sheets in contact with the pressing board, not by the size of the individual sheet.)
Don chose redwood for the structure of the press for its weathering quality, strength, and beauty. I painted all of the redwood with liquid plastic to increase weatherability. He put small rollers on the four corners so that the press could be rolled on smooth surfaces. We decided against larger rollers because of the added cost. The press still weighs a lot so even with the rollers it takes some strength to move it. He used 3/8" plywood for the pressing boards, which are coated evenly on each side and the edges with liquid plastic. They are placed in the press in a pyramid pattern, which is essential for even pressing. The force from the jack goes down and out in a pyramid shape. If a part of one of the pressing boards extends unevenly beyond this pyramid shape, it will warp upward and interfere with the even pressure under the pyramid. Because of this, it is important to stack the boards evenly according to their dimensions within the pyramid shape when loading the press. It is equally important to position the post of paper to be pressed in the center of its pressing board to obtain the most even pressure all over the sheet. The largest four bottom boards are left in place all the time. When pressing, a plastic sheet is laid to cover these four boards, then another board of the same size goes on, then the post or posts of paper as near to the center as possible. The water drains away easily and when the post is ready to be moved, the boards directly under the post and the plastic can be removed for drying. I keep a plastic tarp over the top of the press when not in use to protect the jack from the weather.
There are few parts to break and I believe the press is as safe as we can make it. It is built of sturdy materials to be extremely durable under constant use. As to the expense, the jack cost $50 (available through Sears); the redwood, plywood, and hardware came to $150, and the liquid plastic cost about $20, for a total of $220 for the press.
I do not think a gauge of actual pressure is essential for my work, but Don is working on the possibility of using a strain gauge just in case this becomes important later on. I believe it is satisfactory for me to use eyes and hands to judge what pressure I want to suit the type of fiber and the finished paper I want. I do not recall seeing pressure gauges on any of the manual screw presses that I looked at in Japan although they may have used a series of notches for marking that I did not see. They told me that most of their presses produced a maximum of 12 psi. If a greater pressure is essential to your work, Don has shown on the chart and in the drawing how you can increase psi without changing the basic design by adding one or two more jacks. He tells me that by adding another beam assembly we can have two sets of three jacks for a total of six, but I am still trying to figure out how to turn six cranks without getting all tangled up!
