Looking down at the loom from above, if the loom has empty channels in the castle, then you can add four shafts. If there are no empty channels, then you cannot add shafts. A four shaft loom (without the empty channels) cannot be converted to an eight shaft loom.
Schacht Spindle Company, Inc. was founded during the back-to-earth movement of the late 1960's and its accompanying craft resurgence. Their first loom was a simple tapestry loom, a version which they still make today. Over nearly 50 years, Schacht has developed a broad range of high quality hand weaving and hand spinning tools, including their popular Cricket Loom and Ladybug Spinning wheel. Schacht’s mission is to create beautiful and well-designed products that enhance customers’ weaving and spinning experience through innovative problem solving, creative ideas, skilled woodworking and craftsmanship, and friendly, knowledgeable customer service. Schacht’s family owned business is located in Boulder, Colorado.