The Rubber Horse Brush: Crossed, Notched Ridges on a Leather Plate

"My present invention relates to a horse-brush adapted for use especially after the hair has been combed with a bristle brush." "The edges B need not be sharp like a knife-edge, but are preferably very narrow, as they act as the scraping or polishing edges upon the hair when the brush is in use." "Cut into both series of ridges are notches G, so that the edges in use will the more effectively polish and clean the hair."

Draw a mould in CAD: an open tray 10 × 14 cm inside, whose floor carries V-grooves 5 mm deep at 8 mm pitch in two sets crossing at 60 degrees, with a small rib across each groove every 2 cm to form the notches. Print it in PLA. Spray the mould with release and let it dry. In gloves, mix the urethane rubber by the kit's instructions in a cup, stir slowly with a dowel, and pour it in a thin stream into one corner until the grooves are filled and a 3 mm back has formed. Leave it to cure as long as the kit says, then peel it out. Cut leather to the pad's size, coat the leather and the back of the pad with contact cement, let both go tacky and press them together. Dust a piece of wool felt with flour and count the strokes the pad takes to lift it, then dust it again and compare with the palm of a gloved hand.

**Alexander R. McDonnell** of Littleton, Aroostook County, Maine, filed US 654,751 on 1 May 1900; it is dated 31 July 1900. He made the crossing ridges "from rubber in a single piece". **Honest limits.** A cast urethane stands in for McDonnell's rubber. The notebook treats every ridge top as touching at once. Force and sizes are examples; your stroke counts are the result.