Make the bottom rollers from hardened steel 20-25 mm in diameter with fine longitudinal grooves at a 0.5 mm pitch, and the top rollers from steel cores covered with glued and wrapped leather 3-5 mm thick. The grooves grip the fiber without crushing it and the leather grips with a little give, but the pair works only if both rollers are parallel, true and the same diameter along their length.
Part of Spinning Frame
Choosing materials and making the steel and leather-covered rollers that form each drafting pair.
A Roller Pair Is Two Different Surfaces That Must Act As One
The overview gives the construction. Bottom rollers (driven): hardened steel, 20-25 mm diameter, with fine longitudinal grooves of 0.5 mm pitch; the grooves grip the fiber without crushing it. Top rollers (pressure): steel cores covered with glued and wrapped leather, which grips and yields slightly, with a cover 3-5 mm thick. The two details are on their own pages: Fluted Bottom Rollers and Leather-Covered Top Rollers.
What this article adds is how they combine. The pair grips only along the line where the leather is pressed into the flutes, so every error in diameter, straightness or parallelism changes the grip along the roller. A section with weaker grip lets fibers slide at that part of the nip, and a section with stronger grip pulls them harder. Both show up as an uneven yarn.
What You Need
- Steel stock that hardens (see Tool Steel) for bottom rollers.
- A lathe and a way to cut flutes (Lathe Fundamentals, Gear Cutting for the indexing method).
- Soft, even leather and an adhesive (Leatherwork).
- Journals for the shaft ends and bearings (Bearings and Bushings).
Method: Building A Pair
Step 1: Turn the bottom roller to size and make the journals concentric with the body.
Step 2: Cut the flutes, evenly spaced around the circumference, with a graver, planer or milling cutter. The overview’s pitch is 0.5 mm.
Step 3: Harden and temper and polish the flutes so no burr remains.
Step 4: Turn the top roller core and cover it with leather glued and wrapped; the cover thickness is 3-5 mm. Trim and grind the leather true while mounted on its own journals.
Step 5: Test the pair: mount both, apply the weight, and turn by hand. The top roller should turn smoothly with the bottom roller, with no flat spot or wobble.
Worked Example
A bottom roller of 25 mm diameter has a circumference of π × 25 = 78.5 mm. With flutes at 0.5 mm pitch there are 78.5 ÷ 0.5 = 157 of them around the roller (if the overview’s pitch is measured along the circumference). Cutting them evenly means indexing 157 times with a divider that must not drift; the lesson of Gear Cutting is that spacing errors matter more than flute shape, so an error that accumulates round the roller closes the last flute short.
Common Mistakes
- Mismatched diameters between rollers in a row, so that drafts differ across the frame.
- Uneven leather thickness, which makes the nip pressure vary along the roller.
- Left-over burrs on the flutes, which cut fiber.
- Leather that dries and cracks; keep it dressed.
Safety
Grinding and cutting hardened steel and leather dust
Wear eye protection when fluting and grinding. Hardened rollers can shatter if untempered. Once built, the pair is a nip that draws in fingers, so follow Drafting Rollers and keep hands out while the frame runs.
What’s Next
- Learn next: Fluted Bottom Rollers — making and fluting the steel roller
- Combine with: Roller Weighting — the pressure that presses the leather into the flutes