Pocket Duplex Slide Rule Cursors Evolution Evolution in the Cursors of the Pocket Duplex Slide Rules Shapes, materials and Manufacture By J.G. Fernández

Pocket Duplex Slide Rule Cursors Evolution The Slide Rules The considered pocket duplex models from Faber Castell (1958 – 1975): 62/8262/83 62/83N62/82N 63/8263/83

Pocket Duplex Slide Rule Cursors Evolution The Cursors 62/ / /83N 62/82N 63/82 63/83 62/ / Evolution reasons  Market competition  Technology improvements  Product optimization Evolution tracking  Patents?  Time on sale? [1]

Pocket Duplex Slide Rule Cursors Evolution Cursor Elements Faces (front and rear) or windows 2.Runners 3.Spring strap 4.Closure screw (and nut) 5.Cursor Lines (peripheral and central or main one) 6.Cursor Marks 7.Letters to identify the use of the marks (usage letters) 8.Sliding Rods

Pocket Duplex Slide Rule Cursors Evolution First Cursor: 1956 (62/82, 62/83) Runners Two halves White (green text) Rounded corners (& square) Plastic? Faces Transparent plastic Red peripheral lines at same distances from face edges Main line not centred with face Widths Runners: stability without protruding from rule body Faces: marks and lines layout, readability, end of scales reach, aesthetic ratio? (62/82)

Pocket Duplex Slide Rule Cursors Evolution Main Elements Faces Planar surfaces from acrylic resin “plexigum” (or plexiglass) [4] from injection Holes on top of runners Thicker at top and bottom ends Runners Halves of white resin, poured “through” the cursor face holes. Ambient temperature process, not to affect the faces. Pouring sense Face Runner Assembly

Pocket Duplex Slide Rule Cursors Evolution Other Constructive Elements 1.Riveted spring strap 2.Closure-screw nut 3.Hand assembly elements 4.Metal rods to complete cursor halves fixation

Pocket Duplex Slide Rule Cursors Evolution Lines, Marks & Text Engraving process [4]: Soft impression of lines with a “warm” dividing tool (clean and sharp results) Red colour rubbed into peripheral lines Black colour rubbed into central line and marks Final wet polishing of cursor inner face Printing process: Thermal printing Green colour rubbed into characters Final wet polishing of runner surface

Pocket Duplex Slide Rule Cursors Evolution Engraving Options WARM HOT

Pocket Duplex Slide Rule Cursors Evolution Second Cursor: 1967? (62/82, 62/83) Runners Two halves Integrated in face (white text) Same width as face Faces Transparent plastic Mould-injected piece combines one face and two runner halves Peripheral lines at same distances from face edges Main line not centred with face Only black colour Manufacturing Single injection process completes halves (maybe both at same time) Designed for much simpler assembly and adjusting process (62/82)

Pocket Duplex Slide Rule Cursors Evolution Constructive Elements 1.Openings to hold spring strap 2.Small assembly elements 3.Longer holes for assembly elements 4.Grooves for handling 5.Cuts for assembly positioning Internal spacing surface 7.Star-shaped closure nut 8.Sliding rods 9.Hand-disassembling opening

Pocket Duplex Slide Rule Cursors Evolution Mould Injection Process Summary Injection Step 1: Mould parts (at least 2) are open Injector is filled with melted plastic

Pocket Duplex Slide Rule Cursors Evolution Injection Step 2: Mould is hold closed at high pressure Injector fills mould cavity and plastic solidifies Mould Injection Process Summary

Pocket Duplex Slide Rule Cursors Evolution Injection Step 3: Mould opens Piece is attached to one part Mould Injection Process Summary

Pocket Duplex Slide Rule Cursors Evolution Injection Step 4: Mould ejects the piece Piece falls to container Mould Injection Process Summary

Pocket Duplex Slide Rule Cursors Evolution Injection Step 4: Mould ejects the piece Piece falls to container Mould Injection Process Summary Injection with Insert Step 1: Insert piece is placed in mould with mould open Injector fills with melted plastic

Pocket Duplex Slide Rule Cursors Evolution Injection with Insert Step 2: With mould closed melted plastic is injected in cavity Plastic solidifies with insert Injection Step 4: Mould ejects the piece Piece falls to container Mould Injection Process Summary

Pocket Duplex Slide Rule Cursors Evolution Injection with Insert Step 3 & 4: Mould opens and ejects the piece Plastic piece falls to container Injection Step 4: Mould ejects the piece Piece falls to container Mould Injection Process Summary

Pocket Duplex Slide Rule Cursors Evolution Details of inserted metallic pieces Inserted Nut 1.In a cylindrical hole 2.Knurled body to interfere with the plastic wall 3.Air spaces between nut and plastic Nut has been inserted after injection Inserted Rod 1.Cylindrical hole in the plastic 2.Rod has chamfers in the ends 3.Air spaces between chamfers and walls Rod has been inserted after injection

Pocket Duplex Slide Rule Cursors Evolution Lines, Marks and Texts Engraving process: Lines, marks and usage letters from injection mould Black colour rubbed into all of them Final wet polishing of cursor inner face One mould per cursor (62/82 and 62/83) Printing process: Thermal printing White colour rubbed into characters Final wet polishing of runner surface

Pocket Duplex Slide Rule Cursors Evolution Third Cursor: 1970 (63/82, 63/83) Runners Two halves Integrated in face Wider than face (like 1 st type) Faces Transparent plastic Mould-injected piece combines one face and two runner halves Main line centred with face Peripheral lines asymmetrical from face centre Only black colour Manufacturing Single injection process completes halves (maybe both at same time) Cost optimization by material savings, process communalization and robustness reduction (63/83)

Pocket Duplex Slide Rule Cursors Evolution Constructive Elements 1.Openings to hold spring strap 2.Small assembly elements 3.Openings for right cursor assembly 4.Star-shaped nut (inserted after injection) 5.Plastic sliding rods 6.Internal spacing elements 7.Hand-disassembling opening

Pocket Duplex Slide Rule Cursors Evolution Lines, Marks and Texts Engraving process: Lines, marks and usage letters by thermal printing Black colour rubbed into all of them Final wet polishing of cursor inner face Same mould for both cursors (63/82 and 63/83) Injection Nut Placement Common Engraving Specific Engraving 63/82 or 63/83 Painting in Black Cursor face manufacture process (assumption)

Pocket Duplex Slide Rule Cursors Evolution Fourth Cursor: 1972 (62/82N, 62/83N) Runners Two halves Integrated in face Same width as face Faces Transparent plastic Mould-injected piece combines one face and two runner halves Main line centred with face Peripheral lines asymmetrical from face centre Only black colour Manufacturing Single injection process completes halves (maybe both at same time) Robustness from second type with cost optimization from third type (62/82N)

Pocket Duplex Slide Rule Cursors Evolution Constructive Elements 1.Small assembly elements 2.Star-shaped nut 3.Sliding rods 4.Hand-disassembling opening 53 5.Internal spacing elements 6.Closed holes for spring strap 7.Wrong assembly disabler

Pocket Duplex Slide Rule Cursors Evolution Details of inserted metallic pieces Inserted Nut 1.In a cylindrical hole 2.Knurled body to interfere with the plastic wall 3.Air spaces between nut and plastic 4.Rests of ripped-off plastic Nut has been inserted after injection Inserted Rod 1.Cylindrical hole in the plastic 2.Rod has chamfers in the ends 3.Air spaces between chamfers and walls 4.Heat excess when drilling or when inserted? Rod has been inserted after injection

Pocket Duplex Slide Rule Cursors Evolution Lines, Marks and Texts Engraving process: Lines, marks and usage letters by ultrasounds printing Black colour rubbed into all of them Final wet polishing of cursor inner face Same mould for both cursors (62/82N and 62/83N) Printing process: Thermal printing White colour rubbed into characters Final wet polishing of runner surface

Pocket Duplex Slide Rule Cursors Evolution Ultrasound Thermal Printing First Step: a)US head descends, already vibrating b)The moment it touches the plastic surface, the friction generates heat c)US head ends descent already vibrating Second Step: US stops US head stays in place, cooling the plastic Third Step: US head returns up leaving the printed plastic Extra plastic rims are flattened

Pocket Duplex Slide Rule Cursors Evolution Acknowledgements: Thank you for such good advice and support: -Jorge Fábregas -Antonio Medina -Dieter von Jezierski -Peter Holland …although any mistake is only my fault! Bibliography: [1] “Rechenschieber – Slide Rules A.W.Faber, A.W.Faber-Castell”, by Peter Holland. Fourth edition of 2011 [2] “Exterior hairlines in Faber Castell cursors”, by J.G.Fernández, 2009 [3] British Plastics Federation - [4] Manufacturing process indications recollected by Dieter von Jezierski

Pocket Duplex Slide Rule Cursors Evolution Annex: Open Issues for next… 1.Complete this study (more specimens per type, screw standard…) 2.Why there was no magnifying effect in these cursors? 3.Cursor assembly process in the manufacturing plant? (screws automatically inserted…) 4.Cursor dimensions ratios? Why? 5.Desktop duplex slide rule cursors? Taking Pictures… Impossible colours Impossible thickness

Pocket Duplex Slide Rule Cursors Evolution Thank You! By J.G. Fernández