Draw-Cut Pruning Shears: A Blade That Slides as It Closes

Pruning shears that simply squeeze a branch between two jaws crush the bark and wood on both sides of the cut. A blade that is drawn along as it closes slices instead. Hermann Finken of Rodenkirchen, near Cologne, filed US 1,760,232 on 24 December 1928 (in Germany on 26 February 1927); it was granted on 27 May 1930. In his shears the movable half slides lengthways past the stationary one as the jaws close, guided by a prismatic section in a grooved pivot pin and driven by a link between the handles, "producing thereby the well known clean 'drawing' cut of great power and penetration and without danger of bruising, crushing, or otherwise injuring the parts being cut". This rung works out why slicing needs less force than pushing and tests it on stems.

مبتدئ

About 2 hours

التعليمات

Slice-to-push ratio and force

جارٍ تحميل دفتر Jupyter…

Why a clean cut matters

A graft only takes when both cut faces are clean and uncrushed. The embedded blueprint shows the cuts pruning shears have to make.

Read US 1,760,232

Finken's shears are of the type "in which the one shear half during the cutting movement, that is whilst the two cutting jaws approach one another, aside from this closing movement, is also longitudinally displaced relative to the other shear half". His object is to improve the pivot connection and the means of controlling that displacement. The stationary member is handle 1 and jaw 2; the movable member is handle 4 and jaw 5. The movable member "is provided with an intermediate prismatic portion 3 and slidably intersects the fulcrum or pivot 18". The pivot pin 18 turns in a round hole 16 and has a groove 17 that guides the prismatic portion; a nut 21 and a small set screw 23 set the adjustment. The handles are joined by a link 12 pivoted on lugs at different distances from the fulcrum, and a compression spring 13 opens the jaws. "Upon the shears being closed, the blade 2 approaching the blade 5, there will also be imparted a longitudinal inward ... displacement of the movable member", and because the prismatic part is snugly guided, the blade is not "unduly stressed and deflected in lateral direction so that a clean drawing cut is assured."

Crushed or sliced: look at the cut

Cut green prunings about 10 mm thick with bypass pruning shears in two ways: first squeezing straight down without moving the shears, then drawing them slightly towards you as they close. Hook the spring scale to the end of one handle, with the other braced, to compare the force needed. Look at each cut end under a hand lens: a crushed cut shows torn bark and squashed fibres on one side; a drawn cut is smooth. Measure the blade travel with the caliper to estimate your slice-to-push ratio.

الأدوات المطلوبة:

مقص تقليم (قطع جانبي)

مقياس قوة (ميزان زنبركي)

عدسة يدوية 10x

قدمة رقمية 6 بوصات

قفازات تقليم (مانعة للشوك)

Pruning shears that crush

Pruning shears troubleshooting.

Flow

History and honest limits

**Hermann Finken** of Rodenkirchen near Cologne filed US 1,760,232 on 24 December 1928, with German priority of 26 February 1927; it was granted on 27 May 1930. He describes draw-cut shears as a known type and improves their pivot and guide. **Honest limits.** The slicing formula is a simple model; the cutting forces and lever lengths in the notebook are examples, not measurements of Finken's shears.