Double-volute-spring-havin’ wire rope cutters

Until I got some of the Knipex wire rope cutters shown below, I’d never seen a volute spring and didn’t know they existed. Guess I’ve led a somewhat sheltered life. The uncharacteristically brief Wikipedia article says they can frequently be found as a component of garden pruning shears and, though I have used pairs of pruning shears a few times in my life, long ago in a galaxy far away, I can’t recall their handles being fitted with double volute springs.

The volute springs in use in train car buffers and tracked vehicle suspensions don’t really jump out at you at first glance. A volute spring may be shown fully or nearly fully compressed, so that its visible portion simply looks like a cylindrical piece of metal. There are some blurry but recognizable images, a hand-drawn schematic and a photo-realistic illustration with component labels, in the Vertical volute spring suspension Wikipedia article.

Above is a screen capture of a frame from a YouTube video showing off a mobile app apparently concerned with physics modeling military tanks. The first ten seconds or so of that clip are zoomed-in on the suspension and show two vertical volute springs in action.

Volute Spring History Digression (Sherman tanks, WW2, Chrysler, and Bernhard and Dr. Margaret Sterne)

A Wikimedia Commons entry for some cutaway displays of train car bumper gizmos (which employ volute springs) credits industrialist John Brown (of Atlas Works, Sheffield, England) with inventing volute springs for use in railway carriage buffers in 1848. The most in-depth description of volute springs that I can see online is a 1942 article in SAE Transactions, published in 1942 and written by an experimental engineer at Chrysler named Bernhard Sterne: Characteristics of the VOLUTE SPRING.

Some dots that seem connected: the Wikipedia article on volute springs mentions that they were used in Sherman tank suspensions, Chrysler (which built and ran the Detroit Tank Arsenal) was one of the manufacturers of Sherman tanks, and they went into production in 1942 (the chronology under the heading Timetable of the Chrysler Tank Arsenal in the pamphlet linked above says Sherman tank production began on August 3rd, 1942). That’s the same year that Sterne, working for Chrysler, published his 20-page monograph on volute springs. He also wrote another volute spring paper, The Testing of Volute Springs , that appeared the next year (1943) in the Transactions of the ASME. A reasonably uncommon name helps make Sterne slightly Google-able and I can find traces of him in digitized newspapers from the mid-20th century.

The last mention of Sterne that I turned up is a short piece in the Feb 20th, 1958 edition of the Gross Pointe News [PDF link] (serving Gross Pointe, Michigan) about a talk that a Dr. Margaret Sterne (Wayne State University professor and Fullbright Scholar) would be giving the coming Wednesday evening, to be accompanied by a slide show conducted by her husband, Chrysler experimental engineer Bernhard Sterne, of photos he’d taken during their many European vacations. The article in the Gross Pointe News says Dr. Sterne was born and educated in Deutschland, married there (one can assume Bernhard was the groom), and that she and her spouse emigrated to the U.S.A. in 1925. The Fullbrightscholars.org listing says that Dr. Sterne was an assistant professor of history at Wayne State and that she did her Fullbright year from 1952-1953 at the University of Vienna. A biography of Margaret on the Wayne State U. site gives a fuller picture of her life, but only mentions Bernhard once and regrettably it’s to play up a patriarchy-bad angle on his reported concern for her safety in post-war, early-Iron-Curtain-era, still-partitioned-and-occupied Vienna. Oh well. She passed at the age of 73 in 1977.

Searching on his name in Google Books turns up some interesting results for Bernhard. He was chairman of the SAE Spring Committee in 1962 and, in a different publication from 1961, it’s mentioned that he was at that time supervisor of Chrysler’s Suspension Testing Laboratory. He’s listed as president of Bernhard Sterne Associates in the index of multiple editions of the SAE Handbook, the last of which seems to be the one published 1984, so he may have been doing consulting work post-retirement. A 1980 publication by the Engineering Society of Detroit gives an address for Bernhard Sterne Associates that was likely the Sterne residence: 19505 Renfrew Rd, Detroit, Michigan 48221. The most recent mention that I can find is a 1988 SAE report (Manual for incorporating pneumatic springs in vehicle suspension designs, SAE HS 1576: Report of the Spring Committee) that includes an acknowledgement thanking Bernhard Sterne of Bernhard Sterne Associates for providing many valuable editorial comments during the final compilation of this document. MyHeritage.com listings for his name include just one family tree result, a Bernhard Eduard Sterne (born 1899 and deceased 1987) who married a Margarete Sterne (née Levi) in 1924 and resided for the balance of his life in Michigan. Sounds like our guy.

Tsunoda WC-200 wire rope cutter and Knipex 95 62 160 wire rope cutter.

I got the Knipex tool first and then, out of curiosity, got the Tsunoda wire rope cutter, choosing that model, rather than the WC-150 (a 15cm-long version) because the smaller Tsunoda tool used a torsion spring to force the handles back apart between cuts rather than a double-volute spring (used in the WC-200 and WC-225). Tsunoda has a video about their line of wire rope cutters up at their YouTube account: ツノダ　ワイヤーロープカッター：ワイヤーロープがほつれず切断できる！[Tsunoda Wire Rope Cutter: Can cut wire ropes without fraying!]. Knipex has some YouTube videos featuring their wire rope cutters, too, including a 44-second short from Jan 22nd, 2019 on this particular model: KNIPEX Wire Rope Cutter (95 62 160).

Knipex’s 95 62 160 wire rope cutter, made in Germany, is available in two packages: 95 62 160 (plastic-bag-in-cardboard-box) for €24 (about US $26 right now) and change on Amazon.de at the time (YMMV due to inflation, Amazon price-twiddling, etc.) and, for about €6 more, 95 62 160 SB (SB card/blister). Tsunoda’s WC-200 wire rope cutter, made in Japan, ran ￥98 (about US $13.50 right now) from a seller on Taobao. The card and blue plastic thing that secured the Knipex tool to the card are both made completely of polypropylene. The cardboard backing of the Tsunoda tool’s blister pack was actually a fold-out booklet. Scans of both are embedded a bit further on in this post.

The shaded appearance of the lock symbol on the thumb switch that retains/frees the jaws of the Knipex 95 62 160 is a trick of the light. There’s no paint there. But it is embossed, stamped or milled deeply enough into the side of the part that it’s not going anywhere anytime soon. The branding and Made in Germany stuff are printed (laser-etched?) and in direct light show as yellowish-coppery on the almost-black metal.

I’m a grateful viewer of tool test videos, the kind where the videographer uses (e.g.) Rube-Goldbergian contraptions and weights-on-ropes to try to apply equal amounts of force to each of an array of similar tools while they cut, drill, etc. through a range of materials and busts out a set of hardness picks and a USB microscope to see whether the manufacturer claims for the hardness of cutting edges on these tools holds up and the like. That sort of content often helps inform my decision-making, but I’m still more at a quotidian end-user-with-gripes level for now. Easy-to-wear-away markings are irritating because I can imagine myself, years from now, looking to replace a tool that broke or replace a broken part on one or find an equivalent tool and foresee it being more of a pain than necessary because the model number has been obliterated.

Here’s a montage of the markings on the Knipex tool:

MADE IN GERMANY is embossed on the inner flat surfaces of both handle grips, not just the one that’s in view. The KNIPEX branding in red is, I’d guess, the same red polymer material as the other red bits, protruding from the well into which the blue overmolding was applied. You can probably see what I’m getting at. The most durable marking on the tool is the padlock icon on the jaw-lock thumb switch. Next up are the MADE IN GERMANY lines molded into the inwards-facing sides of the grips and the KNIPEX brand name visible on the outwards-facing sides of the grips, which will outlast the same information laser-etched onto the metal jaws. The most important details, the model number and the cutting capacity, are printed exactly once each, in small black text, on the thin edges of one side of the grips.

Knipex says this tool can cut wire rope up to 4mm in diameter and stranded copper cable as thick as 6mm, so the capacity detail on the tool isn’t even complete.

It’s pretty silly. IANA metallurgist, but I can imagine that milling these details into the jaws or the handles just above the polymer grips might weaken the metal in ways that make the tool more susceptible to catastrophic failure, so what about the grips? Rather than multiple markings indicating where it’s made and the company name, I wish Knipex had incorporated the model number and capacity information into the molds used for the grips.

The Tsunoda tool is only very slightly better markings-wise. At least the model number is laser-etched onto the milled-flat shiny lateral face of one of the jaws. As for the significance of the 238 (or is it 23B?) marking, I have no clue. The grips on the handles are PVC-dipped and nothing is printed or molded into them. Instead of a thumb latch mechanism, a bent-wire loop through the end of one handle rotates up over the tip of the other to secure the handles shut. That’s already left a shallow dent in the yellow PVC material on the opposing grip. Tsunoda says the WC-200 can cut wire rope up to 5mm in diameter (slightly less, 4mm, for stainless wire rope), that the cutting edges have been induction-hardened, and that the jaws have a Rockwell C scale hardness of 54～64, which seems like a wide range, but the information printed on the cardboard backing sheds a bit of light on this. The Knipex product page, linked a few paragraphs up, also says their cutter’s jaws were induction-hardened and gives an HRC value of approx. 62 HRC for its cutting edges.

The card for the Knipex cutter SB version is unremarkable and bears a subset of the information available on the Knipex site. The fold-out cardboard backing for the Tsunoda WC-200, however, gives a bit more (or at least slightly different) detail regarding the HRC value shown on tsunoda-japan.com. Under the Quality Information header on what was the back of the insert when it was slotted into the clear plastic blister, two steps seem to be described: non-oxidation quenching of the entire tool, for an HRC value of 42-50, and induction hardening of the cutting edges to an HRC value of 58-64, which is slightly narrower at the low end than 54-64.