Thicket data repository for the EEG
anil.recoil.org
1{
2 "id": "https://www.tunbury.org/2025/07/27/pulley-diameter",
3 "title": "Pulley Diameter vs Rope Diameter",
4 "link": "https://www.tunbury.org/2025/07/27/pulley-diameter/",
5 "updated": "2025-07-27T00:00:00",
6 "published": "2025-07-27T00:00:00",
7 "summary": "About three months ago, I wrote about replacing a snapped galvanised steel wire rope on a clock winder. Unfortunately, it has snapped again!",
8 "content": "<p>About three months ago, I <a href=\"https://www.tunbury.org/2025/04/21/clock-winder-repair/\">wrote</a> about replacing a snapped galvanised steel wire rope on a clock winder. Unfortunately, it has snapped again!</p>\n\n<p>I am very surprised that the steel wire rope snaps, as the weight it lifts is, at most, 2 kg, however it does run every hour. I posed the question to Claude:</p>\n\n<blockquote>\n <p>Hi Claude, I have a mechanism which lifts a 2Kg weight using a multistranded galvanised steel wire rope with a diameter of 3mm over a 20mm diameter pulley. It works fine, but the rope snaps after about 3 months of operating once per hour. Can you suggest where the issue might lie?</p>\n</blockquote>\n\n<p>“The most likely issue is your pulley diameter is too small relative to your wire rope diameter. With a 3mm rope over a 20mm pulley, you have a diameter ratio of only 6.7:1, which is well below recommended standards.</p>\n\n<p>Key problems with small pulley diameters:</p>\n\n<ul>\n <li>Excessive bending stress in the wire rope as it wraps around the pulley</li>\n <li>Rapid fatigue failure from repeated flexing (your ~2,160 cycles over 3 months)</li>\n <li>Individual wires break from the severe bending, leading to rope failure</li>\n</ul>\n\n<p>Industry recommendations:</p>\n\n<ul>\n <li>Minimum D/d ratio should typically be 20:1 for standard applications</li>\n <li>For your 3mm rope, you’d ideally want at least a 60mm diameter pulley</li>\n <li>Higher ratios (30:1 or more) would be even better for longevity”</li>\n</ul>\n\n<p>With this insight, I was easily able to verify that this is a good assessment. For example, <a href=\"https://www.flints.co.uk/pdf/catalogue/pulleys.pdf\">Flints</a> recommend, “In the case of wire ropes, the sheave diameter should ideally be 30 times the diameter of the wire.”</p>",
9 "content_type": "html",
10 "author": {
11 "name": "Mark Elvers",
12 "email": "mark.elvers@tunbury.org",
13 "uri": null
14 },
15 "categories": [
16 "clock"
17 ],
18 "source": "https://www.tunbury.org/atom.xml"
19}