On Thu, 8 Jul 2021 at 00:39, John Dammeyer <[email protected]> wrote:
> But for metal a spiral, or at least spiral point is a must I think. Time to > do a bit more tuning but impressed as how well it works. I power-tapped a bunch of holes into EN24 with a conventional straight-flute hand tap at the weekend, though it was a bit heart-in-mouth. Bit of a story here. a slightly epic field repair. (literally, in a field) I play with an old fire engine. (US: fire truck). It belongs to the students of my old university (Latin: Almer Mater). They were invited to an event about 50 miles from their base in South Kensington last weekend, by someone they know from the Kew Bridge Steam Museum https://en.wikipedia.org/wiki/London_Museum_of_Water_%26_Steam (home to the second and third biggest steam engines extant). [1] When I say "old" I mean that the fire engine was built in 1916. The fire engine has an overhead worm drive differential, and drive into that is via a "box joint" which is a crude sort of universal joint where a square "knuckle" on the differerential input shaft is driven by a hollow square. The outer faces of square knuckle are radiused, and two bronze "slippers" fit between those and the outer box (it's odd that there are only two, but the knuckle is rectangular, with the slippers on the long faces, to make it square) The knuckle mounts on a taper, pulled up by a nut. There are two keyways at 90 degrees. But we only use one, as two keyways is stupid. (It took about 30 years of our ownership to realise this, but with two keys and a taper either only one key fits, or the taper can't pull up. It is kinematically redundant, in a bad way) Anyway, this all went wrong on the way there. It looks like the nut came loose, and rattled about destroying it's thread, and the thread on the shaft. https://photos.app.goo.gl/GK1MSM6eoTLfKbL29 The keyway didn't do too well either. And the damage to the knuckle is rather serious too. It's not meant to be that shape: https://photos.app.goo.gl/oa5Mt6n9H5y3AKxs6 They got a recovery to the show site, at a museum, though it cost £270 for the 14 miles... Armed with photos and such I was able to figure out that the thread was _probably_ 1.125" x 11tpi and so I spent saturday afternoon making a small selection of nuts. This is where the tapping came in, as we have redesigned the nuts to use a ring of axial grub-screws to pull up the taper. The theory is sound, but... Then on Sunday I drove to the museum with my welder, the nuts, a tool to drive the nuts, lots of files, and anything else that I thought might help. So, we dressed the thread with a triangular file until one of the nuts fitted. This was not fun. My ribs are still bruised. It involved lying on the footboards with your upper body inside the main box: (Here is a photo of here ignominious arrival, the doors we accessed the differential input shaft through are the ones with "London Fire Brigade" on them: https://photos.app.goo.gl/ALR53JEBSozPAZnAA Anyway, after a few hours with the triangular file, we got one of my new nuts to fit. Then we got the knuckle hot with the museum oxy-acetylene kit. and squeezed it back to round in a vice. Then I ground-out and welded up the cracks. Then bolted it all back together and she drove the 50 miles home without issues. [1] The biggest is the Criquis in NL: https://en.wikipedia.org/wiki/Museum_De_Cruquius -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
