Great story. Impressive repair. Now I have two more places to visit when travel becomes easy again. John
> -----Original Message----- > From: andy pugh [mailto:[email protected]] > Sent: July-07-21 6:27 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Power Tapping > > 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 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
