Maurice I searched on "Drop arm" and it returned several posts. Try the search function (remember to select "archived") and see if you can fin the post. Nick
The comment I want to make is regarding the flash marks from the forging process. The picture clearly showed the lateral grooves where the forging flash was cut off. These are stress raisers and need to be ground off leaving only longitudinal marks particularly where the tapered arm meets the clamped end. My concern stems from having a drop arm break with what was a classic fatigue fracture at that point, luckily at only walking pace just a few minutes after having been travelling considerably faster. So my recommendation to anyone who has a drop arm like this is get grinding and then crack test it.
My (industrial metallurgist trained) expectation is that the original drop arms would have been hot forged, but it would be surprising if any flash along the length of the forging had not been removed as a subsequent stage. This would suggest that the offending arms were replacements and not adequately finished. It would be interesting to see a close up image of the fracture face, if you can post it.
In passing the arms on J3 3772 have been surface ground and polished at some time in the past. Is this a common finding?
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Posted - 25/07/2017 : 18:23:57
