This quote from timetraveler in the Everything Else forum prompted me to start a new continuation in this more appropriate forum:
"Interesting, that is why this Forum is so useful, feedback. I do have one little worm of disquiet nibbling away at the rear of my brain and I have had it for years without actually getting round to checking it. Vincents changed the design of their steering head about 1953 from a system whereby the fork at the bottom of the steering head, which went round the outside of the front cylinder head bracket, to one which slotted into the centre of the cylinder head bracket. While ever the B/C oil tank design was used this head lug was held by a very strong weldment, the oil tank, and the change seems not to have made any difference. Once the 'D's came along the same head lug design was still used but this time the only addition lateral support that was present was the fork at the front end of the upper tube. Clearly this does not afford much lateral support so it is possible that the fixing of the steering head lug into the front cylinder head bracket can be induced to move more than would have been possible with the original design. I do have an early type steering head bracket and a spare 'D' top tube lying about and one day I hope to get round to milling the old steering head so that it will take the 'D' item and then see if it makes any difference. If anyone else has tried anything similar then feedback on the outcome would be useful. There was a time when some people thought that lateral support for the steering head was a low requirement as there was a general idea that as one could corner with hands off the handlebars the front wheel did not have to turn and that lateral forces on the steering head were minimal. Look at any of the modern superbikes and you will see just how much effort they put into lateral support of their steering heads."
When I was trying to correct my bent UFM in my incorrectly titled thread "Fuel tank misalignment", I was intrigued and inspired by Davidd's contributions and his "roll your own" approach to casting and machining a headstock. While I had the bent headstock out of the oil tank, I had the opportunity to do some measuring of a few critical dimensions using my milling machine quill and a surface plate and height gauge, since one of the options I considered was to make my own headstock. I too thought that the earlier forked type was probably was more rigid for the forks in concept by fitting around the head bracket rather than in it as the slotted bracket type does. Jacqueline Bickerstaff expressed the same opinion in an early MPH article. I think my bent headstock proved that in practice the rest of the headstock malleable casting, at least for the type A one I have, was not up to the task, since the bends I found were in the tubular portions of the early B headstock. I then sat down and conceptualized how I would redesign the headstock if I was to machine one from billet. What I came up with is a hybrid of the two types. It requires the later slotted bracket and new longer spigots, but should theoretically be a lot more rigid, even when done in a strong aluminum alloy. This would be somewhat heavier than a standard headstock in steel, but not in aluminum. The increased material thickness around critical stress areas like the bearing pockets, tank mounts and steering stops, as David did in his design, should be enough to correct the deficiencies other attempts at simply duplicating the standard headstock in alloy did not address.
Pending the results of road testing my corrected UFM, (unfortunately now moved to next spring), I will probably never make one of these, but who knows. It was an interesting CAD exercise, and would be an even more challenging machining job. It would be fun to see if this type of hybrid fork changed the D handling described in the other forum, or stiffened up the UFM/front head coupling of a B/C under racing conditions.
Ron
"Interesting, that is why this Forum is so useful, feedback. I do have one little worm of disquiet nibbling away at the rear of my brain and I have had it for years without actually getting round to checking it. Vincents changed the design of their steering head about 1953 from a system whereby the fork at the bottom of the steering head, which went round the outside of the front cylinder head bracket, to one which slotted into the centre of the cylinder head bracket. While ever the B/C oil tank design was used this head lug was held by a very strong weldment, the oil tank, and the change seems not to have made any difference. Once the 'D's came along the same head lug design was still used but this time the only addition lateral support that was present was the fork at the front end of the upper tube. Clearly this does not afford much lateral support so it is possible that the fixing of the steering head lug into the front cylinder head bracket can be induced to move more than would have been possible with the original design. I do have an early type steering head bracket and a spare 'D' top tube lying about and one day I hope to get round to milling the old steering head so that it will take the 'D' item and then see if it makes any difference. If anyone else has tried anything similar then feedback on the outcome would be useful. There was a time when some people thought that lateral support for the steering head was a low requirement as there was a general idea that as one could corner with hands off the handlebars the front wheel did not have to turn and that lateral forces on the steering head were minimal. Look at any of the modern superbikes and you will see just how much effort they put into lateral support of their steering heads."
When I was trying to correct my bent UFM in my incorrectly titled thread "Fuel tank misalignment", I was intrigued and inspired by Davidd's contributions and his "roll your own" approach to casting and machining a headstock. While I had the bent headstock out of the oil tank, I had the opportunity to do some measuring of a few critical dimensions using my milling machine quill and a surface plate and height gauge, since one of the options I considered was to make my own headstock. I too thought that the earlier forked type was probably was more rigid for the forks in concept by fitting around the head bracket rather than in it as the slotted bracket type does. Jacqueline Bickerstaff expressed the same opinion in an early MPH article. I think my bent headstock proved that in practice the rest of the headstock malleable casting, at least for the type A one I have, was not up to the task, since the bends I found were in the tubular portions of the early B headstock. I then sat down and conceptualized how I would redesign the headstock if I was to machine one from billet. What I came up with is a hybrid of the two types. It requires the later slotted bracket and new longer spigots, but should theoretically be a lot more rigid, even when done in a strong aluminum alloy. This would be somewhat heavier than a standard headstock in steel, but not in aluminum. The increased material thickness around critical stress areas like the bearing pockets, tank mounts and steering stops, as David did in his design, should be enough to correct the deficiencies other attempts at simply duplicating the standard headstock in alloy did not address.
Pending the results of road testing my corrected UFM, (unfortunately now moved to next spring), I will probably never make one of these, but who knows. It was an interesting CAD exercise, and would be an even more challenging machining job. It would be fun to see if this type of hybrid fork changed the D handling described in the other forum, or stiffened up the UFM/front head coupling of a B/C under racing conditions.
Ron
