Ok, better late than never 😃:
Interesting point you raised- I’m surprised to see no-one over your side of the pond who’s seeing these doors has added any comments on the bolt detail itself.
Better make a cuppa and grab a big packet of biscuits for this one 🙁think):
What you’ve noticed should be common engineering practice on these old vault doors with this type of rack and pinion drive on the bolts. I think it’s probably a case of the different makers did things differently and often tucked things away so it wasn’t always seen.
When you think about the more common applications for rack and pinion gearing, both pinion gear and rack are always guided in some way. The pinion gear itself is always guided by it’s center pivot, and the rack is always guided or fixed, depending on the application.
If the rack is to move, then it’s normally guided either by pins or posts in lanket slots. Consider a free standing safe’s bolt work, whereby the outside handle turns the pinion gear and the rack is fixed rigid to the boltwork in order to drive the locking bolts in and out. The pinion gear can’t twist as it’s only allowed rotation about the axis of the pivot it’s mounted on. The rack can’t twist either- it’s guided by the locking bolts sliding through the boltcase, but will also have one or more ‘bearing’ points on the tail-bars, most commonly lanket slots sliding over guide posts welded to the inside of the door. If it’s an older high-end safe then even these points of friction were no-expense-spared, like massive Phosphor Bronze rollers if it’s a Chatwood Duplextra! 🙁inlove):
Now consider the bolt detail of the big vault door- the pinion gear is fixed on it’s center pivot the same, but although the locking bolt is guided by a massive surface area of steel as it slides in or out, it’s round in section which means only the rack meshing against the pinion teeth are stopping it from twisting. This isn’t good when it comes to meshing gears- in this example the rack, because of it’s unusual application to drive something circular in shape, needs a precise guide to keep the gear teeth meshing perfectly flat together. Any twisting action as a result of a bolt being a bit stiff through lack of lubrication, or from touching the frame it locks into, could cause a twisting action which would then directly strain the mating teeth.
Perhaps most just have a machined block fixed behind that section of the rack which doesn’t often show, or perhaps flats or grooves further out towards the locking edge- there’s quite a few ways they could guide them without it showing, and with the levels of both design and engineering they threw at these big doors I’m sure they wouldn’t have left anything to chance.
Hope this helps and more importantly hope that it makes sense! I’m off to get more biccies……….
