Pugsley Posted June 13, 2012 Share Posted June 13, 2012 I'm having a bit of trouble getting my head round the various mechanics of the brake gear on air braked wagons. Specifically for my ongoing IZA project, but also in a more general sense for other projects I have in mind for later. I've got to the stage now where I know which part goes roughly where, and their function, but one bit that I can't work out is how the various parts around the wheels interact to move the shoes onto the wheels. Here's the type of brake gear I'm talking about: I've managed to work out that the main brake rod pulls in the direction of the red arrow, which moves the RH shoes onto the wheel treads. However, what I can't figure out is how the part in the middle transfers the pushing motion of the RH shoes into a pulling motion to bring the left hand shoes into contact with the wheel tread. If anyone can explain this to me, it would be much appreciated - I am probably missing something obvious. On a related note, I've figured out that somewhere in the brake linkage, I need a crank in the rodding which turns the pushing motion of the brake cylinder into a pulling motion at both ends of the vehicle. Do wheeled handbrakes operate on this mechanism to apply the handbrakes, or is it more likely to act directly on the brake cylinder? Unfortunately I've never looked closely enough at a wagon with a handbrake wheel, nor taken any photographs of one from a suitable angle to see what's going on down there. Again, any help would be much appreciated. Link to post Share on other sites More sharing options...
Titan Posted June 13, 2012 Share Posted June 13, 2012 I'll have a go! First a little more labelling: All points 'A' are attached to the chassis (in blue to match your arrow) Which means link F can move. If we assume point C cannot move to begin with (lets say its a little stiff with dirt/grease/rust etc), then the right brake shoe begins to apply as you have understood. when it contacts the wheel point B stops moving. Further movement of the brake rod overcomes the stiffness of point C, and starts pulling this to the right along with link F. the link moves point D and E to the right (as the point opposite is fixed) and therefore pulls the left shoe in to contact. Further pulling from the brake rod therfore increases the force on both shoes more or less equally. HTH Link to post Share on other sites More sharing options...
Pugsley Posted June 13, 2012 Author Share Posted June 13, 2012 That's great, thanks. However, there is one bit I don't understand, if the link pivots around point C, how does it get pulled to the right? Sorry if I'm being a bit thick here, but I'm really struggling to get my head around this. I understand the rest now, though. Link to post Share on other sites More sharing options...
Katier Posted June 13, 2012 Share Posted June 13, 2012 Ignore the bit about sticking. Assuming the basis of the reply is correct.. When the red arrow is pulled one of two things will happen, either the vertical bar will move right, this will pull F to the right until the pad touches at which point F can't move, so it HAS to pivot around C (which is now static because F can't moves as the pad is in contact with the wheel) and thus pull the left hand pad. Alternatively it'll initially pivot around C and essentially the reverse will happen only the first pad to contact will be the right, not the left. Link to post Share on other sites More sharing options...
Boris Posted June 13, 2012 Share Posted June 13, 2012 There's no such thing as a numpty question on here, the only numptys are the ones who ask a question and then argue with the folks who have answered it! Link to post Share on other sites More sharing options...
Pugsley Posted June 13, 2012 Author Share Posted June 13, 2012 I get it now, thanks everyone. The mistake I was making was to think that the bracket pointed to by the blue arrow was fixed at the top, instead of it being another pivot point. I now see how the link can move to the left, whilst still being constrained by pivot 'C'. I'm still a bit of a numpty for not figuring that out myself earlier though. Link to post Share on other sites More sharing options...
Boris Posted June 14, 2012 Share Posted June 14, 2012 I'm still a bit of a numpty for not figuring that out myself earlier though. Clasp brakes with all their associated cranks and other bits aren't the easiest thing to visualise on a model, you would probably be surprised at the number of folks who get it wrong and have been for years. I'm lucky in that I have access to the real thing quite easily, but even after all the wagons & coaches I've built I still have to go out and have a look on a regular basis! Link to post Share on other sites More sharing options...
jonhall Posted June 14, 2012 Share Posted June 14, 2012 from an East German guide to C&W construction - showing a platform handbrake, but the principle is the same. This pair are under a Cargowaggon 4 wheeler, but don't ask me which type. The handwheels are linked to a gearbox that drives a longditudinal push rod. and this is under a PNA - the layout of the hardware is rather different, but I think it gives a fairly useful view. Jon Link to post Share on other sites More sharing options...
Pugsley Posted June 14, 2012 Author Share Posted June 14, 2012 Thanks Jon, those are brilliant - taken from the perfect angle, which I seem to have failed to do! All is now clear, and my IZA can have a relatively convincing undergubbins. Link to post Share on other sites More sharing options...
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