LNWR Precedent

[adrian]

Thanks, Nick, I'm finding that .010" is showing quite a bit of resistance.

Jon

Sounds like the 0.010" is half-hard n/s sheet. There are different grades of hardness with n/s sheet. If you can find some soft grade n/s sheet it is significantly easier to bend, I have some soft 16thou sheet and have formed belpaire fireboxes shapes quite easily just using finger pressure around a silver steel rod.

 

[Jon Nazareth]

Adrian
I'll reply to you but in my G6 post.

Jon

 

[NickB]

Not much progress recently, what with the G3 Society Annual Show and then the Newsletter, and as I write this the sun is shining (at last) which doubtless will mean a summons from the Head Gardener. In between whiles, here are the tender buffers.

The heads and stocks are fairly straight forward turnings. Here are the stocks rough turned:



and fine turned and polished.



Drilling holes for the rivets, using the rotary table to get an even pattern. That drill is 0.8mm diameter and I decided that the hole is far too deep, so I drilled most of the way using a larger drill and left a couple of millimetres to break through. The rivets turned out to be a good push fit and would probably have held themselves in place, but I added some epoxy to make sure.



Here is the assembly. The stock is drilled deep enough to accommodate the head and the spring compressed, and then continued at a clearance diameter for the screw. The back face is counterbored quite deeply so that the head of the screw remains in the hole when the spring is fully compressed. That way the buffer is fully self-contained.



Nick

 

[NickB]

Now all the soldering of the chassis has been finished, I can attach the plastic parts: axleboxes, springs and water scoop.





The leaf springs are dummies, the actual springing is a coil spring between each leaf spring and the axlebox. One of the compromises one accepts in a working model, and hopefully not too noticeable.



The next big task will be the brake shoes and levers, which is another assembly of lots of little parts.

Nick

 

[Mike W]

All very nice indeed Nick. Next time you have the camera out I'd be interested to see the clearance between the rear wheels and the bufferbeam, with the springs compressed!

Mike

 

[NickB]

Always happy to oblige

 

[NickB]

Each brake pad is attached to a curved frame that has a pivot hole at each end. The whole assembly is pretty nearly 2D, and I thought laser cutting was an option but I discovered that the process wouldn't allow the small pivot holes to be cut accurately enough (and perhaps not at all) in what is quite thick material. So back to the traditional methods, and with lots of little parts, and multiple parts at that, another jig is called for.

This jig is mainly made from a nice offcut of hardwood. Metal would suck all the heat out of the soldering iron. The pivots are simple turnings and are held vertically on accurately located pins. The frame itself is rolled from brass strip.



The next photo show these parts assembled in the jig ready for soldering.




And here is a "before and after" photo. On the right are the first few frames assembled, on the left some rolled strip for the next few, and in the background the turned pivots.



Now the soldering jig is turned into a drilling jig to make one hole to attach the brake pad and another for the crossbars that run between adjacent brakes on opposite sides of the tender. The holes themselves were first drilled in a spare piece of curved frame material and act as a guide for drilling the actual frames.



And here is the finished product. Next up will be the brake pads.



Nick

 

[NickB]

The brake blocks are a more complicated shape than they might appear. They are formed of two circular arcs, but the arcs are different radii and different centres. They could be done on the rotary table, but it would be a tricky setup. Time to bring on my new Secret Weapon - a CNC mill.

Having seen Mike Palmer's machine in action, and occasionally used his services, it's something I have long aspired to. A few months ago the stars aligned and I started building one, based largely around Sherline components. It's a bit on the light side so I've had to experiment with feeds and speeds to get good results. The tender was the first project where I tried it out for real.

It's great to be able to create a component in F360, then use it to work out and simulate on the computer screen a cutting strategy, and download a machining file. This is a brake block cut in the end of a bar of stock. The finsh is good enough that it only needed a quick rub over with a fine file.



The complete set of blocks, in order of manufacture left to right. Look closely and you will see how the shape was improved as I gradually refined the setup and the program. Still very much on the learning curve.



At last I could do a trial assembly of the brakes. The pull bars that link the brakes together on each side were also done by CNC.



There is more fun (and a few frustrations) with this in store.

Nick

 

[Mikemill]

Well done Nick, welcome to the world of CNC . It opens up a whole new world of model making, and heaps of fun.

Mike