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Monkey in the well


Pugsley

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It feels a bit like the old maths question at the minute - there are three steps forward, and two steps back again. The bogie artwork is currently undergoing another tweaking, but I'm hopeful that the mark 3 version will be the final version, as I've just about discovered everything that could be improved upon, I think.. :)

 

It's mostly little things, like adding a couple of extra positioning holes on the parts that are soldered on to the mounting plate, but the frames have required a complete redesign. In this version, the axlebox guides will be soldered on to the main frame, with a spacer between to pack them to the right distance inside of the frame.

 

As a part of the final redesign, I've been assembling the various parts, to check that everything works as it should. The following photos show the secondary suspension mount, with the original trial spring in place.

 

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Since taking these pictures, I've realised that the prototype spring is too powerful - it needed a force of 500g to compress about halfway, which I think means that the 37 would need to weigh 4kg for it to work as intended! I've since cut the prototype spring down to 7 coils, which reduces the spring force greatly (I'm not sure how much by yet, I haven't measured it). I've got some thicker copper wire on order, so will see what that's like, as I think that the brass might still be a bit too springy.

 

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This shows the revised spring length for the secondary suspension, alongside the first prototype primary spring, made from copper wire. I'm not sure if this is final length for this one, the revised frame etches need to be constructed first, so I can work out the height of spring required.

 

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The remains of the moulded springs on the kit sideframe, will be turned into locating studs for the primary springs. i had originally planned to replace the equalising beam mounts with an etched part that would actually pivot, but have abandoned that plan for now. I will give it a go at a later date, but with a suitable casting, the etched parts don't look as good as what's there at the moment.

 

This funny looking part:

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Rests on the secondary springs, whilst also locating the bogie on the pivot. There will be some form of screw adjustment incorporated either into the supports that rest on the slide plates (see next pic), or from the secondary springs to the bolster to give the ability to adjust the ride height.

 

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The slide plates and the bolster bearing surface can be seen in the picture above. The plan to stack etched washer-like parts isn't quite working - I need more than I've planned for in the etch, so this will be replaced by a turned brass part of the required diameter, once the next version of the main etches are back, as I don't know what length the part needs to be to maintain the correct ride height at present.

 

The final picture shows the mounting plate in place on the bogie, but it is too close, as mentioned above.

 

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There's a few more parts to test this week, then hopefully everything that needs it will be amended by mid-week, so the revised file can be sent to the etchers.

 

More soon, with any luck :)

9 Comments


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Martin this project is incredible - are the springs hand made? I can't wait to see a bogie built up! Good luck - I'm very jealous!

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Thanks James :blush: :blush: B)

 

The springs are made by winding the wire around a drill bit of the right diameter (3.3mm in this case) under tension, before flattening the ends and filing so they sit level.

 

I'm looking forward to seeing the built bogies as well, it's getting ever closer and will hopefully only be a couple of weeks now. I just hope that it's going to work after all this! :)

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More amazing-looking stuff, keep it coming. I didn't realise you could make springy springs from brass or copper - I would have thought they wouldn't spring back owing to the metal being ductile/malleable, but that clearly isn't the case. I think I'll have to read The New Science of Strong Materials again...

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I hadn't ever thought about making springs from brass or copper either, until I read the article that inspired this whole little adventure (Chris Pendleton's Deltic article in MRJ). I don't know if it's because they're wound under tension that they work, perhaps?

 

I know that if they didn't work, this whole project wouldn't be feasible, conventional steel springs would look too spindly to be convincing. The LH Loveless Deltic suffers from this to a certain extent.

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So I'm guessing this isn't too much of a voyage into the unknown! How much do the 'springs' compress - and how long lasting are they expected to be? i.e. if you leave it as a static model, sat with it's weight on the springs without moving will they settle and therefore become less 'springy' over time? Will you be able to replace them if needed in the future? Just my engineers hat on - I'm quite interested in this but my head is struggling a bit with the material science involved!

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So I'm guessing this isn't too much of a voyage into the unknown!

Have you only just worked out that I don't really know what I'm doing.. ;) :lol:

 

How much do the 'springs' compress - and how long lasting are they expected to be? i.e. if you leave it as a static model, sat with it's weight on the springs without moving will they settle and therefore become less 'springy' over time? Will you be able to replace them if needed in the future?

I'm not sure, is the honest answer!

 

The primary springs will be easily replaceable, as they'll be a force fit onto the mounting studs. I haven't completely decided on the method of mounting the secondary springs, but I expect the system of mounting to be basically similar, the only thing I might do is solder the springs to the lower mount, but with 145deg solder, so they can be removed relatively easily if required. The rest of the bogie will be assembled with regular electrical solder, with a much higher melting point.

 

The trial primary spring compresses by 1.5mm total, which is about the total movement required from these springs. The idea is that in normal conditions, they'll be compressed by 1mm, giving only 0.5mm of upward travel. The trial secondary spring compresses by 2.5mm, so the plan for this is to have the spring half compressed under normal conditions, giving 1.25mm travel in either direction.

 

I guess that there is a risk that the springs may settle if the model is left on its wheels for an extended period of time, but that's only something I'm going to find out by trying, I think :)

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As an update to this entry, I've since tried stress relieving the wound spring by heating them. Unfortunately it seems to soften the springs to the point of being useless! The final springs will be left in the raw state after winding, only time will tell if they retain their springyness!

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