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Post by tdaharvey on Sept 28, 2020 17:04:32 GMT
Stretchers consisting of a vertical plate attached to angles, which run from one frame plate to the other don't have a lot of resistance to the frames 'working' under alternating piston thrusts. Any chance you can work in a substantial horizontal stretcher? That will improve frame stiffness considerably. It has both vertical and horizontal stretchers and it is the horizontal ones that were distorted. They are made out of 3mm steel with open cut outs. They were only slightly off square but of course this had a large impact upon the frame alignment. I have now straightened the stretchers and rebuilt the frames and the chassis is now straight with wheels sets in alignment.
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Post by 92220 on Sept 30, 2020 17:49:46 GMT
If there are horizontal stretchers, they could run from front to back like on the 9Fs. This is my 9F frames assembly, built exactly to works drawings. I thought the Brits had frame assemblies similar to the 9Fs, so why were horizontal stretchers not included in the original model drawings. The horizontal stretchers were on the fullsize locos to stop frame racking. Whoever designed the model Brit, should have included them for the same reason! 92220 008 by Robert Shephard, on Flickr Bob.
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Post by ettingtonliam on Sept 30, 2020 18:30:49 GMT
Not sure LBSC was that good with frame stretchers, apart from motion plates or pump stretchers.
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
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Post by oldnorton on Sept 30, 2020 19:15:16 GMT
Whoever designed the model Brit, should have included them for the same reason! Bob, The Perrier 5" Britannia does have a massive horizontal stretcher, as per prototype. And the Modelworks versions copy this. You might have gained the wrong impression perhaps from a previous comment about the prototype Britannia's side platforms being mounted on the boiler? I don't know, or are we confirming that the LBSC 3.5" one has no such stretcher? Norm
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Post by andyhigham on Sept 30, 2020 20:16:19 GMT
Narrow gauge locos seem to be a bit shy on stretchers, I wonder if some degree of flex was designed into the frames to cope with uneven tracks
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Post by 92220 on Oct 1, 2020 9:59:52 GMT
Hi Norm.
I just got the impression, from a earlier post, that the 3.5" model Brit didn't have much in the way of horizontal stretchers, to stop 'racking' of the frames. They certainly work well on the 9F. I did actually drop my frames assembly, after I had riveted them all up, ready to paint, onto the front end. I fully expected to have a major problem! In actual fact, when I set the frames back up on the mill to clock up any distortion, I found no damage whatsoever!! The horn faces were still in alignment. It taught me to be a bit more careful though!! I really couldn't believe what I was seeing, but the stretchers are riveted, with dozens of rivets, rather than fitted with screws. Maybe that is where the problem lies.
Bob.
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Post by delaplume on Oct 2, 2020 1:31:37 GMT
Narrow gauge locos seem to be a bit shy on stretchers, I wonder if some degree of flex was designed into the frames to cope with uneven tracks That's where Bar frames come into their own....
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
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Post by oldnorton on Oct 2, 2020 8:30:41 GMT
The talk about frame strength has got me thinking. We seem to benefit greatly due to material scale factors making our small engines immensely stronger than the full size. By stronger I mean more able to withstand abuse. Most of us know that more than one engine has fallen from a trolley onto concrete and survived with superficial damage (most cases are never reported); imagine dropping a full-size engine from a height equal to its own length! Most of the big engines suffered major damage in bent frames with shunting accidents.
I wonder if our model frames can easily do their job with all manner of stretchers missing? and perhaps a single box section somewhere is sufficient to withstand racking.
Sorry if this does not directly address Terry's loctite point, but on that subject I feel that its use is unnecessary if the faces all meet properly and the screws/rivets are tight. But perhaps it won't do any harm.
Norm
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