7mm Scale 7 MOK 9F in Spain

simond

simond

Western Thunderer
Len,

That’s bad luck.

I suspect this is due to the frames being soldered together whilst one side is hotter than the other, and when it all cools down, the contraction is uneven, and that pulls it into a curve. If it’s straight say for 60% of the length, and just curved at one end, you might be able to give it a quick dose of heat over the curved end and if you’re lucky, it’ll settle down.

I’d use a blowlamp, but that’s a bit drastic, particularly if other things are going to drop off.

Otherwise, you’re going to have to progressively unsolder and remake the joints.
 
Dog Star

Dog Star

Western Thunderer
Given the slot and tab method of construction... and the number of horizontal frame stretchers (which resist left/right bending)... then you may wish to consider if:-

a) frame plates were not pressed tight to horizontal stretchers before making the joint (twisting the tabs);

b) tab lengths of the horizontal frame stretchers are shorter than slot lengths in frame plates;

c) tabs not twisted enough to form a tight joint between stretchers and plates.

How "much" of the frame is bent (rough percentage of the length) and what is the amount of the bend at the end of the frame? I ask because the photos are not clear as to which part of the frame is bent and by what degree.

regards, Graham
 
Len Cattley

Len Cattley

Western Thunderer
Hi Graham, it's bent at the rear at about 60/° from the front. I think I will try what Simon suggested, and hope that works.

Len
 
simond

simond

Western Thunderer
If Graham’s suggestion, that it wasn’t properly clipped together when it was soldered, is the case, then my initial suggestion is possibly not the best way forward.

If so, then I would seriously think about a complete dismantling, which will need a blowlamp and “asbestos fingertips”, cleaning up, and starting again.
 
Ian@StEnochs

Ian@StEnochs

Western Thunderer
Len that is a bu##er but you are not alone. It has happened to a lot of us, me included.

It’s difficult to see from your picture whether the whole frame has a curve or it’s straight at part. If it’s a complete curve the only sensible way would be to dismantle and start again. However if it’s straight on a good part then you could get away with local remodelling.

When I had the problem, on a 6 coupled admittedly, I got over the problem by sawing through the spacers on the distorted section, realigning the frames and soldering them back together with a shim, same thickness as the saw blade, between. That way the untouched spacers maintain the alignment. If you are concerned at the strength of the joint you could add a bit of plate to the top or bottom of the cut spacers.

Good luck and don’t give up!

Ian.
 
daifly

daifly

Western Thunderer
It may be an optical illusion but it does appear that the sides and stretchers are not sitting and fitting snugly together. The whole lot should be snug and square before the hot stick is even turned on!

Dave
 
Len Cattley

Len Cattley

Western Thunderer
Hi Dave, no optical illusion, I should have made sure that both sides were square before I got the hot stick was applied ☹
Len
 
Dave Holt

Dave Holt

Western Thunderer
Len, that looks much better and well worth the effort. I take it you checked for straightness and any twist at every stage. A lot of extra work, but it would never have run properly as it was before.
Chance to crack on, now, then.
Dave.
 
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