122 Dmu

Simon

Flying Squad
Thought I'd try a bit more "mission impossible" last night as I had bought some more Mek Pak at Warley

I have strengthened the top edges of the sides with strips of 20 thou styrene, cut off those big sheets from Eilleen's. The outer pair represent the backing and "middle" of the rain strip, a further strip will form the outer edge of the gutter but I will leave it off until later as it will be very fragile.

Cantrail 001.jpg

I have attached a further 20 thou strip behind, this will further strengthen the top edge, the glazing will drop down below this into "pockets" made by applying strips to the rear of the sides around the window openings. The PETG glazing is 20 thou so my cunning plan is to make the pockets out of 30 thou such that when it is all painted the glazing will drop easily into the pocket frames despite a coating of paint.

Cantrail 006.jpg

Well that's the idea at the moment, baked potatoes first then styrene strip cutting - I know how to live:rolleyes:

Simon
 

Simon

Flying Squad
I made the "pocket frames" last night for both sides, plus some strengthening strips on the rear face, positioned so as to put a "floor edge" at 90 and a bit degrees in, which will further strengthen the side.

aapockets 001.jpg

The pocket frames will be completed by strips solvented across them, like the top of a "T" in order to retain the glazing.

Simon
 

Steph Dale

Western Thunderer
Simon,
Just a suggestion, but...:
At this stage it might be worth wrapping the parts up in newspaper and weighting them on a flat surface; I'd then leave them for a week or two to harden off completely. Depending upon the amount of solvent you've used your current approach may lead to distortion in the side. A small amount may look prototypical, but too much and the shaping of the tumblehome and final assembly could be awkward.
BTW; have you not got a copy of Jenkinson's 'Carriage Modelling Made Easy' tucked away somewhere...?
Steph
 

Simon

Flying Squad
I'd have no problem leaving it a week, or two, or three....

But I'm curious to see how far I can get and if various ideas work out. Distortion is a concern but I'm hoping the glazing will keep the window line straightish and in any case I think the key will be the formation of the curve/tumblehome which I think runs along just below the plane of the windows. I'm considering options on this and will try and avoid solvents but more importantly perhaps any voids that the body sides can shrink back into. One thought is a strip of etch waste with the tumblehome shape formed from a narrower strip soldered along the middle and the curve buit up from epoxy filler, this would then be epoxied to the coach side held into a curve somehow as the glue goes off.

If it all goes t*ts up all I have lost is my time and about 50p's worth of styrene:p

One slight issue here is that I'm pretty much guessing the shape based upon my cab castings, which are actually slightly different from one side to the other:rolleyes:

I may attempt some more this evening, it would be great to get this all turned in to a body shell.....

Simon
 

rosspeacock

Modelling on a £1200 table.
Yes the sides are flat and the tumblehome starts just below the window line the sides aren't like a mk1 with a full tumblehome.. I've had plasticard distort after curing but I thought it was the amount id used so newspaper and weights could be a plan:thumbs:

Ross:)
 

Steph Dale

Western Thunderer
S'funny you say that Ross, I dimly recall that the profile of (some? all?) DMUs was related to that of Hawksworth coaches...
Goodness knows how we'd confirm that though; I don't think I've ever seen a dimensioned DMU section drawing.

Steph
 

rosspeacock

Modelling on a £1200 table.
The easybuild 121/2 has a full tumblehome but I think its cos they use Mk1 profile sides in their kit.. some DMU's with a 'Derby' front on had a full tumblehome like 107/8's I think but the ones with high density stock sides like 115's etc were flat then the roll starting under the windows. .

Ross:thumbs:
 

Simon

Flying Squad
That's helpful information Ross, thank you very much.

That was my kind of interpretation based on the drawing in Brian Golding's book and looking at lots of photographs.

On the drawings question, I don't think I have ever seen a "proper" drawing of (any?) DMU. Lots of them still exist and I think the production of decent drawings would be really very useful. In fact thinking on, I'd dearly love to be able to buy a book on the subject that contained all the information you need as a modeller plus lots of good pictures and historical details.

A bit (lot?) like the Wild Swan "profile" books but for say different classes of DMU, and diesel locos too come to that. I think it might sell really well, I'd probably start with the 121/122 "family" and trailers and of course you'd have to have a book on the Class 22s...

Oops, book wishlisting:oops:

Simon
 

Simon

Flying Squad
I have decided to try the tumblehome with all plastikard, a strip of 30 thou that fits between the bottom and waist strengthening strips has had a narrower strip of 30 thou solvented along its length on its central axis, this strip has been chivvied with a knife to give it a generally curved/convex section. The two strips prepared and lying on their respective sides:

tumble 001.jpg

I have now attached the top edge of the two strips to the edge of the upper strengthening strip with Charlie's Citadel thin glue, here is a view of an end which hopefully explains what the idea is:

tumble 003.jpg

I will now let this go off thoroughly before attaching the lower edge to the lower strip in the same way, thereby hopefully forming a tumblehome to the body side. I am working out the required shape by referring to the already cast cab body sides.

Re solvent fumes etc, I reckon all joints are vented at the moment, the central shaped narrow strip isn't actually glued/solvented to the body side itself and so I hope the body side won't deform along its length but rather maintain a nice regular curve when the second joint pulls the side into shape.

The top joint here will be further strengthened by the strip of probably 30 thou styrene that will be put in place to form the lower channel for the glazing and I can do something similar along the bottom joint too.

I can't see why it won't work, but I'll also be surprised if/when it does....

Simon
 

Overseer

Western Thunderer
I hope I am wrong, but I think you will end up with kinked instead of curved lower panels. The styrene will tend to stay straight, or revert to straight, if it can. David Jenkinson's method of rolling the curve into the styrene before assembly does work and the styrene sheet tends to retain the curve. The curve can be formed by rolling the part of the side on a piece of pipe or round bar of a smaller diameter (you need to over roll the styrene so it springs back to the curve you need) or by running the end of a No2 craft knife handle or similar repeatedly along the inside while resting the side on a padded surface.
 

Simon

Flying Squad
Good point, I hope you are proved wrong but putting a bit of a set into the plastikard as you suggest would probably have been a good idea and couldn't have done any harm. The sort of problem that I think I am likely to get is where the plastikard surface "depresses" in places where unflashed off solvent or glue is present, such as along the joint I have just made.

Going back to your idea, apart from it not coming to mind at the time (if I ever had David's book I can't find it now) my thinking with my method is that the curve will be consistent along its length as the "forming forces" are the same at all points. Given that the central narrower strip was shaped and presents no hard edges to the side, and that no solvent or glue has been used along it's length, I'm allowing myself some optimism on this point.

I think what might be tricky is getting the lower edge attached uniformly as the force pulling the joint apart is significant when you bend the side around. Some sort of cunning clamping method is required I think, lots of clothes pegs and strips of thin timber maybe?

It does feel good to at least be giving it a go after so many years of pontification:rolleyes:

Simon
 

Simon

Flying Squad
I have just run Citadel thin plastic glue along the bottom edge of one side and clamped it all up between the kitchen railway bridge plywood and a strip of square beading.

aglued 001.jpg

aglued 004.jpg

Looking along the top edge which is raised by the curve formed in the side by the clamped edge looks pretty straight to me, so I'm hoping for a uniform tumblehome/curve along the side.

I guess it wants to stay clamped for a good while, I think I'll unclamp it and glue the next one tomorrow evening......
 

Simon

Flying Squad
I yesterday evening un-clamped and found that all was good except that the bottom edge hadn't glued in a couple of places. So I cut out a 10mm wide-ish strip of 60 thou styrene and glued and solvented it along and across the joint, positioned so that it will butt up to the floor section that I will be attaching in due course.

This morning I unclamped it all, and then glued up the second side and clamped it up for tomorrow.
I am pretty chuffed with the result, it looks pretty uniform and is a reasonable match to the cab casting as the pictures hopefully show:thumbs:

aaatumbledWT.jpg aaatumbled 001.jpg aaatumbled 005.jpg

Off out to the garden now to clear leaves and hopefully find and sort out a major short circuit:confused:

Simon
 

Steph Dale

Western Thunderer
Neat. A useful development of the Jenkinson method. I may have to try it out in 7mm. Which means identifying another SR carriage I only need one of. Mutter mutter...
Steph
 

Simon

Flying Squad
Thanks for the comments, I have just got in from the garden and leaf clearing aside I am very happy to say that I identified and cured the wiring fault and trains can run again - so no need for battery space on this vehicle:thumbs:

I am going to try and so some more work on the glazing frames later and I am considering underframe options too, having taken 5 years to get this far I'd like to see it finished before its next birthday:p

Simon
 

Steph Dale

Western Thunderer
DS70155 or DS291, would be great to see:thumbs: - both true 'one offs'

cheers

Mike
DS291 is on the list actually and I do have some parts for it in stock. It's similar to the LNWR stock used on the Sunny South Express, a truly beautiful vehicle. And being open inside a great candidate for this method of construction...
Steph
 

Geoff

Western Thunderer
I spent a very pleasant afternoon earlier this week reading the whole thread Simon, what a cracking story and build. It might have taken you five years but the resulting model is looking superb
 
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