Big Train James's US Outline Workbench - sw1500 Kitbash

[Yorkshire Dave]

we are about 3 months out from the annual Chicago March meet

List has already been started for the ex-TNO GP9....

The existing Atlas sideframes are diecast. I'm sure that the same surgery could have been performed as you undertook on your gp9, with a bit more vigor. However, a couple of problems remain. The sideframe is relatively thin, so that even when moved in with the new keeper plate, there is a decent gap between the wheel face and the back of the frame. I'd like to close that up. Another is a lack of depth on the front side of the frame. I'm convinced that concessions were made on these frames to allow them to be fit to the same keeper plate as used on the Atlas sw8/9.

Sounds too much like hard work chopping around the cast sideframes .

I'd be inclined to cast the new sideframes and brake blocks from resin, okay you would lose weight, but it would solve the insulation problem if you mounted the brake gear parts on them rather than the keeper plate. If insulation is still a concern then you would only need to insulate the keeper plate side of the inner pull rods/slack adjusters.

 

[Big Train James]

List has already been started for the ex-TNO GP9....

There needs to be a "Cheeky" emoji.

 

[Jordan]

Thanks for the offer again, Jim!

 

[Big Train James]

It's time to get cracking on this project as I now have a sort of very loose deadline to aim for, namely the big Chicago March meet in a couple of months. I have discussed with another attendee the idea of initiating a kind of show and tell session for models such as mine, ones in progress but not ready for the contest room just yet. Something along the lines of the Prototype Modelers meets at various venues around the country. Nothing against finished models of course, they would be welcome as well. And while several of us are focusing on p48, I think anybody that wanted to show work would be welcome. The idea is to promote discourse on modeling, and get exposed to new ideas and techniques. Quite like the purpose of this forum, as I see it. So I would like to get as much done as possible by that time.

Unfortunately, right out of the gate, as these things are wont to do, my little project is turning out to be slightly more complicated than I had originally thought. Nothing that can't be overcome with a little extra effort. It's just that I made some assumptions which have turned out to be wrong. Things will be duly rectified.

I've been discussing my project with another local modeler, part of a small group of mostly HO modelers that meet each Monday night. My guy is also going to build a p48 layout to go along with his HO narrow gauge layout. He also happens to be a retired machinist. I have need of somebody to do some machine work on this project, so things suddenly are starting to align. In discussing the proposed work to shorten the loco frame, and in measuring to nail down precise dimensions, I have discovered that the frame will require an extra pair of cuts and splices to get everything correct and in the right places.

First the frame as is:

The two areas in the red boxes are the bolsters for truck mounting. The current bolster to bolster dimension is a scale 24'-2". The correct span for an sw1500 is 22'-0", so I need to remove that extra length. The initial though was to simply cut down the middle, remove the proper amount, and splice the two halves back together. But of course it isn't that simple, because doing so would also shorten the span between the motor mounts. I have no intention of modifying the stock Atlas drive or its components, as they are adequately engineered and already perform well. So the mounts need to maintain there spacing. The area in red in the following photo shows the mounts with the plastic motor retainer clips in place.

The next consideration is the distance between the bolsters and the pilot end sheets. This is one of the areas I failed to identify as needing adjustment until just last week. I had assumed that the distance would match between the mp15dc donor and the sw1500, and the only difference in overall frame length was between the bolsters. Of course, that assumption was incorrect. I need to remove 10.5" from each end to shorten the frame from 121.5" to 111".

The net result is that I will need to make four cuts and splices to achieve the correct length. One between the motor mount and bolster on each end, and another pair between the bolsters and pilot faces. Fortunately, all cuts and splice plate locations are feasible and in fact about as ideal as can be hoped for. First up is the rear section.


In the first photo, the red boxes includes flanges conveniently included in the casting. Of course they are there to attach all sorts of electronic wizardry to facilitate toy train control boards. The two yellow boxes indicate the approximate locations for the cuts and splices plates. The idea is that each splice plate will be drilled and tapped along with the frame, and then screwed together from the bottom. There is sufficient length and clearance for an adequate plate, and sufficient depth behind the frame rails for a 3/16" to 1/4" thick plate if necessary. All screws that protrude above the frame will be inside the shell, so will not affect aesthetics.

The second picture is of the top side of the frame. The large masses of zamak are hidden under the cab sub-base, presumably only there to add weight. One option is to position the cut through these solid chunks of alloy, then drill and tap and screw horizontally through one into the other for part of the splice. It's an option under consideration.

The front end is much the same, without the extra mass on the top side of the frame.


Most of the existing holes are of no consequence any longer, so can be ignored, or cut away, or possibly used to attach the splice plate. The bolster is obviously important, plus one of the holes toward the pilot through the screw for the shell passes.

The idea at this time is to cut the fuel tank mass off entirely, to the bottom of the frame rails. It serves no purpose other than weight. There is a finish piece that slides over the core part of the frame. This tank scales out at about 92", while the sw1500 tank will only be 66" long. There will be an issue to resolve with the visibility of the motor, as it hangs down below the frame rails incrementally. At the moment it is hidden inside the fuel tank, but about 1/4" at each end will now be exposed. I will try to disguise the motor with the fuel tank mounting brackets, paint it black and hope for the best. I doubt it will cause too much trouble in the end. I'll fabricate a new fuel tank to replace the existing one, or cut the existing tank down to size.


Now above the frame, I again discovered that I hadn't quite thought things through sufficiently. The section in the red box in the following photo will need to be removed. That's no problem, and has been planned for all along. I had presumed that everything from the low flat section forward was the same length for both locos, with only door, latch, and louver positions needing adjustment. It turns out that there is about 4.5" of extra length in the mp15dc hood, and unfortunately it occurs in the area of the sloped hood, in the yellow box below. So I cannot simply cut a section out and slide the remaining pieces back together. I will need to fabricate a new section of hood for the shorter sloped section, with a steeper angle. Initially I thought I could just do this with brass, but there are some interesting compound curves at the ends of the sloped section as it transitions to flat. I don't think I can successfully manage these, although while typing I had the thought that I could form those areas with filler sanded to shape. But I think what I will do instead is work up a 3d part to be printed. What's one more? Having said that about printing a part, I will also consider fabricating the section from sheet styrene, with 1/4 round strips for the filleted edges. With proper miter, or something close to it, and some filler, I could probably do a fairly tight job of it.




I will most likely be handing off the frame next Monday night for the machine work. I think my next task before cutting anything more on the shell will be to finalize drawings for the etched grills for the radiator so that I can get those off to PPD with plenty of time to spare, especially if the first attempt doesn't work as hoped. I also need to find someone to consult with about casting my sideframes. Once items with longer lead times are in the works, I can concentrate on the shell.

 

[Yorkshire Dave]

Hi James

I'd be inclined to sacrifice the truck bolsters, then shorten the frame between the pilots and fuel tank. This would only require 2 cuts, preserve the motor mount but you would have to make up two new bolsters.

And....

... if the stock Atlas drive shafts use cup and ball universal joints and splines (as in my GP9) then the splines can be shortened to accommodate the revised truck centres (I cannot find a photo or exploded diagram of the Atlas O SW1500 drive to see what it looks like).

 

[Big Train James]

Dave,
My first thought upon reading your post was "why didn't I think of that". I'll run it by the fellow that is going to do the machine work when I see him on Monday. One of my concerns as I think about it is maintaining enough clearance for the top of the gear box. It might depend on where the cut and splice happened.

Something that isn't readily apparent from my photos is the location of the flywheels directly on either side of the fuel tank. I probably didn't mark up the photos correctly in this area, as I have my yellow boxes indicating cut locations in the same place as the flywheels. At any rate, we'll take a look at the whole frame/motor/flywheel/gearbox assembly on Monday and discuss your solution.

Might as well post some pictures.





It's interesting to note that the universal coupling sizes are not the same for the mp15dc as they are for the sw8/9 models. The motors are the same, the worms appear to be the same, but the male and female couplings are not. It won't be a problem. The female has a key slot, while the male obviously has the key. The two pieces can telescope as required for turns. Drive line length should already be correct. Conveniently enough, the sw8/9 donor locos have the proper 22'-0" bolster spacing, and everything is symmetrical on both locos. So nothing should change between the motor/truck/coupling relationship from the donor to the recipient.

By the way, one can see in the second photo how the bottom of the motor, and to a lesser extent the bottom of the flywheels, extends under the walkway. The motor location is ideal in that the drive line and worm are in line.

 

[Yorkshire Dave]

Just seen the pictures above and if you sacrificed the bolsters you will also have to carefully cut and retain the jacking pads for re-use if they are of the correct style for your chosen prototype.

If the bottom of the motor and flywheels protrude a few mm below the walkway and frame perhaps this could be disguised by the air tanks, air lines and air filter.

One of my concerns as I think about it is maintaining enough clearance for the top of the gear box. It might depend on where the cut and splice happened.

I don't think this will be an issue if new truck mounts/bolsters were made from brass into this shape (rough sketch below) and fix it from the underside of the walkway. If you make the cuts at the new truck centres the new truck mount will also act as a support for the rejoined walkway parts.

 

[Big Train James]

Your sketch is pretty much how I envisioned it happening if I went with your suggestion. I could lengthen the outward flanges at the bottom to also function as the splice plate. I'll have a chat about it on Monday evening.

The jacking pads have already been considered. I'm not particularly fond of them. Like far too many details on this loco, the execution seems a half-hearted effort at best. Another detail where the HO version is somehow better. So I was already planning on removing them and adding better ones.

This afternoon I also met with a local jeweler who does custom work. If he couldn't cast my sideframes, hopefully he could point me to somebody local who would. The conversation was fruitful. The jeweler doesn't do any casting himself, but uses a semi local company. He does mill his own waxes, and is willing to mill my waxes essentially at cost. I've got a referral to the casting company, and will be in touch with them on Monday to iron out details, methods, and requirements. This whole aspect of the project could end up coming off much more quickly than I had thought.

 

[Yorkshire Dave]

I'll be interested to see how all this develops.

 

[Big Train James]

I'm working up some etch artwork for the front and top radiator grilles, radiator screens, step treads, and a few sundry other items. The focus is on the specific items. Anything else will be added as necessary to meet the minimum sheet size requirement for PPD. I have some questions.

1) Hollywood Foundry and PPD recommend bar or gap width minimum of 1-1.2 times the thickness of the material. If I start with .010" NS, but half etch part of it, is the minimum in the half etched portion .005" or is it still .010"? Intuition (and hope) says .005".

2) For the two grilles, I will be attempting to make etched members that will be .005" wide x .005" deep. For something this thin, do I still need to half etch a folding line? Is that even possible? In retrospect, I suppose that isn't possible unless I can do a four-layer etch.

3) Which brings me to the next question. PPD says on their site that they can etch to multiple depths, depending on the artwork. Is it possible to do what amounts to a three-level etch, with only a third off the back in some areas and a third off the front in other areas? I'm trying to create an etch with horizontal bars in one plane, and vertical bars in a second. I am hoping to include the flat surface just inside the bars where they turn back to the front of the loco in the etch as a way to stablize the ends of each bar, which is where the third layer comes into play. For the horizontal bars, this flat plate would lie in the second layer of etch, while for the vertical bars it would lie in the third plane. Hope that makes sense , or that a picture will help with clarity.


If that can't be done, or doing so would require extravagant effort, then I will find a different method. My first thought for an alternative is to just do regular half etch, with separate pieces for the horizontal and vertical bars. I had been avoiding this because I presumed I would need to solder or otherwise connect the bars at every corner where they crossed ! I'm reconsidering this now as I think I would only need to connect one vertical to all horizontals, and one horizontal to all verticals, in mid span, to prevent deflection of the bars. Or use CA instead of solder. It sounds terribly tedious, but not as much so as doing every intersection (there are 392 of them!).

Still thinking this part through. The foggy wisps of another solution are already starting to swirl around in my head. I'll sketch something up tomorrow that may simplify things.

4) Very early on when I first discussed this topic, it was suggested that I might consider stainless steel or phosphor bronze for material as it was stronger and could be etched much thinner. If I needed to go that route, which I'm currently leaning away from, how easy is it to solder those two materials as compared to NS?

5) Lastly, for now, when you fold etch back on itself, do you end up with a square edge, or is it discernibly rounded?

I need to get a handle on etching. It's clearly evident by the role it plays in all these beautiful kits I see on WT that etching is a powerful method for producing all manner of parts.

Jim

 

[mickoo]

I'm working up some etch artwork for the front and top radiator grilles, radiator screens, step treads, and a few sundry other items. The focus is on the specific items. Anything else will be added as necessary to meet the minimum sheet size requirement for PPD. I have some questions.

1) Hollywood Foundry and PPD recommend bar or gap width minimum of 1-1.2 times the thickness of the material. If I start with .010" NS, but half etch part of it, is the minimum in the half etched portion .005" or is it still .010"? Intuition (and hope) says .005".

Only to safe guard their process, you can go smaller but at your own risk, I work a lot in 0.40mm and they recommend 0.50mm slots or gaps, I often use 0.30mm (especially for panel detail work. Sometimes it doesn't quite etch right through but a quick pass with a sharp knife helps break the bond.

2) For the two grilles, I will be attempting to make etched members that will be .005" wide x .005" deep. For something this thin, do I still need to half etch a folding line? Is that even possible? In retrospect, I suppose that isn't possible unless I can do a four-layer etch.

For material that thin the only reason to make a half etch bend line is for accuracy and alignment to make the actual bend, but yes it is possible.

3) Which brings me to the next question. PPD says on their site that they can etch to multiple depths, depending on the artwork. Is it possible to do what amounts to a three-level etch, with only a third off the back in some areas and a third off the front in other areas? I'm trying to create an etch with horizontal bars in one plane, and vertical bars in a second. I am hoping to include the flat surface just inside the bars where they turn back to the front of the loco in the etch as a way to stablize the ends of each bar, which is where the third layer comes into play. For the horizontal bars, this flat plate would lie in the second layer of etch, while for the vertical bars it would lie in the third plane. Hope that makes sense , or that a picture will help with clarity.
View attachment 63157

If that can't be done, or doing so would require extravagant effort, then I will find a different method. My first thought for an alternative is to just do regular half etch, with separate pieces for the horizontal and vertical bars. I had been avoiding this because I presumed I would need to solder or otherwise connect the bars at every corner where they crossed ! I'm reconsidering this now as I think I would only need to connect one vertical to all horizontals, and one horizontal to all verticals, in mid span, to prevent deflection of the bars. Or use CA instead of solder. It sounds terribly tedious, but not as much so as doing every intersection (there are 392 of them!).

Still thinking this part through. The foggy wisps of another solution are already starting to swirl around in my head. I'll sketch something up tomorrow that may simplify things.

You might be over complicating things, rather than two half etches one etch will suffice, on the front side you have the vertical bars as full etch on the front and half etch on the back (where they do not cross the horizontal ones), on the rear side the horizontal bars full etch and half etch on the front where they do not cover the vertical ones. This will give the appearance of a layered grill.
If you want two go the two half etch layers, then I'd suggest that around the outside of each one make a carrier / support etch work and put say four holes in it. Make the reference holes and carrier the same for each etch layer, then place both layers on a scrap piece of wood and drill holes to match the etch holes and insert pins, this will keep everything square and registered. For soldering I'd apply a very thin smear of solder paste between the two layers and waft either a hot air gun or blow touch over it. Make two or three grill etches on the sheet, being half etched and so thin there is the risk of it buckling under the heat, eg make back up or practice etch grills to fill the minimum sheet size

4) Very early on when I first discussed this topic, it was suggested that I might consider stainless steel or phosphor bronze for material as it was stronger and could be etched much thinner. If I needed to go that route, which I'm currently leaning away from, how easy is it to solder those two materials as compared to NS?

No idea, not worked in either material but Nickel Silver should suffice, it'll be delicate but should suffice.

5) Lastly, for now, when you fold etch back on itself, do you end up with a square edge, or is it discernibly rounded?

Rounded, however if you deepen the cut with a skrawker or in your case (material thinness) a sharp knife, it will sharpen the fold, however it will also weaken it so it pays to back fill the fold, once folded, with a fillet of solder.

I need to get a handle on etching. It's clearly evident by the role it plays in all these beautiful kits I see on WT that etching is a powerful method for producing all manner of parts.

Jim

Hope that answers some or in part your questions

MD

 

[JimG]

Big Train James said: ↑
4) Very early on when I first discussed this topic, it was suggested that I might consider stainless steel or phosphor bronze for material as it was stronger and could be etched much thinner. If I needed to go that route, which I'm currently leaning away from, how easy is it to solder those two materials as compared to NS?


No idea, not worked in either material but Nickel Silver should suffice, it'll be delicate but should suffice.

James, Mick,

I actually asked the question about soldering the stainless steel material of Piers at PPD and he responded that the feedback they had had was that it was a definite no-no. I have got some liquid stainless steel flux which I got to use on Clive Barker's rail which works quite well and I'm tempted to get a test piece from PPD to see if soldering will work with this flux.

Jim.

 

[Steph Dale]

I've not tried soldering their stainless steel, but with the right flux should be okay.
Phosphor-bronze and beryllium-copper both solder beautifully and make strong fine etches. They're both quite springy though, so any forming in such parts needs to be relatively simple.

Steph

 

[Big Train James]

Thanks for the replies. Still sorting it all out. I hope to have something firm to discuss tomorrow. I'll be moving ahead with Nickel Silver based on everything I see here on WT.

In the meantime, I have some crappy cell phone pictures of the initial progress on the frame machining. First up is the frame in progress next to an unmodified frame. This photo is of limited use as the detail is hard to discern on the black frame.


The most obvious change so far is the removal of the fuel tank weight to match the depth of the frame rails. Removal is necessitated by the need to reduce the length of the fuel tank from 92' to 66" (technically the mp15 tank should only be about 84" but Atlas clearly made it longer to match the length of their standard motor). The removed mass is strictly about weight, as there is a finished diecast tank "skin" that slides over the frame casting. The tank cover will also need to be shortened, which I'll address momentarily. I'll be locating a larger speaker inside the shell instead of in the tank. The motor protrudes slightly below the frame rails, so I need to accommodate that when I rework the tank. But there will be a good volume available in the new tank to add weight back in if needed.

The next photo shows the front end of the frame. To this point, the only work here is to mill off the jacking pads on both sides of the frame, and mill flat the slight protrusions from the ejector pins.


There will be ¼" x ¼" brass bar splice plates running the full length marked in blue, from motor mount to the pilot. There will be two cuts to the frame, one each side of the bolster. Dave had suggested above the idea of utilizing one cut and replacing the bolster, but it was decided that doing so was trading one bit of work for another. The friend doing the work says stick with two cuts, so that's what we will do. I'm leaving those kinds of decisions up to him as he is the retired machinist, and he's doing the work gratis. I'm lucky to have crossed paths with him and discovered he's interested in P48.

Next up is the middle of the frame, where the fuel tank has been removed. Nothing monumental going on in this shot. The tank was milled down to be flush with the depth of the frame rails, which still left sufficient depth to the transverse members underneath the motor mounts. Eventually I'll need to figure out how to hang the revised fuel tank off the frame centered in this area, but I'll cross that bridge later. Obviously I won't be able to use the existing mounting holes to the bottom left and top right of the milled section as they are too far apart.


Things are a little more cluttered on the cab end of the frame. Again, the jacking pads and ejector pin marks have been removed or milled flush. There is an extra wedge of material in one corner of the frame (top right corner in the next photo), which we are thinking has something to do with the tooling or the material flow during casting. It doesn't seem to serve any purpose on the finished model, and would presumably be uniform if added for weight. At any rate, a groove was machined out of the wedge to accommodate the splice plate running end to end. Again, two cuts will be made to shorten the frame, one each side of the bolster. To the right of the bolster, the opening for the truck gear box is fairly tight, and may need to be machined to provide additional room once the cut and splice is finished. From the top side, everything in this area is covered with the cab and sub-base, and there is plenty of room to work with on the frame, so extending the opening shouldn't be an issue.


On the top side of the frame, the short nub for mounting the optical reader for the tach tape has been milled off. It isn't a necessary cut, but as it will serve no purpose going forward, it was removed. There are a few tasks like this which aren't necessary but are part of generally cleaning up the frame for the sake of it. This photo also gives a good sense of the amount of material left under the motor mounts once the fuel tank is removed.


Removal of the fuel tank will leave the bottom of the motor visible below the frame rails. Both flywheels are also visible, although this was always the case. Even once the shortened finished fuel tank is added, the ends of the motor will still be visible as they extend past the ends of the tank.


The plan is to paint the bottom of the motor in flat black to make it less conspicuous. The new tank will cover the vast majority of the motor, and the air reservoirs should sufficiently block any part that sticks out past the tank ends. I will be fabricating and detailing new tank ends, which will need to have a crescent of material removed from the top edges to allow room for the motor. Again, this should be masked by the air reservoirs and also the hanging bracket which attaches the tank to the frame on the real locos. It may not be a perfect solution if someone wants to look really closely, but it is a necessary concession if I want to utilize the existing factory drive.

I'm satisfied with the profile of the fuel tank. It needs to be shortened in length, but it will also need to be narrowed. The tank is wider than the frame, which is incorrect. So material will be removed from the middle and the tank will be spliced back together lengthwise. Not surprisingly, the casting relieved some stress when the ends were cut off, springing open incrementally. This extra width will be accounted for with the cut and splice so that the tank measures the same width as the frame. Overall material removed will amount to about .100" or so. It's not much, but the way the tank sticks out from the frame is one of those things that is readily apparent to the eye just by looking. So the work will be done.




There were raised areas on either side of the speaker opening (in blue, with the screw holes) that were milled flat so that a splice plate could mount cleanly. The plate will also close the hole for the speaker. New ends will be fabricated out of sheet styrene, then glued or epoxied to the tank. I'll trace the inside edge of the tank onto .060" styrene, and the outside edge onto a thinner sheet in the range of .015"- .020" styrene. I'll then offset the outline on the thin sheet to reflect the way the end sheets on EMD fuel tanks are slightly larger than the tank. I'll laminate the finish and substrate sheets together, with the .060" sheet sliding into the end of the cast tank. The top edge of both sheets will be shaped to fit around the motor as noted above. Other machine work will include drilling holes on both side of the tank for fuel filler tubes, plus drilling a hole in the engineer's side of the tank for the recessed fuel gauge. The following picture shows the various bits and bobs, plus the fuel tank end sheets.



I'm hoping to do something with the recessed fuel gauge akin to the backhead water level gauges I've seen on several threads here recently. I've been fretting a bit trying to figure out the best way to form the recess for the gauge, as no part is currently available to the best of my knowledge. At issue is the way the surface is dished rather than cylindrical with a flat bottom. In writing up this summary, and looking at the machined fuel tank walls, I think I'll see if a ball end cutter can be used to form the recess without exceeding the wall thickness of the tank. At first glance, it seems feasible. Upon further review, it looks like Precision Scale may have a part for the gauge, but I'll still need to form the recess.

The next step with the frame machine work is the cutting and splicing. In theory, the solution is pretty straightforward. In execution however, there is a potential issue with mill table travel and clearance with the tool post. Work to this point is being done on a Sherline mill, which is mostly capable, but has a smallish form factor. A traditional full size mill is on premises, but is in the garage, lacking both heat and power at the moment. So fingers are crossed that the Sherline will be adequate for the remaining work. The worst case scenario is that a larger mill is needed, in which case one will need to be found or the work will have to wait until the garage shop is in working order.

I should have an idea by next Monday at the latest if the remaining frame work can be done. In the meantime, I'll focus on etch artwork and the shell.

 

[Yorkshire Dave]

I'm lucky to have crossed paths with him and discovered he's interested in P48.

It's amazing who you meet sometimes.

 

[Ian@StEnochs]

I see the fuel tank has been 3d printed and not had the contour lines sanded smooth!

Ian

 

[Dog Star]

I see the fuel tank has been 3d printed and not had the contour lines sanded smooth!

Maybe the "straight" curve was the result of a weight or material saving design requirement. By making the curve as a series of folds the plate gains strength from the shape and hence the plate thickness could be reduced.

 

[Big Train James]

I'm not sure what the story is with the faceted fuel tank. It's not something I've ever seen with older EMD tanks, and I've been looking at them for a long time. The caveat about vintage is because the newest EMD locos like the sd70ace have a revamped crash-resistant design, and somewhere in the design process they abandoned the smooth curve and went to a series of folds. It's a shame in my opinion, as there was a certain elegance to the older tanks. The relationship between form and function be damned!

 

[mickoo]

The bent tank sides are and EMD trait from early days and are down to simplicity in manufacturing, finding rollers that long and with the strength to roll something that thick to a small radius like that is not easy. Bent tanks came in with the GP30, not sure about the GP20 but the GP 9 does not mainly because it a bath tub style and hasn't got wrap around tops like the later versions.

Bent side tanks are done with a bending brake which can be made with a much stronger bending tool, round bars of the diameter required to form that tank shape over that length will bow in the middle.

The difference between the older tanks and the more modern ones is the number of bends, older tanks have twice as many and maybe even three times as many so the curve is much smoother, but with the right angle of sun and a close up then the bends are still clearly visible.

GP30 from I believe the mid to late 70's


Withdrawn DD40AX


In the SD range the SD24 certainly has a bent side tank, the SD9 does not but not sure about the SD18. A common factor between rolled and bent tanks seems to be the stepped in top to accommodate reservoirs.

Here's a couple of close up shots of a GP40 I took in Florida of the older closer bends tank.

You can barely see the bends and it looks almost smooth but they are there, as seen below.



The front tank looks smoother but the bends are clear toward the rear, this tank has been repaired and the nearer half upper section has been replaced with a tank bent to the new lesser bend type, resulting in the obvious weld line half way down and mismatch with the older rear section. The lower weld from the patch is clear and below that both tanks match, clearly a side swipe of some sort.

Hope that helps

MD

 

[Yorkshire Dave]

Nice close ups of the GP40 tank Mikoo .

Both useful as they also show the tank mounting bracket and how the sand hoses run.