Setting Standards – Minimum Radius

Try a piece of Kapton tape under the cab overhang, where the tender touches it.  This will prevent shorting out in case the tender touches it.  Kapton tape is a special electrical insulating tape used frequently in decoder installs, in case anyone doesn't know.

There is an old saying: "Two wrongs don't make a right." Grinding off part of the tender is one of those "wrongs"! You want to find out what the real problem is! I'd say give us some level shots of the loco and tender sitting on straight track where we can see the "offending" parts in the same image. Maybe we can get lucky. Even if not, we haven't ruined anything!

The de facto minimum radii for LARGE locos has always been (at least for this Geezer) 72 inches.

You mention things not looking "realistic"....the word silly crosses my mind! Remember, Rome was not built in a day.

Meanwhile, Happy Holidays!

Simon

Sounds like an issue I fought for sometime. I eventaully ended up with 90” on the main and a minimum of 80” in the yard to accomodate A Milwaukee Little Joe. As I want to model every part of the Milwaukee from avery to alberton 😅 I decided to pick key scenes and add lots of detail in a more realistic setting. 

This decision to do this limits how much rail you can actually lay (and of course space is a factor) but in the end it’s the attention to detail that wins out for me. Look forward to seeing what you do!

Sarah,

They are a couple of options not mentioned.  Next time we talk I'll run them by you.

Jay

Sarah posted:

 

The CB&Q M-4A by Precision Scale refuses to do anything beyond 68" radius wheel wise. However, the high riding tender touches the cab roof causing a short, even if I couple it with the second drawbar hole. I don't know how to solve that problem, a longer drawbar looks ugly. I might mill that prominent tender part down but does one really want this?NO !

If you have any suggestions about that tender vs. roof problem, I'd be really happy.

Thank you! Sarah

Sarah, Are both trucks insulated from the body on the tender ?   Are there wires running between the loco and the tender ?  How many ?  Do you have a volt ohm meter  and a soldering iron ?   I am trying to determine which rail is ending up as chassis ground on the loco and which  on the tender.   Is the drawbar being used as a power buss between the loco and tender?  You must get both bodies charged from the same rail to stop your short. This could entail insulating one or both trucks and the drawbar on the tender, if the drawbar is functioning as a buss. Rest assured you don't have to use tape or mill any tender body away.  Though kapton tape is a quick but not so proper fix.   Some really nice machines you have there !  They deserve better than a file or tape.  Situations like this make me want to do Skype.   j

Sarah posted:

Dear Friends,

to determine if a future track plan works or not I found that it is time to set up my standards. I unpacked the most problematic pieces of rolling stock and put them into the track laboratory in a clean room. Sooner than I thought I reached the limits of what's possible.

The tightest radius is 61" and the Sunset 4-12-2 manages to negotiate through that curve without a problem. Applause. The 3rd and 4th drivers are flangeless, ok. 

Thank you! Sarah

I just reread your post. Seeing it a second time, it appears to me you need to evaluate your priorities.

Do you want realism (accurate models) or fitting stuff within a particular space. If you blind enough drivers (make them flange-less) you could probably spin the thing like a top (OK, I'm kidding) but the REAL engine did not, to the best of my knowledge  have ANY blind drivers. The Sunset gets around sharper curves by sacrificing the accuracy of the model by blinding those drivers. If that isn't a problem to you, you can make changes to get bigger locos in a smaller space.

Once decided, I am sure Jay can help you get ti=o where you want to be.

Simon

Thank you very much for all the thoughts and comments. 

Simon, I am well aware of the pro#s and con's of Sunset vs. Kohs. I don't want to make compromises but that's just not possible. The biggest compromise has two digits: 48! For sure it's easier to plan a layout with tighter curves and be it 72" instead of 76" radius. I won't cut back any of George Kohs' flanges, I could never look into his eyes! Sunset is indeed the majority of my fleet. But I want to run the other jewels, as well. So I plan ahead for the stiffest loco. The goal is a layout suitable for the finest rolling stock and be it only on Sunday afternoon. 

Regarding the 2-10-4 roof / tender problem I made some additional shots. I think a possible way would be to trim back the cab roof a bit in the corners so no touching would occur. 

This pic shows the gap with the drawbar hole number two in use

Other angle on straight track

Next pic shows the short. Just a little contact. That happens on virtually all radii, also 80 plus simply because the tender board is so high and close.

Here you can see the close coupled tender and that there's just no room for any curve when using the No. 1 hole of the drawbar. 

Dear JohnActon,

thank you for your "thinking inside" of this. Don't worry, I won't use a file or tape :-). The engine is just out of the box first time and straight DC with the drawbar transmitting the other pole to the motor, tender is plus, engine is minus (or vice versa). I will digitalize it some day and then I ensure good pick up and power transfer. The simple fact that the tender chassis scratches along the cab roof is a major problem by it's own.

First I thought I would have to mill down the tender front a tiny bit but altering the roof corners is easier. I'll talk to Jay. An even longer drawbar would compromise the appearance too much. I really appreciate your worries and helping hand! Thank you

Sarah

Very good discussion.   Often this discussion leads to a 3 rail v.s. 2 rail layout.   3 rail curves, easily 1/2 the size of 2 rail, IMO.   Note that smaller switcher locomotives would operate on smaller diameter curves/switches.    I have a 3 rail layout, O54, max curves. I'm always impressed with 2 rail O-scale layouts.   Mike CT.  

Sarah posted:

Dear JohnActon,

thank you for your "thinking inside" of this. Don't worry, I won't use a file or tape :-). The engine is just out of the box first time and straight DC with the drawbar transmitting the other pole to the motor, tender is plus, engine is minus (or vice versa). I will digitalize it some day and then I ensure good pick up and power transfer. The simple fact that the tender chassis scratches along the cab roof is a major problem by it's own.

First I thought I would have to mill down the tender front a tiny bit but altering the roof corners is easier. I'll talk to Jay. An even longer drawbar would compromise the appearance too much. I really appreciate your worries and helping hand! Thank you

Sarah

Boy, if it were me I'd either go with the tape, or think of some other solution that wouldn't "compromise the integrity" of the model. These things are too nice to alter, in my (useless) opinion. 

Mark in (wet and windy) Oregon 

Several comments

- Quite a few prototype locomotives had one or more blind drivers.  The PRR 2-10-0's when built had 3 blind drivers, years later drivers 2 and 4 were retrofitted with flanged tires.    The PRR M class 4-8-2's all had 2 blind drivers.  Note I'm not recommending blind drivers where the prototype had flanged ones.

- I've found most O scale locomotives can be modified to accommodate modestly tight 64" radius curves without significant alteration that compromises appearance.  With fully flanged long wheelbase locomotives (like my Westside PRR J1 2-10-4's the way forward was to provide for increased lateral motion of the drivers in the frame.  A way to test if lateral play is the limiting factor in your locomotives ability to negotiate a curve is to remove the lead and trailing truck and simply pushed the locomotive (without the tender) through the curve - you will feel a bind if the drivers are too ridged in the frame.  I increased the lateral motion on drivers 1,2,4, and 5 by thinning the flanges on the bronze driver bearing journal blocks.  In the case of my 2-10-4's I also had to grind some material out of the cast frame in the area of the trailing truck's second axel to keep the insulated wheel from shorting to the frame.  In profile of the frame was not changed and as a result the slightly narrowed width can not be detected at eye level.  

- IMO in the case of Sarah's Q 4-8-4 it would be better to use a slightly longer drawbar rather than cutting back the cab roof.  It may take only a minor increase in length. 

Sarah,

Please check to see if the tender is sitting too high.  Some models sit high and many times it's possible to lower them.  Check the prototype plans for that model (Mainline Modeler has plans for those engines).  Compare the tender to those plans to see of it is sitting at the right height.

Sarah posted:

 

     While it is possible because of the photo angle I am being misled, it appears, based on the hinge point of the apron, and thinking that the nominal design height* [ assuming the tenders were built or modified specifically for this class  ] in the prototype for the tender and cab deck would be the same, that the tender is riding too high vs the loco.

SZ

*With allowance for the fact that as the consumables are, ah, consumed the tender and hence tender deck will rise........

Edited to add:  Steam Guy beat me to it while I was typing.

Edited a second time:  I got my model mfgs mixed up, so the tender would not have had provision for hirail radii operation.

Steam Guy posted:

Sarah,

Please check to see if the tender is sitting too high.  Some models sit high and many times it's possible to lower them.  Check the prototype plans for that model (Mainline Modeler has plans for those engines).  Compare the tender to those plans to see of it is sitting at the right height.

 

Although judging by the photos that doesn't appear to be the case, this option sounds way better than doing any kind of surgery to either the cab or the front of the tender... 

Mark in Oregon 

Strummer posted:

Steam Guy posted:

Sarah,

Please check to see if the tender is sitting too high.  Some models sit high and many times it's possible to lower them.  Check the prototype plans for that model (Mainline Modeler has plans for those engines).  Compare the tender to those plans to see of it is sitting at the right height.

 

Although judging by the photos that doesn't appear to be the case, this option sounds way better than doing any kind of surgery to either the cab or the front of the tender... 

Mark in Oregon 

Just my opinion but, the tender appears to be at the correct height. However, the deck plate has dropped down below the corresponding mating surface of the tender, i.e. the upper deck on the tender. Maybe the tender is not close enough to the engine, but one way or another, that deck plate should be resting on the upper platform of the tender (just like the real locomotive).

The radius problem with Sarah's engines makes me wonder if my AC4400CW will negotiate 60" radius curves ok? All my 60ft boxcars do ok so took for granted this diesel as well as my SD40-2 would also be fine.

Do you gentlemen think 60" is ok?

Thank you all in advance for your help.

Al Hummel

Sarah posted:

Dear JohnActon,

thank you for your "thinking inside" of this. Don't worry, I won't use a file or tape :-). The engine is just out of the box first time and straight DC with the drawbar transmitting the other pole to the motor, tender is plus, engine is minus (or vice versa). I will digitalize it some day and then I ensure good pick up and power transfer. The simple fact that the tender chassis scratches along the cab roof is a major problem by it's own.

First I thought I would have to mill down the tender front a tiny bit but altering the roof corners is easier. I'll talk to Jay. An even longer drawbar would compromise the appearance too much. I really appreciate your worries and helping hand! Thank you

Sarah

I wish I could see how the rear of the boiler / cab is fastened to the frame of the loco. Might it be possible that the mounting  brackets have been mashed down in transit. Perhaps shims or washers could be used to lift it a mm or so.  I think I would insulate the tender body form both trucks and run a jumper from the trucks to the drawbar, making sure it was also insulated. However even if you do this you still don't want the cab roof rubbing on the tender when in a curve.   j

You have very nice locomotives. I had this problem with my layout, which is a shelf around the wall. I gave up straight away length for very wide curves and I'm really glad I did. Everything looks better, especially long passenger trains smoothly exiting a corner at speed.

Here is a video made several years ago immediately after laying the track.

Not that this comment helps with Sarah's question, but wow! That's quite a train...15 cars!  

Mark in Oregon 

Nice thread folks, really enjoyed I hope you find the right answer.

My minimum period is 72” never below. Several of us have your BooRim M4 and Kohs UP 4-12-2 locomotives not mentioning scale passenger equipment with functioning full width diaphragms. My preference is 110”.  The bigger the better, otherwise go 3RS what’s the point of owning $3k - $7k authentic models and running them on unauthentic trackwork? Opinion 

cutting into a handbuilt masterpiece to make up for a small space, buy HO... 

let this sink in... a friend a retired civil engineer explains....

In reality (1:1), a 16 degree minimum radius on the Union Pacific used on wyes in o scale is equivalent to 90”. 

Comparison for those with 3 rail thinking:

O-108 diameter is 54” radius 

O-72 diameter (full circumference) is 36” from center point to edge

O-120 is the minimum to run my Key Model Imports FT’s, sort of makes me think a little. 

Just some thoughts 

Sarah, my grand daughter's name, this is one more example of broad super elevated curve with speeding long diesels and long passenger cars. You'll notice it is pretty smooth even with a slight S at the end connecting to the straight.

Dear Ed,

I can't express how happy I am about your comments. You are the reason I startet to fall in love with trains. Many years ago I spotted an issue of MR with your Horse Shoe Curve on the cover. I want to express a big thank you here! I guess I have a similar thinking when it comes to alter or not alter a locomotive. I read your suggestions with great interest. Thank you!

Sarah

Dear Ron,

great videos, thank you! Glad you made the right decision. Greet your grand daughter, I hope she's gonna walk in your footprints

Dear Forum Friends,

thank you for all the comments. It is very interesting to have a closer insight into the different, slightly diverging "inner worlds" of O-scalers. 

I have some very strong arguments ad hand now and when I'll take the baby apart there will be more evidence of what's doable with riding hight, drawbar, shimming the chassis ect. That will be a lot of fun, although I'm a bit scared of handling the superstructure. 

The school of big radius curves advocates in O scale with it's "not silly" looking passenger trains is one that I can fully follow. But in layout design, there are some challenges that can only be met by setting the curves a bit tighter. And I mean the portions that can not be seen, like mainly turn back curves, a helix and off layout staging. That's where I would really benefit from a 68" minimum radius curve standard. 

@Erik C Lindgren – I never thought that full with diaphragms are practical. Do you have an example? How do you operate these? With a gap between cars on straight track? Do you alter the diaphragms to span over a bigger distance? Many questions!

I am sure there is a solution for every problem. And it's a weird fun getting there.

Sarah 

Sarah posted:

 

Thanks for the images. Almost seems like the tender and loco are not compatible.

A wild thought, but could the person you acquired your stuff from have had more than one CB&Q loco and mistakenly mixed the tenders?

Far fetched I suppose, but trouble shooting by picture is not easy!

Simon

JohnActon posted:

Sarah posted:

Dear JohnActon,

thank you for your "thinking inside" of this. Don't worry, I won't use a file or tape :-). The engine is just out of the box first time and straight DC with the drawbar transmitting the other pole to the motor, tender is plus, engine is minus (or vice versa). I will digitalize it some day and then I ensure good pick up and power transfer. The simple fact that the tender chassis scratches along the cab roof is a major problem by it's own.

First I thought I would have to mill down the tender front a tiny bit but altering the roof corners is easier. I'll talk to Jay. An even longer drawbar would compromise the appearance too much. I really appreciate your worries and helping hand! Thank you

Sarah

I wish I could see how the rear of the boiler / cab is fastened to the frame of the loco. Might it be possible that the mounting  brackets have been mashed down in transit. Perhaps shims or washers could be used to lift it a mm or so.  I think I would insulate the tender body form both trucks and run a jumper from the trucks to the drawbar, making sure it was also insulated. However even if you do this you still don't want the cab roof rubbing on the tender when in a curve.   j

Sarah I found a site with photos showing how to add pickup wipers to trucks. If you end up insulating both trucks on your tender these wipers are a good way to get power to your drawbar.  Here is a link to the web page and the instructions about adding the pickup wipers is about 2/3 down the page. You should be able to add these pickups without any major mods to the tender or the trucks and they could be removed if need be.  Insulating the trucks is quite easy cut a disk "washer" out of acetate, which can be quite thin, for both trucks and find some nylon screws (eBay) to replace the metal screws that hold the trucks on.  DONE DEAL !     If you wanted to add a wire between loco and tender you could even add pickups for both rails.  The more pickup points the fewer arcs, good thing.     j

https://model-railroad-hobbyist.com/node/15986

Sarah I found a site with photos showing how to add pickup wipers to trucks. If you end up insulating both trucks on your tender these wipers are a good way to get power to your drawbar.  Here is a link to the web page and the instructions about adding the pickup wipers is about 2/3 down the page. You should be able to add these pickups without any major mods to the tender or the trucks and they could be removed if need be.  Insulating the trucks is quite easy cut a disk "washer" out of acetate, which can be quite thin, for both trucks and find some nylon screws (eBay) to replace the metal screws that hold the trucks on.  DONE DEAL !     If you wanted to add a wire between loco and tender you could even add pickups for both rails.  The more pickup points the fewer arcs, good thing.     j

https://model-railroad-hobbyist.com/node/15986

I can't give Sarah any advice it's well above me, but I am following the thread just for interest sake and found the site above interesting for when I add pickups to the tenders on my shock, horror, plastic 0-8-0's. thanks.

Always learning something. Roo. 

Sorry, I meant to add some text to that picture.  I'm pretty sure 6310 is also a PSC (unfortunately it is not mine).  The tender hitting the roof of the cab has not been a problem.  Also, our (Rockford O Scalers) minimum radius is 88" and this engine runs fine at that radius.

John,

It appears that the engine and tender are close coupled and that the deck plate is riding level between the engine and tender.

Alan Hummel posted:

The radius problem with Sarah's engines makes me wonder if my AC4400CW will negotiate 60" radius curves ok? All my 60ft boxcars do ok so took for granted this diesel as well as my SD40-2 would also be fine.

Do you gentlemen think 60" is ok?

Thank you all in advance for your help.

Al Hummel

Alan, as diesels are on trucks, like rolling stock, & without knowing what manufacturers your diesels are, I'd still guess that they'll be fine at 60" radius. Atlas usually state 36" as minimum radius, & I can confirm my SD40 will take that curve and haul stock through it too. It can even negotiate tighter radii than that, by itself, but due to pilot overhang would drag stock off the track.

Yes 36" looks very silly indeed viewed from most angles, but at track level it's not too bad, & some of us have to compromise somewhere to get a layout at all. Mine is 17ft x 8ft, which I bet even a lot of State-side 3-railers would think of as small, but on a British model railway forum, it seems like I might be alone in having an indoors O Scale layout with an oval of track, in an 'average' UK house, as opposed to in a barn or suchlike, or layouts built by Clubs, in larger premises. Most UK 'home' O Scale layouts are end-to-end shelf designs.

Minimum radius for UK O Scale is usually considered to be 6ft for mainline locos and stock, but that is dictated mostly by the couplings - buffers and hook & chain links, rather than eminently sensible buckeyes! 

I think the answer might be in those last two images!

Simon

If you are set on running such a long wheelbase as the Kohs 4-12-2 then you really have set your radius pretty far out there for everything. I'd lengthen the drawbar on the CB&Q engine if I needed to run on tighter radius but you probably won't have to do anything to it if the radius needs to be set at the Kohs levels.

I own, have worked on, and run several Kohs Y6 engines on radius down to 56". I understand that a 4-12-2 won't get down to that level but there are probably some things you can change after some careful observations. Ed Rappe's advice is some that you can really take note of. His work has been tested and proven for many years on several outstanding layouts.

In comparing the photos of Sarah's 6324 with that of 6310 posted by John note that the line of the cab roof relative to the top edge of the tender is lower on 6324 than 6310.  It also appears that the cab floor height on 6310 matches the tender while on 6324 the cab floor is lower than the deck on the tender.  Something isn't right.  I'd check to see if there was an assembly error in mating the boiler to the chassis - or if the rear of the frame is bent slightly downward.  If you have a surface gauge check to see if the walks on the boiler slope downward to the rear.  On most prototypes they were level.

Dear Ed and Christopher,

thank you very much for your comments. John Handlogten's picture really shows the difference. I measured the running boards and they're not level but decrease in hight towards the cab. The engine is not sitting correctly on the axles, the distribution is slightly to the tail. Also the trailing truck journals are half way up and in spring deflection with a lot of weight on it. 

The engine is now apart with the boiler and cab removed from the frame. I'll check for a bent frame tomorrow, the bare eye can't tell so far. Maybe the wheel journals are somehow in a wrong position. To really get into it I'll have to remove all the rods and valve gear first. I don't like to do that when there are other projects still on the workbench, I need room for all the parts to be taped down and sketches drawn. 

I found a couple of other problems with the engine that is brand new but sat in it's box for years. They just don't appreciate parcel cars. Cross head support bracket (the thing that keeps the cross head guides in place) came off and is slightly bent.

That's going to be a lot of ... depends.  

Christopher, I think I found your outstanding modeling on YouTube (goingoscale). Applause!

I'm not the right guy to help here. I don't have any of these engines.

I did have an engine where something would spark and once in awhile throw the breaker. I remember putting a piece of electrical tape on the bottom side of the rear deck platform so it wouldn't short with the tender. That was a quick fix and it worked. Better than cutting or removing the platform. Isolating it would have been ideal. Make a new one from plastic?

 I remember changing the electrical set-up around when I installed command on an engine so that all wheels did the same job on each side of both units. I reversed the wheels on the tender. I simply added wipers to many wheels to get good electrical pick-up on the new insulated side. Then the tender, did not have to be isolated from the engine. I just can't remember which engine each was! One was a Sunset Niagara I believe?

 I think the old way was to have each unit pick-up a different rail. I prefer to have more power pick-up spread evenly thru the whole space. So my 2 rail MTH Allegheny got wipers on many more spots so that it crosses my dead frogs without any issues when I upgraded it.

OK, Here's my answer: I don't think there is anything wrong with the model. Make sure the APRON, which is hanging down in Sarah's image, is up ON the LEDGE that is part of the tender about 2/3 of the way down (like in the image provided by John Handgloten). The draw bar should be set for CLOSE coupling. If you put it together that way, I'm guessing it should work. The hinged apron HAS to be riding on the tenders ledge, which is what I am thinking is what establishes the correct height.

Simon

Roo posted:

Sarah I found a site with photos showing how to add pickup wipers to trucks. If you end up insulating both trucks on your tender these wipers are a good way to get power to your drawbar.  Here is a link to the web page and the instructions about adding the pickup wipers is about 2/3 down the page. You should be able to add these pickups without any major mods to the tender or the trucks and they could be removed if need be.  Insulating the trucks is quite easy cut a disk "washer" out of acetate, which can be quite thin, for both trucks and find some nylon screws (eBay) to replace the metal screws that hold the trucks on.  DONE DEAL !     If you wanted to add a wire between loco and tender you could even add pickups for both rails.  The more pickup points the fewer arcs, good thing.     j

https://model-railroad-hobbyist.com/node/15986

I can't give Sarah any advice it's well above me, but I am following the thread just for interest sake and found the site above interesting for when I add pickups to the tenders on my shock, horror, plastic 0-8-0's. thanks.

Always learning something. Roo. 

there's a poster on this forum that has them cut for sale. I'll try to look for him.

oops!

http://www.rodmiller.com/parts.html