# Cab Forward minimum radius



## US-IT (Mar 4, 2020)

Just introduced in this forum few minutes ago...and I already have a simple question:

I would like to purchase an InterMountain Cab Forward.
You will think..."...and what...?... which is the problem....:dunno:.."

The minimum RADIUS !!!!

Intermountain, in the specifications, indicates the minimum radius as 24" since the second truck, the one below te cab, is not articulated.

The question:
Is there any way to modify this fantastic loco to make it run under my "Italian" layout having curves of 16.5" an 18" ?
For "modifications" I intend "small/secondary modifications" such as eliminating some detail or small things like this, not for sure the rebuilding of the model.

You know, in EU everything is smaller than in US, and in Italy we do not have room at all...:hah:

An alterative is the purchasing of a second hand MTH or BLI, but I do not know the minimum radius for their models.

Thanks for the answer.
Beppe.


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## MichaelE (Mar 7, 2018)

You could either figure out a way to articulate the front truck, or machine the flanges off of some of the wheels so that the wheels float on the rails as it rounds the curve. Many HO steamers have false flanges for just this reason. This is a pretty extreme case.

I wouldn't recommend doing it.

Some locomotives are not meant to be operated on small layouts.

If I were operating an American based layout I would never operate a EMD DDA40X even on 24" radius that my layout uses. It just would not look correct.


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## Cab1 (Jul 26, 2009)

First of all, the Inter Mountain Cab Forward is a beautiful locomotive. I've been looking for one myself for a long time. The detail on this thing is nothing less than exquisite, but extremely fragile. Both MTH and BLI offer far more robust models with fairly close detail across several class versions. I have heard both locos can run on 18" track, but I have my doubts about that. Maybe they do maybe they don't. They are both extremely heavy and powerful by comparison and offer several options, like different color schemes, a smoke generator, front-end boiler details, and marker lights on the front of the cab, which Inter Mountain does not. The problem is the Inter Mountain Cab Forward has been out of production for a long time. I spoke to a factory Rep who told me they were thinking about putting out a new updated release of their Cab Forward, but I should think in terms of several years and not anytime soon. It's also important to keep in mind Inter Mountain has been plagued with problems across their whole production line and their Cab Forward is no exception. They have made quite a few "quick fixes" over the years, which are hard to keep up with. The Rep told me if I'm planning to go hunting around for one in the secondary market I should look for one with a blue label on the box. It's the only one that has all the updates. Stay away from white label boxes, or any other color label boxes. They do not have all the updates and Inter Mountain no longer has the parts to upgrade their Cab Forward should you attempt to send it back to the factory.


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## Dennis461 (Jan 5, 2018)

US-IT said:


> J...
> InterMountain Cab Forward.
> 
> .... my "Italian" layout having curves of 16.5" an 18" ?....
> ...


Welcome to the forum.
I'd say do not throw away your money.
Buy two shorter locos instead.


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## US-IT (Mar 4, 2020)

Thanks for the kind replies!

I am sure, you are right! Thinking on Intermountain can be a mistake, not for the quality, but for the 24" radius.

As Cab1 mentions - sorry for my poor English...I do the best I can - it may be that BLI and/or MTH are the best choice regarding the radius, but the problem is that Intermountain has confirmed they re-run of the Cab forward, while BLI and MTH do not have any item available in stock.

it may be I have to wait long time for BLI and MTH re-run, this is the reason of the Intermountain consideration, even if, I know, the history for these old IM models is rich of bad feedbacks.

One option is the rebuilding of part of my layout, by replacing the 16.5 and 18" curves with 22" an 24", but this is an extreme solution, expensive and in some zones difficult to realize.

As mentioned in my introduction, all my US loco have been modified to run on 16.5" curves
The modification is very simple: just increasing the angle of oscillation of the Kadee coupler...
This is enough to make possible the operations of all my ScaleTrains diesel locos (GTEL-8500, GE-tie4 Gevo, GE39-8, SD40-2 etc).

I hope this will be possible also for BLI/MTH models, when available again.


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## D&J Railroad (Oct 4, 2013)

Running a large locomotive on a tight radius like you have will require almost perfect track work. The slightest problem in the track or the loco will cause derailments that will cause you to loose interest in the hobby. 
Consider a smaller locomotive or get more room from your layout.


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## Cab1 (Jul 26, 2009)

Intermountain has confirmed they re-run of the Cab forward, while BLI and MTH do not have any item available in stock.Where and when did you get this info from? Is that just in Europe? I always keep my ears open for rumors like that. If it's true that's good to know, although it's quite different from what I've been told.


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## Cab1 (Jul 26, 2009)

US-IT said:


> Intermountain has confirmed they re-run of the Cab forward, while BLI and MTH do not have any item available in stock.


Where and when did you get this info from? Is that just in Europe? I always keep my ears open for rumors like that. If it's true that's good to know, although it's quite different from what I've been told.


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## US-IT (Mar 4, 2020)

This is the link:
https://www.intermountain-railway.com/newshocomingsoon.html

The models are 59009...59068 version AC-12...AC-8

This is what I read, but also, the EU German reseller All American Trains, from where I usually order the US models, has placed these IM models as "New and pre-order"

I hope this is a good news for you, not a bad interpretation from me...


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## mesenteria (Oct 29, 2015)

My counsel is to put your mental energy and time into modifying the layout. This is an emotional hobby, and obviously having a Cab Forward is important to you. Why not go to the trouble to modify your track system for not just this one steamer, but for any other future purchases which would make your current situation impossible? Maybe you'll want your AC to pull N. American heavyweight passenger cars of 85+ feet in length...WITH diaphragms.

Can you add 25 cm in width somehow and get larger curves?


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## US-IT (Mar 4, 2020)

mesenteria said:


> Can you add 25 cm in width somehow and get larger curves?


Yes, I can, or at least, is not impossible to modify the layout.
Just difficult and expensive.
At present I am working for the installation of 300 Sommerfeldt electrification masts (italian FS types) and then I am stil in time to modify the radius.

Just evaluating pros & cons in therms of cost


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## MichaelE (Mar 7, 2018)

I'm using Viessman. Far less time consuming than Sommerfeldt.


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## 65446 (Sep 22, 2018)

I agree wholeheartedly with Dennis461.. Plus, I know you have too little room to modify your trackword (which would likely need no less than 20"r curves). And messing with removing some flanges is quite contraindicated [ con-train-dicated :laugh:]
Let your buyers lust float away in a balloon and fuggeddaboudit !! For the price tag of this item (What, $500 +- ?) you could have 2 husky steamers double head the same length train the CF would, ... especially easy if you're in DCC...


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## CTValleyRR (Jul 26, 2014)

US-IT said:


> Yes, I can, or at least, is not impossible to modify the layout.
> Just difficult and expensive.
> At present I am working for the installation of 300 Sommerfeldt electrification masts (italian FS types) and then I am stil in time to modify the radius.
> 
> Just evaluating pros & cons in therms of cost


I think the odds of you getting that loco to run on curves 6" smaller than the manufacturer recommends are somewhere between extremely small and non-existent. The risk is that you ruin a lovely and expensive model.

If you must have one of these locos, then you must redesign your layout. OK, it's time consuming, and may involve additional cost, but it's actually very common for people who have been in the hobby for a while. I'm working on my fourth design modification.


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## US-IT (Mar 4, 2020)

Decided!
I will modify the layout with the inner loop radius of 547 mm - Fleischmann Profi 6133 - and outher loop radius of 647 mm - Fleischmann Profi 6138.
The minimum radius of the inner loop will then be of 21.5” and the outher loop of 25”.
This should allow the operations for almost all models from BLI and MTH (22”) and hopefully for the Cab Forward from Intermountain (24”).

It is not clear to me the meaning of “production confirmed” reported in the IM site.
Few weeks?...or...some years?
Indefinite periods of time are always ambiguous.


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## mesenteria (Oct 29, 2015)

I predict that you will be energized by your decision, and that you will be very happy with it in the end. It expands your layout's utility so much...

I wanted one 'brass' locomotive and elected to purchase a Sunset Canadian Pacific "Selkirk" 2-10-4 about eleven years ago. I finally received it in 2013. I was developing a new layout and understood that I wanted to run this locomotive which the developer/importer (Sunset) claimed would require a 30" minimum radius (76 cm). I'm no engineer, but I understand probability theory, mean times to failure, probability of error as one approaches engineering limits, etc.. I decided to add 10% to the minimum radius figure Sunset claimed to account for my own errors, and track manufacturing errors, and Sunset factory's errors. So, my current shortest radius on the mains is 33".

I think you made a wise choice to go all the way up to 25". Given that pretty much all HO non-brass locos and rolling stock will work on that radius, they'll also look a lot better. The only possible problem would be backing with diaphragm-equipped heavyweights; those diaphragms tend to lift the car out of the rails when backing on curves less than about 26".


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## US-IT (Mar 4, 2020)

mesenteria said:


> ... The only possible problem would be backing with diaphragm-equipped heavyweights; those diaphragms tend to lift the car out of the rails when backing on curves less than about 26".


I have the same problem with the Freccia Rossa 1000, but only in the 16.5 radius 

However today, working at the layout's drawing with AutoCAD, I have decided to proceed with both inner and outer loops with the 25" radius (even more, 647 mm).

The curves at the ends of the loops are not parallel, but approaching the closest tracks at the minimum of 63.5 mm the inconsistency is barely visible.

In practice, after this modification my layout should have only curves of 25", something more (25.5"), that should be enough to guarantee the operations for almost all my ScaleTrains models and the new ones I have in project to purchase in the short time.


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## Dennis461 (Jan 5, 2018)

*some Rivaroddi pictures*

I was given a Rivarossi cab forward some time ago as a gift.
So I have to keep it 

It will not run on my layout for three reasons
1. pizza cutter wheel flanges on code 83 atlas track
2. curves are mostly 18".
3 scenery too close to track.

For these pictures, I sat it on my largest radius, 22.25" (565mm).
The front(rear?) 4-wheel truck barely fits, (will not align on smaller radius)


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## US-IT (Mar 4, 2020)

Dennis461 said:


> I was given a Rivarossi cab forward some time ago as a gift.
> So I have to keep it
> ...
> 2. curves are mostly 18".
> ....


That's strange.
I have the Big Boy 4014 (2019 edition) from Rivarossi (Rivarossi is an Italian brand) and it operates without problems in my present layout with 16.5" curves

The Cab Forward from Rivarossi is not articulated as the Big Boy ?


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