# Accucraft Cab-Forward



## dennissirrine (Dec 27, 2007)

I know this is the live steam category, but this should be very similar to an electric Cab-Forward that we have. Does anyone know how to separate the super structure from the base that holds the wheels and driving rods? I asked Cliff over at Accucraft, and he said he doesn't know. And we have spent lots of time trying to figure out the magic combination to get these two pieces apart. 

We want to file down the wheel flanges on the second and third axles on both sets of driving wheels. Both our Accucraft Cab-Forwards have a very hard time making our 20' diameter curves and the Aristo-Craft #6 turnouts that we have on our layout. And we don't want to do any filing to the wheels with the axles still tied to the base. It will get metal shavings all over the place - places we wouldn't want those shavings to go.

I have seen Accucraft live steam Cab-Forwards do very well with 20' diameter curves and #6 turnouts. But for some reason, our electric Cab-Forwards derail 80% of the time around our 20' diameter curves. (weird huh)

So Please, could someone come to our assistance? It would be so much appreciated! 
Thanks,
Dennis S. 
Conductor - Engineer and all around good guy on the
Palo Verde and Southwestern RailRoad


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## zubi (May 14, 2009)

Dennis,
My best advise is to lift it Cab-Up some five yards high, then drop it. That should do the magic.
Sorry, could not resist it... 
Best wishes from Tokyo, 
Zubi


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## Greg Elmassian (Jan 3, 2008)

I'm surprised that Cliff has never taken one apart.

I would not file the flanges, I would find the root cause... something is not moving properly or hanging up.

I could understand the #6, they need some tuning, but the 20' diameter, that does not make sense... I've been to your layout, I cannot imagine you have a cross level problem, but that is the first thing I would double check.

(of course if it happens on all curves it's not that either)

Hopefully someone with experience on the CF will come up on this thread.

Regards, Greg


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## BigRedOne (Dec 13, 2012)

I'm not familiar with the cab-forward, but it is somewhat common on live steam that wheelsets can be removed either by sliding out the axle, or removing a plate and dropping the wheelset out beneath the locomotive (same as full size practice.)

I agree with Greg about filing the wheel flanges. I think you are likely to end up with flanges that fail to keep a wheelset properly on the rails, and it will ride up on the railhead and end up making a new problem.

First thing I would check is the gauge of your wheels. And do they have sideplay? Nothing caught or binding? Then I would check gauge of track. Measure carefully to ensure your diameter is what you think it is. Track can get kinked, twisted, bent to other than what was originally intended or laid out. Get enough extra track to make a test section of 20' diameter, and put your locomotive on that to observe where the problem is.


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## SD90WLMT (Feb 16, 2010)

Maybe it simply needs more side play for the axles behind the drivers to the frame..such that the ALL 4 axles on each loco frame can shift a bit more...
This would make a world of difference on minimum curves...

Good luck....


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## Totalwrecker (Feb 26, 2009)

It's been my observation that blind drivers are thicker than flanged wheels. Removing the flanges may cause the drivers to drop below rail head.
Check for lateral binds as others suggested.
John


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## Gary Armitstead (Jan 2, 2008)

Dennis,

I'm sure you probably know Jonathan Bliese at EMW. Give him a call. He's very knowledgeable on Accucraft.


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## Chris Scott (Jan 2, 2008)

_*
I agree with Greg, I would not file down the drivers, find the root cause and fix it. *
_


*Additional CF Reference Info*:
The Sticky Thread: Informative Threads Index (Top of Live Steam Forum) has the following items for the Cab Forward:
(You will need to go to the Sticky Treads Forum to get the actual links.)

------------------------------------------------------------------------------------------
Accucraft Cab Forward (AC-12) Upgrade:
Submitted by Charles Bednarik

Thanks to the work of Gordon Watson, Ryan Bednarik and Jeff Redeker; this DYI sheet can help owners of the Accucraft AC-12 upgrade their fine steam locomotives in areas that can improve performance and/or prevent premature failures.
Section 1 - Crossheads/Guides
The main reason for upgrading the cross head is to correct the excess play in the crosshead-main rod connection and the lateral play that ensues.

Part 1 - 530kb
Part 2 - 614kb
Part 3 - 832kb

Section 2 - Dogbone/Levers/Valves/Ports Make an improved flexible steam coupling, add working combination levers, improve the valves and steam ports.

Dogbone Flexible Steam Joint - 686kb
Combination Levers, Cylinders and Valves - 1.37mb
---------------------------------------------------------------------------------------------------

Bednarik’s also have written an “Operating Instructions for the TRS Accucraft AC-11/12” 
(Located on their TRS Services web site – a bit difficult to find,)
http://1stclass.mylargescale.com/charles/AC-11workshop/CabforwardOperationalmanualTRS.pdf

--------------------------------------------------------------------------------------------------

*Questions that come to mind: (You may have investigated some, most or all of these but here goes.) At one time I had 2 CFs, now only one.*
20' dia. (10' radius) is the minimum curve for the Cab Forward; Translation - 10' radius is tight. 
Is 20' diameter the actual track On-Center diameter? OR the diameter of the layout outside diameter of the layout and the track diameter is somewhat less? 
Have you checked the curve radius to make sure there is no variation in the radius (i.e., a possible flat spot)

What derails? One/both of the engines? Leading truck? Trailing Truck? 
Where does derail? At one particular location on the curve? Both curves or just one?

From personal experience with two CFs #6 turnouts are tight. Slow running through is ok, anything higher derailing is possible-to-probable. Large loco's need/want #8 (I realize that's not good to hear costing money to replace.) 
Does it happen with every #6 turnout or only particular ones? 
Does it happen under all weather conditions? Very hot days? Cold days? 
Who's (manufacturer) #6 turnouts are they, some are ok, others are poor. Aluminum rail would be the most problematic.


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## Paul Burch (Jan 2, 2008)

Dr. Rivit might have the answer. I had a Accucraft GS4 over here for some Airwire work. When test running on the layout it also was having some problems with tracking. The driver suspension was very stiff. When I posted about it Dr. Rivit answered with a possible solution. He said the springs on the drivers needed to be loosened up to give them nore play. It wasn't my loco so that is as far as I got with it. If he doesn't respond to this post try to contact him. I really don't think filing off flanges should be the first step.


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## David Leech (Dec 9, 2008)

I would imagine that it might have something to do with the electric drive not allowing as much side to side motion of that driver, whereas typically on live steam there might be a little more.
All the best,
David Leech, Delta, Canada


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## Dwight Ennis (Jan 2, 2008)

I PM'd a link to this thread to Charles and Ryan... maybe they'll jump in here too.


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## Chris Scott (Jan 2, 2008)

Dennis;
Beyond the questions I listed above I just noticed your switches are Aristo-Craft. They’re made for Aristo-Craft’s larger 1:29 scale with their bigger/wider wheels. The smaller 1:32 scale CF will wheels drop between the Aristo-Craft switch rails where the 1:29 wheels pass right over. I think if you get your eyeballs about 6” from the Aristo-Craft switch with the CF hand rolled slowly through it you’ll see the problem. 

As for 20' dia curves, the only reason the CF would have a problem is there's a problem with your curve not being true in radius or flat. Since you’re a sparky Im guessing your track is on the ground so keeping it flat and true can be/is a problem The elevated test track at Accucraft is sectional track 8 ½’ radius laid on a completely flat deck made from 4x8 sheets of heavy plywood so the curve is essentially perfectly true. I watched CF, T1, etc. run on it without any problems at all.

As far as removing drive wheels there is no reason or need to remove the “super structure from the base.” I think it’s the question you asked or how you phrased it.. It's a bit of an odd description versus how to remove a driver. The drivers are each held in the frame with a keeper with 2 screws. Turn the loco on its side remove the two screws on each, unbolt the linkage for that driver, driver slides out. 

As far as Cliff not knowing the answer to your question. Not to put too fine a point on it, my experience, Cliff not knowing is darn near just not possible, on this particularly as how simply a driver is mounted.

As to filing a flange off drivers making it a blind driver, blind drivers, drivers without a flange, are wider than standard drivers so they don’t drop of the rail. So if you file off the flange your just going to have problems with the narrow wheel. Just iin caase, you definitely would want to machine the wheel, filing would probably give a really terrible result.


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## David Leech (Dec 9, 2008)

Chris Scott said:


> Dennis;
> 
> As to filing a flange off drivers making it a blind driver, blind drivers, drivers without a flange, are wider than standard drivers so they don’t drop of the rail. So if you file off the flange your just going to have problems with the narrow wheel. Just iin caase, you definitely would want to machine the wheel, filing would probably give a really terrible result.


Chris,
I doubt that really, as surely a driving wheel can't stick out further than it does, and I would think that the back is back to the bearing anyway.
The fact that you are removing the flange, will actually increase the tread width by the flange thickness.
Maybe you can measure a loco with blind drivers and see if this is so.
All the best,
David Leech, Delta, Canada


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## chuck n (Jan 2, 2008)

David

It all depends on the radius if the curve. It can drop in on too tight of a curve.

Chuck


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## Charles (Jan 2, 2008)

Dennis
Just back from Diamondhead.... Since the production run of the cab forwards we have overhauled many for running and performance. The first run more than the second runs need work on lateral play on the drivers.

The problem is that the hub on the back side of the wheel where the axle inserts is too thick the little or no lateral motion. We solve the problem by milling off enough to allow enough lateral motion thus excellent tracking through the curves.


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## Greg Elmassian (Jan 3, 2008)

Charles is this the same on both the sparky (Dennis') and the live steam?

Greg


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## rbednarik (Jan 2, 2008)

Yes, the lack of lateral play is the root cause for not negotiating tight trackage. The front engine being fixed needs to have some freedom in side-side movement otherwise it is trying to push the large 4 axle rigid wheelbase (something around a 1 foot wheelbase) straight through the curves. 

Commonly we shave .05-0.1mm from each side of the hub on the wheels to generate enough lateral play going into the curve with the fixed engine. You will need to check clearances against the crossheads when doing the driver just next to the cylinders as this may be restricted to less than 0.1-0.2mm total lateral play. 

In addition the pilot truck must be made to help guide the engine into the curve, the addition of a centering spring rig will help this. As it is the pilot truck is along for the ride and once entering the curve the load is placed on the first driver of the rigid engine, which exerts tremendous lateral loads on the chassis and rail. 

It may be possible that the drivers can have the flanges turned without pulling the boiler, however the blind drivers should have a wider tread and be elevated off of the rail slightly to avoid the wheels dropping in on curves and when negotiating switches. 

The live steam cab forwards can exhibit the same symptoms and as 10' radius is really their minimum, this is not surprising. The addition of more lateral play in just the leading drivers of the front engine makes a surprising amount of difference. #6 switches are an issue chiefly with the tender-engine connection. 

I would again be suspect of the track, as you are pushing the minimum and if there is even the slightest change in the diameter or track work it can cause issues. It also depends where the 20' dia was measured. The AC-12 requires 20' dia measured from the inside rail, not the middle of the track!


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## Totalwrecker (Feb 26, 2009)

Not the Middle of the Track? Sacrilege! 
So it's 20'7/8" ga. Minimum ....
The Middle has been a standard as long as I've been playing with trains, expecting folks to know an arbitrary way is ...... silly. IMHO
John


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## Phippsburg Eric (Jan 10, 2008)

Geez! if the 7/8" makes a difference then the real minimum radius is more than 10 feet and by more than 7/8"


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## Greg Elmassian (Jan 3, 2008)

Thanks Charles.

Again, I've seen Dennis' trackwork, it's the most perfect track I have ever seen.

Sounds like he is on the "bitter edge" and your suggestion makes a lot of sense to me (and of course your "track record").

Greg


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## rbednarik (Jan 2, 2008)

Greg,

The engine surely is the root cause but be careful of sectional 20'dia curves as the end of the arc can be pulled inwards enough to cause an issue. Of course if it is bent with a rail bender then disregard the statement.

I blame tired fingers for changing up middle with inside...surely you all knew what was meant.


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## Pete Thornton (Jan 2, 2008)

Dennis,
I believe Geoff Ringle of Old Iron Designs (http://www.oldirondesigns.com/) did a lot of work on the cab forwards for Alan Redeker's flat-face project, including changing the wheels. I'd get in touch and ask him.


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## Dr Rivet (Jan 5, 2008)

I have been reluctant to inject my opinion here... BUT I own two Accucraft Cab Forwards so feel qualified to comment.

[A] My long experience with manufactured sectional curved track [as opposed to flex track curved with a rail bender] is that the radius is at best a NOMINAL measurement and varies slightly among any statistically relevant number of pieces. When you assemble them they almost NEVER have a truly constant radius through more than 90 degrees of curve. This applies to every vendor i have used [LGB, Aristo, USAT]. Unless the curve center line is laid out with a beam compass or trammel line to insure absolute uniformity, with 10 foot radius [20 ft diameter], neither the CF, F4/F5, or Daylight will traverse the track without complaint. A deviation of a fraction of an inch at a single joint is enough to cause problems.

Ryan's solution of milling the back of the drivers is the best [not the only] one. I would not consider milling off the flanges because the wheels then have to be raised off the rails to prevent problems negotiating switches. As soon as that happens, those drivers no longer provide traction and your loco is not going to perform as intended.

I own an Accucraft GS-4 that had some slight modifications made for the previous owner. It removed enough lateral movement in the drivers that the locomotive would no longer negotiate his 10 foot radius curves made from Aristo sectional track, even with the pilot and trailing truck removed. To this day, I believe he has visually imperceptible kinks in a couple of joints and that is why the locomotive would bind in the curves.

One last factor... as an owner of several Accucraft locomotives... do not assume that the gauge or back to back is correct on all the drivers. If one is even slightly too wide, it will be a problem on tight curves [a relative term]. If it is too narrow, then there is almost no space between the frame and the back of the drives, therefore even less lateral play, and a problem.

I hesitate recommending that you rebuild your track with wider curves...but that is really what those particular engines need to be able to run at anything much above a crawl.


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## rbednarik (Jan 2, 2008)

Pete Thornton said:


> Dennis,
> I believe Geoff Ringle of Old Iron Designs (http://www.oldirondesigns.com/) did a lot of work on the cab forwards for Alan Redeker's flat-face project, including changing the wheels. I'd get in touch and ask him.


Pete,

When the prototype and first production AC-6 were under construction here, Alan and I both noticed that the replacement spoked drivers (from the F4/5 2-10-2) had a nearly flush rear hub boss when compared to the original boxpok drivers used on the AC-11/12. When the axle boxes from the -12 were put in the spoked driving wheels, the added lateral motion was a happy bonus. 

As a result the engine will trundle around actual 10'radius curves all day long without a change in speed or drag. It isthe worth mentioning these engines also have a centering spring rig on the pilot truck to help guide the engine through curves. 

To get the stock boxpok drivers on the AC-11/12 to have equal lateral play, the hub bosses on the backs of the driver centers need to be turned down on the lane as there is minimal clearance between the axle boxes and back of the driver hub bosses. You can mill the bosses down but I prefer to chuck the wheel between centers (or on a purpose made mandrel)on the lathe and take light skim cuts off the backs until the desired thickness on the hub is reached. This avoids having to take the wheel from the axle and requarter it, which would have to be done if the job were completed on a milling machine.


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