Choosing a turntable diameter: 120' or 134'

[edwardsutorik]

I'm getting into doing a roundhouse and etcetera.

For a very long time, I've had a Diamond Scale 120' stored against the day.

I finally got it out. As I said: a very long time. The new Diamond Scale ones are far superior, and I've decided to get a new one. So now I'm not locked into a 120' one, and can go with 134'.

On the one hand, the 134' can take "anything", including a Big Boy or a PRR S-1. But I don't intend to get either of those. Anything I have or would get will fit on the smaller one. In addition, there's a wye "over there", if needed (maybe an S-1 will come to visit--one can dream).

Getting either one to fit in the layout is completely equal, so THAT isn't a deciding factor.


Before I pull the trigger on this, I thought I'd just run it by you folks for opinions.

I do admit I'm leaning towards the 120'. But I really am not in the mood to put it in, and regret it later.

Hence I do want to make the right decision. The first time.


Thanks,


Ed

[Baikal]

Apr 6, 2023 16:01:22 GMT -8 edwardsutorik said:

I'm getting into doing a roundhouse and etcetera.

For a very long time, I've had a Diamond Scale 120' stored against the day.

I finally got it out. As I said: a very long time. The new Diamond Scale ones are far superior, and I've decided to get a new one. So now I'm not locked into a 120' one, and can go with 134'.

On the one hand, the 134' can take "anything", including a Big Boy or a PRR S-1. But I don't intend to get either of those. Anything I have or would get will fit on the smaller one. In addition, there's a wye "over there", if needed (maybe an S-1 will come to visit--one can dream).

Getting either one to fit in the layout is completely equal, so THAT isn't a deciding factor.


Before I pull the trigger on this, I thought I'd just run it by you folks for opinions.

I do admit I'm leaning towards the 120'. But I really am not in the mood to put it in, and regret it later.

Hence I do want to make the right decision. The first time.


Thanks,


Ed

Take two mock-ups (cardboard circles) and swap them on & off on the layout over a period.  See if one size is more attractive.  This is a high benefit/cost test project. Cheap.

Since there's a wye nearby appearance superceeds functionality.

[edwardsutorik]

An interesting idea. I do like it.

However. There is currently no place to do such a thing. So, at least for now, I can't do that.

But I DO have a trackplan that is pretty much locked in. So for awhile, it's all on paper. Yes, I could wait until I have the benchwork done. But I kinda want to plan ahead. As it is, I've already ordered a 20:1 worm gear box, and a coupling to connect my likely motor. This will, I think, feed the 50:1 worm gear that comes with the turntable. So total reduction will be 1000:1. Running the motor at 500 RPM should give a turntable rotation speed of 1/2 RPM.



Ed

[cemr5396]

you mentioned steam engines, but what about diesels?

If you have two units coupled nose to tail that pull into your engine terminal and you want to turn them, will they fit on one size of table and not the other?

That may not even be a consideration but I thought I would bring it up.

[edwardsutorik]

A very good point. I did think of it, but didn't go beyond, to actually doing the numbers.

For a single unit, I would have either 60' or 67' (half the table)

Generally, if I average the wheelbase and the coupler face distances, I get an appropriate fit (the wheelbase plus the overhang on one end). For a GP38, I get 51'. Two will fit on either. For a C-424, it's 50 1/2. Still easy.

Now I'll try an E7A. That's 64'. There's a clear winner here, for sure. For everybody's favorite diesel, the SD40-2, it's 63'. Another clear winner, there.


So the longer table can turn two E's coupled. And two SD40-2's coupled. If there's 3 or more in the consist, I imagine it suddenly becomes a pain, as you have to de-consist and re-consist. Potentially using Digitrax. With practice, I'm sure it becomes easier. Easier still is to make all consists double-ended. I DO see that a lot in the various running sessions I go to. I usually do it myself.

I do think it's something to include in the deciding, but I doubt it's going to be that significant.


See. This is why I'm asking you guys: to make sure the bases are covered.


Ed

[wsor]

Or what happens is a shop switcher is needed to push a non-working unit into a stall. So an E-unit and a switcher need to fit together. I'd lean towards the longer table.

The turntable in Janesville, WI on WSOR is 75 foot. A SD40-2 fits well, but needs a Trackmobile to push an ailing unit into a stall. Soo Line 1003 (a 2-8-2) cannot spin on the table, account the overhang hits a pole mounted too close. There is a wye nearby for turning.

[edwardsutorik]

Interesting! And thanks for your thoughts.

I'm still kicking this back and forth.

You are describing prototype operations, because if we're unable to get a loco on and off the turntable, we'll probably take it over to the bench and find out what's wrong. Besides, if it can't go on its own, how's a little switcher going to push it with the wheels locked up by the gearing? So the only reason for ME to choose a table based on this is because the prototype did it for that reason.

If an NP/SP&S Z-8 were on a 134' turntable, there'd be 15' left over for a switcher.

I've just this morning posted on the NP Tell Tale group a question concerning this. Pasco WA (NP) had a 135' turntable. Vancouver WA (SP&S) had a 120' table. Both locations typically handled the same sized engines. Why's that, I asked. The only answer so far mirrors Mike's thoughts, above. I'm hoping there'll be more conversation on the matter.

Really, it probably isn't going to matter which of the two I do pick. It'll just be a bit easier to spot locos on the longer table. Absolute good news is that I'm not stuck with a 90' table--LOTSA trips to the wye with that one.

Thanks again, Mike. And others.


Ed

PS: I found out that Laramie had a 135' turntable. There are plans for it at the up-modelers group on io. These are copies of the original drawings. I see that there was an inspection pit in a section of the pit wall. For the table. Neat!

I'll also mention that this table is primarily for steam operation. It'll be easier and faster to turn a diesel consist on the wye. But the arrival departure tracks are right near the turntable, so it's not unreasonable to spin the single engine and send it back out. "Refueled" of course.

[edgecrusher]

I've never had the space for a round house myself. But I have to wonder, do the different diameters effect the track spacing at all?

[edwardsutorik]

Apr 12, 2023 12:45:08 GMT -8 edgecrusher said:

I've never had the space for a round house myself. But I have to wonder, do the different diameters effect the track spacing at all?

That's exactly what I wondered.

I've drawn an exact track plan with the 120' turntable and 5 tracks into a roundhouse and 5 tracks to a "garden". If I replace the 120' with a 135', that just makes the "front yard" of the roundhouse a little smaller. IF I leave the various radiating tracks alone, then I'm done. And since I'm not changing any of my motive power, there should be no reason to change the roundhouse. When I laid it out, I used 18" long tracks inside the building, with another 2" walkway out past the track ends.

So, really, there's no problem at all if I put in the bigger table. Of course, that's MY particular design. Maybe someone else's WILL have a problem.

Since I'll be scratching my roundhouse, I MIGHT extend one stall, just 'cause. I do currently have a big empty space behind the roundhouse that I have yet to fill up.

By going from a 120' to a 134', I'm only chopping off about an inch of approach tracks. And they don't really DO anything.

Oh, yeah. FWIW, the radial tracks are laid out at 7 degrees.



Ed

[edwardsutorik]

Apr 12, 2023 12:14:09 GMT -8 edwardsutorik said:

I've just this morning posted on the NP Tell Tale group a question concerning this. Pasco WA (NP) had a 135' turntable.

Seems like discussion on this topic over on the NP group has stopped. One poster supplied some attachments. Here's a quote from an NP paper titled "Long Turntables on Northern Pacific":

"The three 135 foot turntables on the Northern Pacific are believed to be the longest ever constructed [1938]. As indicated above, tables which only a few years before had been considered sufficiently long, required replacement or extension to accommodate the new power and it was therefore decided to make allowance for some future increase in the length of locomotives. One incidental advantage in the long tables occurs in the handling of certain dead equipment in and out of the roundhouses inasmuch as there is room on the table for both the equipment and the switch engine."

Office of Bridge Engineer,
Saint Paul, April 15, 1938.


Longer steam locomotives never appeared on the NP.

No one got into discussion of the shorter table at Vancouver on the SP&S. The SP&S was managed alternately by GN or NP. I figure neither railroad was that interested in "futureproofing" Vancouver.

Anyway, I thank you all for your thoughts.


Ed

[edwardsutorik]

Well, I have found that my options, uh, aren't. A very careful measuring of the arrangement finds that, with a 120' table, there's 1 3/4" between the inside wall of the pit, and the centerline of an immovable track. Also, the center of the turntable can't be moved, either. Thus that 1 3/4" gap would shrink to 3/4". To the track centerline. Or 1 scale foot between the pit wall and the end of the track ties.

While physically possible, it sure wouldn't look prototype. As it is, I think I should put up a railing between the pit and the adjacent track, for safety and/or a couple of signs prohibiting foot traffic. Knowing humans, the former solution is probably the better, but it then might impede turning locos that overhang the table bridge.

So the big engines will be traveling to the wye. That'll be Big Boys, PRR S1's, and two-unit E sets.


It's surely been an interesting investigation, both here and over on the NP group.


Ed

[edwardsutorik]

Apr 11, 2023 17:17:46 GMT -8 wsor said:

Or what happens is a shop switcher is needed to push a non-working unit into a stall. So an E-unit and a switcher need to fit together. I'd lean towards the longer table.

The turntable in Janesville, WI on WSOR is 75 foot. A SD40-2 fits well, but needs a Trackmobile to push an ailing unit into a stall. Soo Line 1003 (a 2-8-2) cannot spin on the table, account the overhang hits a pole mounted too close. There is a wye nearby for turning.

Thinkin' on this, if I was designing a prototype roundhouse setup, I'd make an effort to have the stalls directly opposite incoming tracks reserved for dead locos. Then you don't need to turn the table at all. If an engine was currently occupying such a stall, I'd evict it. Or maybe just wait a day--anything that dead is probably not expected back out very soon, anyway.




Ed

[Phil]

As far as pushing locomotives into the roundhouse, I have a couple of dummy steam engines that picked up at train shows and have taken the gears out of. I use an S1 to push them into the roundhouse as part of the engine servicing job. So I went with a longer turntable. Just a thought.

[edwardsutorik]

It's quite amazing what the search term "shop switcher" turns up--"just when you think you've seen it all"...............



Ed