Lengthening an Atlas Turntable?

Discussion in 'HO Scale Model Trains' started by riverotter, Apr 11, 2008.

  1. riverotter

    riverotter Midwest Alliance Rail Sys

    I need a turntable long enough for steam locomotives, but I don't want to have to "dig a hole", so I wondered if I could somehow lengthen an Atlas turntable? Has anyone done that or does anyone have any thoughts about how I might go about that? I think the Atlas TT is about 9" diameter, and for even 4-8-4 I'd need at least 15". Thanks!
  2. Glen Haasdyk

    Glen Haasdyk Active Member

    I suppose you could build a second larger circle on top. Then lay a new piece of track and solder wires from the old track to the new. Of course this would make the unit taller so you would have to bury it somehow, but not as much as a pit-style turntable. but then you'd have to contend with the gearbox on the side.....
  3. nachoman

    nachoman Guest

    the gearbox on the side is your limiting factor. I built a new bridge and glued it on top, and I managed to get to about 10.5". At that length, I had to use a the motor rather than the hand crank. You could possibly go larger if you devised a different kind of motor or crank mechanism, but I don't think it is worth the effort.

  4. MasonJar

    MasonJar It's not rocket surgery

    If you do away with the gearing that is built in, you should be able to extend it to any length you want. You will have to disassemble it to the point where it will rotate on its own, and then turn it "armstrong" style. But even with this approach, you'll still have to sink it into the benchwork somewhat.

    If you are happy with the look of this type of TT (i.e a whole deck that moves), then why not construct your own. All you'll need is a circle of thick styrene (0.060"+) and some flex track. Just be sure you've cut a perfect circle and located the exact centre for the pivot point.

    I imagine this could be mounted directly on the surface of the layout, although you'd have to find some way of powering it - maybe through the phono plug, which would only require drilling a suitbale hole, rather than cutting away an entire section of benchwork.

    Just my $0.02. Hope it helps.

  5. Russ Bellinis

    Russ Bellinis Active Member

    Here is an idea I had for an easy way to make the pit sides for a pit type turntable. Get embroidery hoops from a local craft store to make the walls with. They come in various diameters and are perfect circles. If the pit needed to be deeper than a single loop, they could be stacked and glued together. I went so far as to buy some hoops to try it with, but later decided not to build the layout I had planned to use it on.
  6. pgandw

    pgandw Active Member

    Besides having to clear the existing gearbox, the question becomes whether the Atlas movement and gearing is suitable and accurate enough for a turntable nearly twice the size. Also whether the appearance suits you.

    The Atlas turntable uses a Geneva movement which pauses and is indexed every 15 degrees (older versions used 30 degrees). Larger turntable are generally indexed at 10 degree increments or less, and are set up not to stop at every possible track location.

    If you want to turn an engine 180 degrees, do you really want the turntable to pause 11 times as it rotates? If you speed up the turntable too much to compensate, your little engine crews are going to be getting whiplash. The extra stops may be able to be eliminated by sealing the slots on the Geneva wheel, but this will require some disassembly (note I have not performed this surgery myself).

    Do you really want the fewer and more spread apart roundhouse stalls that result from the 15 degree indexing? The Walters turntables and roundhouses are set up for much closer spacing of stalls.

    Finally, will the indexing be accurate enough with a bridge nearly twice as long?

    Although the Atlas turntable is cheap, it has a lot of limitations, too. Most of the modification stories that I have seen have not lengthened the turntable by much to avoid even more rebuilding. With Walters offering highly recommended, reliable, much more realistic turntables in both 90ft and 130ft sizes (the latter has an 18" bridge, and should accommodate just about any steamer), trying to modify the Atlas turntable into something it is not becomes a case of just not worth the effort.

    OTOH, if you are looking for a base to make a 70ft or smaller TOC turntable, the Atlas is a good starting point, as numerous articles have shown.

    just my thoughts, your choices
  7. 60103

    60103 Pooh Bah

    Fred: I don't think sealing the lots will cut out the stops in a Geneva movement.
    I think what they have is a wheel with a rod sticking up from it mounted at the side of the wheel that makes the turntable. There are slots running in from the side of the TT. The rod enters the slot and, as the wheel turns, the TT is pushed around one position. The TT rests as the wheel moves the rod around the outside of the circle and the rod then enters the next slot.

    Is that clear for not having a diagram?
  8. riverotter

    riverotter Midwest Alliance Rail Sys

    Here's a photo of one modification effort I received that used an Atlas TT + two Atlas deck bridges. The turning mechanism has obviously been removed, but there were no details about how or if the modified TT was indexed. This may be a photo of an unfinished stage of the project.


    I am familiar with the Walthers 90' & 130' turntables, but the location I want to put this TT precludes below-grade installation because of cross-bracing of the benchwork. Since I have 7 times as many diesels as steam locomotives (and the longest diesel is under 11"), maybe there's a way of lengthening the TT by an inch on either end -- or perhaps there is a longer surface-mounted TT like the Atlas but mfgd by someone else.
  9. pgandw

    pgandw Active Member

    Problem is that what you are looking for is not prototypical, and therefore not likely to be made recently with the rage on about prototypical detail.

    In prototype practice, about the longest gallows or A frame turnouts were 65ft. Anything bigger required a significant pit to fit the bridge under the track. There were some decked turntables in colder climates were snowfall packed into the pit would be a problem. San Francisco cable cars still use decked turntables because of their location - the decking allows people to walk across the turntable when it's not in use.

    I believe Fleischman (and/or Faller) made a 14" surface mount plastic turntable in HO in the '60s and '70s - my Dad had one. It took some tinkering to get it to work properly.

    I believe the Bowser turntables are all pit turntables. The Walters pits are only 1.75" deep, IIRC.

    The other possibility is to modify the benchwork or build the turntable and engine houses higher to give room for the pit. One of the advantages of L-girder benchwork, with screws driven from underneath, is the ease of moving a joist to make room for specific features. Although not as easy in other construction styles, moving a support should be doable. If need be, add headers around the turntable, similar to windows in walls in wood frame construction.

    The other option, instead of butchering an Atlas turntable that will still need a drive and indexing mechanism, is to design and make your own. Building the ring to a low height using cut plywood or laminating bent wood is quite feasible. Then adding a center pivot (lazy susan hardware) and the bridge of your choice to finish off.

    Or an old record turntable from a discarded stereo could be a good starting point. These were generally quite shallow with very free turning cast metal

    just some thoughts
  10. stuart_canada

    stuart_canada Member

    i have two of these tuirn tables one of the older ones and the newer model
    first thing i did was cut the base of my layout so the turn tables would sit level with the rest of the layout.
    there are various write ups in the model train magazines on how to modify the table to make it look more realistic.
    but i think the easiest way to deal with it is to buy a turn table big enough to handle your biggest locomotive and put in the pit.
    after you go to the cost and trouble of re engineering the atlas model you still have the most basic turn table out there.
    no matter what you do to the table, it will have the jerky movement, and bad drive controls.

    i only kept mine be3cause my grandfather got it for me the year before he died for christmas, then i got the roundhouse and found out the table layout changed so i had a turn table and roundhouse that did not fit so I got the new table. on my small layout it works and fits in.

    to modify it, you have to remove all the track openings that are in the atlas model, add to the bridge and hope it balances.
    buy new turn table to fit or sell off your bigger locos
  11. riverotter

    riverotter Midwest Alliance Rail Sys

    Sell my biggest locomotives? :eek: I'd rather sell my left kidney.:mrgreen:

    <sigh> I guess I'll have to break out the saw. Any and all ideas about how best to go about this, given that the solid "table" surface is already installed, are welcome!
  12. pgandw

    pgandw Active Member

    Do not cut a hole until you have the turntable in hand! The Walters turntables - should you choose to use one - are suspended by a lip around the pit wall. Other makes of turntables have their own installation methods. You need a pretty accurate measurement before you cut.

    I'm assuming you have a plywood table surface with a support passing underneath the turntable area. Cut 2 frame pieces to be mounted perpendicular to the existing support, long enough to reach parallel supports on either side. Then cut the existing support, and mount these "headers" as a T to the cut existing support. This will frame in an area free of supports, where you can cut the plywood with a jig saw.

    PS Don't forget to move wiring out of the way before you cut. Don't ask me how I now know to do this. :eek:

    hope it goes well
  13. stuart_canada

    stuart_canada Member

    more money for the right kidney....
    how thick is the top ?

    when i lowered my turntable the first time it was in plywood, i traced the turntable out and used a jig saw to cut it out. ( 3/8 thick plywood) used the cut out piece to hold table in place with two boards screwed to hold it in place.
    this time the layout is on 2 inch thick foam,used the rotary tool to cut the material out and shop vac to clean up.
    good luck
  14. riverotter

    riverotter Midwest Alliance Rail Sys

    There has been some really great feedback on this thread - thank you! One result: I decided not to attempt this jerry-rigged solution. Then I started looking into a "real" turntable - one that I'd have to "bury". I got great step-by-step comments about how to do this.

    There are days when I contemplate this project that I think it would be less of a hassle - and less expensive - to just install a Wye to turn my locomotives. wall1
  15. stuart_canada

    stuart_canada Member

    wye would work , takes up some space but works well
  16. riverotter

    riverotter Midwest Alliance Rail Sys

    Turns out I have a "natural" spot for it near my staging yard -- I'd just need to put a triangular corner piece on the existing benchwork for one of the curved segments.

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