I am starting some long range planning on the layout to be. Being a steamhead, a turntable will be a must have. The Atlas TT is not long enough for the LL Mallet so scratchbuilding will be in order. My question relates to full scale practice. Did they tend to use 7 1/2 degrees or 15 degree spacing between roundhouse tracks. If 15 degrees was a normal spacing, the Atlas TT mechanism would be usable underneath a scratchbuilt trestle. Needless to say the Atlas mechanism would be a cheap and dirty way to get accurate indexing. I will be following eastern railroad practice ( Reading/CNJ ). What do our experts think? Len
Spacing varied with the design of the roundhouse and space available. However, I think that 7.5 would be closer to protoype for most cases. Certainly 10 degree is the most (ala those Euro TT's which still won't hold a Mallet.) that would look realistic in N. There are a few options out there, more expensive than Atlas, that seem better, such as Diamond, AAA Precision TT's, and CMR. They all have ads in various mags. I suspect all require a fair amount of skill to build, but I think CMR would build yours for you, if you can afford money better than time or skill. Not sure,, though.
7 1/2 degrees seems to be a reasonable figure. I have worked out the geometry, etc.. to modifiy the Atlas roundhouse components for that spacing. The prototype can get down even lower but the facility becomes very large in real estate (the tighter the angle the further back from the center of the table the building walls have to sit). There are prototypes that use tighter spacing but, like the Atlas unit, they sit very close to the pit and the back walls of the stalls get very wide. Charlie Vlk
Len, The two replies so far cover a lot of ground. I used the Walthers pit and bridge for mine. The pit has a big hole in the center where I mounted the bridge to a 0.4 RPM geared motor assembly. The 0.4 RPM is at 12 volts, and the thing will turn with about 2 volts--which is very slow. The biggest problems were mounting the geared assembly solidly and precisely, and mounting the bridge precisely to output shaft. It is NOT indexed. The first time I did this, it took days of fiddling--I would have been better off scrapping the pit in favor of something robust like plywood. By the time I reinforced the pit enough to hold the geared assembly solidly, I couldn't take it apart--so I had to start over on the new layout. I used the pit again--but mounted the assembly to the bottom of the layout benchwork. I haven't started fiddling with the new one yet, because I just started putting decoders in my steam engines, and the weather's been too nice outside. It's still gonna required a lot of fiddling. But, in addition to the turntable kit (which I bought years ago), the geared motor assembly was about $50. Here's a look at the top:
My thanks to all. I had a suspicion that 7.5 was about right. Unfortunately, that means that the Atlas TT mechanism can't be used...........or can it. I haven't taken it apart yet to determine how it works. In any event, the route I will take will be sweat equity and a few "Damn Yankee Tricks". The main issue, as I understand it, is accurate indexing. I think it is doable if the mechanism is kept simple and manual. I may end up eating my words . Len
Len, I've already listed what I thought were the two biggest problems I had with turntables. After some more thought, I realized there was a third--getting the "fan" of tracks laid down with consistent spacing. I'm not familiar with the very expensive systems--can someone tell me if they have a "jig" or something on the outer rim to align tracks? Pete
Len: You can use the Walthers TT with the Atlas TT mounted beneath it for 15 degree indexing. Dan Crowley has a good thread on this method.
Pete Your roundhouse/ TT setup is beautiful. I was taught not to covet.............but I am feeling a huge tinge of envy. I have a feeling that rebuilding the Walthers may be the way to go. I would rather cuss and fuss, as opposed to spending big bucks. I have a gearmotor out of some WW II device, possibly a camera. It is, however, a bit on the clunky side. Where did you get your motor? I will try to build mine as a unit that can be dropped in a hole in the plywood. That could solve the track fan problem. I would start with a small hole in the plywood and lay out the 7.5 degree radials from there. On top of that will go the template for the TT. The theory sounds good but there will be plenty of problems to solve. Heck, that is what makes the hobby fun. Start with the impossible and end up with something similar to your facility. Bob I had initially thought about using the Atlas mechanism underneath a Walthers TT or a scratchbuilt pit and bridge. The only thing I don't like is the 15 degree spacing. It may be possible to adapt an Astroflight gearbox if they make one in a 2 to 1 ratio. One of my other hobbies is RC electric airplanes. There is a lot of neat hardware from that field that may be usable. It may turn out that 15 degree spacing may be more than enough for my needs. In the end, that might dictate how much effort is worthwhile. By the way, I found Dan Crowley's write up in the Nscale.net site. I hate those websites that don't allow you to print out the full width of the page. To print Dan's article, I had to cut and paste into MS Word and print from there. It would be nice if there were an easier way to do it. If I come up with an elegant solution for the TT, I will keep a photographic record. Len
Len, I found the geared motor assembly at my local Grainger outlet--an industrial supply store. They had a bunch of them in different voltages and gearing. I picked up the 12 vdc 0.4 rpm model for about $50. It's strong--if my house were on a pivot, it would probably turn it. It also works at about 2 volts, which is a real creep. While it is not indexed, I can get it lined up very well. I'm pretty sure that my tracks are not at 7.5 degrees anyway; more like 7.4 and 7.6 degrees. I mean, if I slide the TT 0.01 inch in its hole in any direction, it's out of alignment. The way the Walthers bridge travels in the pit--sort of a two-piece V-pulley assembled in a hole--didn't work for me--too much friction. I used the two pieces--and a lot of styrene block--to mount the bridge to the gear assembly. But then I cut a bigger hole, so the whole bridge/gear assembly "floats" in the opening, and can be leveled by adjusting bolts at four corners. I'm not sure the Astroflight gearbox is the answer unless it is exactly 2:1. I guess I've had too many gearboxes that were 47:24 in the past! The big roundhouse is three Heljan kits that I bought in the 70s. They're now available from Walthers. IIRC, I paid about $18 each back then. I think they are nice kits--lots of room inside for lights and details. One of my ongoing problems is that the 18-stall roundhouse is somewhat warped. It traveled from Boston to Albuquerque in the same box as a basketball--hey, the BB fit really perfectly in the center. In other words, it arrived here in a shambles after a bouncy 2400-mile trip, and never went back together perfectly. What was I thinking?
Just the word moving makes my teeth itch. The last one was thirty years ago. If I win the lottery, I will buy a bigger house and use professional movers. I would be willing to bet that my friend in the geology department has a Grainger catalog. I'll have to check that out. I also need to put the power to that surplus motor I have. Dollars to donuts it is a 28vdc motor. It may do well on 3-12 volts. I have thought of everything from no indexing, to some scheme where a bearing assembly drops into a "V"groove. Each grooved thingy would be set up individually. There is much to be said for the 0-5-0 switcher turning the TT. I am not running a public display. By the way Peco makes a manual TT. It sells for about 19 Pounds Sterling. Have to love the Britts telling the Euro to take a hike . As always, thanks for the info. May have to put the Walthers kit on the next order. More importantly, I had better grab another Kato Mike before they are all gone. Len
Len, I think I got distracted last night and lost my reply to the ether. Which usually means I hit the "Back" button before I hit the "Add Reply" button. Here's what I think I said. With the Walthers TT, you can extend the tracks beyond the bridge onto the lip of the pit. That's the only way you'll get a Big Boy on it. This extension is not neccesarily bad for building the TT--having the rails from the bridge "rest" on the lip of the pit prevents some vertical alignment problems. But that's ONLY IF you get the bridge mounted almost perfectly. The slightest discrepancy in vertical alignment around a 360 degree turn will throw things off. If you think about it, 1/64 of an inch is enough to jimmy things royally. Over a ten-inch diameter, you are dealing with an error of 1:10,000 or so. That's pretty precise. Now I'm not sure wood has sufficient dimensional stability--actually, even metal would need some compensation, no? The plastic pit on the Walthers kit doesn't come close.
Pete Thanks for the heads up on Walthers. I would hate to think of the precision needed for Z-scale . Somewhere in my file of MR's from the 70's or 80's, I have a two part article on building an ATSF TT. Being designed to handle Big Boys and such, I think the N&W prototype should fit. I have blind faith that a bearing assembly can be found. I did find an old Graingers catalog, but they were not specific on the rpm ranges of their gear motors. I will have to look in a newer one or try the web site. The surplus motor I have is obviously a gun camera motor. The output rpm is out of sight, even at 12 volts. Powering the TT is low on the list anyway. If I keep beating my head against the wall , all problems will be solved. Len PS: congrats on the moderators job. I hope it goes smoothly.
I came up with an idea for the center bearing of a TT, which may or may not be practical. While disassembling a defunct hard drive to harvest the magnets, I found myself staring at the attachment of the platter to the spindle. That center bearing is about as precise as you can get. On this particular model of drive, the base of the drive would be used almost intact to mount the assembly. The down side that is immediately obvious is the fact that motorizing it will take some creativity. If I follow up on this I will keep a photo record. Len
Len, If you have a local Grainger's outlet, just walk in and ask a counterperson. That's what I did, and he found it for me in about 10 seconds. I'm still building this second iteration. I'm using powered tracks in the pit instead of the hopeless gizmo that comes with the turntable. I'm hoping the tracks might supply the needed precision vertically. I'm not fussing with it too much right now, as I've got a ton of other, less challenging projects. But it will be working by Christmas!
Len: Chris333 modified an Atlas TT by making a pit in it and scratchbuilt a new bridge. I think he increased the length of the bridge as well. This scratch built Atlas TT was a recent thread on the Atlas Forum. It did look quite interesting BTW. Stay cool and run trains....
I use a comercial Peco table modified for the diesels that I run. It is not motorized. But, I wanted to say that I thought the hardest part of making a turntable was to locate the pivot in the center? If it is not exactly centered, and if the table is not centrally mounted, then the ends of the table will scrape the sides. Not true? I say this because I once saw a turntable made by mounting the mechanism in the center of a deep dish pie plate. A wiper arm was put into the mechanism. Then, the pit was created by wiping the wiper arm so it kept the cast plaster at the side. It exactly located the center of the pit. All seemd to work okay. maybe this was all because the table was scratchbuilt?
Bob I'll look up Chris's articles. Using the Atlas mechanism is far and away the easiest way to go, and what I was originally thinking. I could put a bridge on it big enough to hold two Mallets . It also helps that I have one, along with the motor kit. The bottom line is the capacity of the roundhouse complex. The theoretical max capacity is 23 storage tracks.......which should be enough. Besides the info on the internet, I have a bunch of back issues of MR going back into the seventies. Lots of stuff on designing the bridge. Ever notice how much better MR used to be? At this time , nothing is set in stone. Len
