Can someone explain this process to me, assuming the turntable being reinstalled is not the original? Turntable clearances don't leave much room for error to be off-center. Thus far, most installations have been old turntable-new pit, except for Steamtown's, which was vice-versa.

http://photos.nerail.org/showpic/?2003060520591024777.jpg:bysearch:roundhouse:SEARCHTYPE=SIMPLE&PAGE=8&SEARCHSTRING=roundhouse&BOOL=ANY
ryarger@rypn.org

> Can someone explain this process to me,
> assuming the turntable being reinstalled is
> not the original? Turntable clearances don't
> leave much room for error to be off-center.
> Thus far, most installations have been old
> turntable-new pit, except for Steamtown's,
> which was vice-versa.

Take two points on your circumference and connect them. At the center point of this line make a line perpendicular at 90 degrees - this is the center. Now take another two points of your circumference and find the center and draw or make another perpendicular line at 90 degrees- this is also the center of your circle. Where the two perpendicular lines meet will be the center point of your pit.

G

greg@skittercreek.com

http://photos.nerail.org/showpic/?2001112809340616913.jpg:bysearch:roundhouse:SEARCHTYPE=SIMPLE&PAGE=20&SEARCHSTRING=roundhouse&BOOL=ANY
ryarger@rypn.org

But how is this physically done, with a transit, strings and plumbobs, or what? Doing it full size is a bit different than drafting class. Not much room for error, as the rails will hit on one side if it is off just a little. The gap at the ends of the rails is usually less than one inch, even less when it is hot. I presume the 90 dgree angles can be approximated with a 3/4/5 triangle, but this is not always accurate. Also, I suspect some elongation of the bolt holes where the center bearing is bolted down to its foundation will allow a little shifting, but not much.

> Take two points on your circumference and
> connect them. At the center point of this
> line make a line perpendicular at 90 degrees
> - this is the center. Now take another two
> points of your circumference and find the
> center and draw or make another
> perpendicular line at 90 degrees- this is
> also the center of your circle. Where the
> two perpendicular lines meet will be the
> center point of your pit.

> G


ryarger@rypn.org

It is critical that each line be measured at the point where the longest measurement is noted. This ensures that the line crosses the center, rather than the chord of the circle. A long tape measure is adequate, but it must be held very taut to avoid errors due to sag. The point could be reliably transferred to ground level with a plumb bob.

Actually, the angle between the lines is not critical, but 90 degrees would be a very good choice. Taking a number of measurements across the pit rather than two will help reduce the error.

If these lines do not all meet at the same point (assuming the conditions above were met), it would indicate the pit is out of round. Eventually, with enough measurements, a zone (probably eliptical) would be described by these intersection points.

It would be easy to locate the center of this small zone, greatly reducing any possible error.

As for center bearing footing height, one could use a taut wire, water level, or laser level to provide a reliable reference line.

Of in a perfect world, one might find the new pit's center bearing footing was at the proper level and its anchor bolts were still usable and located at the right locations. Not likely, but it possibly could happen...

Hopefully this will help.

Steve Hunter,
Cardinal, Ontario

> But how is this physically done, with a
> transit, strings and plumbobs, or what?
> Doing it full size is a bit different than
> drafting class. Not much room for error, as
> the rails will hit on one side if it is off
> just a little. The gap at the ends of the
> rails is usually less than one inch, even
> less when it is hot. I presume the 90 dgree
> angles can be approximated with a 3/4/5
> triangle, but this is not always accurate.
> Also, I suspect some elongation of the bolt
> holes where the center bearing is bolted
> down to its foundation will allow a little
> shifting, but not much.


s.c.hunter@sympatico.ca

Well Bob,

I don't know how most people do it, but I can tell you how we are planning on doing it, hopefully this year.

The original center stone has a center mark depression, not sure if the New Haven, Middletown and Willimantic Railroad made it, or if it was made by one of the museum members before I got there. Also in the top surface of the stone there is a raised platform where the cone sits, and the drafting technique can be used on that, or use the opposing mounting bolts to make an X for the center point (4 bolts hold our cone).

First we are going to install the cone. This involves installing new bolts into the stone, by using a non shrink epoxy in 4 new holes, and about 2 inches of leveling compound to bring the surface to the right level. Then the cone is installed and bolted down.

Second, the walls are moved out, in our case about 6 inches on the upper wall, to clear the bridge length, directly below the install point of the bridge. Then the bridge is lowered to the correct height.

Third the bearing, bearing plate and saddle are installed along with the (8) 2 inch diameter bolts that support the bridge.

Now that the bridge is installed and supported by the cone assembly, the rest of the upper wall can be shifted to keep the correct gap between the wall and bridge, by rotating the bridge.

_______

Probably if someone wanted to adjust the wall at the same time, they could do the following:

-Drill and tap 1/4" threads in the centers of the bolts and use them to hold a center post. Or install your 4 new bolts and use them to hold the center post. The center post needs only to be a plate with a rod sticking out perpendicular from the center of the plate with a pin on the top for the string.
-Measure the diagonal length of the bridge (from the end of one girder to the far end of the other) and divide by 2.
-Use that length to make a string that will rotate freely on the post to tell you how far to move the upper wall, and work your way around.
-Then install the bridge, as described above.

Rich Cizik
MoW Foreman
Ct Eastern RR Museum
Willimantic, Ct

> Can someone explain this process to me,
> assuming the turntable being reinstalled is
> not the original? Turntable clearances don't
> leave much room for error to be off-center.
> Thus far, most installations have been old
> turntable-new pit, except for Steamtown's,
> which was vice-versa.


Connecticut Eastern Railroad Museum
rcizik5519@earthlink.net

> Can someone explain this process to me,
> assuming the turntable being reinstalled is
> not the original? Turntable clearances don't
> leave much room for error to be off-center.
> Thus far, most installations have been old
> turntable-new pit, except for Steamtown's,
> which was vice-versa.
Bob; I have never set a turntable, but I have set machinery such as punches and spacing tables that
covered nearly 200 lineal feet. With this experience I would recommend that you combine the methods described by Steve Hunter and Rich Cizik
using Steve's plan first. My reasoning on this is that the original table was probally set using surveyors instruments and aligned so that the tracks converging on it came in aligned with the center of the pit. The more stalls the table serves, the more important it is to have this uniform.
Jim

rrfanjim@charter.net

> Can someone explain this process to me,
> assuming the turntable being reinstalled is
> not the original? Turntable clearances don't
> leave much room for error to be off-center.
> Thus far, most installations have been old
> turntable-new pit, except for Steamtown's,
> which was vice-versa.

Bob; I want to add a PS to what I said.
After you locate the center set some reference stakes so after you get the pivot set you can check to see if you are doing what you think you are doing.
As for the perimeter rail, be sure it is accurately set with reference to the center pivot or the table will be difficult to turn. I saw this happen on one of our tables and on the table
at the San Lazaro narrow gauge terminal in Mexico.
I got to help push on that last one !!
Jim

rrfanjim@charter.net