Mystery bind in wheel/rod motion

[KenG]

I agree with what Richard said. I have the same problem on my locomotive and I traced it to bad quartering on one axle. The binding at 45 degrees is the clue. If rod length was a problem it would bind when the rods are at 90 degrees.

I found the culprit by removing one coupling rod at a time. Temporarily solved the issue by ovaling one of the rod bushings.

Ken

[Chris Hollands]

Do you have any run out on yours wheels to the axle - are the wheels pressed on square to the axle - very hard to get perfect unless you machine the wheels after pressing or your faith in certain loctites .
If there is any runout then that will change center distances and could create binding .
Can you turn the wheels and frame upside down and turn the wheels by hand with the axle box keepers removed and see what the movement the axle boxes have , does one or more boxes move in a certain direction at a certain position .
If you can turn the frame upside down and turn the wheels and you see the axle boxes move ,use feeler gauge or shim stock to move the axle boxes one way or the other and see if the issue gets better or worse , a few thou here and there could make the difference .
If this makes a difference then you maybe able to shim the axle boxes sliding surface to suit depending on your axle box design .
Remember you don't want tolerances to tight as the engine moves down the track the rod / wheel center distances will change constantly with engine and suspension movements .
10 thou clearance for an axle box in the frame is quite normal and any less may create issues in its self depending on the wheel arrangement / suspension of the engine .
I found that a few thou change here and there can make the difference between an engine turning quite freely or binding .

[SteveR]

Couple of references:
Measuring distance between crankpins for rods
http://www.chaski.org/homemachinist/vie ... 8&t=103255

Allen mogul siderod project
http://www.chaski.org/homemachinist/vie ... =8&t=99961

Also search Chaski for "Quartering" and there are more discussions.

So far I've made a couple of sets of rods for my locomotive, the problem with adjustable rods is once you get it adjusted, then you have to measure carefully to make real ones. There has to be a better way. (Bill posted the idea that you make adjustable rods, then solder them into place and use forever .)

The ones I have now work, but are not perfect. In my non-existent spare time, I'm working on some calculations in Excel to try to simulate the problem. What I quickly found is that for a 2.5" crank radius, a 1 degree mismatch between two axles corresponds to 0.043" length change. 2.5*(Sin (1degree). I believe this is ok for 2 axles since it's constant, but when you add a 3rd axle and a 4th axle, the mismatch from Axle4 to Axle1 or Axle3 to Axle1 starts to vary. Maybe smarter people can verify this.

The solution I'm working on now is to indicate the cranks to each other - in particular crank 4, 3 and 2 all back to #1. Maybe everyone knows this is how you do it, but this is a learning experience for me.

I take comfort in the fact that there is a quote from someone who said these locomotives never run better than when the rod bushings are almost all worn out. Can't find it right now.

Excelsior!
SteveR

[RET]

Hi,

If you are going to make adjustable side rods, once you have adjusted them for the best performance you need to measure the center to center distance.

Make two pins that are a close fit with the crank pin holes in the adjustable rod (only one or at the most two thou clearance on the pins in the holes) with shoulders on the pins. Use a dial vernier to measure over the pins and between the pins. In each case, out of a series of measurements, take the lowest ones. Having a shoulder on the pins will help with the accuracy of measuring. Threaded pins with nuts will also help because there are fewer things to hold onto while measuring. Once the "OD" and "ID" measurements are taken, half way between will be the true center to center measurement. Hope this makes sense to everyone.

If the quartering is out and the wheels are a press fit on the axles, you need to be able to reliably move the wheel a very small amount on the axle. Spaced pins on a bar with the pins in the spokes would be one method where one short bar would be placed in the vise and a much longer bar would be used on the other wheel on the axle to rotate the assembly by a very small amount. I'm sure there re a number of different ways that come to mind.

You also need to take scale into account. 1/16th full size is going to require a higher degree of accuracy than 1/8th scale, but remember, its still a locomotive, not a watch.

Hope this helps bit.

Richard Trounce.

[FKreider]

remember, its still a locomotive, not a watch.

Excellent advise!

[Harold_V]

This topic is an excellent example of where the word "tolerance" (degree of accuracy) is confused with proper dimensioning.

The commonly held belief that things are built with "too tight of a tolerance" is absolutely wrong. Tolerance denotes the degree of departure from a nominal dimension, meaning that an open tolerance allows for a greater variation than a tighter tolerance. Common sense should then tell you that if there is an issue with a fit, opening up the tolerance is a mistake, as it offers an opportunity for an even greater departure.

Plain and simple. If one works to "tight tolerance", but dimensions correctly, that simply can't happen.

Get it?

If you don't, keep reading and trying to understand, for, until you do, you will struggle with getting it right.

Be it a watch, or a locomotive, it must be dimensioned correctly if one hopes to have it operate as intended. In BOTH cases, a tight tolerance will assure that happens.

H

[Steamin]

I had to use the hydraulic press to get the wheels off the axles, and to press them back on. I used heavy center lube for the press fit, not Loctite when putting them back on.

RET, after several reads I finally get what you mean about making a radius gauge. At this point I have not done this since each pin is slightly a different dimension after removing a minimal amount to get them round again. I'm thinking I could make the gauge with the smallest pin, measuring the wheel, then enlarge the bore to the next larger pin, measure that, repeat four more times.

I did measure the distances between the main pin (axle #2) and front driver (#1) using 45 degree steps (it was easier).

Setting 45 degree angle to measure crankpin distances

The rod on the opposite side was still attached as I did the measurements.

Using inside micrometer to measure

I went around the clock twice, here's the breakdown of the measurements

Measured distances

Columns E and F are the two set of measurements of the Engineers side; columns G and H the Firemen's side. Column A is the angular position of the Engineers crankpin, zero is on top. I averaged the two measurements shown in column B. Without moving the wheels or angular position, I measured the Firemen's side, the average is shown in column C. When the Engineer's crankpin is at the top Zero degree position, the Firemen's crankpin is at the 270 degree position.

As I measured around, it looks like the axle boxes, which now freely float in their openings, contributed to the differences in the readings.

[Steamin]

As viewed from the engineers side, the binding occurs around 135 degrees.

Here's what the chart 1 data looks like when plotted:

Line graph

Same chart 1 data shown around the compass:

compass graph

[Steamin]

Right now I am working on setting up to measure between centers to check the quartering. Here I am using a test bar to first get everything in line with the table.

Setting up to measure between centers

My focus is checking the quartering, then coming up with (another) way to measure the pin radius, then maybe an adjustable rod.
Steamin

[Gary Armitstead]

This topic is an excellent example of where the word "tolerance" (degree of accuracy) is confused with proper dimensioning.

The commonly held belief that things are built with "too tight of a tolerance" is absolutely wrong. Tolerance denotes the degree of departure from a nominal dimension, meaning that an open tolerance allows for a greater variation than a tighter tolerance. Common sense should then tell you that if there is an issue with a fit, opening up the tolerance is a mistake, as it offers an opportunity for an even greater departure.

Plain and simple. If one works to "tight tolerance", but dimensions correctly, that simply can't happen.

Get it?

If you don't, keep reading and trying to understand, for, until you do, you will struggle with getting it right.

Be it a watch, or a locomotive, it must be dimensioned correctly if one hopes to have it operate as intended. In BOTH cases, a tight tolerance will assure that happens.

H

Steamin,
I have been watching this thread for a couple of days. I KNEW Harold would step in sometime and thank goodness he did . Thank you Harold.

When I started to build my Gene Allen ten-wheeler more than forty years ago, I was already a journeyman die sinker. I knew that getting the wheels quartered correctly, getting all six pins located correctly and getting the wheels keyed to the three axles correctly was going to be the most difficult thing to accomplish on that locomotive.

The first thing I did was to finished the frame and the the pedestal bars just as accurate as I could. Accomplished by using accurate mics, both inside and outside. Then I setup the frame on a granite table (because I had access to one). Double checked the centerline measurements to each set of pedestals for the still to be machined journal boxes. Done with a height gauge. Made notes from these dimensions so I could mill the journal boxes to size. During this whole procedure, I worked as close as possible to get tolerances as tight as possible. This is NOT difficult to do with matching accurate measuring tools. Installed the journal boxes and they were held tight by using a .001 shim on each side of each journal. Set the frame assembly with journals on the granite table and checked dimensions between center of each journal bore for the bearings. These dims were held to plus or minus .001 again.

Next step was to finish the drivers and bore for the 1 inch axles. Layed out a center line through the axle center and out through the section of the casting where the crank pins would be located. Took these drivers to a broach company and had them cut the keyways. Got the drivers returned and then I made my first fixture to setup on my mill to drill and bore for the individual crank pins. I had a one inch diameter spud on a flat plate that was pressed into the plate (it could not turn). there was a keyway and square key installed on the spud. Then all I had to do was drop the keyed driver onto the spud and dial over on the mill the EXACT amount of the half stroke of the engine design. ALL six drivers were done withe same setup, not MOVING anything on the mill. What this accomplished was that all the drivers were guaranteed to be EXACTLY the same.

I then made two more fixtures for drilling and boring the main rod and side rod. Again, just one setup and everything pinned and held in place during machining with tight bushings.

The last thing I did was quarter the three axles. This was done with a square 5C collet block and a one inch 5C collet. Never removed the axle stock until the quartering was finished. Cut both key slots with one cutter and just turned the collet block. Now all three axles were keyed to exactly 90 degrees and all three axles were exactly the same.

All of this was done on a so-called "cheap" Enco round column mill drill, BTW! I started to assemble the running gear. Pressed the first driver in place and assembled this to the bearing in the journal box. Crank pins all pressed in place. The big test was about to come. The side rods fit beautifully on the first side and NO binding whatsoever. Put the second set of side rods on and they fit beautifully. The bottom line here is that working to tight tolerances (knowing that accumulation of error is always an issue, just avoid it by remembering to be accurate and use the same STANDARD of accuracy throughout the ENTIRE machining process, start to finish.

Sorry for the long dissertation. I just wanted to pass along what my experience was in doing side rods and quartering on my Allen ten-wheeler.

[Steamin]

Appreciate all the feedback. As this locomotive was built 30+ years ago by {unknown} builder, this rebuild is largely a 'setup and measure' exercise for me to determine what I need to re-machine and repair.

Using a test bar to align the centers to the table

After squaring the centers to the table, the spindle was centered directly over the centerline of the test bar and the saddle locked.

The height of the center was measured using a height gauge, the crank pin OD measured, and a stack of parallels used to set the crankpin exactly on center with the axle. The adjustable parallel on the top of the stack was set using a micrometer.

Stack of parallels putting the crank pin on center with the axle

Moving to the other crankpin, if it was quartered correctly, we should get the same number measuring both sides of the pin, since the center is theoretically at zero, same as the axle.

Measuring the back side crank pin distance from zero

Results:
Driver 1: 0.055 difference between the forward pin measurement and back pin measurement.
Driver 2: (main) unable to measure -- the center in the chuck did not stick out far enough; the longer crankpin hit the chuck before the center supported the axle. I didn't feel like re-indicating the whole setup again if I unchucked the center and pulled it further out.
Driver 3: 0.009 difference.

With actual measurements, I am much closer to proving the actual issue -- a quartering problem on Driver 1.

And the fix for this problem is familiar to me; I faced a similar issue back in 2005 with my pre-machined Mikado wheels (http://www.neidrauer.com/HeavyMikado/Se ... %20031.jpg)
I'll press the wheels off axle 1, then press out the pins. I need to make a keyed chucking mandrel to stack the wheels together. If the pin holes do not align when stacked, I've confirmed the problem and can bore the holes in line. If the pin holes align then I'll focus on the axle shaft quartering.

[RET]

Hi Steamin,

It took a while, but I think I've figured out what's going on with your locomotive. If you look at your "line graph," it tells you pretty much everything you need to know. On the front axle, the quartering is off a bit, but the crank pin radius is wrong too.

By the way, when you are setting up and taking these measurements, you need to block up the suspension so the axleboxes are all in the same position, ie, in the middle of their travel.

Here's the reasoning behind the above statements. If the quartering was good (and the crank pin radius was right), there would be no sinusoidal trace on either side, both sides would be straight lines or very close to being straight. Because there is no binding with the front coupling rods off, that says the problem is with the front axle.

When you measure, I'm pretty sure you will find that the crank pin radius on the front axle is too great on the engineer's side. Make up the crank pin gauge that I described before for just the front axle and use the gauge to check the crank pin radius on the left and right wheels of the front axle only. You should find that the engineer's side is wrong (probably too long). The reason I say this is because the engineer's side trace is pretty good and that trace is controlled by the side rod and crank pin radius on the fireman's side. You get the distorted trace on the fireman's side because the engineer's side isn't right.

The quartering is off, but not by a lot. If it was, the engineer's side trace would have a markedly greater sinusoidal appearance. Most of the error you see in the graph is due to the wrong crank pin radius. The next thing to do is to go and do the measurements and then you can tell me if I know what I'm talking about or not. Please let us know what you find. I for one will be quite interested.

Richard Trounce.