Mystery bind in wheel/rod motion

[Greg_Lewis]

The mystery of the century. Perhaps it's time to look at the alignment of the planets.

[Bill Shields]

Why take the wheels off to measure? Put a center turned to the correct diameter on each end of the axle and measure all from there..

If the diameter of the center is the same as the crank pin..it is a no brainer

I would shudder at pressing wheels and cranks on and off.

[Steamin]

In the end, I could not find the single one item which causes the binding.
I learned a lot about measuring, measuring accurately and repeatably. Mostly that I could not repeatably measure accurately.

I would say my my efforts to measure pin-to-pin distances with the assembled axles/wheels in the frame was not successful because I did not block the axle boxes from moving in the openings. My skills at measuring the quartering between centers on the mill table improved, but not to a repeatable result. I was most reliable using a single tool such as outside micrometer to measure Pin and Axle box diameters, or the co-axial indicator for the rod and frame centers.

I re-measured the new machine work on rods again, those measurements repeat within 1 thou, which is smallest my mill DRO can report. Each new bushing is 7.00 on center relative to each other, which is what the print calls for and to the best of my ability what the frame openings measure. There is 5 to 8 cumulative error from hole 1 to 3 which I attribute to the coupling rod joint behind #2 which has a little bit of play in it.

The axle boxes in main axle #2 were a sliding fit in the openings. It took pressure to move them up and down, they were not loose. I removed 2 thou on the front and back box openings for both left and right side.
Now the boxes freely float in the openings. This additional clearance appears to give the bind somewhere to go; the wheels roll without issue with the rods on. All the boxes do shift back and forth as the wheels roll around. Before this only #1 and #3 moved, and they did not move together.

Time to move on!

[Greg_Lewis]

Chalk it up to cumulative error. Glad it's finally resolved.

[Bill Shields]

In general I drill my rod bearings oversize to allow for differences in axle elevations.

An extra 0.005 in bearing clearance goes a long way toward making for a smooth running loco.

Remember. You are building a steam loco.. not a watch.

There are times to be a urologist and times to be a blacksmith. Most of a steam loco is somewhere in between

[Builder01]

Bill, I think you mean horologist. A urologist, is something completely different, LOL!

[Greg_Lewis]

...
There are times to be a urologist and times to be a blacksmith. Most of a steam loco is somewhere in between

And I sure hope they don't mix up their tools and techniques!

[Bill Shields]

Spell correct seems to have changed horologist to something else...sorry

[RET]

Hi Steamin,

Glad you got it sorted out. My hat's off to you. The suspension has to be flexible so the wheels can follow the track.

I have found that as long as that is possible, the locomotive will stay on. It may bounce around all over the place, but it won't come off.

Best of luck.

Richard Trounce.