Machine Shop / Locomotive Drive Work

[Jay Criswell]

Jim,

In retrospect, I should have demanded we trade gearboxes so I could finish the destruction of the one you have in hand. It needs to be given a proper Viking burial and be put to rest...permanently.

Jay

[E7]

Don't laugh , I'm not a machinist by any stretch of the imagination, but what if the ends of the worm were threaded to screw into the opposing pieces? Threads cut on the ends of the worm opposite the rotation so they would not unwind.

[R.K. Maroon]

Jay was kind enough to send me a replacement Pearce worm assembly and gearbox casing for the SP 4-4-2. Here are the worms for comparison. The bottom one is the damaged worm. The top one is the replacement from Jay:



Same diameter, same pitch, so I'm in business. Hopefully the new worm will mesh with the old gear with no issues.

Here are the gearcases, Jay's replacement to the left, the original (with offending hole) to the right:



I've got to clear my workbench, but I should have the gearbox back together and installed for a test run in a day or two. I will report back.

THANKS, JAY!

JIm

[Jay Criswell]

Jim,

Does look somewhat better. If needed, I do have the worm gear too.

Always glad to see these things turn out successfully.

Jay

[up148]

Looks great to me. Nice job Jay!

[ScaleCraft]

The good thing about having a dead shaft and worm, you can install it in the new box, spray paint it after sticking an old axle in the axle holes, and no masking required!

[R.K. Maroon]

One thing I hadn't thought of with the new worm and gearbox for the 4-4-2 was the possibility that the new gearbox case wouldn't fit the chassis, but that is what happened. The axle bushings protrude inward from the frame rails, not leaving enough space for the gearcase to fit between them. I looked at the old gearcase and sure enough it had been narrowed to get the required clearance. One solution would have been to reuse the old gearcase, but I decided against it for two reasons. First, I had already pressed the worm assembly together, which captured half the new case, and I didn't want to reverse that and do it again. More importantly, the old case had been machined more one one side than the other. Machining narrows the case bearing to the shaft, and that one side was looking pretty thin. So off to the mill with the new case.

The first step was to figure out how much needs to be removed from each face. I did that. The next step is to WRITE IT DOWN. I'll do that next time.

Next, mount assembled gearcase to mill. To ensure that the cut to the case was orthogonal to the axle, I slid a piece of 1/4" rod into the gearcase and secured it with a collet chuck in the headstock:



I had to support the back surface of the case on a boss made from a stack of 1/4" brass precision washers:



The assembly was ready to be machined when the rod could be raised and lowered in and out of the hole with no binding:



It's simple from there. Replace rod with an 3/8" end mill and face the case by the prescribed amount.




Finally, flip it over and repeat. Then clean, lubricate, and install:



Everything snugged up with no wobble. The mechanism turns clean and smooth. THANK YOU, JAY!!!

I couldn't wait to install the motor and give it a test, but...ha!...this locomotive has a tender drive.

More later
Jim

[bob turner]

Why is there a worm on that extension?

I would make it a solid shaft with a self-aligning rear bearing, then behind that a large NWSL horney ball socket.

On the tender, a Toyota hose from motor to the horney ball. Drawbar length to suit the coupling, with only a pin at the tender, for really easy uncoupling.

[ScaleCraft]

Why is there a worm on that extension?

That was covered in another of Jimmy's posts. Raised worm. Odd. I think it cools the driveshaft at speed.

[R.K. Maroon]

Why is there a worm on that extension?

The second worm is there to drive a mechanical chuffing mechanism. Here is what you get when you take the boiler off:



The piston fits into the boiler cavity:



The chuffing cylinder is vented through holes drilled into the bottom of the boiler assembly tube just above the steam chest:



I have read of these things but had not ever seen one until this locomotive arrived. I was tempted to dispense with it, as it seems likely to rate pretty high on the "cheesy" scale, but somebody went to a lot of work to put it in there and they did care enough to gear the chuffer at twice the driver rate, which is correct, so I am going to reinstall it and give it a whirl. I am not sure how much and what type of lubrication would be best, but I am thinking either a heavier oil, like Labelle 102, or a light grease, like Labelle 106. Feedback and comments are welcome.

Jim

[bob turner]

Take it out. Too many really good sound systems are available now.

Use the excess power to smoothly pull trains. Noiselessly.

[ScaleCraft]

I have one here. Took it out of an engine. Cylinder, piston, rod, phenolic worm gear with a ball bearing insert, bracket, and Pittman with worm.
Totally separate from the drive mechanism. I THINK there was a heating element, but can't recall now. Stupid.

[R.K. Maroon]

It has been nearly two months to the day since I last posted about the SP Atlantic (see posts above for background). The project was near completion. A new 3D printed pilot beam support was in place, as was the new gearbox from Jay. All I had to do was to put it all back together. But then I couldn't find the remaining parts -- the pilot and trailing trucks and a bag of hardware. Frustration and embarrassment abounded, but I knew they would show eventually. Sure enough, I decided to clean and reorganize the storage room this week and the parts magically appeared. Of course, the container they were in was in plain sight -- but unlabeled -- the whole time. So, at last, here it is:



It runs fine on the test bench. I recall some problem with the tender drive setup, so I may revisit that. I'll give it a test spin on the layout once we get it setup again (it's still packed up after the Southwest O-Scale Meet last weekend).

More soon
Jim

[bob turner]

It has nice lines for a low drivered Atlantic. Whoever built the tender was a master.

[R.K. Maroon]

One of the attractions for me was that this locomotive is lettered for the T&NO. I will get better photos, including closeups of both engine and tender, and post along with a video of it in action.