Hi, Ive finally given up and plan to finally buy half a dozen of NWSL gearboxes for some engines that seriously need some new gearboxes (notably PFM engines which no matter what I do still run noisy).
From what I've read, 28:1 gear ratio is pretty much an industry standard. My question is, do I get 0.3 mod or 0.4 mod gearboxes? NWSL recommends 0.4 for "heavy" steam and 0.3 for "light"...but what does that mean? Is there a downside to simply using 0.4 mods for all?
I need gearboxes for the following:
2-8-0
4-6-2
4-6-4
4-8-4
What do you guys recommend?
Thanks!
Charles
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Modeling the Santa Fe & Pennsylvania in HO
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Just to be clear:
You're planning on disassembling these 5 locos, pulling off a driver and the existing worm gear, installing a replacement worm gear, and requartering the driver you had to pull off to do this.
Right?
As reference material:
United steam engines brought in by PFM typically had 40:1 gear reduction.
Tenshodo typically had 36:1, although their GN O-8 had 48:1. I think some of the Tenshodo crowns had 48:1, also.
It appears that the smaller the "mod number", the smaller the gear set. So a gearset and gearbox with a 40:1 reduction would be physically smaller in .3 mod than in .4 mod.
My inclination would be to get the largest "mod" where the bottom of the gearbox will clear the track (actually, 1/32" higher would be a better choice). Scraping the bottom of the gearbox is considered bad.
Going too small will have the potential to overload the gears, maybe ripping out a tooth or excessive wear.
Note that 4-8-4's have a larger driver diameter than 2-8-0's. So you can fit a bigger gearbox in a 4-8-4 without dragging on the track.
Note also that, whatever gear set and gearbox you choose, it has to actually fit, in an assortment of dimensions--width, height,......
Since you're considering standardizing on the .3, I recommend getting a gearbox setup suitable for the 2-8-0. While you have it and are fitting it to that loco, you can "hold it up against" the bigger ones; that might help make the decision.
Ed
Hi, yes, that's how I plan to add the gearbox. I've done it twice before, its actually rather simple. NWSL gear puller makes it a breeze.
I admit I havent checked what gear ratios PFM engines were previously. I did just check with my only PFM engine (PRR K4s) I have on hand currently and it was indeed 1:40. I sense PFM (and Tenshodo) chose such a high ratio due to the huge drivers and the old open frame motors not having good slow speed.
I will decide whether to get 1:36 or 1:28 for each engine once I return home. Idk if this true, but I heard somewhere that BLI uses 1:28 gears in all their steam engines. Two out of two of my sunset locos (PRR K4s, H10s, a good variety of large and small wheels) with can motors also use 1:28. I think 1:28 is a pretty solid gear ratio for a modern can motor mechanism.
Interesting view, I had always assumed one would determine the mod based on how heavy a load an engine would pull. With smaller mods having more shallow teeth and therefore a greater chance of ripping teeth. Never considered the bottom clearance to be an issue. As you can see my knowledge of gears is lacking haha. That helps though, I'll just use the table provided by NWSL to choose one. NWSL's stock of gearboxes seem to be hit more miss recently, lots of them are out of stock. In 0.3 mod, only expensive ball bearing varients ($40-70) are available. Many axle diameter varients are out of stock. Charles
Charles,
Sounds like you're on top of things!
I'm surprised you're having troubles with the original gear boxes. I wonder what's wrong with them. I do recall the gearboxes on my Tenshodo GN S-1's were/are pretty sloppy. Kind of a surprise, what with all that fine craftsmanship, and all.
I suspect Tenshodo and the United crew were gradually improving the boxes over time. For good reason, apparently.
Good luck on this, and please feel free to report back on the good, the bad, and the ugly.
Yea, I'll go with 1:28 for my engines, will just need to figure out axle diameter when I return home and I'll be on my way! These gearboxes are so expensive haha, wouldnt want to mess up and buy the wrong one.
To clarify, the engines mentioned above were a PFM ATSF 1950 class, PFM PRR K4s, Tenshodo ATSF 3460 class, and PFM ATSF 3776(?) class. All were fine tuned to run very smoothly. However the PFM engines still make lots of noise despite removing some of the gearbox slop (adding washers to worm to prevent sliding back and forth and carefully sanding down the bottom for a better axle fit) and realigning the motors. Im rather picky about my engines running quite, so new gearboxes are an order.
'Mod' is short for 'module', which is the way metric gears determine gears that will 'mate' cleanly. It is the gear pitch diameter divided by the number of teeth. The more familiar 'pitch circumference is simply the module times pi.
Here is a useful reference that explains metric gear spec:
https://www.sdp-si.com/D805/D805_PDFS/Technical/8050T017.pdf
NWSL has a table with different measurements for 0.3 and 0.4 module but I suspect it won't make full sense until you appreciate how the gear measurement works.
Are all the gears bronze or brass? I had an old Westside K5s that was grumbling. All the gears were bronze. I replaced the idler gear with a fiber gear and a light machine oil. One of my quietest locomotives now. I also weigh down my brass as heavy as I can. Eliminate things that vibrate by gluing down from the inside of the shell. Snip off the long tails on grab irons and details that go through to the inside.
Just a few things I have learned over many, many years.
wrench567 Are all the gears bronze or brass? I had an old Westside K5s that was grumbling. All the gears were bronze. I replaced the idler gear with a fiber gear and a light machine oil. One of my quietest locomotives now. I also weigh down my brass as heavy as I can. Eliminate things that vibrate by gluing down from the inside of the shell. Snip off the long tails on grab irons and details that go through to the inside. Just a few things I have learned over many, many years.
PFM gearboxes go from steel worm to a brown plastic(fiber?) worm gear (on the axle). You never want metal against metal (like steel to brass) as it makes tons of noise, like on Rivarossi locos. Thanks for the info on mods Overmod! Yea Im trying to learn more about gears...but its been tough.
Early PFM catalogs referred to the worm gears in the Tenshodo and United lines as being made from "phenolic".
It's been a long time since I've looked at one, but my recollection is that the stuff had some sort of (maybe cross-directional) fibers in it--it wasn't just homogenous plastic. I also suspect the gears were cut, not molded.
7j43k Early PFM catalogs referred to the worm gears in the Tenshodo and United lines as being made from "phenolic". It's been a long time since I've looked at one, but my recollection is that the stuff had some sort of (maybe cross-directional) fibers in it--it wasn't just homogenous plastic. I also suspect the gears were cut, not molded.
I recall the cross sectional fibers too! It made me think they were fiber, but I wasent sure.
I searched up phenolic and it looks to be exactly what the gears are made of:"Phenolic sheet is a hard, dense material made by applying heat and pressure to layers of paper or glass cloth impregnated with synthetic resin. These layers of laminations are usually of cellulose paper, cotton fabrics, synthetic yarn fabrics, glass fabrics or unwoven fabrics." So resin covered celluose material. Fascinating.
All I know is that it doesnt melt in Acetone (thank god) when stripping paint!
My most likely candidate for a new gearbox is my Tenshodo 0-8-0. It runs fine, but it is very noisy. It always has been.
I also plan to remotor it.
I have a NWSL gearbox, but I just bought one I found in stock at a hobby shop. I have no idea if it will actually work.
-Kevin
Living the dream.
In my experience, NWSL's 0.3mod gearboxes will do well for small to medium size steam engines (like an 0-4-0 or up to a 2-8-2). For anything larger than that, I'll go with 0.4mod.
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