Scratchbuilt machined gearboxes

[Brian McKenzie]

This solid one-piece brass gearbox was completed today (all manual work), replacing the side plates of a standard Slaters GB30R-3M, which provided the Canon motor and gears.



It's for my current locomotive project, where more distance or height was needed between motor shaft and the powered axle.
By arranging the intermediate shafts to be in a straight line, another 5mm was gained over the curved routing of shafts in the Slaters arrangement.



I'm quite intrigued with the complexity of the Slaters gearbox, which I hadn't seen before. Busier than I would want to be making and assembling - but well done.
-Brian McK.

 

[simond]

Lovely bit of machining!

I’m perplexed by that, Brian. It’s probably the camera angle but I can’t see how the gear train works. I’m guessing the larger of the two gears on the middle intermediate shaft does not mesh with the smaller on the lower intermediate shaft, but that leads me to wonder how the gears (presume wormwheel, and pinion) on the upper shaft are arranged…. The clearance between wormwheel and the middle pinion must be minimal?

 

[Brian McKenzie]

Simon yes, there is very little clearance between gear teeth and the boss of the gear on the next shaft! From the motor shaft, a 9 tooth spiral gear meshes with a 15 tooth.

The 15 tooth is visible here. Photo shows the unfinished gearbox about to be first tested using an almost dead battery ex smoke alarm.


Arriving at and getting 90degree shaft spacing correct for spiral gears (and worm gears) is the only tricky part in cobbling up gear trains.

From measurements under high magnification, I judged this to be 0.268 inches. Without knowing what DP or Module these rather nice gears are, different formula values were tried, and it seems this pair of spiral gears are imperial 70DP - if indeed such terminology applies here.

The P.C.D. (Pitch Circle Diameter) of the

. . . . . . 9 tooth gear. . . . . . 0.07 (for 70DP). . x 9 (teeth) divided by π 3.1416 = 0.2005 inches

. . . . . 15 tooth gear. . . . . . 0.07 (for 70DP). . x15 (teeth). . . . " . . . . . . . . . " . . . = 0.3342

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . = 0.5347

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Divide by 2 . . . = 0.26735 inches 0.268" had to be good!


However, this gearbox was easier than others made, as the motor position can be adjusted if necessary by sliding it along in the narrow recess which accommodates the plate that comes screwed to the motor.

-Brian McK.

 

[Brian McKenzie]

A clearer view of the gears. After the holes were drilled and reamed in the brass, the gears were placed externally on temporary shafts and given a spin to check all was well.




A 23x28 Maxon powered bronze gearbox for an earlier loco (still to be finished) with Module 0.5 gears all homemade. The housing can be split at the axle and the bottom section pulled off on the dowel pins.
It is whisper quiet with the Delrin gear. (Plastic gears are OK when they are cut from bar stock. It's moulded gears that can give grief.)

Edit: Module size should read 0.5, not 50 !!

 

[michael mott]

This solid one-piece brass gearbox was completed today (all manual work), replacing the side plates of a standard Slaters GB30R-3M, which provided the Canon motor and gears.

View attachment 227907

It's for my current locomotive project, where more distance or height was needed between motor shaft and the powered axle.
By arranging the intermediate shafts to be in a straight line, another 5mm was gained over the curved routing of shafts in the Slaters arrangement.

View attachment 227909

I'm quite intrigued with the complexity of the Slaters gearbox, which I hadn't seen before. Busier than I would want to be making and assembling - but well done.
-Brian McK.

I have to agree with Simon beautiful work.
Michael

 

[GWRfan]

That is a beautiful job some very good machinery work going on there.

 

[paulc]

It is indeed a thing of beauty and machined out of solid bar .
The two that I've made started with hollow brass square section then just machined one side out of it so i take my hat off to you Brian .