1/16 scale 1916 Case 65 HP Steam Traction Engine

[Krypto]

Lots of work, but that really makes the gear train look realistic!

[Admiral_dk]

Beautiful Gears  + it looks like you have then Mesh really well too 

Per       

[raveney]

Wow, I really appreciate the positive feedback on how the gears turned out.
 

The mesh was set using the DRO on the mill and 1/4"dowels rather then the calculated pitch diameter and they do turn very smoothly. I spent extra time tapping the chuck of the rotary table true before cutting this set, and that seems to have made a very big difference. The 1916 Case catalog had a very detailed sketch of the gear train which I referenced for the different spokes and slots of the model.

thank you all for watching

[Kim]

Wow!  That's quite an interesting picture!

So, what's all the curved spring looking like stuff in that middle idler gear?  Is it like a cut-away view of what's inside the gear or something?  And is that bevel gear behind it?  Is it some kind of clutch mechanism or something?

Kim

[raveney]

Hi Kim,
I believe that is called the differential gear. Its explained well in another Case Owner's Manual online. Basically its similar to the detroit locker or posi traction in the muscle cars allowing one wheel to slip going around turns, but locking them together when inline.

I skipped a working version. Also skipped the clutch but want to figure out a way of disengaging the idler gear so the model could run while staying stationary; maybe just sliding it outward.

[internal_fire]

Basically its similar to the detroit locker or posi traction in the muscle cars

Actually the differential is much simpler. It merely allows the wheels to rotate independently in turns while driving both at an "average" rotation speed. There is no locking at all in the manner of posi-traction. If one wheel it in the mud and the other on solid ground the mud wheel can take all of the "average" rotation and spin freely.

The springs are just shock absorbers for the entire gear train.

Gene

[Kim]

Fascinating!  That's really cool.  I never realized that these traction engines had differentials. But of course, they'd need it! 

Kim

[Zephyrin]

I too made a 1/16 scale steam tractor several years ago, largely copied from Len Mason's Minnie.

A complicated set of pins allows to have either the 2 rear wheels coupled to the axle for straight running only, or only one wheel coupled to the axle, the other wheel remaining free for running in curves and finally a shorter pin, where only a cable drum is coupled to the axle, to pull a load with the cable with the wheel brakes applied...

Obviously it's quite inconvenient to use, and I must admit I don't play with it very often; I did a demonstration at my club a few weeks ago.

https://photos.app.goo.gl/Z7y6RQHvE7wFMwAk8

the differential gear was not present on some traction or ploughing engines, the picture below shows the dowels' disposition

[raveney]

Thank you for the additional information and correction

Hard to believe that a tractor that lived mainly in dirt fields didn't have a locking differential, but if I had bothered to read the catalog carefully I would have known that too 

Here is a video of a fellow that made one that works on a Burrell tractor
<a href="https://www.youtube.com/watch?v=O7qYsHtSlTM" target="_blank">http://www.youtube.com/watch?v=O7qYsHtSlTM</a>

[internal_fire]

Hard to believe that a tractor that lived mainly in dirt fields didn't have a locking differential, but if I had bothered to read the catalog carefully I would have known that too

The differential did not lock, but there was a lock available.

Starting from the gear attached to the clutch there was an idler gear and the ring gear around the outside of the differential. These three gears were constantly in mesh, with no way to disengage.

The left-side bevel gear on the differential was keyed to the countershaft. The left end of the countershaft was rigidly attached to the left pinion. The right-side bevel gear on the differential was directly attached to the right pinion. The right pinion was mounted on the countershaft, but it was not firmly attached to the countershaft. It could rotate freely. Both pinions directly drove their respective bull gears.

This arrangement provided the typical differential arrangement allowing the wheels to move independently as needed.

Locking the wheels was provided by the rear axle.

In normal operation the right wheel was pinned to the rear axle and the left wheel was free to rotate on the axle, with only a keeper to prevent the wheel from falling off. The pinions drove both wheels (separately). The axle did not provide any motive torque.

To lock the wheels a pin was inserted into the left wheel keeper in order to lock the keeper (and axle) to the wheel. Now both the left and right wheels were locked to the axle. The differential played no real part in the locking, but of course it continued to provide the drive to the pinions and bull gears. The axle could carry a lot of torque if one of the wheels wanted to slip or virtually none if the wheels were both on firm ground.

I suspect the springs in the differential functioned both as shock absorbers and as slack to accommodate possible rotational misalignment from the rather crude axle locking system.

Gene

[raveney]

Hello again,
Traditional looking fasteners were made to replace temporary screws in several places as I needed to lock down the side "horn" plates to the engine. Had to fill in a shaft hole that was drilled earlier at the drive pinion. I opted to use bronze TIG wire and clamped the thin sheet to a brass backer bar to avoid distortion.

Then made the shaft bearings and riveted them to the sides after careful alignment. I gave a small radius feature to each on the visible inside face. This was for looks and because the rivets I had were too short for a full width bearing.

Next I will attempt to replicate a functional clutch so the boiler can steam while remaining stationary like the real one. Several iterations of design, but decided to clone the real Case clutch design after considering the theoretical friction of the thrust bearing versus clutch shoes.

I don't know if this will work, but it looks feasible so far.

[Kim]

That clutch will be a great detail on your tractor!  Very interesting! 

Kim

[crueby]

Thats prety cool - how does the cluth get engaged? Does the gear/hub slide on the axle?

[raveney]

Yes the pinion gear is connected to the center link that slides over the crankshaft. The center link spreads the rods to force the clutch shoes against the flywheel.
It seems to function as tested here...
<a href="https://www.youtube.com/watch?v=YRN3ubRRd6c" target="_blank">http://www.youtube.com/watch?v=YRN3ubRRd6c</a>

[raveney]

I attached a marked up copy of the CAD model showing the direction of force vectors. I sketched it out as a determinate statics freebody diagram and calculated the shoe friction forces and it seemed that the smaller the angle is between the spoke plane and the rods, the higher mechanical advantage the input force had. This way the friction when pushing against the pinion gear hub doesn't kill the engine rotation much.
I hope to refine the engagement mechanism  so a scale lever will engage and disengage the shoes. Right now the "clutch fork" wants to walk out of engagement as the pinion rotates against it. The real one would have a thrust collar here I believe?