Sliding shafts on trucks

[Glenn Brooks]

Hello all,


I need to fab up a pair of powered trucks for a loco Iam restoring. Only way to power the trucks from a line shaft, that I can see, is to use a sliding splined shaft, or a square sliding shaft to connect the engine output shaft with a right angle gear box mounted on the truck. like on a Shay. As the truck swivels thru an arc, the shaft needs to extend along the arc to the end of travel. Then retract into the spline at nadir.

Any suggestions or recommendations how to design and machine this to work?

Particularily, what minimum length of shaft engagement engagement should there be between a male and female parts to maintain the shaft connection?

Also, I’ve never machined a spline. Wondering what the angles and depth of the “grooves” are?

Thanks
Glenn

[jscarmozza]

Glenn, splines are a different animal; you will need a special cutter similar to an involute gear cutter to cut the male end and a matching broach to make the female end. The clearance and fits will give you fits, not something suitable for the home shop. The machinist's handbook has some examples of square tooth splines with a low number of teeth that can be more readily adapted to the home shop. John

[RET]

Hi Glenn,

You might try looking at Tol-o-matic's Float-a-Shaft for your application. The Tol-o-matic company has been around for a long time. Their "Float-a-shaft" is a right angle gearbox with two helical gears inside that give a 1:1 power transfer. The gearboxes have a grease fitting to allow greasing the gears and bearings. We used them at Corning and they worked very well with very little power loss. They are available with either plain bearings or rolling element bearings (ball or roller).

To make them work in your application, you cut a keyway the length of the shaft (or shafts) that you want the float-a-shaft to slide on; then you make a special key that has tabs on the ends that prevent the key from coming out of the float-a-shaft gearbox when it is assembled on the shaft. The shafts cross one another, ie. they are not in the same plane.

This should be a lot easier than trying to use splines, although they might be available from a bearing supply house if you looked hard enough.

Perhaps this might help?

Richard Trounce.

[Steggy]

Keyed Shafting
Splined Shafting
Solid Couplers

[Glenn Brooks]

So, also considering making a square shaft, such as found in the Shay?

Any disadvantages??

Glenn

[Glenn Brooks]

Keyed Shafting
Splined Shafting
Solid Couplers

BDD, thanks much. Wondering if the length is long enough to allow the shaft to slide in and out?

(Had a thought- what about pressing two of these, end to end, into a bored out tubing or pipe to achieve desired length??)

Glenn

[Steggy]

So, also considering making a square shaft, such as found in the Shay?

Any disadvantages??

I think square shafting is inconvenient in terms of connecting to other parts. Also, a square shaft is more likely to bind under load when there is sliding involved. Splines are much better for sliding joints—less sliding friction due to the involute spline tooth shape, and will last a lot longer, since the torque load is spread out among six or more smooth-sided spline teeth, versus four relatively sharp corners.

[John Hasler]

So, also considering making a square shaft, such as found in the Shay?

Any disadvantages??

Glenn

I have old farm machinery with square shaft couplers. I don't recommend it. It's only good for low speeds, binds up easily, has a lot of play, is noisy, and wears quickly.

Can you use a splined shaft salvaged from an ATV or something?

[Glenn Brooks]

Richard,

Just emailed Tolomatic to ask about their sliding shaft gear box. I think the shaft needs to move 2-3” in and out as the truck swivels. Thinking fitting an after market spline shaft would be much more resistant to wear and binding...

BTW, the more I look at these, the better they seem. A perfect solution for my trucks, I think! I’ll just make the drive shaft a few inches longer than it needs to be and let the shaft slide in and out of the fixed gear box, as the truck swivels to the side. SIMPLE!

Only took me weeks to think of it!

Many thanks for calling this out.
Glenn

[ccvstmr]

Glenn,

Had a small switcher years ago where a sliding 4-tooth spline. Consider this the poor-mans spline. Used a 1/2" square rod in a 1/2" square ID tubing. In other words, the square shaft "telescoped" inside the square tube. Don't believe there was ever a problem with binding. If you use heavy wall square tubing...you can probably install a grease fitting as long as that doesn't bear against the square shaft. File off any burrs on the square rod. Maybe even bevel the corners slightly. Just make sure the rod slides in/out easily. If your project is for something larger, consider upsizing to 3/4" square rod and tube.

In our application, the ends of the square rod were turned down to produce a 1/2" round which was pinned or welded to a universal joint. Used (4) U-joints to get from the driven jack shaft to a right angle gear assembly on the inboard axles of both trucks. Avoid sharp angle U-joint connections. The closer you can keep the drive line straight, the better off you'll be...but you still need to allow for truck swivel. Axle to axle drive used sprockets and chain. Would have been nice to use Tolomatics on the inboard axles...but there was no room to fit those in the space available.

If you've already been to the Tolomatic website, you've seen (as RET indicated) where their right angle gear boxes are available with bushing or bearing designs. Also have several different speed reduction ranges to choose from AND various drive/axle input/output shaft sizes. There's a lot of those gear boxes out there in the hobby. Just need to remember to periodically, get the loco up in the air and grease the gear boxes. If there's a "bleed screw"...remove that before you start pumping grease in. You can imagine what happens when there's a "goes in"...but no "goes out"!

Carl B.

[LIALLEGHENY]

Glenn,

Check out surpluscenter.com for shafting, gear boxes, etc....all sorts of stuff that might help you with your trucks, and other projects.

Nyle

[jkimberln]

What sort of diameter of spline and socket are you needing?

JerryK