The William Harris Steam Donkey Engine in 2.5 inch Scale

[Pipescs]

Caught a mistake earlier this evening and worked it out.

I have received a few more references from contacts. I really like the look of the original cast Drum Side Frames. And since I plan on this being one of the six patterns I make for this project, it is doable. Not totally to scale just to TLAR Standard.

Also a few drawings that showed how the cylinders were bolted to the frame.

[Pipescs]

Gear Talk

Morning all, I should be in the shop on the Forney but have to run to town to pick up new car tires later.

This morning's question is for the engineers out there.
The original 1.5 inch project by Bill Harris used a set of gears sold by Boston. They were the NA 90 and NA 22B with a Pitch Diameter of 4.5 and 1.1 inches. I originally thought I would just buy gears at twice the size. While the NA 180 was the right diameter, it has five slender spokes that will not support the clutch as Harris designed it. There is no direct 2.2 pitch diameter gear available, only a 2 inch. The biggest problem with this idea was the extremely high cost of the gears in that range. If they were available the cost would be over $600.00.

This led the local discussion of making the gears in shop. I have all the tooling needed and Spur gears seem to be a fairly straight forward project. Thinking I would go this way I was once again stunned at the current cost of nine inch diameter cast iron disk or rods.

Having made a number of wheel patterns for projects the plan now is to make the patterns and do the castings for the drum gears, drum clutches, drum brakes, the engine flywheel and the drum side frames.

So this becomes the question for the engineers out there. The original 1 1/2 scale gears were 20 Diametral 14-1/2 degree Pressure Angle. Should I stay with this when scaling up to a nine inch gear or would it be better to go to a 16 D.P?

Original Gearing.JPG (17.29 KiB) Viewed 5191 times

Original Gears from a photo

[Soot n' Cinders]

I doubt we’d be able to wear out cast gears. The trick would be machining them. I don’t have a gear hobber!

[SZuiderveen]

Charlie

It seems from the drawings that Bill Harris’s original gears were oversize. In 3 inch scale, scale gears would be a little less than 7 1/2” PD. In 2 1/2 inch scale, scale gears would be 6 1/8” PD. I think there’s room for modification here

Tristan, the problem isn’t getting the gear cutters, what’s going to be required is a dividing head. As Charlie has already pointed out to me, the gear cutters can be gotten from eBay without buying a complete set.

I just double checked my Boston catalog. Charlie has been looking at the spur gear section of the catalog. Perhaps we should be looking at the change gear section of the catalog.

Steve

[Fender]

I think you should consider buying the pinion gear and making the larger gears from a casting. The smaller pinion should be less expensive, there are fewer needed, and a different cutter would be used anyway, because of the more “open” angle of the teeth. Also, the smaller pinion could be made from steel to run on the softer c.i. gears. Lastly, the pinion could have an odd number of teeth to equalize the wear on the gear, since different teeth would be meshing on each revolution, assuming the number of teeth on the gear was not a multiple of the number of teeth on the pinion.

[Pipescs]

I doubt we’d be able to wear out cast gears. The trick would be machining them. I don’t have a gear hobber!

But of course, you know someone with one.

I spoke with Steve on the gears. I priced the gears on the sheet above and the ones we would need are just under $300 each. I will keep this in mind and draw the plans to be able to use a casting or to order a gear to machine. This still leaves the need for the cast iron disks for the clutch plate and brakes.

More later, Down to the shop on the Forney. May is fast approaching.

[Harold_V]

The trick would be machining them. I don’t have a gear hobber!

I've done precious little in the way of making gears, as the work I've done in my many years in the shop didn't require any. I know little about gears as a result. However, that hasn't stopped me from making a few, and I've yet to purchase a cutter. It's not that hard to hand grind a single profile (think fly cutter) to shape a gear tooth, and that's exactly what I've done on the few occasions that one was needed.

If the material to be machined is gray iron, assuming it's not chilled, or impregnated with sand, fly cutting the teeth would be quite easy---just a slow process. If one has a dividing head at one's disposal, that's half the battle. Great way to go for the guy with more time than money.

H

[Soot n' Cinders]

A fly cutter wouldn’t be hard, I only have a conventional rotary table though but it can be made to work. Just gotta have meticulous counting for however many teeth there are

[Harold_V]

A fly cutter wouldn’t be hard, I only have a conventional rotary table though but it can be made to work. Just gotta have meticulous counting for however many teeth there are

My most recent project was a ten tooth gear, to replace the one I wore out on my Harbor Freight mixer. It is the gear that turns the drum. I use the mixer to tumble scrap steel and iron to remove rust prior to melting. I used my rotab, but being ten teeth made it easy (no need to set anything but degrees). The the gear was made of steel, not iron. Indexing was a piece of cake, and cutting turned out quite nicely. I roughed the gullets with a side cutter prior to using the fly cutter. Made it go a lot easier--although in gray iron it may not be necessary because of the ease of machining.

I'll try to remember to upload a picture of the setup. A bit of work for me, as my camera (an older Sony) does not communicate with my computer.

H

Edit:
Ok, for what they're worth, here's three pics of the setup, flycutter and gear.

Note that the fly cutter has the form ground only on one side. By making the second cut on the back side, the same tool can be used for both faces of the teeth, and that helps tremendously in reducing area in contact with the tool. Beyond that, any time you can avoid a wedging cut, it's to your advantage to do so, as that type of cut tends to bind the tool in the cut and increase cutting pressure immensely.

The gear in question mates with stamped teeth on the periphery of the drum. They are far from precise, so I didn't lose too much sleep over the tooth form. In fact, the tool was ground to the form presented in Browning's catalog. Close enough for such an operation, and it works like a charm.

[milwiron]

Unless you need to do compound indexing simple gears are pretty easy in the shop, single pointed or milling cutter. I did many a number of years ago the worst being a 101 tooth gear that I compound indexed on a 40 turn dividing head. It was a change gear for a 60 year old G&L vertical gear hobbing machine.
Other options would be waterjet or laser cut from plate. I've never done a gear either way but did cut a couple of different size motorcycle chain sprockets for a friend on a waterjet out of prehard 4140. He ran one of the sprockets for years.
Waterjet with minimum kerf taper specified would get my vote. You wouldn't want to use one for a precision gear train but for a low speed open-gear donkey engine they'd be fine.
Denny

[Soot n' Cinders]

Unless you need to do compound indexing simple gears are pretty easy in the shop, single pointed or milling cutter. I did many a number of years ago the worst being a 101 tooth gear that I compound indexed on a 40 turn dividing head. It was a change gear for a 60 year old G&L vertical gear hobbing machine.
Other options would be waterjet or laser cut from plate. I've never done a gear either way but did cut a couple of different size motorcycle chain sprockets for a friend on a waterjet out of prehard 4140. He ran one of the sprockets for years.
Waterjet with minimum kerf taper specified would get my vote. You wouldn't want to use one for a precision gear train but for a low speed open-gear donkey engine they'd be fine.
Denny

Water jetting is an interesting idea if it can be made to work with the clutch mechanism Charlie is designing. The machining work needed for the clutch would make me leery of prehardened but I doubt we would ever run any of these engines enough to wear out cast iron or mild steel gears anyway. They'll probably spend most of their life riding around as show pieces.

[milwiron]

I agree, in this instance I don't see a need for prehard. The rear chain sprockets I jetted were a different story plus we had a ton of prehard drops laying around.
Denny