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Thread: Model Steam Donkey Engine

  1. #1
    Join Date
    Mar 2008
    Location
    Barrie, Ontario, Canada
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    4,714

    Default Model Steam Donkey Engine

    Now that I have the capability to cut spur gears, (I just purchased a complete set of 24DP involute cutters and an arbor)I have been searching thru all of the Youtube postings of Steam Donkey engines, and decided that there are many different types and configurations of said engine. I think I would like to try building one myself, and of course I will post build drawings as I go along so that others may join in the fun if they wish. I don't have any experience with donkey engines, and I don't have one close at hand to run out and measure, but that probably isn't as large an issue as one would think. I have found a youtube video which I will post a link to, and it shows the one I may try to design/model/build. This much I understand---there is a double acting cylinder on each side. The crankshaft is actually a long pinion-shaft that reaches from side to side, and since the engine would have to be self starting, the crank throws will have to be 90 degrees out of phase. I know that the pinion and the very large gear are constantly in mesh, and that the big gear is fixed to the large winch shaft so that the winch shaft turns whenever the engine is turning. The winch itself is supported by bearings which "float" on the main winch shaft, and there is a clutch mechanism (which is explained very well in captain Gerrys article) that transmits torque from the main shaft to the winch drum. This clutch mechanism is operated by a manually engaged lever.---I think the lever and clutch mechanism only has to be at one end of the winch drum. I can't see any good reason that this engine would ever have to go into reverse, because when cable is pulled off the winch drum, the drum can "free-wheel" to play out the cable. Some of this type of Donkey engine was used in mine hoists, and consequently had a large ratchet and paul assembly, but I don't think that was needed on a Donkey that winched logs across the ground. Also, Jerry makes reference to an external band brake which gave him difficulty, and I'm kind of wondering why it was there. To the best of my knowledge, this type of winch only pulled, as you can not push with a wire cable. why then have a brake on it at all? I welcome all discussion, as I'm just getting my head into this thing now. I am not trying to steal any of Captain Gerrys thunder, as his post and machine are excellently done, and mine will be somwhat different. Comments and helpfull hints or theories please.----Brian Rupnow
    http://www.youtube.com/watch?v=VM3qR...layer_embedded

  2. #2
    Join Date
    Mar 2008
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    Barrie, Ontario, Canada
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    I have been setting here eyeing all of my models, and I keep going back to the Popcorn engine. It is such a smooth runner, and I already have it modelled and detailed. With a bore of 1/2" and a stroke of approximately 1" it is close to the right size. There is a potload of work in that crosshead guide, but it does work so well-----. I really like the shape of the cylinder, and it would be very easy to complete in right and left hand versions to make up a twin cylinder engine. I think I will stick with the single drum version, as per the video posted in my very first post, with an internal expanding clutch ala Captain Jerry, and an external band brake courtesy of yours truly. The flywheels would become much smaller, in fact virtually dissapear, but thats not such a big deal with a twin cylinder double acting engine with the crank throws offset 90 degrees. When I built the Popcorn engine, I was workingf from Stews early plans and converting them to British Imperial, however I got ahead of myself and forgot to "unmetricize" the crank throw, making for an very unususl stroke length of 0.984". If I use that engine as the basis for my Donkey, it would give me a chance to correct that.

  3. #3
    Join Date
    Apr 2008
    Location
    winnipeg/manitoba
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    149

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    I have little that might be construed as useful comments or hints, other than to express my amazement at your ability to develop, and complete the array of engines that you've made! My hat is off to you, and your time management skills! By the by, where did you settle on for purchasing your gear cutters and arbor?

  4. #4
    Join Date
    Mar 2008
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    Barrie, Ontario, Canada
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    Bought them thru http://www.traverscanada.com/index.asp Good speedy service, reasonable quality parts.

  5. #5
    Join Date
    Nov 2009
    Location
    Winchendon MA
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    755

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    Brian PM sent.

  6. #6
    Join Date
    Jul 2007
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    1,502

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    Brian, there were quite a few variations on the donkeys, depending primarily on the size of the "show," the type of rig,and the size of the logs. With REALLY big stuff, there was a triple drum unit, as the haulback was so heavy, it had to be powered out to the limit of haul.
    In Scotia, CA is the biggest donkey rig I have ever seen. The boiler must have been nearly 8 ft in diameter and 20 ft tall. this unit was used in hauling redwood, back when an 8 ft diameter log was nothing special.
    I bought W. M. Harris's book from Village Press. It is a double drum unit with 1" cylinders. It is an excellent book and well worth the investment. He, unfortunately, used Stuart cylinders, and when I priced a pair, I nearly choked-160 quid, plus postage, for a pair of pokey little cylinders, covers and steam chests! ANYWAY, I am convinced that a DETERMINED DESIGN INJUNEAR could fabricate a pair from brass bar stock and a little silver solder. Oh and he bought the two gear sets, but YOU can cut your own .
    By the way, in central Vancouver Island, "back in the days," a single "side" with a donkey setup, would clear a semicircle of 1200' radius. Back in 1963, I saw an abandoned donkey sled at Kelsey Bay. The "runners" were logs over 6' in diameter and perhaps 60' long. The spreaders were 2' square, mortised into the runners.
    Good luck and keep us posted. Hint in advance: REALLY nice cable would be downrigger line-multistrand stainless and VERY flexible. That is NOT freshwater downrigger gear! Know anybody on the west coast?
    Duffy, Gatineau, Quebec

  7. #7
    Join Date
    Feb 2004
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    199

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    Here is a link to one being built that might give you some ideas.

    http://www.homemodelenginemachinist....p?topic=9212.0

  8. #8
    Join Date
    Mar 2008
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    Barrie, Ontario, Canada
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    Scale and proportion---Where do I start? Well, the stroke of my engine is going to be 1", so the crank throw will be 1/2". If you look at the "flywheel" end of the connecting rod in the video, you will see that where it connects to the "flywheel" is about 1/2 way between the center and the outside of the rim. That would make the "flywheel" 2" in diameter. The main large gear appears to be about twice the diameter of the flywheel, so that would make it 3 1/2" to 4" in diameter.The length of my cylinder is fixed, to accomodate the 1" of piston travel, and the distance from the end of the cylinder out to the end of the piston rod at full stroke is now established by the length of cylinder and the stroke. In the attached picture, there is only a slight gap between the front of the boiler and the flange of the drum, which is roughly the same diameter as the large gear. The center of the cylinder is just marginally on the far side of the boiler centerline. The position of the crankshaft relative to the position of the large gear wheel and winch will be established by the pitch diameters of the large gear and the much smaller pinion gear on the crankshaft which engages with it. In both the video and the attached picture, the boiler diameter is equal to or slightly smaller than the diameter of the large winch gear, which makes it roughly 3 1/2" in diameter. The overall width of things will be established by how tightly I can fit the cylinders and valve bodies to the sides of the boiler. That gives me enough information to start laying out the components. I will make a preliminary layout, then compare it to pictures and videos of old existing full size Donkey engines, and move things around until get a good visual match. Thats how i start a project like this.

  9. #9
    Join Date
    Jul 2007
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    1,502

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    Dont forget to allow for some boiler lagging, at least 1/4" thick.
    Duffy, Gatineau, Quebec

  10. #10
    Join Date
    Oct 2002
    Location
    Cheyenne Wyo
    Posts
    643

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    There's another youtube video that shows a hoist engine, posted by Stonyson, that might explain the extra brake. Not exactly a donkey engine, but also used for logging. Looks like they can pay out line off the drum by letting it freewheel, but control the speed with the brake. I couldn't tell if it was an external band or not.

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