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Originally Posted by mjefson
I like the idea. What scale are you thinking. I recently redid the pattern for my John Deere 6600 Combine and drew all the interior pieces. I have not done all the shafts pulleys counter shafts and chains yet but really interested in your idea. Here is a 1/32 scale and 1/64 scale photo of the outer shell.
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Oh, I hadn't really addressed the scale issue yet... I was considering prototypes and which would be best to model... I'd think aiming for a model about a foot to foot-n-a-half long would probably be best... large enough to see, small enough to model and the parts not be too heavy to turn/reciprocate...
Then there's the issue of finding small gears and such. Pulleys can be constructed from heavy cardstock or even wood or plastic as needed, but small gears and chains/sprockets to turn things like the bed augers under the concave on conventional walker-type Deere combines would be more of an issue... those would likely need to be "off-the-shelf" hobby-type parts... and finding a small electric motor with sufficient torque and the correct speed to turn the combine thresher at a sufficiently slow "scale speed"...
When I was considering prototypes, I have two that instantly jump to mind, mostly because of my own experience and access to the prototypes-- We still have our 1972 Claas "Senator" (sold in the US as a Ford "640"), which was a conventional cylinder and concave/straw-walker type machine. The other possibility is the BIL's 90's model Deere 9600 conventional/straw-walker combine... The main difference between the two (other than sheer size-- back in the day in the early 70's, the Ford 640 was one of the largest combines you could buy in North America-- now they don't even make one that small... hence "scale" will depend greatly on the proportion of the size prototype one chooses to model the size of the finished operational model one envisions-- ie the later model combines are SO much larger than even the "big combines" of the 70's or 60's that the size of the finished model, and therefore the scale chosen would be considerably different depending on which you chose to model). I have all the books on the Ford 640 and can measure things like pulleys on the real combine in the barn and "reverse engineer" the actual speeds of the shafts/pulleys based on known speeds or "chosen speeds"-- ie the book says to set the combine engine governor to achieve 200 RPM on the straw walker crankshafts at full throttle/no load speed (thresher and header engaged but sitting and not harvesting crop). The rest is just math-- ie if the straw-walker drive pulley is say 30 inches in diameter and the cleaning fan pulley is 6 inches in diameter, and both are run off a common belt (they are on the Ford) then the fan speed is 30/6 X 200 or 1000 RPM; the clean grain and tailings auger are driven by another pulley running off this same belt (can't remember the pulley size offhand but say it's 10 inches, then the auger speed would be 30/10 X 200= 600 RPM (but there's sprockets from that pulley to both augers, so I'm sure there's another "gearing down" through the sprockets driving the augers, which would be taken into account as a "compound gear drive" or modeled with correctly scaled chain/sprockets or something similar to get the correct speeds. The cleaning shoe eccentric bearing that oscillates the cleaning shoe and fan is behind the same pulley turning the straw-walker crankshafts, so its speed is directly tied to the straw walkers. The Claas used a grain pan to "shake" the grain back from under the concave to the rake and chaffer/sieves, so there would be no need for an "auger bed" like the Deere and IH combines used to move grain from under their concave and deliver the grain and MOG ("material other than grain" as modern combine design engineers call it, what we farmers call "chaff") to the chaffer and sieve...
Another issue that immediately springs to mind is "how to create augers"... Typical METAL auger flighting is made from straight lengths of flat iron strap material fed through a "spiral machine" (there's any number of videos of the process on YouTube) that forces the flat strip of steel "bar" or plate through a series of rollers that turn it into a curled spiral edge-up piece of auger flighting (something like a rotini pasta maker machine) BUT the difference is, metal is stretchable and bendable and compressible, paper is not. Typical "farm toys" make "faux augers" typically by having two halves of a plastic mold that make the auger by having a series of interlinking angled pieces like this "/\/\/\/\/\/\/\/\/\/\/" that give the "appearance" of a spiral auger... and for "kids toys" this is fine, but not particularly "realistic" for a combine model... I know there are a number of auger spiral calculator design programs on the internet that could assist in laying out the spiral from flat rings of material (which would be the easiest to do with paper-- make a series of flat disks that have a single cut across from the inner hole to the outer edge, which are then "opened up" into a spiral shape and glued together into an overlapping pattern to make the spiral auger flighting... the main thing is determining the correct "pitch" of the auger flighting (distance between flights, or how far sideways it moves the material in one auger revolution-- which isn't that big of a deal-- just the distance between each spiral on the auger tube...) The more important and difficult part is calculating the size of the hole in the center so it fits properly on the tube when the disk is "opened up" to the correct pitch of the flighting (since the hole "gets smaller" when the flat disk is twisted into a spiral), and of course the disk also has to be made "oversize" on the outer diameter as well, for the exact same reason... the outer diameter of the paper disk gets "smaller" as it's pulled into a spiral shape... so these calculations need to be either done online using a spiral calculator tool or empirically through trial and error on the workbench... A spiral layout design tool would be much easier though...
The rest would be just figuring out sourcing for the gears/sprockets/pulleys and belts (probably rubber bands). Of course the prototype and manuals probably need to be available, either online or nearby, so that proper sizes (and thus component speeds) can be determined.
The feederhouse chain and slat assemblies would be challenging as well (and a double challenge on a Gleaner combine, since they had not only the feederhouse chain-and-slat arrangement but the "grain raddle" assembly inside the combine itself as well... Then the other issue would be the clean grain elevator and tailings elevators, since they are also a "chain and paddle" type arrangement...
With the availability of access to the prototype for measuring (if possible) and access (either online or hardcopy) of the combine owners/operators manuals, it should be easily possible to "reverse engineer" all the speeds of the shafts and components in the combine by 'working backwards" from components turning at known speeds, simply by figuring the gear ratios (step up or step down) depending on the driver/driven pulley sizes and numbers of sprocket teeth on the driver/driven sprockets... once shaft speeds have been determined, it's possible to 'work backwards' from there to determine the speeds of everything else driven off that shaft or belt, depending on THEIR sprocket/pulley sizes, in a daisy-chain fashion until everything is "known" about what speed it's turning in full operation... Of course basically just making all the pulleys/sprockets the same size as the prototype will create the same gear-ratios in the model when it's operating... but it might complicate selection of "off the shelf" gears or components, which one could "make changes" and select different sizes/number of teeth on sprockets or gears depending on what's available and STILL keep the same (or very close) gear ratios by selecting the proper combinations of gears/sprockets, and thus get the correct model component speeds on the finished model...
For some things, like the cylinder speed, one would have to "choose" a threshing cylinder speed... for instance, if one wanted to model a soybean platform head, one would want to size the drive gear/sprocket/pulley to turn the cylinder at say 1600 RPM, while still turning the rest of the combine components at the proper speed (since combining soybeans requires you to speed up the cylinder speed with the variable speed drive). Obviously there won't be any "variable speed drives" on a model... If one modeled a corn head, the cylinder speed chosen would be more like 600-800 RPM, since that crop is threshed at a slower cylinder speed. A corn head would present some interesting design challenges, requiring several gear sets to make the gathering chains turn properly at the correct speed and driving the stalk rollers at the proper speed, as well as the header auger... A platform head would require coming up with a "wobble box", most likely made from a piece of bent music wire turning a loop or sleeve to make the sickle oscillate... making a cardstock sickle wouldn't be hard... sickle guards would be a little more daunting but more repetitious than difficult... The Claas had a "wobble bearing" (angled metal block with a large ball bearing installed over it) that oscillated the sickle on it, on the main header drive shaft, so it would be easy. Deere/IH combines using wobble boxes would be more difficult but not impossible to model, since they all work on the same principle... Heck some early model combines simply used a "crankshaft throw" or wobble on the main shaft operating a rod connecting to a 90 degree bellcrank to oscillate the sickle, which would be even easier...
The straw-walker crankshafts would have to be scaled and bent from hard music wire, like model airplane control rods, which is readily available at any hobby store. It's just a matter of determining the "throw" of the crankshaft and the timing of the walkers, and making two IDENTICAL crankshafts, one for the front and one for the back of the straw walkers... of course there's one throw per walker (so a four walker machine would be easier to make a crankshaft for than a five or six walker machine) and the throws need to be identical in size, so that they don't get 'closer together" or "farther apart" as the crankshafts turn in unison, with the walker mounted atop them... but that's easy enough to do... it's just bending wire with pliers after all... a pre-cut hand-drawn template would greatly assist the process I think and make ensuring they're both "identical" easier... Small paper "bearings" similar to the wood bearings typically used on combine straw walkers would be easy enough to make and glue in place... lined with soda straws or coffee stirrers for a slippery bearing surface IMHO...
The side sheets of the combine with all the locations of all the shafts (where the bearings would be on a real combine) would need to be carefully laid out and duplicated... either on two plastic sheets (to make it see-through so one could see the internal components operating) or make one side out of heavy cardstock or a similar suitable material (fiberboard) and the holes carefully drilled so all the shafts are "square" to one another and turn true... basically photocopying the pattern and adhering it to the parts while drilling hole locations would be easy enough to do... The rest of the sheet metal of the combine could be easily duplicated with cardstock/paper, and glued to the side sheets at the appropriate "weld" or "bolt" lines (with the appropriate glue of course). Shafts could be either metal wire or rod, wood dowel or plastic tubing of the appropriate size, or for large tubes, rolled from cardstock (platform augers for the combine headers, just like the real things rolled from thin sheet metal). I've already discussed the sizing/construction of auger flighting for the combine's header and internal augers... Straw walkers could be laid out and constructed from cardstock or paper, as the real things are made from mostly sheet metal bent/stamped to shape and welded together. Grain pans and auger beds/troughs can similarly be made from paper since again they're made from shaped sheet metal in the combine factory.
In fact, designing and building such a model would basically emulate the same procedures used to design and build the prototype, more or less... the electric motor driving the internal components of the model could be "hidden" inside the engine block and transmission/gear case of the model, and geared down appropriately, since it's obvious the model would be driven by an electric motor and not a diesel one like real combines...
It's an interesting project that I've been slowly tinkering with and have thought about quite a bit...
Later! OL J R
