Has anyone ever successfully rigged up a design to attach a treadle to a straight crank shaft? I just keep thinking that there’s got to be a way to do it!
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I have not done this. It shouldn’t be too difficult with a decent machinist. One would have to figure out the dimensions to get the correct throw.
It involves an eccentric. I do not have a drawing program to show an illustration, nor a scanner to show a sketch.
Visualize a pulley about 1 1/2” across the cheeks. The cheeks are of an appropriate diameter and bored at the center to fit the shaft. The center of this “pulley” is machined round, but eccentric. It has a shaft bore offset from that of the cheeks. An eccentric strap is fastened around the off center or eccentric portion. The cheeks and the eccentric may be machined from one piece or from three and fastened. The assembly must be fastened to the shaft. Maybe a Woodruff key. When the shaft is rotated, the strap oscillates. In actuality you want the treadle to move the strap to cause the shaft to rotate.
Regular lubrication required to the eccentric.
Any machinist wizards care to chime in?
There is probably another way to do it using a stub shaft attached to the flywheel. This has a specific name that I either cannot remember, or never knew. An appropriate crankshaft would be formed from about 3/4” bar stock. The treadle would be in the center of the press, but would transmit motion to the left outside the plane of the flywheel.
A rod would connect to the stub attached to the flywheel. The stub is eccentric to the flywheel center.
Very firm attachments must be made to the floor.
All this from my design theory prompted by the question. I have not done either.
If you take a look at the treadle operation and linkage on a Golding Pearl press, you will see something similar to what Inky is describing.
Re making a specifically NON treadle platen into a treadle platen, perhaps I cant see the wood for the trees, so somebody put me straight, by all means, and possibly help the one that really needs to know, in view of all the goobledegook about introducing an eccentric con rod onto an existing straight shaft (fine in the middle of the machine), but what is the other end going to attach to, on a machine with no corresponding counterpart? genuine treadle platens have a corresponding secondary crank pin attached to (as an eccentric) invariably, almost certainly, on the outside of the machine!!!! it cant work any other way LOGIC dictates, surely. How can you utilise your nicely fitted after market con rod, to a machine that wasnt designed as such. Would love to see a schematic diagram as to how it would be achieved. Once again do please correct me if I see it wrong, if some eccentric con rod is fitted to a straight shaft, in the middle of the machine, with nothing for the upper end to connect to, surely back to the drawing board? next if a crank pin was fitted to the fly wheel, without pear shaped protrusions in the spokes to accomodate threaded or bolted crank stubs , what would seem to be the only way to drive that? another shaft attached to the actual foot pedal, with a retro fitted primary shaft, plus wheel or boss to accomodate the primary crank pin, and how to fit that shaft, line bore the casting at the base? or fit outrigger bearings to very ancient cast iron, U bolts, braze, weld, steel plate under machine base with countershaft???? Any which way, would seem like serious engineering at presumably serious Dollars.
One other way to make it work would be to cut off the end of the crank shaft opposite the flywheel as close to the drive gear as possible while leaving enough to mount a steel disc about 6 inches in diameter welded onto a collar fitted to the shaft. Near the rim of the disc drill and tap a hole for about a 3/4 inch bolt (I’d use a longer bolt that has a straight section of the shank under the head about 2 inches long, and a lock nut on the back side of the disc to keep the bolt from turning). Then make a treadle with a configuration similar to the kind used on the Golding Pearl, with an attachment for a connecting rod outboard of the press directly under the bolt in the disc. The connecting rod would be pinned to the treadle with another bolt, with an eye on both ends of the connecting rod for the bolts. I designed a simple treadle made of welded steel angle iron for a 12x18 C&P so that part should be pretty easy.
Personally, after having only a treadle press for several years, I grew to like and appreciate electricity very much. I suspect your knee and hip joints would appreciate it also… something about repetitive stress injuries.
Ad Lib , that set up also describes adequately the drive of a peerless i once had but let go a while ago .
I have given this additional thought. Using an eccentric and an excentric strap to change rotational motion to reciprocal (probably called rectilinear) motion is proven mechanics. Going the other way from treadle to rotational via the same eccentric may be problimatical. At the minimum it would require a good spin of the flywheel to get the iron turning and be willing to keep turning as the strap attempts to turn the eccentric.
I would want to see this modeled up small scale before trying it on the press.
Inky HALF RIGHT but think it through? if the eccentric strap is in the middle of the machine, terminating in rectilinear motion, against an existing straight shaft, the only possible way to transfer rectilinear i.e up and down motion to rotary, would be to incorporate a cog, (acting as a pinion) on the straight shaft,and being driven by a rack, from your rectilinear thruster, but it would have to incorporate a free wheel on the return stroke, otherwise the top shaft would keep turning under flywheel inertia and rip the teeth of the rack or the pinion (cog) Just as a 45 second experiment, hold a piece of material (rectilinear rod) VERTICAL, !!! Place another behind HORIZONTAL (i.e.machine shaft, with cog) move the vertical rod up and down, whilst rotating the shaft in the chosen direction and observe the only way it would work, with the free wheel device, operating on the return stroke. PLUS in case U.S.A. Health and safety are on the case, give the initial impetus to the fly wheel, by pulling the fly wheel towards you, so that any mishap, throws your valuable hand and arm, out of the way rather than vice versa???????
It seems to me that the strap would cause a certain amount of friction which would make it less effective, and the fact that there would not be any downward drive from a strap encircling shaft and eccentric, as the strap would simply slide with no real force being applied to the mechanism; the shaft attached to the strap would mostly stay in the same vertical position. I think the old guys already worked this one out.
My husband is in the process of designing a prototype that seems to be working.. Will post pictures and diagrams when its done. Thanks for the input.
I think that it would make more sense to remove the straight shaft, cut a 2” section out of the middle, drop it down the same distance as on a crank shaft and then weld it back into place using 2 - 1/2” thick straight flat bars.
A bit tricky, but a good machinist and welder could handle the task. I plan to do one myself some time soon and will post the results - here and on my web site. This is a solution the community needs. I hope to be able to offer it as a service someday - IF it works…
I’d guess you might have trouble with strength of the weld or braze, given that the shaft is cast, and therefore more brittle, and subject to internal stresses from the heating and cooling, plus keeping everything lined up so the shaft is true could be tricky. Plus the joint will have potentially double the weight of the operator tweaking it on every start-up and stop of the press using the treadle. But I’ll wish you luck, Alan!
I believe that the shafts on C&Ps were/are steel, otherwise they wouldn’t withstand the constant wear. The curved shafts were probably hammered into shape rather than cast. I remember cutting the end off of a shaft (still have the scar), and it was much harder to cut than any cast iron with which I have come into contact. A well done weld will be stronger than the connecting metal, but you would have a hell of a time getting the right angles to be able to feed the treadle back through. I can’t imagine the machinist’s and welder’s bill, you will probably spend as much as you spent on the press, and have a less valuable press for your efforts. That doesn’t really change what Bob stated above about aligning the shaft. It is difficult to do and any variation will either cause wobble in the wheel, or in the connecting gear.
I’ve seen a couple of photos on Briar Press of C&Ps that were dropped or the flywheel hit somehow, and the shaft snapped off clean without bending — I don’t think forged steel would do that, and if you look at the crank portion of a press shaft it definitely looks cast to me. I believe they were perhaps cast steel, though I don’t know about the relative brittleness of that versus cast iron. In any case welding the crank in would be a “hair shirt”!
After having an OS 8x12 C&P take a fall down a flight of stairs and snapping the crank shaft in two, I can tell you, it is cast.
I have a quote from a machinist to have a new, straight shaft made to the proper specs (unless I can find one here from someone who has an 8x12 parts press).
re inky’s suggestions to natdeck re making a crank so that a foot treadle could be used on a clamshell press.
After putting the ideas and comments of others on the “back burner” for some time, perhaps I have been able to visualise what is suggested.
There is a problem with the word “strap” as the connection between the treadle and the shaft which is required to turn steadily in only one direction. If we substitute the word “belt” perhaps the picture becomes clearer?
Now for my try: draw two circles (wheels) on a sheet of paper, draw a belt connection around them so that if one wheel turns, the other will also. If they are of different diameters, they will turn at different rates, slippage neglected. Then, draw the shaft for one of these wheels (or flat pulleys, that will help visualisation) in the centre of that wheel. But, for the other wheel, draw the shaft as being part-way between the centre of the wheel and the circumference; then, as this wheel rotates, the circumference where it meets the belt will be at a constantly-changing radius. The other wheel will still rotate, but the position of its shaft in relation to the shaft of the eccentric wheel will be constantly changing. If force is applied to the shaft of the concentric wheel when it is moving away from the shaft of the eccentric wheel, that should tend to drive the belt steadily on its direction of travel. This arrangement of flat pulleys and a flat belt should do what is needed, but without facilities to experiment, I can only suggest that the belt should be of adequate size. The arrangement should allow the treadler to slow down the rotation in the usual manner.
There are several ways to convert linear motion to rotary motion. I had thought of using a bicycle chain and a bicycle ratchet cogwheel (sprocket) in a particular manner, but that would not allow the “slowing-down” action.
If you are really interested, try to find information about the first known machine which was not powered by animal (or human) muscle; it was a steam engine, invented in France to tow artillery pieces; look for the name Cugnot. The story included that a replica was built in U.S.A., and occasionally displayed on a road demonstartion, at various celebrations.
Look at the photo on j falstroms post golding pearl 3 its on the beginners section , there is a drive similar to that of the treadle peerless ,you have a balance weighted flywheel to get the inertia started ,it not the worlds best drive but it worked for many hand power machines .
Alan, the only trouble with you idea is that the various segments of the eccentric pulley/wheel would act as wheels of different diameters, so that the speed they impart to the belt would be different. This would mean that the driven pulley would speed up and slow down, or the driving pulley would have to. I’m not sure how comfortable or functional that arrangement would be.
Alan, the only trouble with your idea is that the various segments of the eccentric pulley/wheel would act as wheels of different diameters, so that the speed they impart to the belt would be different. This would mean that the driven pulley would speed up and slow down, or the driving pulley would have to. I’m not sure how comfortable or functional that arrangement would be.
Bob: It was just a suggestion, how much variation is there now with a conventional treadle? Would a flywheel make the shaft turn at a steady pace? I think it could not be rigged so that there could be a result of that elusive “dwell”? The relative speed of rotation of the shaft carrying the large pulley would depend on the relative masses and radii of the various parts, much too complex for my mathematics. A lightweight eccentric connected by a belt to a large mass in steady rotation could be expected to follow the dictates of the large mass [multiplied by the (technical) moment lengths]. Sorry I do not have the scientific words to describe the relationship, but I think you understand what I am trying to describe. Put it another way, visualise the large eccentric flat pulley as being made with a heavy concentric centre, and a light eccentric cam as the outer part.
The reason the C&P treadle set-up worked so well is because it was simple, direct, and efficient. If you examine the existing belt and pulley systems that are needed to operate a press I think you will find that you would be creating a system that would take much more effort to manually operate than you anticipate. As soon as you add another pulley into the mix you are forced to increase the momentum of the power source needed to operate the first pulley to transmit that power to the second. Considering the space you have to work in you would have to calculate the size of the pulley attached to the shaft, then determine the size of the second pulley needed in order to produce the revolutions needed to power the press. I think that you would end up with a pulley that is too large to operate in the space allotted. There are formulas for calculating the momentum gained or lost through pulley systems, and it would be worthwhile trying to calculate this before you commit to anything.
If you can pull either the drive gear or the fly wheel off, and place a one way bearing in the the middle, I think it would be fairly simple to make it operate similarly to a treadle. The only addition would have to be either a spring to return it to the top, or a strap over your toes and you’d lift it back to the top. That, and a small arm extending from the outer race of the bearing…
That’s the type of sprag bearing I’m referring to.