Jacob's Ladder

[b.lindsey]

Despite not having much time lately to work on the Wright Bros. engine, I have still had to be in the shop at work a lot to supervise the project prototypes going on this time of year and wanted a small project I could spend even a few minutes on here and there between answering questions and helping the students. One such project had been in the back of my mind since our engine show last fall...a fellow had build a Jacob's Ladder out of wood with a hand crank and using marbles to "climb" the steps. At the time I thought it could be adapted to metal and scaled down to be run from one of my larger compressed air engines. At the same time, I had always wanted to do something with a Geneva Cam mechanism and this seemed a good application for that, replacing the hand crank in the one i had seen at the show.

The basic design is a series of 10 steps operated by a simple cam from underneath, with the cam driven by the geneva mechanism on one end. I chose to scalel it down to a size using 1/4" steel balls instead of marbles, but think it  could be scaled to even half that size.

I have taken a few pictures along the way, not really a detailed build log but more to show the various aspects of how it works. Those will follow in the posts below.

[b.lindsey]

First up I cut the blanks for the 1/4" x 1" wide steps overcutting each lengthwise



Then i set the vise to mill the top  angle on each step, still leaving the overall length longer than needed for later trimming the flat bottoms to the exact length for each step




After the top angle and length were machines the steps looked like this, however i realized that I had intended to angle the tallest step in a secondary direction to faciliitate ball return so that one had to be remade.




The tallest step is shown below with both angles cut even though the side to side angle shows up more clearly.




This final picture shows the final step along with the one just preceeding it in the ladder....again the side to sidei angle was intended to help the balls feed into the return hole in the intermediaite side plate.

[b.lindsey]

With the steps done, I cut and milled to size the two end plates and the back plate and the rough layout looks something like this.



Each of the two end plates were then drilled for the 5-40 screws that would secure the main frame parts together and tapped ...a total of 8 holes per piece, four each on the front and bac side.



The holes in the next picture on the lower half of each end plate were drilled and reamed for the addition of bronze bushings for the 1/8" cam shaft

[chuck foster]

looking good bill, this little set up should have lots of eye candy 

chuck

[b.lindsey]

The next task was the intermediate side plate on the near side which finished enclosing the steps but with the addition of two angled holes, one adjacent to the top step at its highest position and the other adjacent to the lowest step at its lowest position...simply providing an exit and reentry point for the balls to recirculate. To get the angle, I figure the required height difference from one end of the plate tot he other and made a riser from a scrap piece of aluminum to raise the elevated end. Since the two holes were at equal angles but reversed directions the other hole was drilled the same way but with the riser block under the opposeite end.



Then the outer sideplate on the near side was machined to size, bolt hole pattern drilled and a trough milled out on the back side to provide a chute for the balls to travel down from the top hole to the bottom in the previously described part. This was roughed out with only the two end machined to a specific depth from the top of the piece to match the hole locations in the intermediate plate.



The vise was then set at the proper anlce to clean up the bottom of the chute as shown in the following picture.

[Don1966]

Gee! When you put your mind to a project, you don't waste any time Bill. I had just read you first post. I am curious to see this one complete.

Don

[b.lindsey]

With the main "box" done I turned my attention to the geneva cam mechanism which would drive the cam shaft and lobes raising and lowering the steps in alternating fashion.

The "driver" part of the mechanism was turned on the lathe first



I then transferred it over to the mill to locate and drill/ream a hole for the 1/8" pin for driving the other part of the cam.



This was set aside for a bit to get to the same point on the "driven" half of the mechanism...turning the outer dimension then milling the 4 slots for the driving pin to engage.



With that done, the back side was faced off to the final thickness needed.

[b.lindsey]

Bear with me Don, just taking some time to post everything up.

Bill

[b.lindsey]

To finish the two parts of the geneva cam, a couple of simple fixtures were needed for the rotary table. These are shown in the next photo, the upper fixture is for the brass "driver" part and the lover one for the "driven" part. The two pins locate the face between the slots for milling a radius in the correct position and the part can then be indexed to each of the four faces that need that radius. The 3/8"-16 SHCS is for securing each fixture to the threaded center hole of my Sherline RT. In the upper fixture a spacer had to be added underneath the part so it's diameter would clear the top of the SHCS.



The next picture shows milling the four sides of the "cross"

[Bearcar1]

This, is going to be way cool!   I *think* I see where you are going Bill, but am anxious to see the final result anyway. These sorts of Rube Goldberg types of things have always been fascinating to me both in there form and their simplicity. (Although the later can be debated at times  )


BC1
Jim

[Chris J]

Gee! When you put your mind to a project, you don't waste any time Bill. I had just read you first post. I am curious to see this one complete.

Don

I'm curious to know what it is 

[b.lindsey]

Thanks guys, I'm getting it posted as fast as i can

[b.lindsey]

A short note here on the geneva cam mechanism. I chose to use one with four index positions, although most any number can be used given shanges tot he sizes and geometries of the driver disk and driven disk. One can imagine that a 12 position cam would have a larger driven disk and a much smaller driver disk.  There is some information and videos one these if you google "geneva cam."  At any rate I chose a 4 index position for two reasons...one to act as a speed reducer....4 revolutions of the driver disk for each 1 revolution of the driven disk...and two, to provide a pause or dwell time at each position, mainly to allow time for the steel balls to exit when the top step reaches it maximum height and again when the lowest step reaches its lowest height to allow balls to re-enter.

OK...that said, it was on to making the lobes for the camshaft that will lift and lower the 10 steps. I cut and faced to a fairly precise length, 10 pieces of 1/2" dia bronze. They were then transferred to a set up in the mill to drill/ream the offset hole in each one as shown



As to assembling them on the camshaft, the first one was loctited onto the shaft and allowed to set. The arrangement is such that each alternating lobe is 180 degrees apart from the next. The second lobe was added then and my caliper jaws used to orient it such that they lined up 180 degrees out of phase.



Once these two were fixed, I could lay the assembly donw on a flat surface and add the remaining ones, butting each up against the next and alternating their ipositions. The final assembly is shown below as it fits inside the main box.

[Chris J]

Thanks guys, I'm getting it posted as fast as i can

It looks fabulous, whatever it is 

Great photography, what are you using ?

Chris

[b.lindsey]

These last three photos may help show how this will work.  The first and second photos show the cam with the steps installed in the two extreme positions positions. At each position different pairs of steps match up at their top angles allowing the balls to in effect roll downhill to the next step to the right, and at the same time going higher and higher up the ladder as each successive pair of steps match.  At 1" width for each step there can be up to 4 balls across on every other step ascending up the ladder. The final picture shows the geneva cam end though without the intermediate and outer side plates for the ball return arrangement.

I will note here that a little fiddling had to be done to the bottom of the steps to allow enough clearance for them to fall via gravity into the area between the lobes to either side. Likewise, the 1/4" steel balls don't have enough mass to traverse or skip over any mis-match from one step to the next so a little caareful filing had to be done there also just on the highest part of each step's angled top. 

That said it does work well so far. There are a couple of additions I want to make...a couple of feet for the while thing to sit on and an acrylic top so as to keep everything inside the box. The balls as well as the steps will fall out if turned upside down !! I also want to sand the outside so that all the various plates match up seemlessly just for appearance sake.  I will get it all assembled again this afternoon and try to take a short video.