Someone asked me if I knew where I could find a pattern for a double-fall marble game he saw on the Internet.
I Google searched this, including searching for the image, and all hits led back to 1 unit that was for sale on a web site called Zebrahall.com. This unit is no longer for sale on that web site. So, I don't know who the original designer was.
I have made many improvements to Dug North's marble automaton game, which you can see here.
What is different about this design is that the marble falls down two versus one incline. The cam lifters are also skinnier at about 1 inch wide versus the 2 inch wide design I have been using. The cams are also a smaller diameter.
I took my improved Dug North design, and modified it to match the double-fall design shown above. I entered it into Google Sketchup.
Of course, you don't really know if the design works until you build one
If I get time, I will build one of these.
I put my design into the Sketchup Warehouse for others to use.
The routed track for the 2nd fall of the marbles is hard to make. You have to set up the router table, take a couple of passes, then do 2 angled cuts on the table saw.
It might be simpler to just use an angled piece of wood for this track. I modified the design to show this. This design requires no router to build.
Lot's of Trial & Error Required
I went ahead and CA glued the center section together. Then I took it to the miter saw, and kissed both ends so they were all the same length.
I then tried out the marble game. I had all kinds of issues with my original design.
1. The marbles got hung up after the 1st fall. I had to add clearance in the middle
divider to allow the marble to go around the bend. The 18 degree angle on the
top turn-around did not work either. I ended up doing some angle
experiments and determined a 5 degree compound angle works the best.
2. The marbles got hung up after the 2nd fall. I had to add clearance in the same
middle divider as above. I also changed it to a compound 5 degree angle.
3. Because I changed to a compound angle, the triangular piece the marble rides
on for the 2nd fall also had to have its angle changed.
4. The marbles got stuck on the driven wedges. I started with a 3/8" offset on the
cam (distance from center of cam circle to actual driveshaft hole). The lift
is twice the offset distance, so my initial design was a 3/8" offset which gave
a 3/4" lift. I changed to a 1/2" offset which gave a 1" lift.
I ended up breaking the CA glue joints in the center section by applying a chisel on the ends, then sanded off the CA glue. On an experimental project like this, I should have used a little hot melt glue, or just a few spots of CA glue.
Here are two photos of the experimental set-up I used to optimize the design:
Updated Sketchup Drawing
I updated the Sketchup file to show all the design mods I made to get this working nicely.
The sketch below shows the compound 5 degree angles..........
Experimental Mode Video
This video shows how well the game operates after all the trial & error work was completed.....
Final Glue Up and Clamping of Center Assembly
I got out the old fashioned wood clamps because I could rest them on the assembly table while I clamped it (I could not do this with newer steel clamps).
Stain and Varnish
I did 2 rounds of 220 grit sanding and a coat of polyurethane. Here are the parts on the drying rack.
Here are all the pieces required to build 1 double-fall marble game (except the 7 dowels)...........
Baking Parts (not Cookies)
To speed up the drying of the stain and 2 coats of polyurethane, I bake the parts at 100 to 150F for 10 or 15 minutes at a time. If you use higher temp, or bake longer, you will probably get bubbles in the polyurethane. I often put the small parts on a piece of scrap wood to act as my "cookie sheet".
Adjust Lifter fit after Varnishing
The lifters have to be just loose enough to function properly. 2 coats of poly adds some material to the lifters. It is hard to tell just what the right amount of sanding is to allow for the 2 coats of poly. If the lifter fit is too sloppy, the game won't work right either. I usually end up doing a last trial fit, and sanding any lifters that need it.....on the belt sander. I apply Johnson's wax to the lifters, and any areas I sanded off. The resultant color of Johnson's wax on the wood about matches the golden oak stain color.
I made a Youtube video of this marble game in action.........
I updated my Sketchup model to include all of the revisions. You can download a copy here.
Once I got the trial & error development work done, this was a fun project to build, and even more fun to operate
This game should keep the grandkids entertained a little while