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Pyramid Ball Game

After completing the very difficult hand-cranked worm gear marble lifter mechanism, I decided to tackle something much easier. This book has a lot of neat plans, including one for a wood ball mechanism.

Wood Balls

I could make the 9 balls with 1.5 inch diameter and the 5 with 2.0 inch diameter, but I would rather buy them versus spending all that time on the lathe. I bought them from one of my suppliers I use for wood components, American Woodcrafters Supply.


I always put the pattern design into Sketchup for 2 reasons..............1 is to get familiar with the design...........and the 2nd reason is to find mistakes.

The book recommends making the base plate from 1 piece of 5/8" thick wood, drill the 9 holes, and then use a combination of Forstner bits and hand carving to remove material in the center to give the balls clearance to turn.  Since I am not a hand carver, I am going to change the design/process.

1. make 2 blanks.  One will be 1/4" thick and the other 1/2" thick.

2. tape the 2 blanks together and scroll saw the 2 outside curves.

3. drill the 9 holes

4. separate the 2 pieces. Scroll saw the middle clearance area

5. glue the 2 pieces together

6. drill the horizontal hole for the crankshaft connecting the 3 middle balls.

In Sketchup, I noticed there was almost no material left between the ball holes using a 1-3/4" diameter bit.  I have a 1-5/8" forstner bit which should work better and leave more stock as well.  Maybe the book author did not a 1-5/8" Forstner bit, just a 1-3/4" inch bit?

It is a common practice in scroll sawing work to stack several layers, tape them together, so you can cut multiple pieces at the same time. Going to use that concept on this project.

2 Pieces taped up

Sketchup print-out glued to 2 pieces

Drilling and Scrollsawing Completed

Glued and Clamped

Drilling the 1/4" diameter shaft holes

I put the piece vertical in a vise on the drill press and drilled the first hole depth. The bit is not long enough to  drill the whole distance.

I put the piece in the vise and tried to eyeball drill the rest of the way through using a long 1/4" diameter 16" long bit............and I failed miserably !!  Had to ream the holes using the long bit to get a good dowel fit. I am not sure to improve the accuracy of this process.

Then I did the following process to drill the 1/4" hole in the balls.

-chuck in lathe and mark center with pencil and turn a little indentation in end

-clamp ball in vise on drill press, try to get hole vertical, drill through

I got lucky on the first ball and it had no run-out of the OD of the ball to the 1/4" shaft bore :)

But I failed miserably on the next 2 balls.  They would not spin freely in the 1-5/8" holes because of too much run-out !!!!!!!   I took them back to the lathe and tried to remove the high spots.

I have tried drilling in the center of wood objects using a drill press in the tailstock of my old 1939, and never had very good luck.  I tried it once again........

1. Chuck ball in lathe

2. Mark center with pencil while lathe turning

3. Stop lathe. Line up drill bit center on the center mark and bolt tailstock to bed

4. Start lathe. Push tailstock by hand, or use big Sears screwdriver to pry it into the wood.  My mechanism for using a handwheel to move the tailstock in is worn out.

5. Stop lathe and remove ball

I did 2 in a row and had zero run-out !!!!!!!!!  I will throw 2 bad balls away and lathe drill 6 more to get 9 total.   I am still surprised the 1939 lathe could drill in the center !!

Using a bigger 1-3/4" hole versus a 1-5/8" hole would give more allowance for run-out in the balls, maybe that is why the book author chose the 1-3/4" size?

And I thought this was an easy project!

Did not have enough clearance for big balls.  So flipped over and used Forstner bit to remove material, got enough removed for big balls to rotate...........but they don't because hit each other, lifting them off the center driving smaller balls??

I have small balls on 1- 55/64" centers in both directions. Go back and check pattern from book.  Book pattern has 1-55/64" in both directions!!

In book, they use 5/8" thick base board and drill horizontal dowel holes in the center, which means the shaft holes are 5/16" down from top...........then they say to remove 1/4" in center...............leaving only 1/16" above axle center.

When I flipped my main board over, I started with 1/2 of 1/2 or 1/4" clearance. I had to remove almost 1/4 in center, which is 0 clearance to make balls fit..........which is close to the 1/16" in the plans.  Wonder why my geometry model is so far off from reality?

Now What?


1. make a new base and increase distance between the small balls.  But the larger the distance, the more clearance I need.

2. Reduce diameter of big balls so they don't hit each other. Don't know how to do this?   Searched Internet, no easy solutions

    to sanding a ball. Found unique way to make small balls on belt sander, basically cut cube and let it bounce around in box!

You really don't need the whole center section, so what if I make another base with more distance between small balls and try that?

I drew up a new base with a 2.0 inch center distance, and I cut out the middle section completely.  Let's see what happens :)

From a common sense point of view, if you are putting 2 inch balls on the 2nd layer, and you don't want them to interfere with each other, the center distance of the smaller balls needs to be at least 2 inches !


2 Inch OC for lower balls worked !!

I had to taper the 4 spots on the wood because the big balls were hitting them.

Material Selection

I assumed, that deadly word, that this was a simple model and it had been debugged by the book author, so I went with good maple for the base.  Usually, if I am inventing a new hand-cranked toy, I go with pine, then replace it after I get the model developed.  I had to throw the nice maple piece away. I grabbed a wide piece of what I thought was pine and cut the new base.........then I found out it was cedar, not pine !!  It is relatively brittle and broke after the holes were drilled, so I glued a piece of 3/16" thick Luan plywood on the bottom to stiffen it up.........and it is going to work.


I'm going with a dip in Mineral Oil on the whole assembly.

Updated Sketchup Design

I raised the base board up higher than the pattern to give clearance for your hand to crank the model. I also added my rotating handle which the outer piece stays fixed in your hand while you crank the model. I usually use an 1-1/4" diameter dowel for the handle, but for the first time I shrunk it down to a 3/4" OD dowel because the model is small.

Large Sketchup File Size

Whenever I use spheres or balls in a model, the file size gets huge and slows down the program. I wish I knew how to draw spheres that take very little memory. I googled it, but found no tips.

I ran an experiment in Sketchup. To draw a sphere, you draw a vertical line, say 100 inches tall. You draw a circle at the center of the line with a 50 inch radius..........erase half the circle.  Extend the vertical line some, then draw a circle perpendicular to the first circle. Click on the top circle OD, hit Follow Me key, and click on semi-circle below.

 The 2 variables are how many line segments you have on on the semi-circle and the top circle.  If you reduce these to 25 each, you get an ok looking sphere with a small file size.

This problem has frustrated me for several years, so I made a YouTube video on how to make spheres with small file size. You can use this link to watch this video.

Sketchup Warehouse

I uploaded my model to the Sketchup warehouse. You can use this link to see or download the file.

Model Performance

The first layer of 4 balls, before  you put the top ball on, works great. I noticed some of the corner small balls do not rotate at all. I'm guessing the axle geometry for the small balls must be perfect for all of them to rotate..............and my holes are not perfect due to the drill bit wandering.  When you drop on the top ball, it slowly rotates and I wish it went faster.

I found on a previous project where I was trying to drill long straight holes, one can use a different technique where you use square holes made by a table saw or router. You split the wood, make 1/2 of the square hole in each of the mating pieces, then glue the mating pieces together. You can the square hole the same size as the dowel diameter you want, or make it a little smaller, and the square hole will guide the drill bit straight.

Finished Model

YouTube Video

I made a short YouTube video of this model in action. You can use this link to see the video.

Closing Thoughts on This project

I thought this would be a super easy project, but boy was I wrong!

The first issue is that the pattern in the book is wrong, because it has the center distance between the 1.5" diameter balls at  1- 55/64" or 1.8 inches. This did not work because the big balls hit each other!!   Common sense says if the 2nd layer of balls has a 2.0 inch diameter, then the small balls should be at 2.0 inches.

The 2nd issue was the difficulty of drilling straight holes for the 6.5 inches across the base for the 1/4" dowels. I did my best, but had to "wallow out' the holes to get the 1/4" dowel to fit right.

The 3rd issue was drilling 1/4" diameter holes in the 9 balls with 1.5" diameter.  If you have too much run-out, the balls hit their openings and will not turn.  Figured out how to get my  old 1939 wood lathe to drill good holes using the chuck and a bit in the tailstock.

The 4th issue was with Sketchup. My balls used up way to much computer memory and slowed the program way down. I figured out the secret to make balls with small file sizes.........and converted this to a Youtube video to help others.

After I got it all built, some of the corner balls don't turn.  I suspect because my 1/4" axle holes are not perfectly aligned with the other axle holes.

If I built another one, I would try a long-hole drilling technique of making a square 1/4 by 1/4" hole for the 1/4" dowel (or make it 3/16 by 3/16" and drill 1/4" hole), using the table saw or router table. That way the axle holes should be perfect and the corner balls would rotate.

I think the grandkids will still have fun with it.

Project Follow-Up

I am curious to see if the game performs better if I make the 3 axles holes more perfect using the square hole method. I'm going to make a new base from pine and see how this long hole drilling method works.

I plan on using the router table with a 1/4" bit to make a 1/4" wide groove, 1/8" deep, in the top and bottom pieces. I need to have a good guide surface for the router fence, so I will make the blanks like this:

Planned Process

1. Make rectangular blank as shown above.

2. Print out full-scale pattern above from Sketchup

3. Using paper pattern, mark 3 slots on edges to be routed. Drill 1/8" holes where center of small balls is.

4. Route 1/4" wide groove 1/8" deep on both boards. Do test cuts first to set router bit depth so I end up with 1/4" deep square, test with 1/4" dowel.

5. Glue bottom and top pieces together. Align slots as close as possible.

6. Scroll saw curves on 2 ends, bore 1-5/8" holes, scroll saw inside portion

7. Ready to slide in 1/4" dowels into the small balls.

If I had a 3/16" router bit, I could make the slot 3/16 x 3/16", then drill with a 1/4" bit. I'm going to try just making the slot 1/4" by 1/4" and see how that works.

Starting to make square hole base

One hick-up I ran into was that my router table fence would not go big enough to route the middle groove, so I had to temporarily clamp a fence on to do the middle groove.

The fit of the 1/4" dowel in the square hole is a function of the dowel diameter and the square dimensions. The one square dimension has to be right, since the bit is sized to 1/4", the other direction is a function of how deep the bit it.

I set the depth as close as I could, but when I clamped the 2 halves of the base board in the vise, the first dowel would not fit.  The 2nd dowel, which had been sanded some previously, fit in with a lot of force.  I decided to quit on routing, glue up the 2 pieces, then run a long bit 1/4" drill through the square hole, and see how that works.

I saw several long-hole wood drilling youtube videos where people make the square hole a little smaller than the final size, then they drilled it.  The bit tends to exactly follow the square hole so it should be straight.

Drilling Square Holes

I drilled them with a 16" long 1/4" bit, and it hardly took any force to push the drill thru, since most of the hole was made. Boy, this is as straight of holes as I know how to make!!  It will be interesting to see if the straighter holes have any impact on the game performance.  Right now, I am waiting for some more wood balls to arrive for this game.

Smaller crank handle

I scaled down the crank handle I usually use with 3/8 or 3/4" driveshafts...........down to one for 1/4" driveshafts.  It worked very well for 1st pyramid model, so made 2nd one for this model.

Drilling 9 balls 1.5" diameter with 1/4" hole

Did same method as on 1st model:

1. chuck ball in lathe

2. turn on lathe, pencil mark center, shut off lathe

3. Spur 1/4" drill bit in tailstock, slide tailstock up and put spur in center of marked circle, tighten down tailstock

4. Drill hole using big scewdriver to push bit into headstock

5. Remove ball from lathe, drill in bench vise rest of way through

2nd Model

This one works better in terms of......

-more of the lower layer balls turn

-2nd layer turns better

-top ball turns better

A couple of the lowest corner balls don't turn 100% of the time, but it is because the ball is driven to the outside edge by the 2nd layer ball, and there is not enough friction to spin it.

With 1.5 inch balls and a 1.625 hole, the balls can move 1/8" to the outside.  I'm not sure of best way to fix this, maybe on the 4 corners the center of the holes should be shifted 1/8 towards the center?

YouTube video on how to drill a long and straight hole in wood

Finished 2nd Model

2nd Model in action

Closing Thoughts on this 2nd Model

I like the trick of making a square hole very straight, then drilling it.  I will use this on future projects where I need a long and straight hole.

I will probably give the balls 1 coat of mineral oil, just to protect them from dirt and smudges.