How Much Drive Weight Does My Clock Need? Factors

Hello Clayton,

My grandfather is now reading your explanations and has a question about the weight that is needed for the copper weights.  Is it necessary that these weights are approximately 6 pounds and 1 pound (we don’t know the exact needed weight of the small contra weight) or can this also be different weights in the same equation? For example; 3 pounds and ½ pound.

Kind regards,
Genesis by Clockmaker Isaac Neuman (demonstrating weights)

Aloha Nick, in the Genesis design there is no weight in the small counterweight tube.  The Genesis counterweight tube remains empty.  The purpose of the counterweight tube is only aesthetic, allowing the clock to look balanced, and to keep the wind cord from tangling.

The large tube is the weight tube that contains the mass that drives the clock.  

As the clock runs, the drive weight slowly lowers toward the floor.  The Genesis is then rewound by pulling down on the counterweight tube while gently lifting the drive weight tube back up toward the clock.  As the clock runs the drive weight goes down, and the counterweight goes up toward the clock again.

The exact weight necessary to drive any clock is to be determined at the end of the build, and depends upon the craftsmanship that the builder has put into the clock.  Poor craftsmanship leaves excess internal friction in the clock's train, and good craftsmanship leaves much less internal friction.  It is the amount of internal friction left in each individual clock that determines the actual drive weight.

The Genesis's recommended "six or seven pounds" of drive weight is actually excessive.  My Genesis runs on about three pounds of drive weight, but because Genesis is a beginners clock, I expect there may be room for some improvement in craftsmanship, and I want everyone to be able to hear their clock tick.  A well made Genesis should run easily on half of the recommended drive weight, with zero pounds in the counterweight tube.

If a builder wants to know how much drive weight his clock takes to run, I have him add enough drive weight to get his clock running and then put a scale on the floor under the drive weight.  When the clock stops with the drive weight on the scale he can simply read the number of pounds of drive weight required off of the scale.  I then recommend adding back an additional ten percent of that amount to keep the clock running during humid days.

BTW, be sure to read over the section on "Depthing" in my FAQ's to help find and eliminate any residual internal friction that may be left in the clock's train.  

Three of the very best things a builder can do to get their clock running nicely is 1) following the Depthing procedure, 2) not get any finish on the tooth surfaces of the gears, and 3) not add any brass tube bushings unless specifically called for in the plans.

Enjoy!  Aloha.  Clayton


Tooth Forms, Including Involute Tooth Form

Bob L. emails:  Hi,  I am considering your Toucan clock plans.  I have a little past experience in gear design, and am thinking of making the gears by a different method than scroll sawing.  Because of this, I wonder if you tell me:
1)  Do the gears in the Toucan have the common "involute" profile or are they a different profile??
2)  What diametral pitch are gears in the Toucan??

Toucan by Jeff Hecht
Aloha Bob, it is nice to hear from you and I'm glad you enjoyed viewing my site.  The Toucan is a wonderful, fun and easy to build clock.  It's my top design engendering the creativity and personalization of the various builders.  You can see many of their delightful "brain children" in the Flickr' pool of builder' pix (link on the Toucan order page).  Those pix really are worth viewing for some great ideas.

And how can I say that it is easy to build?  Because when you are looking through the Flickr' pool of builder's pix the first one is of a 13 year old boy that successfully built the Toucan.  Of course, maybe he's just a genius(?).

Gear design is a very popular topic and lots of time is spent on gear design in engineering books.  I write many pages in my book about gear design as it relates to wooden clock building, and I really do need to create a blog post about the topic.

First we have to ask ourselves what the purpose of the gears really is, and what is their real function?  

We could simply have two circles turning edge to edge and get the same ratio, but without the addendums and dedendums (the uppity and downity parts of the tooth) of spur gears our circle gears could easily slip.  Slippage would cause a deficiency of the transmission of the driving force through the system, but more than that, in a clock slipping wheels would also cause the hands to show the incorrect time and even cause a desynchronization of the relationship of the minute to hour hands.  

However, that does not mean we cannot use edge driven circles in our clock designs.  Take a look at my Horologium and you'll see that the hour wheel is actually a pulley run by the drive weight cord.  The gear ratio is maintained by the barrel diameters of the drive pulley and hour wheel.  http://www.lisaboyer.com/Claytonsite/horologium.htm

So basically the "teeth" on a gear do two things for us; they efficiently transmit the driving force, and by doing so they prevent misalignment caused by slippage of the wheels.

When we are contemplating tooth forms for a particular mechanism, a couple other things that need consideration is the speed of transmission of the drive force, and the direction of that force through the gear train.  

In a clock the transmission of force is extremely slow.  In the normal grandfather clock the fastest wheel only turns one revolution per minute.  This slow transmission of forces allows for some very forgiving tooth forms.  There are medieval metal clocks that are still operational with simple triangular shaped tooth forms.  Some of the teeth in the very early wooden clocks were created with hand tools and look as though some teeth were hacked into shape.  These inefficiency of these irregularities and imperfections many times can easily be overcome with a bit more drive weight.  

It is only when we have gears rapidly moving together that we actually need the perfect involute gears with close tolerances that we've all learned about in physics class.  There are other very efficient ways of transmitting power through the system without the use of involute gears.  Take a look at my Vortex.  Vortex has straight sided teeth on all of its gears.  Straight sided gear teeth are about as far from the perfect involute curve as you can get.  Scroll down the page a little further and take a look at the side view and you'll see how I created the roller lantern pinions that perfectly match with the straight sided tooth forms of the wheels to give excellent power transmission and minimize contact friction. http://www.lisaboyer.com/Claytonsite/vortexpage1.htm

And the last thing to consider is the direction of the forces transmitted through the gears.  Clocks run in only once direction.  Clocks do not ever run in reverse.  That means that the back side of the gear tooth never gets used and can be created in any form that the designer favors, as long as it does not interfere with the incoming tooth from the other gear.  Most of the time we simply make it a mirrored reflection of the front side of the tooth, but that mirroring is not necessary since that back side of the tooth is never used in a clock.

Most all of my tooth designs are of a modified involute design because even as forgiving as these wonderful mechanisms are one of the goals of a good design is to try and decrease the amount of driving force required.  Involute-like teeth help with that, but as we've discussed above involute tooth forms have no particular spiritual holiness sent from the God of Physics.  This gives us a tremendous latitude in design.  We can make our teeth straight sided, curved sided, or perfectly involute, but I have to chuckle because whatever tooth form we choose, we still don't need the back of it.

Enjoy!  Aloha.  Clayton


The Tea Dipper

New!  Clayton's uber-cute, animal-interchangeable, smile-inducing, tea dipping machine!  Plans available now at www.lisaboyer.com 

Our friend Adrian Iredale has been as busy as a Christmas elf making this hand-cranked version for his family for Christmas Day:

As usual, Adrian did such a wonderful job on his video (and I just love his accent, don't you?), and look at his googly-eyed bear!  Thanks, Adrian, for being the friend and intrepid test builder that you are.  If you like this video, you should check out his YouTube channel, because he's quite the builder of...well...everything!  Watch and be amazed: Adrian Iredale Videos on YouTube

Happy Holidays from Clayton and Lisa Boyer!  


Happy Holidays from Boyer Designs!

New!   The Tea Dipper kinetic sculpture--this is the Holiday Version.  Plans available VERY SOON at www.lisaboyer.com....maybe even today!   Plans available now at www.lisaboyer.com ! The sculpture has a doggie and bear tea dipping version, but we just couldn't resist showing you this silly reindeer version today and wishing you Happy Holidays.


New: Organic Clock

Organic by Clayton Boyer, Wall Mounted Version

Organic built by Bob Brown, Tabletop Version
Clayton's newest design, "Organic" is now up on our website.  Please visit to check out the details and to see them in motion.  A big thank you to Bob Brown for testing the plan, his beautiful work and customizations, as well as photos of his work.  Happy Holidays!

Sneak Peek: "Organic"

Shhhhh.  Still working on the photos and videos.  Soon!

11/27/17  Organic is now up on our website, and the video can be found on YouTube.


Too Short Run Time Troubleshooting

Dear Clayton,  I can only get about 12 hours on a wind, but the (Genesis) clock is accurate to within about 15 sec during this time. I am temporarily mounted about 3 inches low, not enough for 12 hours difference. Any suggestions? Love the clock by the way.


Aloha Bob, congratulations, and I'm happy you love your Genesis.  It really is a little wonder.  So simple, yet such a great runner, and one of my quietest designs.

Things that cause short run time are generally related to how far the drive weight gets to drop before it hits the floor.

The height that the clock is mounted on the wall is of course the first consideration.  The higher it is mounted, the longer distance the drive weight will have to fall.

The length of drive weight itself is important because an extra long drive weight will hit the floor before a short, squat drive weight.

Also if a larger diameter drive pulley than specified has been installed, that will mean the clock will run on less drive weight, but since the circumference of the pulley is much larger, the cord it reels out with each turn will be much greater and thus give us a shorter run time.

BTW, in my book the Practical Guide, I tell a story about how Thomas Jefferson mounted his clock at the peak of the ceiling in his dining room so that he could get an extra long run time.  He ran the drive weight along to one corner of the wall and marked the days of the week on the wall so that his drive weight could also do double duty as a calendar showing the days of the week.  The only problem is that he didn't calculate his drive pulley barrel radians correctly and had to drill a hole in the floor so that weight shows Saturday in the basement.  The clock is still there in Monticello.  This story always makes me feel better when I do my calculations incorrectly.  Ha.

This story tells us that there is another possibility for a short run time - thick drive cord.  The thinner the drive cord, the more turns your drive pulley barrel can handle.  A thick drive cord will take up much more space as it builds up quickly on the drive pulley.  Thus Jefferson could possibly have solved his short run time problem with some thinner drive cord.  Maybe this will work for you, too.

However, considering that your clock is only running twelve hours, when it should be running thirty hours, tells me that something may be slipping inside the clockworks.  Possibly some wheel or connector or pinion did not get glued tightly, or a glue joint has broken.  A slipping joint would allow the weight to turn the gears, but also as it slips the weight will reach the floor sooner than anticipated.

Enjoy!  Clayton