10/22/11

An Interesting Email Exchange about Bob Construction...and Fire...and Beer!

 Kaleb Prather has this question for Clayton:

"So my dad and I have been picking away at the Simplicity, and having a spectacular time. I got curious after looking at the parts for the face- how on earth do I drill a 1/4" hole 3/8" deep from the opposite side? Do I just need to overlay another print of the face on the back side to mark those holes, or is there a better way? This build has been a fantastic experience for both of us, and I can hardly wait until our construction lives."

Clayton answers: "Aloha Kaleb, so wonderful to hear you and your Dad are having a great time! That's what this hobby is all about, and I love hearing the stories of families coming together to build these wonderful mechanisms.

Yes, you are correct. You can simply use another pattern and go from the back, or you can drill a little hole (usually 1/16 is as small as people might have) from the front and that will locate where you need to drill the holes in the back. Then a little filler for the 1/16th hole will cover the tiny flaw."

Kaleb: "We are making great progress on the Simplicity, slow but steady. I was wondering if there is a target weight we should shoot for when putting together the pendulum bob. So far so good- this has certainly been a great learning experience. :)"


Clayton: "Bob theory is pretty interesting.

The period of the pendulum is determined by the length of the pendulum, and the length of the pendulum is determined by the pendulum's center of gravity, and the center of gravity is determined in part by the weight of the bob.

So that means that a light bob will simply take a longer pendulum shaft to find the same center of gravity as a heavy bob.


 If you follow my instructions for constructing your bob, knowing a specific target weight is not important because the slight difference between a light weight and a heavy weight can be adjusted for by that little nut on the bottom of the bob.

A light bob will need to be lowered slightly, and a heavy bob will need to be raised slightly to find the same center of gravity and thus the same period for the clock's pendulum.

I probably should, but I don't weigh my bobs. I determine all of my bob weights for any specific clock design by experimentation. Then I write down the instructions for making that particular bob.

Some of my bobs are filled with lead, some half filled, some have BB's instead of lead, and some bobs have no extra weight added at all. They are simply wooden pucks. The length of the pendulum shaft in each plan reflects this.

However if you try to use BB's in a bob that calls for being filled with lead, you'll need to lengthen your pendulum shaft much more than you will be able to adjust with the nut on the bottom of the bob.

Also where you live makes a difference. Whether you live on a mountain top or at sea level will affect where the very same bob needs to be set."


Kaleb: "Wow, bobs are complex little critters. The plan is to empty the lead from some old 12 gauge shells we've got lying around (with care, of course). It sounds like this is within the scope of what's called for, so I will build precisely to plan specification, and adjust as necessary. Thank you for such a wonderful work, designing these clocks. Not only has this project stretched my mind as to what I'm capable of, it has also provided my dad and I some priceless quality time together. I can hardly wait to hear her tick for the first time!"

Clayton or maybe not Clayton or maybe Clayton's lawyer writes: "YIKES! Before you go ripping into shot gun shells (shudder!), wander down to your local tire balancing shop. They have lots of used lead weights that they will probably be happy to simply hand over to you. (Yes, the new bismuth, lead substitute, weights work just fine.)

You have a couple of options with those lead weights. You could snip them into tiny pieces and fit them into the bob's voids, or you could (and as a secret aside...here is usually how I do it) build a separate, sacrificial bob, and with a torch in one hand and pliers holding the lead weights in the other, melt the weights into the voids of the sacrificial bob (wear eye protection, gloves and long pants - lead splatters on bare skin is somewhat uncomfortable).

When the lead cools completely it will shrink a little so you can lift it right out and you can then transfer it to your finished bob. If you do your bob weights this way, you'll find that the wooden sacrificial bob is actually still usable. The lead really isn't hot enough to burn through the wood. The lead will just scorch the wood a little. I have made some bobs using the sacrificial bob as the actual bob. It works just fine.

But since this method involves fire, and molten lead (but hopefully not beer--you know those famous last words..."Hey, watch this! Here hold my beer!"), you didn't hear it from me...right?

Aloha. Anonymous..."



Here are some interesting and/or beautiful bobs we've seen:



Greg Payne's Simplicity Bob




William Ball's Simplicity Bob




Fr. Bedemeyer's Solaris Bob




Gene Collier's Solaris Bob




Gwilym Fisher's Number Six Bob

And finally, Adrian Iredale's wombat bob:

Really - I can't tell which of my designs inspired him to create this Wombat clock - or was he just making that part up?

1 comment:

  1. "Clayton or maybe not Clayton or maybe Clayton's lawyer writes:"

    Funny!

    ReplyDelete

I love comments, but in order for me to have more time playing in my sawdust, I cannot respond to them here. If you have a technical question, please do not post it here, or I will have my wife answer it for me and her technical knowledge is highly suspect. For technical questions, check out the FAQ section of my website, or find my email link there. Mahalo and Aloha, Clayton