Intro and misc. questions

[Sculptor]

Hi, I am a long time professional woodworker and sculptor.  I am preparing to design and build a weight driven pendulum clock.  I have a bunch of questions that some of you with experience in clockwork may be able to answer.  I'd appreciate hearing from you.
1.  What gear form is best suited to wood wheels and pinions.  Why?  Do you recommend a particular gear generator program?  I will not be using a CNC, but a G-code generator would be nice.
2.  Does anyone have experience with using resin stabilized wood for the meshing portion of gears? 
3.  What is the effect of scale on a clock design?  For example, if a design is doubled in size, what is the effect of weight requirements, friction and other functional aspects?  (I am not talking about changing pendulum length, I understand those principles.)
4.  What do you recommend for a train calculator?  Are there free online programs that work well?  If not, what do you recommend that I purchase.?  Or, do you recommend doing all the calcs myself?
Thanks so much.

[steve323]

Welcome to the forum Sculptor,

There is a lot of good info on this forum, but the traffic is somewhat light.  Sometimes I only check for new posts every couple of months.

Here are some answers based on reading and web searching.  Hope it helps.

1) There are basically 2 different tooth profiles used on clocks and watches.  They are either involute or cycloidal.  Both roll along a single contact point without sliding, so friction is low.  Old hand cut gears were usually cycloidal.  Modern gears are usually involute, possibly because they are easier to cut by machines.  I recall reading somewhere that involute gears are more tolerant of continuing to operate with spacing errors that might occur as the clock bushings wear out.

2) No idea.  I could see some advantages with very nice looking color options.  Personally, I prefer the look of natural wood.

3) A wheel that is double the diameter and thickness will weigh 8X as much.  This might imply that it would take 8X as much energy to move it with each tick.  However, the pendulum friction remains the same.  The escapement could still be left small to reduce energy requirements.  I would guess that the weight requirement for a 2X larger clock would be bound between 1X and 8X and probably around 2X. 

4) The calculations for the train are fairly straightforward.  Search for recent posts here and you will see some examples.  You will eventually need a gear designer.  There are a few of them out there in the $100 or less price range.  I have been successful using a free gear tooth profile generator at http://woodgears.ca and exporting it in a file that I could upload into my CAD program.  I clean up a single tooth and array it around a circle to produce the entire gear.

Steve

[Sculptor]

Hi Steve,
Thanks for the reply.  It does look like the traffic here is pretty light.  Do you have a recommendation for a more active forum?

I agree with you about the look of natural wood.  I do my own stabilizing, and don't use crazy colors, so the look is pretty natural.  It does feel different because it is heavier and denser.  My main reason for considering stabilized wood is to reduce friction and wear.  From doing a little testing, it appears that I can get substantial reduction in both areas, but only time will tell for sure.

My intuitive feeling is that losses due to friction at bushings and teeth will be disproportionately greater in a larger train.  I understand what you are saying about the pendulum.  I hadn't thought of that, but it seems make sense.

I have looked at the woodgears.ca gear generator and a few others.  It's difficult for me to know which will be best.  I appreciate your thoughts on woodgears.

I assume you are making wood clocks.  Been doing it for long?
Thanks again,
Brian

[steve323]

Hi Brian,

I don't know of any other more active forum on wood clock building.  I scan the Yahoo group mlhorology (horology for mini lathes).  It is more geared towards brass and metal clock making.  The user base is similar to this one, many hobbiests with interests in clock building.  The traffic is slightly higher than this one.

I am intrigued about the stabilized wood.  I can see the advantages in reducing some of the uneven wear that could result from the growth rings on natural wood.  Any reduction in friction is good.  Can you cut the teeth before stabilization when the wood is softer?  Maybe leave the center portion intact to cross out later.  Would this reduce or even eliminate movement due to humidity changes?  That would be quite an advantage.  There are many wood species that look great, but are too soft to consider for clocks without stabilization.

I have been working towards building a wood gear clock for around 5-10 years.  None have made it to completion yet due to small kids, new house, and life in general keeping me busy.  My goal is to have a fully equipped shop to tinker in when I retire in around 10 years or so.  I have a few designs that are close to completion.  I enjoy the process even if I am only taking baby steps.   

Steve

[Sculptor]

Hi Steve,
Yes, stabilized wood is resistant to changes in moisture content.  That is a feature of the material I didn't mention in my previous post, but it is actually what got me thinking about using it in the first pace.  Even stabilized wood will gain or lose moisture, but it does so much slower.  I haven't run any controlled tests, but I suspect the difference is at least an order of magnitude better than untreated wood.  I can submerge a piece of stabilized wood for twenty-four hours and have only minimal weight gain.  Evaluating the effects of humidity are much more difficult.

The teeth could be cut in a gear prior to stabilization, but I don't think it would be the best way.  True, the wood is much softer, but it also tears much more easily.  A better finish is achieved cutting stabilized material.  Also, there is always some distortion during the stabilization process.  I have not stabilized any plywood, but it would certainly be much more stable than solid wood.

I have thought about building a wood clock for many years, but have never tried it.  My experience is such that the mechanical aspects are not at all daunting, and I have plenty of equipment.  I just need to decide what materials I want to use and get a design worked out.  I read conflicting information about the value of the various tooth forms; I need to get a better understanding of that.

Somewhere on the forum I think I read that you cut gears with a CNC.  Is that correct?  If you would like to communicate more directly, send me an email.  [email protected]
Brian

[steve323]

Hi Brian,

The stabilized wood sounds like a good improvement over regular wood.  It seems like it keeps the nice look of solid wood with the stability of plywood.  I don't see much advantage to using it with plywood, since good plywood is already naturally stable.

Yes, I cut gears with CNC.  I also tried out the router with templates clock kit from Woodline and like cutting the gears with it.  It allows you to control cutting speed as needed.  It is a fairly slick setup, although it locks you into using their design.  CNC gives much more flexibility to scale the design. 

Steve

[Sculptor]

I think that stabilized wood would be a benefit to stability, but It adds weight (maybe could be offset by smaller sections).  the other question is friction.  I've done a little testing and it seems like the friction is reduced.  I'll let you know if and when I try it.

[EdMorgano]

Hi Sclptor,
I'm relatively new here and new to clock building, but as with most people, I have some opinions and also some questions.

I've built several clocks so far and I've worked toward making them smaller to reduce mass and thus the weight necessary to drive the gear train.  As to wood, I'm not familiar with what you call stabilized wood, but I've been soaking my gears in a 50-50 mixture of turpentine and poly.  After making the various shaft assemblies, I melt Johnson's paste wax and dip the assemblies in that.  Also, I've used Cherry, Maple and Ambrosia Maple for the gears.  Of the three, I like Cherry best.  It cuts smoother than Maple or any other wood that I've tried cutting on my CNC.  I've noticed the light traffic on this forum, but I keep coming back anyway hoping to learn some stuff.

Cheers,

Ed

[Sculptor]

Hi Ed,
Wood can be stabilized in several ways.  The method I use is resin stabilization, a process that fills the empty cellular structure with a resin which hardens in the wood.  It adds density and strength, and makes the wood very resistant to changes in moisture content from variable relative humidity.  This is important because wood changes dimensionally in proportion to its moisture content.   You can read a little about stabilization at http://www.challisgrips.com/Stabilization-of-1911-grips-s/1838.htm

I am going to be designing and building a large clock for a private school in Sacramento.  Minimizing friction is therefore of major concern.  I need to make my gears of stronger material so they can be large in diameter without adding any more weight than necessary.  I am experimenting with a gear design that should be very strong, lightweight and extremely resistant to dimensional changes caused by changing humidity.

It would be nice to have CNC capability; I cut all my gears by hand aided by a Bridgeport mill.
All my best,
Brian

[Sculptor]

An update: my new wheel concept turned out great.  Extremely strong, and it should be very resistant to dimension changes from varying humidity.  As a bonus, it is an elegant design.  I'm excited to get it into a clock.

[kilsonvorra]

Design a pendulum clock is really not an easy task. You should have to do some research on pendulum clock. This is a good place to find more information on pendulum clock. 

[Sculptor]

I'm happy to report that my first clock is ticking away.  It was made from plans, not my design; I wanted to start there to get some experience.  It started with the first swing of the pendulum.  It is exciting to see it come together.

I used my new wheel design concept for the minute wheel.  It seems to be very strong and looks great.  Best of all, it should be very resistant to dimensional changes consequential to varying humidity.  The aesthetic design of the escape wheel is my own as well.  It is made of home made plywood.

[EdMorgano]

Sculptor,
Can we see some pictures please?

[Troy Hendricks]

Nice work.

Thanks

[Troy Hendricks]

Hi,
   I'm new for this forum, and interested in clock designing.
Thanks