Gear for a clock

[jcs0001]

I started this in another thread as I needed to know what brass alloy to use to make a clock gear.  Since the preamble to that isn't too long I'll quote it as a starting point for this small project:

Making a gear for an older clock

I recently was involved in moving my mother's house full of contents as she has downsized and moved to a senior's home. Included in the belongings were three clocks - a grandmother clock, a square "mantle" clock and a cuckoo clock. I had heard indirectly that a nearby neighbour collected and repaired clocks so introduced myself and asked him about the clocks. He helped pack up the grandmother clock as it was being moved to another relative and he repaired the other two for me.

    He showed me around his collection and I was amazed. He has clocks everywhere and they range from grandfather clocks on down to very small clocks - many different styles - lots of cuckoo clocks, dome clocks, wooden cased clocks from plain to extremely fancy. He mentioned that he has many packaged up as there is insufficient room in his residence to display them. His collection left me in awe.

    He refused payment for repairing the two clocks. I asked if he needed any clock parts made as there was a possibility that with my two metal lathes and small mill (and limited amount of skill in using them) I might be able to help him out. I have made one brass gear in the past successfully and figure I can make more with time and care.

    He has just recently provided me with the carcase of a clock (not sure if this is the correct word but it's the "guts"). It is missing a gear. The clock is a Junghans Weurtettberg two 2 jewels W200.

    I need to make measurements of the existing gear and the distance between it's centre and the shaft on which the missing gear fits. I believe I can manage that as I have a number of accurate measuring devices. Care will be taken as I don't wish to damage either of the shafts or the existing gear. With those measurements I believe I can determine the tooth count on the missing gear and then create a new one. I may have to make a new dividing wheel depending upon the tooth count but that shouldn't be too much of a problem.

Several people responded in the other thread suggesting that I source cz120 brass for the gear so I will be doing that.

I would post some photos and have in the past using photobucket but it is giving me great grief with firefox and with two other browsers I have tried.  Will figure this out and post some soon.

John.

[jcs0001]

First a photo of the clock as I received it a couple of days ago.  I haven't seen it in the case.



The stainless steel bar is pointing to the pinion (?) which is missing a gear.  The gear that it meshes with is up a bit and to it's immediate right.





The other side of the mechanism.



And another shot of the existing gear and bare pinion.

I haven't yet measured anything - that is my next step.

John.

[jcs0001]

Starting to make some measurements:

I had to lift part of the mechanism to remove the existing gear.  Three decent sized screws allowed me to lift it up and release the gear once the set screw was loosened.

 

The screwdriver points to one of three screws.  What appears to be damage to the screwhead is a bit of dirt.



The existing gear.



My fancy micrometer holder along with cheap inside measurement guage (spring loaded).

I used my digital calipers to get an idea of the distance between the inside of the two pinions and then set my micrometer a bit shy of that (5 thou or so).  Used the micrometer to set the inside measure guage and tested with the guage to see if it just fit between the pinions (if this isn't the correct term someone please advise).

A few trys with the micrometer and guage resulted in the guage fitting very nicely between the pinions.  The micrometer was used to measure the guage and it came out within a thou of the digital caliper reading (must have been an accident).

Measuring the outside diameter of the gear is fairly trivial and measuring the depth of the gear teeth shouldn't be difficult either.

I will draw up a sketch of the measurements as my next step is to figure out the number of teeth for the new gear.

John.

[sparky961]

Hints for using a telescoping gauge:

[jcs0001]

Sparky:

Interesting video - it gives me confidence that I can get accurate measurements from the inside even though my telescoping guage is from offshore.

In this case I was using it in the "opposite" manner - using the micrometer to set it and then checking the gap between the pinions.  The reason for this is that I was concerned that the spring in the guage would be strong enough to move the pins apart - they are supported on one end only - and thus give me a high reading.  The micrometer gave me the ability to set the guage in very small increments.

More to come.

John.

[jcs0001]

First off if this thread should be in another part of the forum, moderator(s) please move it.  I realized after I started it that it was pretty minor compared to a lot of the threads in this area.

I made a number of measurements and calculations and figured that the outside diameter of the missing gear should be 1.505 in. (and circumference =4.728 in.)   That number does not account for any "slop" in the gearing - it would be very tight to the existing gear.

The existing gear has 30 teeth and is .764 in. outside diameter.  Thus the circumference is 2.400 in. and the teeth per inch of circumference is 30/2.4 = 12.5 teeth per in.

Using the above calculation of 12.5 teeth per in. for the new gear we end up with 59.1 teeth.  I believe that the .1 extra tooth is due to the fact that my calculations allow no clearance between the gears (and possibly measurement error).  If I treat this as a 59 tooth gear then the diameter would be 1.502 in. (and circumference =4.719 in).  That make sense to me as it would allow several thou clearance.

In order to check the above I made up a small aluminium disk as shown below.  I found that my 5/64 in. drill bit made a hole the correct size for the pinion.  I should note that I first made up a brass disk of about 0.864 in and was amazed that it was too small.  It turns out that I was still asleep and used the radius measurement for the diameter.  The disk turned out very nicely so maybe I can use it for something else.



Fitted into place in the clock with the existing gear resting on top.



The result - not happy with the wide lines.  I later used a bent pin and got a bit better result.  I used a marking out spray can and it doesn't seem to stick very well.  Maybe should have left it bake in the sun for a while.


The lines on the aluminum disk did allow me to check my calculations and they do match quite well.

I will now need to make up a disk divided into 59 and figure out how to mount it in my taig mill.  Will also have to make a gear cutter - last time I used a single point cutter but this time I believe I'll make a cutter in the lathe - may be easier to get the tooth shape that way.  Since the centre hole in the gear is so small I will have to make up an arbour (perhaps a two piece with a couple of pins that go through the gear.  I do have a spin index and 4 in. rotary table with a tailstock so may be able to adapt one of these for my purposes.

Any ideas are welcome

John.

[chipenter]

59 teeth dosn't make sense it's has to 60 the chimes are linked to the front cam the bit with 4 slots , it must be an even number to work , the gears are probably module http://www.myvirtualnetwork.com/mklotz/ lots of small programs for gear cutters and gears hear .

[Pete W.]

The teeth on that gear look to me to be cycloidal (rather than involute).

[jcs0001]

Jeff and Pete:

I'm in over my head obviously.  I have no idea how the clock works.

Is my method of calculating the number of teeth ok.  Basically I calculated the number of teeth per inch of circumference on the existing gear and then used that figure to calculate the number on the new gear (ie 12.5 x circumference of new gear).

One aspect that seems clear to me is that there is a size constraint on the new gear based upon the distance between the two pinions and the size of the existing gear.

I will do some research to try to get "up to speed" on this type of gear but any help would be appreciated.

John.

[Lew_Merrick_PE]

Here is the Boston Gear manual.  See if this helps....

[jcs0001]

Lew:

Thanks - that is reasonably straightforward in contrast to some of the other literature I found on the web.

John.

[vtsteam]

No need to move this thread at all! I'm interested in reading how you progress, and sorry I have no clock knowledge to help with. Raynerd would be able too if he checks in. I'm sure there are others. Nice photos! 

[chipenter]

The first quarter chimes the 30 tooth gear rotates once , half hour rotates twice three quarter three times and four on the hour , I have two similar clocks will have a count .

[jcs0001]

Jeff:

I would really appreciate it if you are able to make a count.  I agree (with no knowledge to back this up) that 60 teeth make more sense than 59.

In the meantime - not having done this before I figured that making a 59 hole plate would be interesting - I made this:



I didn't have any suitable aluminium but had quite a bit of very nice 12 mm marine ply (lots of smaller scraps).  It's approximately 7 1/16 in (18 cm) in diameter.  If nothing else perhaps I can integrate it into some type of wind chime.

I cannot source cz120 or anything similar nearby so have decided to use regular brass for a test run.  Bought a 6 in. piece of 1 3/4 in. brass yesterday (after taking out a second mortgage)   Told my daughter that it would be left to her as part of my estate.

Once I make a suitable gear I will source the proper material and make another.

Steve - thanks for looking at this.  Pretty small compared to your lathe project.

John.

[vtsteam]

I think Mike's Workshop might have info on making gear cutting tool bits using taper drills. There was an old ME series on doing it with two disk buttons you make -- which was cool, but the taper drill method built on that method and and seemed even cooler.

Then, there's the Gingery method of just grinding to shape by comparison with similar teeth. And probably a million others. Ivan Law's book is always highly recommended by people.

[Bluechip]

I assume from your spelling of 'aluminum'  that you're from North America ??

This may be of help:

http://www.amazon.com/Making-Clocks-Stan-Bray/dp/1854862146/ref=sr_1_1?s=books&ie=UTF8&qid=1437074640&sr=1-1&keywords=making+clocks

I might point out I have no ambition whatever to make or repair clocks. I was sent the book in error a couple of years ago and I did find it an interesting read before I sent it back. 

Dave

[jcs0001]

Steve:

I'm hoping to make a cutter in the lathe - should be easier to shape it to the teeth that way.  Plan to use drill rod and harden and temper it afterwards.  I am however open to any other reasonable suggestions.  The last gear (and first) that I made I used a single tooth cutter (fly cutter) and it worked well however it was a larger gear and larger teeth.

I did a check for Mike's workshop and found a fellow who sells jigsaw blades and some small drills.  Didn't see anything about making cutters - do you have a link?

Dave:
I have no interest in clock repair itself.  Making gears and pieces interests me but I have too many interests already - have to draw the line somewhere.  I am from Canada - should put that in my profile.

Thanks,

John.

[jcs0001]

Steve - I found Mike's workshop and lots of info looking up "button gear cutter".  thanks,

John.

[chipenter]

Counted the gears 60 30 is what I have .5 module cycloidal teeth .

[jcs0001]

Jeff:

Thanks very much for the information.  Unfortunately I won't have much time in the near future as I've unexpectly been tasked with sorting out an estate.  I did order Ivan Law's book on gears and gear cutting yesterday so should have that in a couple of weeks.  Have also found some other sources of info and am trying to get my tired brain around various definitions etc.

Thanks again,

John.

[jcs0001]

Finally got back to this project and made a gear blank on the lathe.  Pretty simple lathe work so I don't have any photos.  One photo of the blank beside the gear that it will (supposed to) mate with.



The blank is a bit thicker than it's mate however I can reduce this later if it is a problem.  There is lots of room for it so I don't anticipate problems.

I'm still awaiting my book on gear cutting so this will be it till I can go through the book.

John.

[raynerd]

John, if you are using brass bar for your blank then you should be fine as this will be some form of free cutting brass. I'd advise cutting against a good sacrificial back plate - if the brass isn't great, it'll stop the teeth bending (which shouldn't happen as it looks pretty thick) but it'll stop throwing big burrs and give you a good clean cut. I'd use aluminium if you can afford it, but ply would be better than nothing.

Based on your calculation of the known gear, OD = (N+2)xM
19.4(mm OD)/32 = 0.6 Module ??

Working backwards from that, I calculate backwards from your 1.505" blank would be 61 teeth - which isnt correct as it should be a 60 tooth gear.

Something isn't right!

[jcs0001]

Raynerd

Good idea about a backing plate - I've got lots of aluminium so can easily come up with a piece to match.  I'm still awaiting my gear cutting book and haven't had a lot of time to look into it otherwise.  I do accept that I may have to cut more than one gear before getting something that looks like a gear and works.  I hope it doesn't turn into a lifelong project (cut one gear per week trying for the right shape and size ).

Any suggestions etc. are appreciated but please keep them simple as I really don't know much about gears.

John

[sparky961]

Ok, this will be really simple...   Use what works.  Yup, that's it. 

Sure, there are lots of different forms for gears and such, but you can usually very effectively hand-grind a tool blank and single point it.  Using only a few test pieces you can refine the profile until you get something that meshes very well when you view two mating parts with strong light behind.

Of course this isn't going to work for all applications so don't go off on me about "proper" gear cutting methods.  I've made a few custom timing pulleys this way, and there's a thread somewhere on here showing a bandsaw worm wheel that I cut and "ran in".

I'm not sure how critical it is in a clock, but I'd think that a bit of backlash in there wouldn't matter too much.  You'd think the most important part would be to get the number of teeth right so that it keeps time properly.

So.... tell me - how naive have I just proven myself to be about clocks? ;)

[raynerd]

Sure, there are lots of different forms for gears and such, but you can usually very effectively hand-grind a tool blank and single point it.

Where on earth are you when I need you in my workshop! :-) I've never been able to hand grind single point cutters for clock gears. I have a friend clockmaker and he can do it.... it can be done. I'd certainly need a cut wheel to match the profile to while I cut it. I have a cheap fat grinder and I just can't get such a small intricate profile of the blank cutter even with my grinder and array of slips and stones. As they say, a poor workman always blames his tools.

Jcs0001 - I've missed what book you are waiting on arriving?