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?

[jcs0001]

Sparky - I suspect you have just been in violation of all sorts of physical laws regarding clocks 

Today I made some time between flea marketing and trying to get a boat project out of my shop.  A mandrel was in order so I went through my stash of metal and decided not to turn down a big piece into a little piece and a bunch of swarf.  I had a short piece of 1/2 in. round bar steel of some sort and another shorter piece of round bar steel about 1 1/4 in. in diameter.  I cleaned them up on the lathe and drilled the bigger piece 1/64 in. less than 1/2 in.  Then turned the end of the 1/2 in. bar down to about .003 in. greater than the hole in the larger piece.

Into the press it went and in short order, one solid piece.


Another view of my "new" press:


The single piece:


The piece was cleaned up in the lathe and a 1/16 hole drilled through the center for about an inch.  It was then set up in the mill and after centering it I used the x/y axis travel to put 4 marks (with a centre drill) around the face:


Two opposite holes were drilled and tapped #4-40 and the other two left as is.  I figured on using a small transfer punch however my set does not go that small.  I sacrificed one end of my steel knitting needle and using the file in the lathe got it down to the correct size.  It was used to mark two hole locations in the gear blank and they were drilled a bit oversized so that the 4-40 screws fit easily through them and into the end of the mandrel (shown with the transfer punch beside it):


I've used the drill bit to centre the gear blank on the mandrel.

John.

[jcs0001]

Raynerd:

It's the book by Ivan Law - Gears and Gear Cutting I believe it's called.

I plan to make my cutter in the lathe similar to a recent posting about making cutters (drill rod) for thread cutting.  Here is the link:

http://madmodder.net/index.php/topic,3523.0.html

I suspect that my grinder would be similar to yours - ok for bigger cutters and useless for small ones like this.  However (not having done this) I would likely use my dremel with various cutting disks and the like if I didn't have a plan for the cutter made on the lathe.

Realize that this is just speculation - I have yet to make the cutter.

John.

[raynerd]

Pm sent.

[jcs0001]

Over the last few days I made a gear cutter on my lathe.  My larger lathe (10x22) is ok for this but this is quite picky work and I've had to use a magnifying glass a few times to see things a bit better.  I have a taig metal lathe however do not have a compound on it so cutting angles isn't the easiest.  I suspect it would work better for things of this size and detail.

I started one cutter using 3/8 drill rod but quickly ruined it so started another with 1/2 in. drill rod.  The cutter will be used in my taig vertical mill and must fit into either a 3/8 or 1/2 in. hole in a mandrel that screws on to the business end of the mill.  A photo of the cutter installed in the mandrel (rather a rough one but it runs true):



I ground a 1/4 in. HSS cutting bit for the lathe as I find them easier to shape than larger ones.  Using that along with a couple of round small files I shaped the cutter to make it as close to the tooth pattern on the 30 tooth gear as I could.  I am anticipating having to fine tune the ends of the gears once cut and have a variety of small files for that purpose.

Hot off the lathe with a pencil end for scale:



I made this "jig" some time ago.  It's a piece of hex brass with a 3/8 in. hole in one end and a 1/2 in. hole in the other.  It's handy for indexing things like milling cutters for cutting the teeth.  In this case I've put the cutter blank in the 1/2 in. end and secured it with a setscrew.  Before putting it in the holder a flat was milled on the shaft of the cutter - it will be needed later on to assist in holding it in the milling mandrel:


Note that the teeth have already been cut in this photo and the one immediately below.

Another photo of the cutter blank in the hex holder.  Note the calculations on the paper (more to follow on this):


I was not sure how to cut the teeth (3 in this case) on the mill and found a very nice pictorial representation of making a 6 tooth counterbore on Dean's site:

http://www.deansphotographica.com/machining/projects/mill/cbore/cbore.html

In that description he gives a formula for calculating how deep to cut the teeth - measuring from the top (in the taig mill) of the cutter tooth.  In my case the diameter of the cutter itself was .490 in. and I calculated that the end mill should be positioned .267 in. down from the top.  Lacking any better information that is what I did.

A photo showing the set up in the mill.  There was no real need to make sure that the end of the hex was even with the end of the vice however I did this as practice for other projects.  Cutting was easy - bring the end mill down .267 below the top of the cutter blank, move it so that it cut almost to the base of the "teeth" and then slowly feed the cutter into the end mill.  Keep the end mill in the same position but move the cutter away from it (y axis) and then open the vice, turn the hex two positions and close the vice.  Repeat the cut and move two more times.  The set screws are not flush with the sides of the hex so a spacer was used in one position to allow the vice to hold the hex properly.



Once cut I applied a bit of blue magic marker to the teeth and filed relief immediately behind the cutting edge.  The marker allowed me to see that I wasn't cutting at the tip of each tooth.

The cutting end of the gear cutter was then heated with my turbo torch propane torch until orange hot and plunged into cold water.  That hardened it to  brittle hardness but it needed to be tempered.  I used my wife's oven and left the piece at about 450 F for an hour or so.  My wife complains that the oven is always too hot so I expect it was more like 475 deg. F - might make a difference to the muffins but shouldn't hurt my cutter    The thick end showed a nice straw colour after so it appears that the tempering went well.

I need to hone the teeth now and then set up the mill and cut the gear.  I have no idea if this will give me a working gear or not but at least it should be round and have some teeth by the time I'm done.

John.

[sparky961]

Excellent to see you using what you have and building your own tools.  Sure, it may need some tweaking but don't give up on it.  You'll make it work.

[jcs0001]

Sparky:

Thanks for the encouragement.  I made the gear this morning with the following setup in my taig mill:



A closer image showing the cutter behind the gear blank:



The upright rotary table used to divide the gear into 60 teeth:



The final result meshes quite well with the gear from the clock:



I've tried the gear in the clock and unfortunately it is a little bit too big in diameter (Raynerd you were correct ).  I will recalculate the diameter and cut the gear down a bit and then recut the gears (as long as I can get the cutter properly indexed to it).  If this doesn't work it will be time to cut another gear blank.  It looks like the cutter is in the ball park as far as shape.

John.

[jcs0001]

I decided to cut the first gear down to size and then re cut it in the mill.  However I didn't get the cutter aligned properly and it made a mess of the teeth.  Since it was still mounted in the mill I decided to cut the remaining teeth to see how it fit for size.  Got that done a couple of days ago and found that it does fit. 

We've had visitors and i've had other obligations so I will have to do further checks and remeasure the screwed up gear before posting anything further.  I'll make another blank and with the new information should be able to get closer to making it right.

John.

[raynerd]

Nice job John, look forward to seeing the complete wheel.

If you can hand grind a cutter, then a quicker and easier way is to make your cutter  is on a disk, cut the entire disk in half and off set the mounting hole for the arbour. That way you get relief and to be honest, a single point tool is often more accurate than a home made multi point in my experience. The slightest amount out of true and you are only cutting on one point of the multi tool anyway.

Nice job... More photos of the clock wheel please when completed!

[jcs0001]

Finally!!!

I cut a gear yesterday using the following specs:
OD of gear blank - 1.465 in.
depth of cut for teeth - 0.079 in.

It meshed properly and worked however it seemed a bit "loose" to my eye and I decided to change the specs a bit and cut another.  This time I used the following:
OD of gear blank - 1.475 in.
depth of cut for teeth - 0.074 in.

That did the trick and it now meshes nicely and rotates well. 



I need to reduce the thickness of the gear somewhat, drill and tap for a setscrew and drill some lightening holes in it.  Considering the lack of horsepower that a clock has there will need to be some testing by my clock repair friend to see if this is indeed alright.  I will clean the teeth up with crocus cloth or something similar so that it runs as smooth as possible.

At least now if I need to make another I know I'm quite close to where it needs to be.

Raynerd - just noticed your reply.  You are correct in that this 3 toothed cutter is a bit out and one tooth cuts more than the others.  Will have to experiment with other types of cutters in future.  I have recently purchased a plastic 40 tooth gear for my lathe at a cost of about $55.  The existing gear has been cracked since I purchased the lathe.  I plan to make another out of aluminium as I don't plan to buy any more at that price.  It should be easy since I can use the existing gear to make a cutter and it's a lot bigger than this gear.

Once I've completed clock gear I'll take a few more photos.

Thanks to all for your encouragement and help.

John.

[jcs0001]

The "final" photos.  It will be up to my clock repair friend to test this out and he won't get it until sometime into October as he lives a couple of hours away.





John.

[sparky961]

Looks great!  It's always a great feeling to be able to say "I made this".

[raynerd]

I missed this, great work!!!

[jcs0001]

I did get the gear to Phil, my friend, before Christmas but he has been busy and didn't get it installed and tested till recently.  He reports that it works well and he has the clock back together.

His wife sent me a photo with the gear installed:



We discussed the fact that the gear was not made of suitable material however Phil isn't that concerned.  He has hundreds of clocks and I expect this one won't be run a lot. 

I want to thank all those who contributed to this thread and also pass along Phil's thanks.  We are both well satisfied with how this turned out.

John.