Gear for a clock

[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.