cutting clock gears

I used to read everything I could find on clocks and watches of the mechanical type, and one of the things I noticed was that, in general, clock and watch gears do not need to have 14.5 or 20 DP perfect-teeth. Not enough power transmitted to matter. The gears have almost square notches, with the corners of the tooth rounded-off. I really think you could use a thin slitting saw, width selected to match your mating teeth, and file the teeth a bit with a diamond file and do very well.

And I do confess, I've never tried this. But look at the pictures of clock teeth in your books and see if I'm not telling the truth.

Brownnsharp

That is true. If your interested in the specifics look in the technical section of

Clock gears have pretty straight sides but they have a definate profile on the tip. Your idea of modifying a slitting saw might work if the correct profile could be ground on the corners of the blade. However I have found a source for clock gear cutters; They are not cheap, but not all that much more expensive than other gear cutters.

chuck

Model Engineer magazine used to have a lot of clock projects in them, a lot of guys made their own cutters. There also use to be a lot more horological supply places around. "Wheel-cutting engine", IIRC, was the term used for the combination indexer and cutter. Many were hand powered. Some of the older back issues had ones you could build, too. One method used was to rig up some sort of dividing head on the lathe headstock and use a flycutter to cut each tooth to depth. The flycutter was driven from an overhead jockey pulley setup and was mounted on a vertical slide on the lathe cross-slide. The cutter itself was carefully filed out to shape and hardened. I suppose you could do the same these days with a mill and rotary table. You could probably file out a cutter out of keystock and caseharden it and it would work for use on brass.

The clock articles I've seen usually called for half-hard brass sheet of whatever thickness, I'm not sure what you can get these days that would be the equivalent. I imagine the author used whatever he could get, mechanical clockmaking not being what you'd call a burgeoning industry. Sounds like it's what you'd use for engraved nameplates and signage. Trophy shop?

Stan

The cutters are called HOBS - or Hob singular. Search for those maybe MSC has them under the code name. Otherwise - www search. Often these are made by the user or by a craftsman for a order. I think you will find them.

Martin

I suppose I should clairify. I managed to find industrial cutters for "normal" gears in the industrial catalog. They were not called hobs though. They were called involute gear cutters.

I believe (and I could be wrong) that a hob is a unique cutter for an automatic machine that cuts the entire gear at one time where an gear cutter cuts one tooth at a time and need to be manually indexed to the next tooth.

I have read several clock books now and all of them show cutting clock gears one tooth at a time using an indexing attachement.

The bottom line is that you need to buy clock gear cutters from a clock place, not an industrial supply place. BTW, good clock gear cutters cost about 100 each. Low volume item I suspect.

chuck

Greetings Chuck, You really can make your own wheel cutters. For cutting brass especially. A flycutter will work quite well also. In fact, if just a few wheels are gonna be made the fly cutter is your best bet. A piece of steel turned to the profile with four teeth cut in it is an easy way to go. After cutting the teeth a file is used to make the clearance then the wheel is case hardened. A small wheel cutter could be made from a washer mounted on a shank and a file could be used for all the shaping. ERS

Hey Eric,

How about a little pix, or a bit more explanation for dummies like me. OK, just for me then!! I'm trying to envision what you mean. Sounds interesting.

Thanks. Take care.

Brian Lawson, Bothwell, Ontario.

Hi Chuck,

Most home shop guys making a few gears single point them. Steve Conovers Foliot Clock or American Clock Movement construction books are excellent introductory works in clock building.

If you are really interested in clock and pinion making , J Malcolm Wilds "Clock and Pinion Cutting In Horology" book is excellent. Overkill for "wonder if I can make a clock that works" level of interest, but worth the $50 price if you're interested in really learning the details.

The sheet brass from hobby stores is quite hard, usable but not the preferred material for clock construction. Leaded half hard (AKA engraving) brass is far nicer to work with. S LaRose stocks it in sheet form, 8X12 sheets are about $15 and are available in several thicknesses. Merritts, TimeSavers, and S LaRose all have wheel blanks in solid or spoked pattern. If the OD is close, these can save quite a bit of time. The pre crossed (spoked) wheels have to be close to the desired OD, naturally the solid wheels can be cut down as needed. All of the crossed out wheel blanks I've seen are 4 spoke, some designs just look better with a 5 spoke pattern.

Merritts stocks single tooth cutters in all standard modules for clock work, with the exception of the 0.82 module found in some American antique long case clocks.

A googling on "Horological Gear Cutting" might turn up some useful links to fill in the gray areas.

Cheers, Stan

Charles A. Sherwood wrote:

I used the technique described here:

flycutter article) I've cut three wheels with my first cutter and once I got the rake angle correct (thanks to John Shadle for taking the time to help me out) cutting wheels was a snap.

cutters are really nice. Cheers! Ian.

Stan Stocker squeezed out:

Thanks. I bought a used one from Alibris for 10 bucks.

Thanks again. I already ordered most of my brass from McMurry in TX. Cost was reasonable at 4 bucks a pound, but the shipping was a killer. I bought 1/16 x 12 x 12 for about 10-12 dollars.

Still looking for that so I appreciate the help.

chuck