Motor Barrel design; I have often complimented some makes of watches for their superior "Motor Barrel" design. More often than not the Waltham 16s Models 1888, 92, 99 and 08 which incompromisingly applied the advantages of such a design to 16 and 18 size watches decades before other USA watch makers.

This design "Motor Barrel" actually contains the "motor" (Mainspring) in a shallow "Barrel" that does not rotate during the running of the watch. Instead the watch is powered from the Spring arbor connected to the center coil of the wound mainspring. This arbor is attached to a large diameter toothed wheel at the outer diameter which engages the center wheel pinion and runs the watch.

The Motor barrel is only turned when the watch is wound up to hold the mainspring power for driving the watch. The Bulova Watchmakes school sketch below explains this design.

This is a "real life" picture of the Waltham Design Motor Barrel showing the motor barrel holding the main spring and the arbor/wheel assembly that drives the watch . . .

GOING BARREL; The earliest watch movements were miniature clock movements with no main spring "barrel" at all. So when the smaller, more fragile watch mainspring (always) broke or exploded it destroyed the movement completely by flying about in the movement wheels shattering and bending things. To reduce this damage sometime in the 18Th century watchmakers began putting the main spring in a "Barrel". In "non-fusee" movements the outside rim of the Barrel had a toothed edge to drive the watch movement. These are called "Going Barrels". The Bulova Watch School describes it very succinctly;

This is a "Real Life" picture of the "Going Barrel" with the main spring and winding arbor installed but the cover yet to be snapped in place

Now you can more easily understand WHY I say the (true) Motor Barrel is far better than a "Going" barrel for time accuracy. Note the "Real Life" pictures show the Motor Barrrel is always powering the watch from an arbor on a very short torque arm attached to the main spring, whereas the Going Barrel is always driving the movement from the outside end of the mainspring that is attached to the barrel.
Because of the very short Motor Barrel torque arm to the main spring attached at the center arbor driving the watch, the difference in torgue from fully wound to fully unwound is actually reduced to about 25% of the difference of that torque output to the OD main spring attchment used for the "Going Barrel". This issue with the "Going Barrel" was first addressed with great expense by using a chain drive "Fusee" (pg 71 or so of the price guide) that attached the mainspring barrel to the watch movement by a micro-chain connected to an ever increasing Radius Helical Spiral pulley that compensated for the drop in spring torque at the OD of the spring barrel by proportionatly increasing the torque arm between the motor and the drive wheel.

In short the advantages of the incredibly complex Fusee design is accomplished with the simple Waltham type Motor Barrel design.

BUT! "Experts" and other people have broken into another school of thought that argue the Going Barrel designs named "Motor Barrel" by Hamilton and others are truly Motor Barrels. The Bulova school (again) tries in a very diplomatic fashion to describe the rather complex Hamilton "Motor Barrel" as follows;

Isn't this a safety barrel and though designed differently, be the same as Elgin's safety barrel as used in the 240 and 372? Safety barrel and motor barrel are used interchangeably, but I was under the impression that they are not the same.

The term "Safety Barrel" refers to the cup or "Barrel" used on all Motor or Going barrel watches including Waltham and Elgin (excepting some Dollar watch movements) to contain the main spring so when it breaks or explodes it does not destroy the watch movement.

The "Safety Pinion" is the second protection for this issue;
The pictures below show this little jewel at work;
1. Main spring end "pop's OFF" at full wind!
2. In about 1/1000 of a second the main spring releases all it's power and in doing so self destructs (in this case into 10 separate pieces ).
3. The main wheel with it's "pinion "meshed" to the main spring barrel . . .
4. Gets hit with the enormous torque shock of the breaking spring that is driving the barrel backwards. The SAFETY PINION instantly unscrews harmlessly leaving the mainspring barrel to absorb and contain all the pressure.

Without a Safety Barrel and Safety Pinion the wheel train is destroyed.

My reply refers to Waltham and Elgin's design.

I was under the impression that a safety barrel design did not need a safety pinion but that a motor barrel design did.

I will leave that one to the experts among us. It is possible that the watch movement can better survive a spring failure contained by a true motor barrel. My hunch is that would depend on where the break occurred in the spring as the collective torque shock of the spring will deliver itself through the shortest mechanical path much like electricity flows through of the shortest wire.

https://ihc185.infopop.cc/eve/f...181063821#7181063821

This is an archived linked, where I got my info from.

Thank you for the link. Ed Uberall's explanation is clear and I must admit that I have always thought of the advantages of the true motor barrel and never the issue of whether or not a Safety Pinion was needed.

David, I enjoyed your illustrations. I have an Elgin 372 that has a safety barrel. Their later grade 494 and 540 is supposed to be a motor barrel.
I still find all this somewhat confusing.

So are the later mainsprings such as Elgin's durapower truly unbreakable?

Many of the Elgins had safety barrels, on the 494 and 540 both were 23 jewel and both were a bit of an enigma in regards to elgin movements. I would think the later alloys were much less likely to fracture than the normal carbon steel mainsprings.

Prior to the grade 571 only two Elgins were adjusted to 6 positions, some of the 21j grade 506 and all of the grade 23j 494s were. Maybe since both the 494 and 540 were made after Elgin had introduced the invar type mainspring, hairsprings, and balance wheels that Elgin went to a less complicated system.

I would think that the work needed for the do the extra machining for the safety pinion could be eliminated via the motor barrel.

With this post, I hoped to relay a better understanding of named "Going" and "Motor" main spring barrels used in most 19th and 20th century watches. Sadly, the discussion has advanced to mainspring design, definitions of "safety" Barrels and Pinions which muddied the waters of the originasl post.

My experience is unequivocal; EVERY main spring CAN BREAK! I have seen EVERY TYPE BREAK INCLUDING DELAMINATED "WHITE STEEL"! A fully wound breaking main spring can and WILL suffer considerable damage upon the watch wheel train UNLESS the "Safety" products are doing their job.

If you look at the exploded spring I posted above, the outer hook on a Waltham Motor Barrel watch broke delivering the full force of the mainspring as an explosive shock to the center arbor which IS the driving arbor for the wheel train. When this outer hook or spring failure happens in a Motor or "safety" barrel design WITHOUT a Safety Pinion, it would blow out the wheel train. I Have seen these and posted once on IHC185 a picture of the escape wheel with escape teeth wrapped around the pinion due to the huge devastating torque shock.

Sorry to muddy the waters. My point was that both Waltham's and Elgin's early designs were really safety barrels and that a motor barrel has no more safety features than a going barrel. That a motor barrel is a better time keeper or not I don't know. If safety is the only concern, then why not just use a safety pinion, which just involves some threading. Why is it that a lot of the earlier watches used safety pinions. Seems like good insurance for a reasonable price. If this also misses your intent of your thread I apologize, but is my two cents worth.

Thank you David, for a very informative and direct explanation of Motor Barrels and their relation one to the other....

Not being a watchmaker, I have often wondered what was ment by the term 'Going' when used to describe the barrel type of a watch movement....

Thanks, again, for your time and effort to help educate some of us to better understand this hobby we all love so much....

Regards,

Jerry

Thanks Dave, great explanation!You have a knack for explaining watch technology, that's for sure.I once took apart my lowly but great running '08 model 15J 620 grade Waltham, I was surprised to see it has a motor barrel in it.I always thought those were only used in higher grades.Also wanted to say that one of my 992 Hamiltons that I bought as a non-runner had a broken mainspring, and the safety pinion didn't do its job, the gold center wheel and third wheel had a couple of teeth knocked off.I could never understand why Waltham never marked "motor barrel" on their movements when they pioneered their use long before the rest...Thanks again, Ted.