First "Clockmakers" tools - broaches, pivot file..?

[Ninjak2k]

I think Colin's point about a tapered hole being a better bearing surface is spot on, though. You want the least amount of contact possible between the bushing and the pivot for the least amount of resistance in the train. The equation for friction is includes surface area, so the lower the surface area, the less friction. A straight hole would have more surface area contacting the pivot, so more power being robbed from the train.

~Dan

[Horology101]

I have managed to move this thread quite off topic but to clarify, the writing was a word for word quote. Harold, I think we are talking about the same holes, those that the pivots fits in.

Anyway, regarding my questions such as broach sets and tweezers .. any suggestions as to suitable sets?

Chris

[Jerry Kieffer]

Originally Posted by Ninjak2k

I think Colin's point about a tapered hole being a better bearing surface is spot on, though. You want the least amount of contact possible between the bushing and the pivot for the least amount of resistance in the train. The equation for friction is includes surface area, so the lower the surface area, the less friction. A straight hole would have more surface area contacting the pivot, so more power being robbed from the train.

~Dan

Dan
For the benefit of any beginners who may read this, I have to respectfully disagree.
Unfortunately there is no free lunch.
When Arbor tension remains the same, and you decrease pivot contact area you will increase contact pressure. Another words when you take a given pressure and limit it to a smaller area you increase pressure on that smaller area increasing friction. This in turn cancels out any overall decrease in friction on the system as a whole. In addition smaller contact areas with higher pressure will increase the chances of rapid wear per Colins Quote. This in turn can cause the pivot to move out of proper location increasing tooth contact friction and requiring premature repair.

On the other hand a straight pivot in a straight pivot hole, properly fit and finished with proper lubrication will offer the best of all worlds.
When a load is spread out over a wider surface you will have less surface tension on any given point than a narrow contact area. In this case we are talking about the full width of a bushing or plate. Under these conditions with proper lubrication, you have a good chance of forming a oil film between the pivot surface and hole surface. When this happens no metal to metal contact exists, and you have far less friction than any metal to metal contact regardless of how small it is. In addition the full width contact will maintain proper arbor location and operation of the movement for the long haul.
This method has been used exclusively in the manufacture of Watch, Clock and Chronometer movements by the finest makers for at least the last 150 years.

Chris
For Tweezers I personally use Dumont and Erem Brands simply because they have given better service over the years. Again personally I have found 7SA and 3C patterns to be the most usefull.

As indicated I only use broaches for non critical work or where a taper is required. The ones that have held up best, have been made in the USA and Germany. Sizes will of course be per your needs.

For critical work I use harden and ground Gage Pins ground to about a 12 degree angle with a fine grit stone. (Attached Photo) When reaming a hole they give far superior surface finish than typical broaches. In addition, when used in steps, very accurate hole sizing is easily controlled They are available individually or as sets in .001" (Metric by .02mm) steps.
Better quality harden and ground Import sets are generally less expensive than similar range quality broaches. Since gage pins are the same diameter over the length of the pin they have another advantage.
When reaming a Bushing for example, you can enter the opposite pivot hole and ream from the back side of the bushing. This assures perfect arbor/pivot hole alignment that is almost impossible when reaming/broaching free hand.

Jerry Kieffer

[Ninjak2k]

Thanks, Jerry, for that explanation. I definitely have much to learn.

Is it possible to find gage pin sets that are already like that for reaming, or can precision drill bits or boring tools be found to accomplish the same thing?

Cheers,
Dan

[Jerry Kieffer]

Originally Posted by Ninjak2k

Thanks, Jerry, for that explanation. I definitely have much to learn.

Is it possible to find gage pin sets that are already like that for reaming, or can precision drill bits or boring tools be found to accomplish the same thing?

Cheers,
Dan

Dan
We all have much to learn of course including myself. At last count, I figured maybe about 280 years worth. (Bull headed and slow)

The answer to your first question is no. Drills can certainly be used in the same manner but will not give the same nice hole finish. In addition they are not available in the small steps required to adapt to the sizes generally needed.

Jerry Kieffer

[awolff]

Interesting discussion regarding tapered vs straight holes got me curious as to just how much taper is involved. So, I took a medium sized cutting broach and measured the diameter with a micrometer at two places, 2 inches apart. The diameter changed .0175 over 2 inches. This is approximately equal to .00055 over 1/16 of an inch. If your plates are 1/8 inch thick, the diameter of a hole cut by this broach will be .0011 inches bigger on one side than the other. Now if you broach from both sides, and just happen to cut exactly the same amount from each side, the center of the hole will be .00055 smaller than each end of the hole. Pretty small difference in my book. If the broach is wobbled a little bit while cutting, or the smoothing broach is used on the hole, who knows what the dimensions across it will be.

In the end, it is really not that exact of an operation especially since we are dealing with two plates separated by a distance that is substantially larger than the diameter of the holes. Unless these holes are EXACTLY aligned, a straight hole is probably worse than a tapered hole. The tapered hole will allow the pivot to run slightly skewed whereas a straight hole will bind at the edges.

Still, I find the technique of using small gage pins as reamers to be very clever and look forward to using them on a future project. Thanks for sharing that idea Jerry!
Allan