How do they make bushings?

[kinsler33]

Since we seem to have a number of experienced industrial machinists and instrument people here, I was wondering if anyone knew how bushings are manufactured. I assume that they're done on an automatic screw machine, but I don't know any details. And: who the heck makes bushings, anyway? There seems to be more than one source, but it's tough to see how the enterprise could be at all profitable.

World War II story:

My father was a mathematician at the top-secret Aberdeen (Maryland) Proving Grounds, which is where they invented artillery and did weird secret research. One fine day in maybe 1943 someone came in with an automatic screw machine swiped/captured from a German factory. Everyone gathered around while they hooked up a 220V ac transformer to power the motor. And when they turned on the switch the machine started making tiny instrument screws, one by one, and dropping them into a little hopper.

There was a simultaneous groan from these scientists (one of them was von Neumann, of computer fame) and engineers, for in front of them was evidence that the Germans could out-engineer the Allies (us) with no trouble whatsoever, and the general opinion was that the war was lost.

M Kinsler

...and indeed the outcome was awfully close.

 

[dickstorer]

Great story, Mr. Kinsler.

 

[novicetimekeeper]

1943?

Where did they get it from? In 1943 territorial gains were made in Russia and Africa, and that certainly showed a change in direction, but it was a long time before Germany itself was overrun wasn't it? Italy dropped out of the war in the autumn that year perhaps something from there?

 

[MARK A. BUTTERWORTH]

It is amazing really. We make our bushings in runs of 50,000 pieces. First, we buy the brass from a mill that uses a grinding process to make the outside diameter within +/- 0.01mm. So we buy the bushing wire for a particular size, say 2.7 mm for KWM #III reamer. Then we decide which bushing numbers within that 2.7mm that we need. Usually we make about 10 different numbers. That is different bores and different heights. The machine has a multi spindle head that can do several operations- bore the hole, cut the outside chamfer, and the inside oil sink, and then cut off the bushing. So it is about 5,000 pieces of each bushing number made at a given time. Then they need to be washed to remove the machine oil. We buy 2" x 2" bags for them, label the bag, and weight out 20 to a bag. We actually sell them in 20 piece and 100 piece but they are all put in 20 piece bags. It is a lot of work for only $0.20-$0.25 depending on the 20 or 100 piece purchase] a bushing I think most would agree. I retrospect I don't know if we will break even on the investment in my lifetime, but it is very interesting. So we make the bushings to both the various KWM and Bergeon sizes and have made up several million by now. Like any learning curve, we have boxes of bushings that simply didn't meet our standards to outside diameter sitting in a corner and that is an expensive loss, but we want everything right. To my knowledge there are only two, maybe three others doing this in the world.

As an addendum, to see a room full of these machines, all automated, in Germany spitting out tiny parts is a real experience and I think helps one understand that whether buying a movement or just a part for the movement it is quite a bargain. In the old days in the Black Forest, an entire village would pool its capital to buy one Swiss screw machine to make certain parts. Another village would buy a different machine to make some other part of the clock. Maybe cuckoo bellows for example. The history of this I believe is very interesting.

 

[Len]

Love these stories..

 

[kinsler33]

That is exceptionally interesting, and thanks for writing it. What sort of tool is used to cut the inside diameter of a bushing? The inner surface of bushings has been discussed here a great deal, and my impression is that it's likely about as smooth as it's going to get when it comes from the factory. Others vigorously disagree.

As for the automatic screw machine swiped early in World War II, there were lots of spies on both sides long before soldiers marched anywhere, gleefully stealing each others' coding machines, radar sets, bomb fuses, metal cutting tools and alloys, and nuclear secrets. OSS, the ancestors of our CIA, likely spirited the screw machine out of Germany; they were good at that sort of thing.

I wanted to post a video of an automatic screw machine but quickly discovered that they're very difficult to make because the workpiece is completely surrounded by cutting tools, chips, and cutting fluid and thus you can't see what's happening. Here is one video that shows the operations, though likely not as they'd appear in a real factory: .

There is, however, a video of this 1871 model, used at Waltham Watch Company. Apparently our antique clock parts were not exclusively filed out by hand:
Charles Vander Woerd's automatic screw making machine invented in 1871, made and used at the Waltha

Mark Kinsler

 

[David S]

I just sectioned one of Marks 3.5 od bushing and a KWM made in Germany, and they both look similar and appear to be drilled under 20x magnification. The scoring on the KWM looked a bit more pronounced.

David

 

[kinsler33]

The only reason they lost was because they were being led by a madman.

That indeed seems to be the case. In 1945 Hitler gave a radio speech that was carefully analyzed by the Allies. While it was determined that the speaker was indeed Hitler, everyone who knew him agreed that he sounded like a very different person by then.

I'll bet Hermle made bomb fuses then.

Mark Kinsler

 

[MARK A. BUTTERWORTH]

Even if I ordered all my bushes from you, the postage would still be the killer cost.

Our mailing charges for bushings to US addresses are free. Overseas is surprisingly inexpensive. Send a note asking for a quote to butterworth@butterworthclocks.com

 

[Ralph B]

I'll bet Hermle made bomb fuses then.

Mark Kinsler

Only because they didn't have to last long........

Ralph.

 

[MARK A. BUTTERWORTH]

In fact the timers were made in the watchmaking area of Pfortsheim at the northern end of the BlackForest and I was told that in one night of bombing over a quarter of the 60,000 residents were killed.

 

[novicetimekeeper]

Many moons ago in a former life I did a lot of work with a Swiss engineering company in Schaffhausen. As a Swiss German the MD was quite the Anglophile and we got on well. He would often tell me stories about the war and his family experiences.

They were stiil finding unexploded ordnance at the time and he told me that when bomb disposal approached a bomb they hoped it was German, if not they would want British, but the thing that worried them the most was American. Apparently the least predictable of them all.