BabbageDifference Engine #2 at CHM - Photos
Installation April 9 - 21, 2008

and Maintenance - December 30, 2009
and Move and Repair during CHM renovation - July 2010

Photos and text by Ed Thelen

Comments:

• This document focuses on the activities of only 5 people who were preparing the Babbage machine for demo at CHM. Many other people planned and did a) the move, b) constructing the environment of two walls and a Victorian Setting, c) electrical and mechanical work, d) and the usual hidden things needed for smooth operations.
• The machine arrived rusty. The engineers were horrified that the polished steel in London,
  now looked similar to the bronze.
  There was a continuing priority struggle for 2 weeks, polish or improve function.

  The machine arrived with many screws and taper pins loose - and the machine had evidently been dropped or thumped - witness broken counter weight cables, "settled" stereotyping mechanism and column height problems.

  This document is not intended to be comprehensive, just some uncommon views of machinery and people -

  We made liberal use of private 1401 Restoration tools, and CHM tools and facilities to handle the unexpected Babbage machine problems.

Table of Contents

May 9th, Day 1, arrival Tightening Steel rusted, looks bronzy Special Tools Carry Problems First OOPS need parts from London

Removing a column of carry levers Shifting a rack of arms 0.019 inches Stereotyping and Proof Printing End-of-page problem Time's Up, The two weeks allowed are up. Other and Visit

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Principal Actors	(At the end of the last day of a long 2 weeks ;-))
Doron Swade Started the Babbage "restoration" effort 23 years ago at Science Museum. Continuing leadership. CHM Guest Curator.	Richard Horton Helped Reg Crick build 1st machine. Engineer in charge of building this machine.	John Shulver Filled in for technician. Engineer in charge of steam engines at Science Museum	Tim Robinson Made Babbage Engines from Meccano parts - see here and here. Heads docent Babbage training effort.	Judith Haemmerle CHM Volunteer, mechanical enthusiast.
Babbage Arrival	Richard Horton and John Shulver arrived from Science Museum to install it.
We are all waiting	Tim Robinson showing Richand (left) and John Shulver (center) a portion of Tim's approximation of Babbage Analytical Engine	Tim showing Card Reader	At last ...
Reporters	Removing Bracing
Tightening
Many screws & taper pins loose, some fell out - Tim spent hours checking and tightening.		This pin had fallen into the oil drip tray below.
These situations required machine rotation or parts removal to check/tighten.
Steel rusted, looks bronzy
The "bronze" on top is steel. You can see some protected steel inside.	Three containers of BRASSO, emery cloth, and abrasive rubber pads were used to remove rust.	Tim working on the stereotyping engine. Maybe 80 people hours of polishing?	Tim and Judith polishing, John is probably polishing also -	Judith adding BRASSO to her polishing rag.
Special Tools
	The "L" shaped steel tool in the center adjusts the carry arms. Note the pry bar -		This unusual screwdriver is shaped to fit screw heads perfectly and leave fewer marks and burrs.
	This "FoodLube" smells better than the oil used in London :-))		And a neutral smelling grease ;-))
Carry Problems
Tim provided a list of what each column of 31 figure wheels should contain each cycle	- to localize missed or extra carries The circled items indicated a missed carry in "D3", a really trouble column. Tim and I verified the 4 carry triggers on each of 7 x 30 figure wheels that are involved with generating carries.	Doron explaining the carry system to Al Kossow (bitsavers.org)	Note the carry lever bending tool near Doron's left hand. This tool helps correct local missed carries and false carries.	Richard Horton bending part of the cast bronze carry lever - a few thousandths?
First OOPS
Confusion while adjusting the "D3" axis left some carry levers set when the crank was turned during part of the set-up. This breaks carry levers.	Emergency call to Science Museum (London) yields box of replacement carry levers.
Removing a column of carry levers
Column removal and replacement is a one to two day adventure :-((		Marking the layout table to organize parts for replacement in the same relative location.
		Very snug fit, no slop	A little help	During the reassembly process, Richard polished, lubricated, and checked smooth operation of all parts going onto the third difference shaft - several hours of meticulous work.
0.019 inches	Shifting a rack of arms 0.019 inches
Game plan: use double shims totaling 1.019 inches. Actually needed double sided tape to secure during installation.	John making holes with little burring
Stereotyping & Proof Printing
Wooden handles help wind up weights during debug	Control lugs of 30 individual impression wheels	Characters to make impressions in stereotype media
Spools for paper for proofing	The "jaws" facing inwards lock the impression wheels while being lowered toward the stereotyping plate	note brass screw and nut to hold alignment during insertion.	Another view of locking jaws	A complete assembly
End-of-page problem
About 2 hours before leaving Monday for the Going Away Party, and engineers back to London -	an impossible problem came up. The control for the clutch stopping operations at end-of-page failed	Every thing seemed correct - but it would disconnect at strange times - Maybe we are suffering from battle fatigue?
Time's Up, The two weeks allowed are up.
	We then wrapped the machine because the wall would be sanded tomorrow. - Right, Many Thanks Good Bye Party
Other
	Babbage School	Tim Robinson instructing
Visit
Visitor's 1st view Movies in black TV on right	<- Analytical Engine -> Difference Equations	Judith and John Apron means docent	The Engine is scheduled to be at CHM until - UPDATE - Nathan Myhvold has extended to loan to December 2009 :-)) - then off to his living room, with the tyrannosaurus rex.

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Maintenance - December 30, 2009

Sorry this is so short - I was in a hurry to go elsewhere when :

Randy Neff had dropped by the 1401 Restoration area to give us an interesting ad. So I went to his area to see what was happening -

Julie Neff (left) and Tim Robinson examining the cranking end of the 2nd Babbage Difference Engine, currently housed at the Computer History Museum

In a quite voice, Randy Neff explained that:

• Tim Robinson (our master Babbage Engine Mechanic) had just returned from England (his home land) and while there had consulted with Richard Horton (the builder of this edition of the Engine) about problems with this engine. (apparently carry levers are breaking at a greater than expected rate).
• They compared timings, decided that the carry timing on this machine was different (and not correct) compared with the original Engine at the [British] Science Museum.
• When the CHM Engine is moved to another location, as part of the complete reorganization and re-curration of CHM, Richard Horton will come to CHM and do a major rebuild of the carry section - including the replacing carry levers currently broken.
• This type of operation is shown here
• Randy mentioned that this month PBS had carried an interview with Tim Robinson about the machine, and the next Wednesday about 150 guests tried to crowd into the 2:00 P.M. Babbage Engine demo -

Tim (center) and Randy lifting a big heavy gear assembly from the Engine.

onto that prepared wooden stand. In the background is a drawing of the Analytical Engine, and the chalk board docents use to help explain the arithmetic of the machine. At the far right is a TV with a talk about the machine.

Isn't that sweet, almost sets my heart a-flutter !!

Babbage is looking unhappy :-(( OK, he always looks unhappy - Tim is driving in the 1st pin securing the position of this bevel gear

and the 2nd pin

Time to reassemble - That heavy gear assembly slid in with a deep solid authoritative THUNK - just wonderful :-))

Julie is re-attaching the machine angle pointer.

I hope no one asks me why they were doing all of this !!

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Move and Repair during CHM renovation - July 2010

July 2010 - the 2nd Babbage machine was moved to another location in CHM to make way for a major museum internal rebuild to support the new desplays and organization. (The new Grand Opening should be late in the fall of 2010. These pictures are from Herb Kamer, on Flickr After the move, the machine is partially disassembled to insert new carry levers which were broken over the past 2 years. The reason for the breakage in now understood and corrected :-)) The operations are very similar to those previously in Removing A Column Of Carry Levers above. Tim Robinson (left, CHM Babbage Expert) and Frank King (1401 Restoration) are discussing the possibility of brazing/welding repairs to broken carry levers in the future. The tolerances on the position of hook on the lever are really tight - an error of 0.003 inches disable the operation. There is a bending tool to bend the solid metal to achieve correct operation.

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Other Info

• a fun (New Yorker) article about Nathan Myhrvold, who funded and owns this machine. Wouldn't it be nice to imagine "the rest of us" could handle serious money in such a fun useful way? - link from Roy Ogus - Local copy
• a current Myhrvold interest
• A 2007 visit by Nathan Myhrvold to CHM
• How to calculate the eight Babbage Difference Engine #2 parameters for arbitrary functions and other Engine info -