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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

"The final demonstration will be January 31, 2016."

Len Shustek introduces Myhrvold & Swade Discuss Babbage's Difference Engine at CHM

"Plan 28 Blog" (project to build a Babbage Analytical Engine)
Winter 2021 report to the Computer Conservation Society

Photos and text by Ed Thelen
More detailed info on the design and construction of the Difference Engine


Table of Contents

May 9th, Day 1, arrival
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
Maintenance June 2010, - April 2011
Refurbished Inking Rollers
Filming for Docents before shipping to Seattle - Jan 25, 2016
Party Time - I only got the inked printer demo - Jan 25, 2016

Principal Actors

(At the end of the last day of a long 2 weeks ;-))      

Doron Swade
Started the Babbage "restoration" effort 1989 at Science Museum. list of videos. ... history ... video )

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 ...


Removing Bracing


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 (
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

& 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



Babbage School

Tim Robinson instructing



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.

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 (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 !!

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.

Babbage down for a few weeks - April 2011

This is a report from Jim Strickland's CHM "Volunteer Information Exchange", Volume 1 Number 7, May 16, 2011.
(CHM regards most of the contents private.)

Refurbished Inking Rollers

Monday Jan 11, 2016, Tim Robinson showed me two inking rollers which he had just received from a refurbishing company (in London?). These rollers are used to spread the ink before applying the ink to the type faces for printing onto the check paper strip. The previous rubber had become "gummy" and not usable. The new "rubber" is synthetic and should survive longer.
     The pink scale was sized to match the reference automobile key and inserted into the picture.

Filming for Docents before shipping to Seattle - Jan 25, 2016

John Plutte (CHM Director of Media) arranged to video record Tim Robinson (Master of the Babbage Difference Engine) giving a sample docent introduction to the engine today. Serious "film making" is a serious business. Lots of specialized lighting and multiple supporting staff, and lots of careful setup before the inevitable retakes ...
Fatiguing for this point_and_shoot guy, but the results are much superior -

Starting - before 8:30 ;-((
Director Plutte bending over table, Tim Robinson (red shirt) as the solo actor.

Discussing 1st Scene
Director Plutte and Actor Tim Robinson discussing 1st scene.

Tim Cam Stack
Tim pointing to and explaining the Cam Stack. We see the "Steady Cam" in use. Lowell Klaisner is polishing (off camera)
Lisa Robinson
Lisa Robinson is a volunteer helper (and machine polisher and makeup artist)

Lowell Klaisner
Lowell Klaisner is a volunteer helper (and machine polisher)
Lisa doing hair
Lisa Robinson tidying up Tim Robinson's hair

Tilted Table
The table was level for the first shot, but now tilted for the second shot and better view.
Director Plutte
Director Plutte and assistant checking progress.

Adder Parts
Tim demonstrated how these interacted, moving up and down under control of the cam stack.
Print Faces&Gears
The narrower set prints with ink on paper for monitoring progress. The wider makes impressions in (like plaster of paris) for making tables.

The building was rented by a group matching genetics to medical treatments. The room above had one of the presentations. The noise in this echo chamber was very fatiguing !!
By about 4:30, the printer was the last topic.

Party Time - I only got the inked printer demo - Jan 25, 2016

Vibration Damper added a few weeks ago. Machine seems more stable to crank, and no further troubles :-)) The leather strap is a dog leash.
Details of the fix. Babbage would have been proud of the Elizabethian solution ;-))

The white paper toward the upper right is to be printed as an "on-line" check.
This is the printed paper, first time for this machine. Clearly there is an alignment problem to be solved.
However, Marc Verdiell posted a YouTube of the Babbage machine at the going away party,
and I get my millisecond of fame (2 minutes and 50 seconds in) ;-))

Other Info