Later Tamaya Scale Lighting Systems

29 03 2013

This post was preceded by one on overhaul of the earlier Tamaya switches.

Early Tamaya sextant scale  lighting systems used a switch that was obvious in action and simple to overhaul. Later ones used a fully moulded handle that had no obvious way of accessing the switch contacts, an essential requirement of an electrical system working in a salt water environment. I covered the older Tamaya switch in the previous post in this category and have also covered the even more mysterious structures of a couple of C Plath switches in the “Interesting Overhaul Problems” category. In response to a recent enquiry, I now give an account of later Tamaya systems.

If we begin with the battery handle and remove the screw cap from the bottom we are faced with a deep dark hole, but if the light is right, one can see a spring at the bottom, secured to something with a plated brass screw. The end of the spring is supposed to receive the negative pole of the battery and observant owners will have noticed that there is a “+” sign engraved into the inside of the screw cap. Undoing the screw at the bottom of the hole allows the switch button with attached parts to be removed and when this is deconstructed one can see its structure, as shown in Figure 1.

Figure 1 : Structure of switch exploded.

Figure 1 : Structure of switch exploded.

Note the  contact screw that passes through a solder tag and a couple of washers into the sloping face at the upper end of the handle on the right. Figure 2 shows the parts assembled outside the handle. When the switch button is depressed, the end of the shouldered screw that passes through a bush and spring into the plastic button, moves to the right and makes contact with the end of the contact screw. We can now trace the current as it passes from the negative pole of the battery, through the spring and screw at the bottom of the hole, into the bush and switch contact and then into the contact screw on the side of the handle.

Figure 2 : Switch parts assembled outside handle.

Figure 2 : Switch parts assembled outside handle.

The path of the wire that is attached to the solder tag in a Jupiter sextant is shown in Figure 3 . It is wrapped in a clove hitch around the upper leg of the handle to secure it and then passes through a hole in the index arm and  under a rectangular cover on the front of the arm to the bulb.  The path is similar in the Spica sextant but the bulb arrangement is different.

3 Wire

Figure 3 : Path of wire.

Figure 4 shows how the wire makes contact with the bulb. The wire is soldered to a thin bush and when the bulb is screwed into the holder, its lower contact makes contact with this bush. The lower contact is insulated from the threaded body of the bulb and the latter makes contact with the chassis of the sextant. The lower leg of the sextant is screwed into the side of the large brass bush into which the lower battery cap is screwed, so we can now follow the current from the side screw on top of the handle, through the wire to one contact of the bulb, through the bulb and its body, into the frame of the sextant and back to the positive pole of the battery.

Figure 5 : How wire contacts bulb.

Figure 4 : How wire contacts bulb.

Figure 5 shows the bulb in place in a Jupiter-type sextant and Figure 6 shows its position in a Tamaya Spica sextant, which employs a different shaped light guide to illuminate the scales.

Figure 5 : Bulb in Jupiter and simllar sextants.

Figure 5 : Bulb in Jupiter and simllar sextants.

Figure 6 : Position of bulb in Spica sextant.

Figure 6 : Position of bulb in Spica sextant.

If, like me, you love fine instruments and want to know more about the structure of the nautical sextant, may I suggest you buy my book “The Nautical Sextant”, available via Amazon, direct from the joint publishers, Paracay and Celestaire and from me, or through any good bookseller. You may also be interested in my latest book “The Mariner’s Chronometer” You will find in it a detailed illustrated account of the structure and function of the the marine chronometer with instructions on how to overhaul one with relative safety. There are also chapters on rating and transporting these delicate instruments and the book finishes with an historical chapter from a structural rather than social viewpoint and two appendixes for the advanced worker. It is available direct from Amazon and through large booksellers.

Hughes and Son Admiralty pattern micrometer sextant

14 02 2018

I wrote about a Hughes and Son Admiralty pattern vernier sextant on 23rd June 2011, concentrating on its telescopes, its rising piece for the latter and its sealed mirrors. Recently, I acquired an Admiralty pattern micrometer sextant, probably part of a batch ordered in the closing days of WWII. The main difference is in the micrometer mechanism while the index arm bearing, mirrors, shades and telescopes are essentially the same as in the vernier sextant, certified in March of 1939, so I will not cover that ground again. Figure 1 shows the instrument as advertised by the seller, who seems to have photographed it through a light green filter. This explains the green cast to the blue-grey paint (I have removed the bright green background).

As bought

Figure 1: As bought.

The sextant was in a rather grubby condition, with paint beginning to perish and flake off in parts. I suspect it had been well-used, rather than spending nearly all its life in a cupboard.

Figure 2 shows the front view after a complete strip-down and restoration. In it I have labelled the main parts of a micrometer section for the benefit of newcomers to my site, and those who may not yet have purchased my book “The Nautical Sextant”, which looks in great detail at the structure of these instruments.

A 1 GA front

Figure 2: Front view of restored sextant.

Figure 3 shows the rear (or right hand side when in use). Here it is possible to see why this sextant, weighing in at 2.05 kg (4.52 lb) is so heavy. The cast bronze frame is very heavily ribbed compared to most other sextants, and features like the rising piece, the Index arm bearing cover and the complex arrangements for sealing the mirrors have all added to the weight. Earlier Hughes and Son instruments with scale lighting made the battery handle out of wood, but this one is of molded Bakelite with a brass battery cover. Happily, it contained no batteries nor signs of corrosion.

A2 GA back

Figure 3: Rear view of restored sextant.

Figure 4 shows details of the micrometer mechanism. The worm engages with the rack, which is cut into the edge of the limb. The rack is in essence a segment of a worm wheel having 720 teeth. Also cut into the edge of the limb is a groove which accepts the free edge of the two keepers. These prevent the index arm from lifting off the limb.

A3 micrometer detail

Figure 4: Details of micrometer mechanism.

The axial pre-load spring, which is shown out of place, is U-shaped with one upright of the U being forked to embrace the worm shaft and press on the flange immediately to the left of the thrust bearing. The worm shaft inside the bearing is conical, so it aligns the shaft axially and radially with a further bearing providing more radial guidance. This spring is a simpler solution to providing thrust pre-load than the more complicated systems used by Hughes and other makers prior to WW II.

The worm is held in engagement with the rack by a beryllium-copper radial pre-load spring. A simple cam bears on an arm extending from the swing arm on which the bearings and worm are mounted. When the release catch is operated, the cam causes the swing arm to rotate around a substantial bearing  and the worm disengages so that the index arm can be swung rapidly to a new position. When the release catch is let go, the spring swings the worm back into engagement with the rack and rotation of the micrometer drum provides fine adjustment.

There is a guard extending from the swing arm to provide some protection to the micrometer drum and the worm shaft. The shaft is often bent when a sextant is dropped or knocked and, as replacement parts have long been unobtainable, a whole worm and shaft have to be made. See for example “A Worm Turns” on this site on 23rd June 2011. The worm itself receives some protection from a sheet metal cover, seen in Figure 3.

Figure 4 shows the front of the index arm in the area of the worm. The screw that secures the axis about which the swing arm rotates has been removed to show a washer that is prevented from rotating by two pins into the swing arm, so that the screw can be adjusted to remove end shake in the bearing, while preventing movement of the swing arm from loosening or tightening the screw.

A4 micrometer front

Figure 5: More micrometer details.

There seems to be little point in providing a vernier to the micrometer, as the racks of this era often had errors in excess of 0.5 minutes and in any case, observation errors due to uncertainties about refraction and dip would often swamp instrument errors. Most makers after WWII abandoned micrometer verniers, but some were still made, presumably to satisfy conservative mariners and military procurement officers.

This instrument was provided with a fairly comprehensive kit of telescope and tools, shown in Figure 6.  Most mariners probably never used anything other than the Galilean (“star”) telescopes in the 20th century.  The higher powered ones were probably used mainly for artificial horizon shots in ports of known longitude to correct chronometers. This was made obsolete by the advent of radio time signals, but Tamaya in particular continued to provide them to the very end of sextant manufacture.

A6 telescopes etc

Figure 7: Ancillaries.

The eyepiece shades are useful for finding the index or zero error of the sextant by looking at the sun or moon, but again, most mariners would simply have used combinations of horizon and index shades, or used the horizon to avoid strain on the neck from looking up at the sun.

A very useful feature of the Galilean telescopes is the provision of hoods to prevent glare from around the horizon mirror reaching the eye, as the hood limits the field of view to the mirror alone (Figure 8).

A5 telescope hood

Figure 8: Telescope hood.

Figure 9 shows the sextant and its telescopes etc. in its fine mahogany case. As usual from about 1900 onwards, the corners have box comb joints. In all Hughes and Son sextants, the handle is on the right hand side, to avoid setting down the box on its hinges.

A7 in box

Figure 9: The sextant in its case.

Figure 10, shows the case standing on its left hand side. This, together with the hook latches which always face to the left, so that they tend to remain latched in the carrying position, identifies the sextant as a Hughes and Son, if it were not obvious from the circular “Husun” emblem attached to the index arm.

A8 latches

Figure 10: Hook latches in closed position.

If you have enjoyed reading this account, you will find much more of the same in my book “The Nautical Sextant”, but do not expect to find anything about in it about navigation. It is about the structure of the sextant.You can find plenty of positive reviews of the book on the web site.




29 12 2013

This alphabetical list of posts may help you to find what you want. When you have found a post of interest, enter the part of interest as a search term in the search box.

A10 vapour pressure bubble chambers, Sealing

Admiralty pattern vernier sextant

Admiralty pattern micrometer sextant

AN 5851-1 bubble sextant averager., Gummed-up

AN 5851-1. Jammed shades carrousel

Battered Observator sextant, A

 Battery Handle Structure, C Plath

 Box Sextant, A

Broken legs

 Bubble Horizon Attachment, C Plath

Bubble illumination of Mk V and AN 5851 bubble sextants

Bubble sextant, land use conversion of Mark IX     May 2021

Bubble Sextant Restoration Manual, A12

 Bubble Sextant Restoration Manuals, A10 and Mark IX series

bubble sextants, Aircraft

Bubble sextant, Hughes Marine 

 Bubble Horizon, A Nautical Sextant

 Byrd Aircraft Sextant, Update on

Byrd Sextant Restored, A

Carl Plath’s Earliest Sextant

C Plath Sextant Lives Again

 C. Plath Drei Kreis sextant, Restoring a

 C. Plath Vernier Sextant, A Fine

C Plath Yachting Sextant

C18 sextant named J Watkins

C19 sextant restoration

C Plath Sun Compass

Carl Plath micrometer sextant

 Carl Plath Sextants, Eighty Years of

circular sextant mirrors, Making

Compass, a C Plath sun

Compass, an improvised sun

Damaged Rising Piece, A

 Dip Meter, A Russian Naval

 Dip Meter, An Improvised

Distance Meter, A Stuart

Distance Meter, Fleuriais’ Marine

Drowned Husun Three Circle Sextant, A

Ebony quadrant, restoring a

Errors, Backlash and Micrometer

Faking it., Is it a SNO-M or is it a C Plath?

 Filotecnica Salmoiraghi of Milan, A Fine Sextant by

Freiberger scale illuminator    May 2020

Freiberger Drum Sextant (Trommelsextant)

Freiberger Skalen Sextant

Freiberger Yacht sextant

A French Hydrographic Sextant

Half-size Sextant by Hughes and Son, A

Half-size Sextant by Lebvre-Poulin, A

Heath and Company’s best vernier sextant

Heath Curve-bar sextant compared with Plath

Heath Vernier Sextant Restored

Hughes Marine Bubble Sextant

Hungarian sextant via Bulgaria, An

Hydrographical sextant, a French

Ilon Industries Mark III sextant

Jesse Ramsden and his Dividing Engine

 Keystone Sextant Case, Making a

Land use conversion of Mark IX bubble sextant     May 2021

 LEDs 1: miniature screw bases., Adapting to

LEDs 2: Plath bubble horizon unit, Adapting to

Lefebvre-Poulin, a Half sized sextant by

left-handed sextant, Unusual

Legs, broken

Mark V / AN5851 sextant bubble chambers, Refilling

 Markk V/ AN5851 sextant bubble chamber, Overhaul of

Mending a 1975 SNO-T sextant

MHR1 position line slide rule, A reproduction        June 2021

mirrors, How flat are sextant ?

Mercury amalgam mirrors     May 2021

 monocular mounting, Making a sextant

Observator Classic sextant, restoring a

Observator Mark 4 sextant

 Prismatic Monocular, Making a

 Quadrant Restored, An Early C19 Ebony

Quadrant Restored, an old wooden          June 2018

Reproduction MHR1position line slide rule, A       May 2021

 Scale Lighting Systems, Later Tamaya

Sextant ‘scopes for myopes

Sextant Mirrors, New  for Old

Sextant Calibrator, A

Sextant Frame, Evolution of the

sextant shades, Polarising

Sextant, 210 years on,

Shackman sextant and a link to Jesse Ramsden

 Shades-adjusting Tool, Making a

Simex Sextant(s

Skalensextant, Inside the

SNO-T Mirror Bracket Repair

SNO-T sextant, Mending a,     October 2020

 SOLD KM2 Bubble Sextant

Sounding Sextants 1

Sounding sextants 2

Sounding sextants 3

Spanish Vernier Sextant, A Late

Spencer, Browning and Co sextant

Sun compass, a C Plath

Sun compass, an improvised

switch overhaul, Tamaya

Tamaya Collimation Blunder

The Case of the Broken Screw

Troughton and Simms Surveying Sextant

Turn-of-the-century French Sextant

US Maritime Commission Sextant, A

USN BuShips Mark II sextant: some design oddities

USSR SNO-M sextant, The

USSR SNO-T sextant, The

 Vernier Sextant, British Admiralty

Watkins, J, A C18 sextant named

Which lubricant?

Worm with wrong thread angle?

Worm Turns, A


26 10 2008

Here is the unusually detailed hierarchical table of contents and a sample of the text. There is a 14 page index too.

Please note that in this post there are minor differences in font and layout from those in the book.


Table of contents                                                         

Table of Figures                                                             



Chapter 1


Chapter 2

          Anatomical overview                                             

Chapter 3


                   Tools, materials and workplace                    

                   Removing the sub-assemblies                      

                             Brandis and their successors              

                             SNO-T and Freiberger sextants          

Chapter 4

 The Frame                                                           






                             Tapered shaft and socket                   

                             Parallel shaft and bearing                    

                             Ball bearing                                       

Chapter 5

 The Micrometer                                                   


                   The rack                                                     

                   The Micrometer mechanism                         

                             Micrometer screw bearings                

                             Swing arm bearings                           

                             Release catches                                 

                                      C Plath, Tamaya, USN

                                      Mark III and clones                  

                                      Brandis and USN Mark II         

                                      Hughes and Son                      

                                      Heath and Co                          

                             Micrometer drums and verniers          

                   SNO-T and Freiberger Präzisionsmechanik  

                                      micrometer dis-assembly          


Chapter 6             

 Vernier scale                                                        



                   Tangent screw assemblies

                             Usual pattern                                     


Chapter 7

 Mirrors and mirror mountings


                   Index mirror and mounting                          

                             Tilting foot                                        

                             Tilting mirror                                     

                             Tilting mirror, Brandis variant             

                             Spring-opposed screws                     

                             Sealed mirror                                     

                   Horizon mirror and mounting                       

                             Early sextants                                    

                             Common twentieth century


                             Survey sextants                                 

                             Circular cast cells                              

                             Hughes Admiralty pattern sextants   

                             Kelvin Hughes Survey sextants        

                             Full view mirror                                 

                   Adjusting screws                                         

Chapter 8

 Shades and shade mountings                                




                             Tapered pin assembly                        

                             Shouldered screw assembly               

                             Parallel pin assembly                          

                    Eye piece shades                                         

                   Uncommon shades                                               


                             Wollaston prism                                


                             Intra-telescopic shades                      

Chapter 9



                             Galilean or star telescope                    

                             Keplerian or inverting telescope          

                                      Ramsden eyepiece                   

                                      Huygenian eyepiece                  

                             Prismatic monocular                          


                   Telescope structure                                     

                             Galilean or star telescopes                  

                                      Objective lens                          

                                      Blooming of lenses         

                                      Eye lens                                   

                             Keplerian or inverting telescopes        

                                      Objective lens                          

                                      Eye lens                                   

                             Prismatic monocular                          

                             Sighting tube                                     

Chapter 10

 Telescope mountings                                           

                   Fixed pillar and ring                                     

                   Vee and flat without collimation          

                   Vee and flat with collimation                        

                   Rising pieces with fine adjustment                

Chapter 11

 Legs and handles                                                 


                 Plain handles                                               

                 Battery handles                                           

Chapter 12

Scale magnifiers and illuminators                           



                          Shaded lamp                                               

                          Light guide                                        

                          Photoluminescent magnifier                

Chapter 13

The Case                                                              

                 Box structure                                              

                 Box furniture                                               

                 Securing contained parts                                       

Chapter 14

Cleaning, restoration and repair                              



                          Inspection for damage                                 



                          Bearing bush                                     

                          Bent legs                                           

                 Index arm                                                   

                 Micrometer  and rack                                  

                          Micrometer worm                              


                 Swing arm assembly                                    

                 Tangent screw assembly                              




                 Mirror mountings                                        


                          Clip-securing screws                         

                          Adjusting screws                               

                 Shades and their mountings                         


                 Telescope mounts                                       


                 Lighting systems                                         

Chapter 15


                 Perpendicularity error                                  

                 Side error                                                   

                 Index error                                                  

                 Collimation of telescope                              

Chapter 16

       Calibration of sextants                                          

                 Multiple collimators                                     

                 Rotary table and autocollimator                    

                 Two autocollimaotrs and surface table          

                 Micrometer calibration                                 

Chapter 17

       Some sextant makers                                            









                 1 Effects of mis-collimation on

                                             sextant error                   

                 2 Analysis of centring errors                        

                 3 Recipe for resilvering mirrors                    


Short glossary                                                             


Have a browse through a few pages  to get the “flavour” of the book. Don’t forget you can click on the image to enlarge it, though the quality of the photograph won’t be as good as the original in the book.