Restoration and restoration techniques

 



Restoration and Restoration Techniques

restoring old & antique telescopes - why bother?

In an age where telescopes of every feasible variety are either mass or custom manufactured and many are available off the shelf, it may be ligitimately asked, "Why resurrect a Victorian behemoth, a dinosaur of an age long past and largely forgotten?" Apart from the visual appeal of brass and blackwork, if a large Victorian telescope is capable of being restored to a fully functional state, you may be surprised at how well it performs compared to its modern counterpart.

Late C19th, early to mid C20th telescopes made by firms such as Cooke Troughton & Simms, Ross, Grubb, Steward, Watson, Wray, Zeiss, and Ealing Beck are the most marvelous examples of mechanical engineering and optical excellence. If you think in terms of a permanently housed telescope, it is no more costly to procure and restore an old telescope than order a new one.

How far you take the restoration process and whether you choose to modernise the pointing and drive control system is up to you. There are two schools of thought here; purists who deplore any modern refinements or additions because they merely wish to collect, and amateur telescope makers who have as their goal a fully functional telescope. Personally, although I quite sympathise with the collector seeking an authentic example of a brass refractor for the study window, I veer towards the ATM school. Better to have a big observatory class telescope fitted with a stepper motor control system, and housed in a modern observatory; the best of both worlds.

where to find old telescopes?

Finding old observatory class telescopes is not difficult. Keep a weather eye on Astronomy Now's classified ads, the JBAA, or Loot. Recently I went to see a 12.5-inch f/7 Calver on a #2 pedestal equatorial. The mirror was signed and dated 1912, and apart from a bit of superficial damage to the brackets that carried the dec clamp and slow motion, and a missing RA vernier, it was in perfect condition. It still had the original ball governed falling weight drive in an unworn condition which is rare. The man was asking £3000. It recently appeared on the market again having been procured by Peter Vlasuk for a museum in Florida. They decided they couldn't afford the shipping costs and are now asking £3850.

I also came across a 12.5-inch f/8 Calver mirror in its original pie-tin cell, signed and dated 1912, and still silvered! I acquired that for the Richmond & Kew Astro. Soc. for £500. It came with the original secondary holder, flat, and a very nice brass rackmount which turned out to be an Irving c1960. I had Ron make a brass adaptor flange for it so I could use it on my Calver.

You can also bid for old kit at auctions held periodically by Bonhams, Phillips' or Christies. Most of the telescopes or parts thereof however tend to be very old refractors. Refractors can be a trial to restore because apart from the awkwardness of the mechanics, their lenses tend to leave a lot to be desired. There are exceptions though. In early 1996 a colleague purchased a very nice example of a tripod mounted altaz Troughton & Simms 4-inch f/16 achromatic for £4000. Zeiss kit, especially the early C20th stuff is also well worth collecting.

whether to make an offer?

If you are chasing down a classified, never buy a 'pig-in-a-poke' and never offer the asking price. Arrange a visit so you can check it out fully, and take a friend, and take your time over the process, including some photographs that you can look at later if you decide not to make an offer on the spot. Some old telescopes are beyond repair, particularly those with badly damaged setting circles and wheelwork. Unless you know someone who enjoys rebuilding clocks and has equipment for cutting cogwheels, and unless you know a precision instrument engraver with a dividing engine, don't make an offer for such a telescope.

making an offer

If the telescope is neglected and requires either nothing more than elbow grease, or some basic lathe work to repair, then haggle by offering between a half and two-thirds of the asking price, and take it from there. If the seller refuses to barter, leave your card and walk away. When they get back to you, reduce your last offer and haggle further. If you end up paying more than three-quarters of the asking price you've lost out. Bear in mind that in all likelihood it will be up to you to dismantle the telescope and clear it off site. That can cost. When I collected the remains of my Calver from Cyril Belchem's home in Farnham Royal in 1981, it cost hundreds to hire a mini-van and rent a suitable heated storeroom. When I relocated the telescope from Forest Row to Little Eversden in 1996, it took a crew of four, plus a local carpenter, and a 28 foot low loader. All in all it cost well over £1200 to shift.

restoration techniques

Begin by stripping down the tube assembly and mounting, making detailed sketches and notes as you proceed. Make a particular point of identifying fasteners, where they go, what they mate with, and idents associated with mating parts. This is important. Old telescopes were hand built by master craftsmen. They will only reassemble one way. They are not mass produced, and each component is a one-off. If a part needs replacing, make an engineering drawing of it, and take both it, and the drawing to a skilled machinist for a quote.

You may have to scout round for a suitable substitute finder, rackmount &c. These too are not that difficult to come by. Irving always has a stock of such items. Brass thin walled tube may be a problem. Smith's no longer maintain stocks and only supply to order. If you have problems sourcing brass tube contact me and I'll see what I can do, although I make no promises.

Starting with the mounting remove the axles from their bearing housings. You may require drifts, the use of a fly press, and/or a hub extractor. Bearings can be replaced if worn (look for deformation of the ball cage, scoring &c), a useful supplier is Skefco. If they are plain bearings be careful not to abrade the mating part of the shaft. I can supply stearic grease if you need to regrease the ball bearings, or regrease the sleeve bearings.

suppliers of restoration products

Remove old grease and paint using a stripping agent such as 'Nitromor's', and degrease the metal afterwards with thinners. Iron and steel work can be reblacked using 'Haemetite' salts. Take care when cold blacking, the salts contain selenium dioxide and nitric acid. Bronze bearing shells can be blacked with 'Tourmaline' salts in a selenium solution. If you have difficulty getting these from a local merchant try Myland's on 80 Norwood High Street, Norwood, London SE27 9NW, or Alec Tiranti's at 27 Warren Street, London W1P 5DG. They also sell lacquers, brushes, emery paper, waxes, and polishes and just about anything else needed. A useful clock parts and tool stockist's are Meadows & Passmore in Crowborough, East Sussex.

removing old lacquer and polishing brasswork

Brasswork should be delacquered using hot methylated spirit and a buffing wheel dressed with hard soap. If you need to repolish old brass parts with emery, start with a fine grade and polish out with finer papers until you end up with 1600 or 2000 crocus paper. Polishing out scratches, sleeks and pits is a bit like fine grinding a mirror. You need to work your way through the grades. Once the brasswork is restored to a high polish, degrease it and then either lacquer it using shellac dissolved in warmed methylated spirit, or seal it with 'Tung' oil, or 'Renaissance' wax. 'Renaissance' wax is a microcrystaline cosmoloid wax obtainable from Picreator Enterprises Ltd., 44 Park View Gardens, Hendon, London NW4 2PN. I use it on drawtubes because they need to be free of oil and lacquer, but tend to tarnish rapidly. Renaissance wax retards tarnishing for several weeks.

lacquering brasswork

Brass lacquers come either clear, pale-gold or green-bronze. If you are relacquering the entire tube assembly plus mount fitments, then I would recommend mixing a deep golden yellow lacquer. Matching lacquers is a matter of trial and error. Apply shellac lacquer in a warm, dry atmosphere (between 70 and 80 degrees F). Tubes should be mounted on a wooden mandrel in a lathe and spun slowly as the mop is dragged along the surface in a continuous spiral from the head to the tailstock. Never go over the same place twice and keep the tube turning slowly until the lacquer dries, and then leave it for several hours until it hardens. Small parts may be placed on a steel tray in an oven at its lowest heat setting, with the door agar. Apply the lacquer using a Zorino mop (a type of brush).

chemical blacking and flat blacking

Flat blacking may be done using either Tourmaline, Haemetite or matt black paint. Humbrol do some good quality coloured and flat black lacquers, but the best flat black lacquer of all is a Xylene lacquer supplied by Stirling Varnish at Trafford Park Manchester. I have a gallon drum, and can supply it in small jars if you wish to try it.

lubricating focusing mechanisms

Helical and rack and pinion focusers should be greased using Stearic grease, known in the trade as 'crab fat'. It is this peculiarly sticky, viscous grease that gives camera lenses their classically silky feel. I can supply stearic grease to order, in small quantities, having bought a carton from Castrol a few years ago. Its expensive and its difficult to get hold of. I reckon I've got enough to last a lifetime though.

setting circles

Setting circles that are hard to read because the previous owner has polished the graduations down with 'Brasso!" will need re-engraving. This is a skilled job, done with a dividing engine. The only remaining firm I know of is O.H. Kamph's in Wimbourne Minster. They made an excellent job of my declination setting circle in the mid 1980's.

brass finders and rackmounts; worms and wormwheels

If you need a new period style brass finder, and/or rackmount or wormwheels remachining and replacement worms, try Ron Irving. Iving is still able to do this type of work, and makes an excellent job of it, although he takes his time. But he always has. Ron Irving is notorious for taking a long time over the most trivial of jobs. This brings to mind a quip about Jesse Ramsden referenced by King in his 'History of the Telescope'. .............'Ramsden was notorious for his disregard of time. Although a brilliant and thorough workman when the occasion suited, he had the inconsistencies usually associated with genius...... ........on one occasion Ramsden attended, so the story goes, at Buckingham Palace precisely, he supposed, at the time stated by royal mandate. But he was, as the King remarked, punctual to the day and hour while late a whole year. Ramsden had, apparently, mislaid and forgotten the King's memorandum until it accidentally turned up a year later." I first met Ron Irving in late June 1971. I took a flat to be remounted in a secondary holder. I too have a complete disregard for time, in fact I'm noted for having no sense of urgency. This stood me in good stead as it happened, for when I showed up almost a year to the day, Ron said he'd been expecting me, and produced the mounted flat which he had just finished the day before! So if you're the sort of person who expects everything doing yesterday and get irritated when jobs take longer than anticipated, don't go to Ron Irving. If however you're the patient, 'no worries' sort, you'll get along just famously.

casting lead weights

If you need to cast replacement lead counterweights, either because the original weights are missing or badly corroded then do so in either brass or bronze shells. You will need to make a thick steel baseplate with a register lip to locate the shell, and a mandrel with the screw thread machined on it, or a plain mandrel to locate a bronze sleeve. The shells should have a register lip machined within the wall, and located into the lip should fit end plates either machined from brass or bronze flat. Make sure the shell seats snugly on the baseplate otherwise the lead, when molten will search out gaps and leak onto the heat source. I cast my weights on the hob of an old fashioned electric cooker. I heat the baseplate and shell, until strips of lead placed in the bottom start to melt, and then fill the shell with lead strips and then skim the slag off when it reaches the top. The end plate can be placed over the sleeve to seal off the shell when this is done, the hob turned off, and the shell allowed to normalize. The bronze will oxidize in the heat and will need to be buffed up before lacquering. It is important to ensure that the baseplate and shell are completely dry and that the lead strips are added piece by piece and allowed to melt otherwise the whole melt may erupt and spit and froth and generally do rather nasty things. Brass or bronze shells can be procured from Meadows & Passmore, or machined from thick wall phosphor bronze or brass tube. If you cast the lead around a threaded mandrel, coat it with graphite grease, and make sure there is a hex or square end protruding from the shell so it can be released with a wrench. The type of thread is important too. Make either an acme or a coarse whitworth thread with a long lead and truncated crest, otherwise the mandrel will shear the lead thread as it is wound out.

cleaning telescope mirrors

I'm often asked about cleaning telescope optics, especially mirrors. The best method I know of cleaning dust and dirt particles off a mirror is to use the type of compressed air canister sold at photographic stores. If you need to get grease off the mirror, then get a CO2 fire extinguisher and blow dry ice over its surface and then blow the slurry off using compressed air. Don't allow the CO2 to play on the surface for more than a few seconds at a time though, or the mirror may crack if its plate glass. And keep your fingers away from the nozzle. I normally avoid brushing aluminised mirrors. In fact apart from occasionally blowing the crap off them with compressed air I leave well alone. When the surface looks too awful to contemplate, I get it recoated. I do not have my mirrors overcoated with silicon monoxide either, because it makes recoating difficult. The SO2 as it becomes, is glass hard, and takes a strong acid solution to remove, which may etch the glass.

reassembly

When reassembling the telescope take care not to force shafts into bearings, or component parts together. They should go together snugly, and if they don't then something's wrong and needs fettling. Check for play in bearings and on seating faces; there shouldn't be any. Ensure worms are well bedded into the wheels, that the teeth are correctly aligned (not crossed) and if necessary lap them in using a paste made from grease and jeweler's rouge. Wormwheel teeth should have a mirror finish if periodic error is to be minimized. Any wheelwork should be lightly oiled using Möbius or turret clock oil, as should arbor pivots. Clockwork should never be heavily oiled or greased. It is acceptable to grease wormwheels, but only if there is noticeable and unadjustable end float in the worm. I dislike worms mounted in roller bearings because of this. If you take a look at my RA worm housing you will see that the worm is held between centres which are adjustable. The worm is held hard between centres so it cannot float. If you decide to rebuild the drive system do the same, and instead of driving the worm via mating spur wheels, use an antibacklash Schmidt coupling. If your worm is driven by a clock via a prop shaft and Hooke's joints, make sure the joints at either end are parallel, otherwise you will introduce synosoidal variation (periodic error) in the drive speed. Most importantly ensure everything is spotlessly clean. If you have fettled the parts in a workshop, clean your bench and floor so that rust and metal particles don't find their irksome way into mating bores and shafts. Being meticulous, and attending to every little time consuming particular saves time in the long run, otherwise you'll end up spoiling the proverbial ship for a ha'ppeth of tar.

metal stockists and finishers

Brass, bronze and steel flat, bar and sheet may be obtained from Thames Stockholders, Unit 5W, Woodall Road, Ponders End, Enfield EN3 4LQ. They can also supply duralamin and aluminium alloys and continuous cast iron and forgings. If you need patterns making, I suggest you contact Phil Horrocks, 42 Calderbrook Avenue, Burnley, BB11 4RB; likewise for realuminising. If you need stock gears and drive components I recommend either Reliance Gears, St. Helens Gate, Almondbury, Huddersfield HD4 6SF, or HPC Gears, Unit 14, Foxwood Industrial Park, Chesterfield, Derbyshire S41 9RN. Plating and finishing can be done by Ashby's, Alexandra Road, Enfield, EN3.

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