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TELESCOPE AND INSTRUMENT RESTORATION METHODS AND TECHNIQUES
Jon Slaton

 

NOTE: this is not a complete primer on restoration techniques; rather it is a few precautionary notes coming from personal experiences.
I really like the John Wooden quote: "If you don't have time to do it right, when will you have time to do it over?

                               

First, my compliments on searching out the correct way to restore your telescope. Second; please read this article completely before trying any of the methods, as procedures may not be in the order you may take and skipping a step may diminish your chances of a good restoration. The first thing I ask people who are contemplating a restoration of any type is: are you really sure it needs restoring? Many times, a good cleaning, proper lubrication and adjustments, and possible replacement of worn or missing parts (mostly bolts, nuts, etc.) will have the instrument ready for use. I had a clock shop for over 30 years and did thousands of repairs, a few quick fixes, but few full restorations. A thorough restoration is always costly, time consuming, and without a doubt stressful to owner and instrument. Proper and frequent lubrication is the key to longevity for telescopes and other instruments.

I personally do not like to see a shiny brass tube on an old instrument. It looks like it is new, or at best, looks like it came from a showcase. I do agree that there are times that stripping and polishing a tube are in order. I have had a few come through the shop, which were harshly abused by soldering things on them, painting them pink, or partially polishing them to where part or all of the lacquer is gone. When parts have been replaced so that the new ones stand out like a sore thumb, stripping may be necessary but first try to make the new parts match the old ones. My first rule when restoring anything is to leave as much of the original as possible. This includes not only the parts, but also the finish. Once you decide to turn a part down in the lathe or file it to make it fit a new piece, you can never put it back. The best policy is to make the new piece fit the old. If you cannot make the replacement part fit the old one, make a completely new piece from scratch. Remember, restoration is not a quick fix, it is costly and time consuming.

Pits, dings, and scratches show some of the history of an instrument. (Sorry antique tractor and car restorers. I know your vehicles really look great but obviously very few, if any older things survive without a scratch.) In addition, a proper patina will camouflage the imperfections nicely, and that includes using Lemon or Tung Oil to coat the instrument. If you have dents or dings that impair the functions or movement, such as on a tube, you can turn a piece of wood on a lathe to just fit the inside diameter of the tube. Remove ALL screws and stops from the tube, and drive the wood through, being careful not to cause any further damage. I have made a series of wooden wedges (they look like torpedoes) in order to smooth out tube dents - starting with one just big enough to start pushing the dents out, and getting a little bigger each time. If you try to push all the dent out at one time, things may not turn out as you expected. You can use this same procedure on flat or curved pieces by making the wood fit the original shape, then pressing or hammering the wood together with the brass in between. If you try and use a hammer on the brass, it will surely dent and have lots of small dings where before you had one big ding. 

Many times the brass does not need polishing, it only needs cleaning. Be cautious as to what you use - ammonia products will eventually eat away at the brass. I have seen brass works from clocks virtually ruined from soaking in ammoniated solutions. I assume these were especially dirty and were left in overnight or longer, but still the cause and effect are clear. Do not use window cleaners, as they too have ammonia. Try warm water with soft liquid soap added in, and lots of time and clean rags. The tendency is to go ahead and use something stronger, and clean it off when done. To do so you are harming the very thing you are trying to preserve. There are some brass cleaners, which specifically state for brass, but upon reading the labels, you see they do indeed contain ammonia. Not to say that ammonia does not clean brass - it does, but rather you need to look at the long-term effect on the brass.

I do not use any type of buffing wheel or the like, as it is easy to very quickly remove square edges, ending up with rounded corners and smoothed out details. A few passes with the buffing wheel and some of the lettering is almost illegible. The names engraved in script on the faceplate of one of my telescopes is so delicate that a small amount of polishing will probably remove the faint ends of the script. Avoid using polishes which are in padding or wadding type, as they seem to polish rather aggressively. Find a cleaner that does not attack the brass. It might take longer to polish, be harder to use, and not clean as quickly, but you minimize the risk of permanent damage. As a side note: I don't polish brass or silver any oftener than absolutely, as you have to notice the black on the rags when you polish it: the dirt is part of the metal which is removed by the polish. Clean and/or polish the tube assembly to your liking.  Depending on how much polishing or cleaning you have done, it may look like a new piece of brass. Clean out cracks with a soft toothbrush, and use toothpicks or whatever to get the cleaner from screw heads and other tight places. It is imperative that you clean the brass thoroughly.  I use lacquer remover, acetone, Xylene, or some other strong solvent to make certain that every trace of the metal polish is completely removed. (Use masks and/or other precautionary measures for your safety.) The brass must be almost surgically clean. After you are sure it is this clean, wipe it down with another clean rag just to be sure. Then use lemon oil or tung oil. (Plain tung or lemon oil, nothing else in with it.) Use a clean soft cloth to apply the oil on the brass. Let it sit for a bit and then rub it down gently until most of the oil is removed. I let it sit for a day or so, and then I reapply the oil, rub it down again, and let it sit again for a few days. You can gradually lengthen the interval between applications to where you finally do it maybe once a year. The brass will gradually darken and have a nice patina. I have not had any corrosion using this process. If you miss a place and some of the polish remains, it will soon show up but you can clean it, and apply the oil finish again without too much trouble. I like to use clean tee shirts for rags. I usually tear them into small pieces to use them more effectively. Once I use one, I don't turn it over or inside out, as I figure there are body oils on it by then. Use a new one and have plenty on hand before you start. I made a new cell for a transit scope, and used lemon oil on the new parts. It stood out for a while, but after a couple years it is starting to match the tube.

I try to do the least amount of polishing, to a point where will look "right."  I have used different types of wax, which will last for about a year, depending on how much you will be using the telescope. Once again, check to be sure there will be no harm done over time. Some waxes turn green and gunky over time and obviously are detrimental to the brass. I have used lacquer on brass and bronze pieces, but I think the oils work better. As a bonus, they are easier to apply. l will not bore you with many of the problems and solutions I have had. Before I did anything to my Alvan Clark brass tubes, I checked with people; asked more people; and called the manufacturer to make sure the product would not attack, corrode, pit, turn green, or anything else with the brass over time. Sometimes the answers were rather surprising, considering what the products were being sold for. I have stripped and re-lacquered one of the tubes twice, and it looks bad again. I bought lacquer from the people that make the lacquer for top-name pianos. You would think it would be good. But it spotted very quickly. Big brown spots right in the middle of the tube. I stripped it, called the manufacturer, and he told me I probably had fingerprints or something on it. I didn't think so, considering the care I had taken preparing the tube for lacquering, but I stripped and re-lacquered it again. Within two weeks it did it again. I called him back, and he asked me if I had mixed the corrosion inhibitor in with it. I replied that he had failed to mention it, along with failing to send it. So I added it, and within two weeks it did it again. Rather than call him back and ask what else he forgot to tell me, next time I will use Tung or Lemon oil.

Some of the parts, such as the piers, are simply a cast metal piece and I see no harm in bead blasting to remove layers of paint. I carefully took layers off a transit base, and preserved a small area of the original paint so the color would be available for future restorers. On other places, such as setting circles, silver inlays, etc., I polished using 3 micron Alox in alcohol applied with a very soft rag. It works fairly quickly, but I polish the bare minimum to make the lines or letters show up. I don't care how careful you are, or what you are using every time you polish something a small part of it goes away with the polishing rag. Try cleaning a new piece of brass or aluminum. Then clean it with Xylol or something. Then clean it again with the solvent. When you're sure it is clean, use some metal polish on a new rag. The rag will immediately turn black. This is part of the metal coming off. That is why I don't polish often and hard. I am not advocating leaving dirt and grit on instruments, just be careful as to how much, how often, and how hard you polish something.

Very clean steel rusts quickly, so it is important that you must protect it from rust.

 

Important restoration techniques

I begin by stripping down the tube assembly and mounting, taking lots of digital pictures, along with detailed sketches and notes. It sounds like a waste of time to do it, but I write down everything about how I took each piece off or apart. During reassembly, your notes can be a real lifesaver because they can tell you that you need to put a certain piece on before you put the one in your hand on - even though it looks just the opposite. I managed to forget a piece and had to take apart the whole mechanism on a clock drive just to put a spacer in which looked like it should go on last. Bolts, nuts, screws, and other small pieces look identical, but often are not interchangeable. I once had the Clark mount taken apart, and put 6 bolts which looked identical in a pile. After I cleaned them, I found out they were the same size, same thread, and the same length, but they were not identical. Each had been screwed in tightly, then they were filed or cut off to make the visible portion underneath smooth to the touch. I not only had to find which bolt went in which hole, I also had to match the original torque. I cannot tell you how many times I removed those bolts. I now use a piece of heavy paper or cardboard with notes directly on it as to where each piece came from, and if applicable, which piece it mates with. I draw the piece on the cardboard, punch holes where the bolts go, and keep each bolt in the hole until cleaning - and even then I only clean one at a time, so as to not mix them up. Many old telescopes and instruments were hand built and therefore will only reassemble one way. Many old instruments are marked with the dot system. A punch is used to make a "dot" in the metal, and pieces which go together have the same number of dots. Just in case the dots are wrong, or perhaps in time past someone substituted parts from another instrument and the dots were different, I still make notes as to which dots match up because you can never be too sure.

Making and repairing parts, and modifying and using tools properly

Many times, there will be parts missing, or perhaps replaced with newer parts which may or may not be obvious. These things really take up your time. Try to locate another instrument like yours, or at least study other instruments and see just what is missing or replaced. I hope that you will have a good idea then of what the piece should look like, and how it should function. It is hard work designing a missing piece; it is also not easy to repair an old one. Note that brass comes in several varieties - try to match what was there. Sometimes the piece is there, but bent. This can be especially frustrating. The tendency is to bend or hammer it back in place, and hope for the best. The problem with this attack is that it is just that - an attack. First, ascertain just what caused the piece to bend or break in the first place. Usually you will find that it is due to one of two causes: the operator did not know or tried to exceed the limits of travel of the piece; or the piece was stressed to the point of damage due to friction. (read: lack of proper lubrication.) Try to fix the underlying problem first, then work on the damaged piece. Many times brass will break if you try to bend it. Try heating it a little and gently see if it will bend back. If not, heat a little more. You may need to anneal it. I use leather or cardboard linings in my vice or pliers when working with brass, as it seems to scratch so easily and removing those marks I just made is really frustrating when they could have been avoided in the first place. Broken pieces are repaired by silver-soldering. I have found that usually silver solder, even though not the same color, barely shows after repairs - if you are careful and do not get it all over everywhere. Use enough to make a good connection, but not too much. This is one of those times where you may need to practice on a few test pieces to see how it works before working on the actual instrument. The joint is strong, so if the piece is bent as well as broken, try fixing the break first then try straightening it, as it will be easier to get it to the correct shape if it is all there!

            Bolts and screws, as mentioned before, are rarely interchangeable. Oftentimes the first person to take them apart marked them with a series of small dots, or punch marks. You will notice that (usually) if there are say 6 bolts in a pattern, one is punched once, one twice, and so on until you get to 5 punches. One is not marked. Please use the correct tool for the job. All too often screw heads are seen with gouges halfway or two-thirds of the length of the screw head slot. This is caused by using the wrong screwdriver blade. Buy a good set of screwdrivers, and keep them separate from your regular screwdrivers, because you are going to file or grind them for instrument use only. Get a magnifying glass and take a good look at a screw head slot. Take a screwdriver, which is the same width as the slot. If you don't have one the same width, use one a little wider. File or grind the sides down to make it the same width. Then start on the thickness and shape of the blade. The blade should fit the slot all the way down to the bottom of the slot, one end to the other, and the sides of the blade should touch the sides of the slot all the way from bottom to top. This fitting of the tool to the screw ensures that you will have maximum torque available to remove and reinstall the screw with the least chance of damage. If the screw does not readily unscrew, apply penetrating oil and let it soak for a while. I know, it is such a time waster because you only have one screw left to remove, but it is better to have all 6 original screws to use again than to have to make one or more. The same advice goes for bolt heads, nuts, and any adjusters on the instrument make your tool fit the instrument, not the other way around.

Which brings up the next subject screws or bolts. Sometimes they simply will not come out without damage, or maybe they were missing to begin with. I try probably harder than I should to match the old screws. Many people see nothing wrong with retapping a slightly larger hole and using a newer, readily available screw. I have done this when the threads are stripped or an replacement simply could not be made. But if I can, I make a new one. If you do not have a sample to go by, you can take a piece of round wood and make it slightly larger diameter than the hole.  Round the end a little, and thread it in. If you are careful, you can then unscrew it and have a thread pattern to go by.

If the screws are all there, but are damaged, you can make them look and function better by carefully and lightly tapping the metal back into shape. I am assuming the screw heads were damaged by an ill-fitting screwdriver. Take a very fine file and clean out the screwdriver slot. The same thing can be done to pieces that have  been hammered on, dented edges, etc. Notice that brass is a soft metal and dents easily with a hammer. If you are trying to straighten a bent piece, use a piece of wood between the hammer and the brass the wood will take the brunt of the force, and the brass should not dent from the hammer blow. It is not as easy to un-dent. The metal parts of the instrument which are flat usually have a pattern to it. This is called the grain, and most metals have grain just like wood. When polishing or cleaning, go with the grain. If this is not clear, get a new piece of flat rolled brass or steel and look closely at it. You will see the grain. Polish it, and go with the grain. Clean it to where it shines. Then polish it just a little across the grain. Clean it again and look at it you will see that where you polished it across the grain it looks scratched. Enough said.

Focusers

Most types of focusers should be greased and/or oiled regularly. One of the major causes of damage in using older telescopes is that they are too stiff to use. This applies not only to the focuser, but to the whole thing. The tendency of many people is if it won't move easily, a little more muscle won't hurt, so force it. I have used specialty waxes on some focusers, and light grease on others. Either way, keep the parts to where they work freely without having to force them. Clean the old oil or wax off regularly and reapply as necessary. A buildup of anything causes binding. Many focusers have a small piece of felt surrounding the drawtube. Make sure this felt is not gummed up with anything, especially tiny pieces of dirt which act just like sandpaper. Incidentally, I have seen some focusers which use a special sticky grease. If you clean them and use something else, they seem to have a lot of play and don't work properly. I have only seen these on new(er) telescopes.  This sticky grease is available from new telescope manufacturers, and some petroleum suppliers.

Reassembly

When reassembling the telescope do not force shafts into bearings, or any other parts together. They should fit snugly, and if they don't fit then something is wrong and needs investigation. Check for play in bearings, worn bushings, and gouges or prick marks on seating faces. Make sure worms are properly aligned with the wheels, and that the teeth are correctly meshing. Worm wheel teeth should have a mirror finish. It almost goes without saying that you need to have everything absolutely clean prior to, and during assembly. A flat surface which is used for something else to slide or rotate on needs to be flat, or at least even. This is one case where you might need to remove some of the original material. Dirt and grit can get into or between the surfaces and the dirt causes the surface to have raised areas, like prick marks. These areas need to be flat. You don't necessarily need to smooth it down to where all the gouges are gone, as many times any removal of metal will cause the mating part to be in the wrong location. You do need to remove the high spots, though, on both parts. I have found that many times a surface is used for a bearing surface and then painted right up to the area where it turns or slides. These are very difficult to repaint, and remember that the working surface needs lubrication of some sort.

Lubrication

Practically all the bearing surfaces, sliding tubes, the screw threads on knobs, and other places need lubrication not only to function properly, but also to prevent wear. I cannot go into every place that needs lubrication, as it is nearly impossible to come up with every occasion. Check the instrument over, and if something rubs, slides, contacts, or threads into or onto another part, chances are it needs proper lubrication. There are some important exceptions: gear teeth are usually meant to run dry. The ends of gears (pinions), where they go through the side plates, are to be lubricated. Worm wheels are usually meant to run dry, and they are also meant to be run clean. By the way, when you are cleaning gears and worms, don't use a screwdriver, awl, wire brush, or anything hard to clean the gunk from the teeth. Once again, use a toothpick, or let it soak in oil a bit to loosen up the offending material. After all, these are precision made pieces and you don't want to scratch them up. If you do, you take the chance of introducing errors, uneven tracking, or even stopping the instrument. It would be a real shame to discover that something only needed a cleaning, but that you were the one that ruined the (gear, part, or whatever) by digging at it with a screwdriver. Once again, it takes longer, but you're after the end result.

            There are various types of oils and greases. Check around and ask to find out which will work best for your application. Be careful, as some lubricants will squeeze out if much pressure is applied. On some of the larger telescopes, there is a lot of weight and torque on the shafts, and it takes special oils and greases to remain in place. Just because the label says for everything under the sun does not mean it will work in your thing. Likewise, some things need the thinnest of coatings, and you would not want something thick and greasy on it.

SUMMARY

Stop and think about what you are doing. Then think it through again. Be sure to take twice as many pictures as you think are necessary. Digital pictures are cheap. I thought I took way too many, yet missed an important angle last time. Before disassembly, ask yourself if you are capable of doing the whole project. From having the clock shop all those years, I can tell you it is very hard to take a box full of parts someone started working on, and then making a working mechanism out of them. Usually you have to fix the problems the last person caused, then fix the original problem. With something like telescopes, it is much the same thing but compounded with the added problems of optics. I usually have several projects going at once. Some are waiting for me to make a piece, some waiting for optics, some waiting for the newly applied finish to dry a while, and some are just waiting their turn. It is almost impossible to go from one to another without some kind of notes or pictures. This is when you'll find out that you should have taken a picture of the underneath of that assembly, in addition to every side. If I only knew which side goes up first, then I could assemble it without having to take it all apart again and turn it over....