FILENAMES: Dgage1.jpg Dgage2.jpg DESCRIPTION: These are pictures related to the text below concerning dial gage repair. Posted by Ted Edwards . Ted provided the following description: ======================================================================== Overhauling a Dial Gage E.M. (Ted) Edwards 990827 I will not address replacing broken/damaged parts (except the crystal) in this write up. I have purchased, surplus, two Fedral dial gages reading in tenths and a good friend purchased a similar Starrett. All three of these were esentially unservicable due to them sticking. i.e. The reading did not return to its former value if you pushed in the plunger slightly and then gently and slowly released the pressure. After overhauling them as described below, all three are working beautifully. One of mine had a broken plastic "crystal" as well as being sticky. I have also overhauled a surplus Starrett Last Word DTI. While the mechanism is quite different, the same principles apply. Basicaly, overhaul consists of disassembly, cleaning, lubricating and re-assembly. However, there are a few tricks and "gotchas". You might be tempted to think that complete disassembly is unnecessary. Why not partially disassemble and thoroughly clean in an appropriate solvent? I tried this twice on one of my Federals - it just didn't do the job. Dissasembly Re-assembly is much easier if you keep the parts of the various sub-assemblies separated. This is not necessary if you have photographic memory - I haven't. :-( I use small (about 3"D x 1-1/2"h), thoroughly cleaned, empty cat food cans. Loosen the lock and remove the bezel (front) of the dial gage. The Federals have three small screws around the edge. These screws have reduced diameter unthreaded ends that run in a groove. They hold the bezel in place while allowing it to rotate. The Starrett has a special circlip-like ring. There is a hole in the edge of the bezel which allows you to poke the bulges in the ring to release the bezel. There are three bulges. Find the one furthest from the others and release it first. Tip the bezel up gently and work your way around 'til you get the bezel off. Remove the hand(s). Ideally, this is done with a watchmakers hand puller but it can be done with gentle prying using two screwdrivers, one on each side. You *do* want to pull straight. The dial and (usually) a wave spring or washer can now be lifted off. Next mark and remove the back. This is easy - it is held on with with two or more screws. The ones I've seen will only go on one way due to (apparently deliberate) asymmetric screw placement. Now carefully study the mechanism before going further. Photo DGAGE2.JPG shows the mechanism of one of the Federals. The two major sub-assemblies are the frame with plunger and the gear system. The plunger has a rack cut in the side of it and a spring pushing it out. You can see the spring in the Federal. The Starrett has a coil spring on the plunger at the cap end. The gear train has a pinion that meshes with this rack. The two screws at the 3 and 9 o'clock positions in the photo and the slots they run in provide an adjustment for the engagement of rack and pinion. This shouldn't be sloppy but musn't bind. The Starrett has a similar arangement. Note the spiral spring on the gear that can be seen sticking out at the bottom right of the gear system. This gear and its spring preload the gear system to eliminate backlash. Read all the rest of this paragraph before proceeding further. Loosen the two screws that hold the pinion engaged and rotate the gear system to disengage the pinion. While doing this, keep the gear with the spring from rotating by applying light pressure to the teeth with something soft (like a toothpick). Let the spring unwind slowly and observe how much it unwinds. This determines the preload that you will want to restore on re-assembly. Remove the cap at the top - it unscrews. Under it is a screw threaded into the axis of the plunger. This screw stops the plunger from comming further out. Remove this and the tip at the other end of the plunger. You should now be able to move the plunger enough to disconnect/remove the spring and remove the bar that keeps the plunger from rotating. You can now completely remove the plunger. Remove the two screws you just loosened above and remove the gear carrier. The spiral spring is held to the carrier with a pin in the Federal and a sleave and colar in the Starrett. In the Federal, the pin must be removed before the top of the carrier to avoid damaging the spring. Remove the top face of the gear carrier (the other four screws you see in the photo). Observe the locations of the gears for re-assembly. If you have a digital camera, a photo might be handy later. While the gears can only fit in one place, it can take a bit of fidling if you forget which goes where. JUST DON'T FORCE ANYTHING! Cleaning I used 50/50 Xlyol(Xylene)/Acetone for solvent. All the parts except those with painted markings (dial face) were soaked in this for a while (10 or 15 minutes). Then each was removed, sprayed with clean solvent for a final rinse and gently dried with **clean** compressed air. The dial face can be gently cleaned with soap and water if necessary. At this point, bent hands can usually be straightened with gentle persuasion. Re-assembly and Lubrication Re-assembly is basically just the reverse of dis-assembly. Re-assemble the gear system then lubricate the bearings. Use one small drop of a good grade of light oil, applied with a needle, in each bearing. I used Starrett's Tool and Instrument Oil. A small bottle is a bit pricy but, if used only for its intended purpose, is enough for you, your children and grandchildren. Watchmakers oil is also very good. Some so-called turbine oils are ok but I find Maytag's a little too heavy for this use. DON'T EVEN THINK ABOUT USING WD-40 OR 3-in-1 oil OR ANYTHING SIMILAR. Only a very high grade of light instrument oil will provide long life and resist becomming gummy. I filled a 1 ml hypodermic (with a fine needle) with the oil. I would then let a small drop form on the needle with *very* gentle pressure on the plunger. I would then touch this to the pivot where it stuck out through the bearing and it would flow into the bearing. Other than using an inappropriate oil, the biggest mistake most people make here is too much oil. Install the gear system in the case leaving the screws slightly loose - you will need to adjust the pinion engagement. Position the carrier so the pinion is clear of the rack and re-assemble the plunger mechanism. Lubricate the relevent places: Top bushing, bottom bushing, rack and anti-rotation arm with a drop or two of the same light oil. Now preload the mechanism by turning the gear with the spring the amount you observed when dismantling the gage. This should probably be in the neighbourhood of 1/4 to 1/2 turn of the gear. You should be turning it in the same direction that pushing the plunger in would move it. Gently engage the pinion by turning the carrier. You want good engagement but don't use *any* force bottoming the pinion teeth - everything *must* move freely. Tighten down the locking screws and check that everything moves freely troughout the plunger travel. Place the dial and washer on the front as they were and re-install the hand(s). On my gages, I like to set the hands to read a little below zero when the plunger is free - say about 1/4 to 1/2 turn of the main hand coming up to zero. This way, zeroing the gage on my height gage, lathe or mill slightly preloads everything. I lock the hands in place on their tapers with a tap from my little instrument maker's hammer. This hammer has a head about 1-1/2" long and about 1/4 or 3/8" in diameter. Don't over do it but you also don't want the hands to slip on the taper if there's a sudden plunger movement. Replace the bezel and back and you're done. Note that there's a notch in the dial which should lock into a protrusion on the bezel. Dammaged Crystals Here's how I made a new "crystal" for one of my Federals. This was after checking with several local watch makers to find that a) they didn't have anything of appropriate size and b) if they did the price would be somewhere between astronmical and outrageous. Get a piece of Lexan (polycarbonate) plastic about 1/16" thick (actually it was 1.5 mm). Cut out a square piece of 1/2" MDF (medium density fiberboard). Chuck this in the 4-jaw and carve a bowl shaped hollow with roughly the same curvature as the original and somewhat larger in diameter. I did this by unlocking the compound angle and swinging the compound and a cutter by hand. I was able to position the cutter to give roughly the right radius - it's not critical. Cut out a piece of the lexan about the same size as the MDF and fasten it to the MDF with four small wood screws in the corners. Heat the lexan with a hot air gun and, with a folded up clean, lint free rag, press the lexan into the bowl. Hold it 'til it cools. Put the assembly back in the lathe and, using a parting tool turned parallel to the lathe axis (90 degrees from the usual), cut out a circle a few thou larger than the required "crystal". Pop this into the besel of the dial gage and admire the result. Photo DGAGE1.JPG shows the old and new crystals along with the MDF "mold". The new crystal is installed on the gage. Note also, the aluminum adapter to go from the dovetail and rack that was on the gage to someting I can mount on my lathe/mill, magnetic base or height gage. There's a setscrew you can't see behind the rod. This locks the adapter in position. There's also two more threaded holes in the adapter so the rod can be placed in different orientations.