In this instructable I will try my best to show you how to take apart your mechanical pocket micrometer and clean and lubricate it.
I bought this Starrett pocket micrometer at a garage sale for a US Dollar.
I have other micrometers, but this one was designed to fit in your pocket.
Step 1: Take It Apart
There's a rule of thumb, and that is that if it behind a rivet, it is not necessary to remove it to get it apart. There were only a few screws holding the entire assembly together.
You should photodocument your steps. I am very sorry, I do not own a digital camera. I have to rely on my cellular phone camera. I wold love to get good macros, as I love macros, but I cannot afford a digital camera.
The needle indicators pop off, upward. Be careful not to mar the dial face plate. You cannot hurt the mechanism by removing the needles.
Pay attention to the spring tensions on your device. It will save you from having to guess and disassemble/reassemble like I had to do. I only decided to make this an instructable halfway through this so I do not have any taking it apart pics.
This micrometer is very old, looking at the plastic dial cover. But Starrett is a great brand, and built very well.
Something you should be aware of, and that is that you may be able to get 90% of it properly lubricated without taking it apart as far as I have. But, I am really anal about this sort of thing, so I took it all apart.
Step 2: Clean, and Begin Putting It Back Together.
Put oil in every bushing, and every shaft and on every tooth of every gear. Some may say this is over kill, but you will never have an under lubricated mechanism this way. I use Break Free CLP, available at Wal-Mart.
Start with the spring loaded gear at the bottom. The end of the spring is held between a screw head and a brass spacer. Don't over tighten it, you can collapse the spring.
Do you remember the tension? If not, you will have to wait until you get the pivot gear (Oddly shaped brass gear) and pinion gears assembled.
What you are looking for, at full extension of the micrometer (The largest opening) is a spring that is tensioned, but not so that the coils are overlapping. You can bring it up to that point, but if you do, back it off a few teeth. Hold it there with the backing plate on with a small screwdriver.
The purpose of this spring is to keep tension on all of the teeth, all the time. This is because nobody can maintain perfect 1/100,000" meshing of all of the teeth on all of the gears. A simple spring keeps everything tight and ensures an accurate instrument, all of the time. Neat, huh?
I did not do much cleaning of the internal components. They are generally pretty clean. But if you want, you can use a small wire brush to clean the teeth, but don't go nuts. The teeth are tiny and very delicate.
Step 3: Keep Putting It Back Together.
The larger spring was held in place by the tension of the screw on the pivot gear, and by a keeper also on the pivot gear. Creating adequate tension was very difficult. Too much tension and the spring coiled over itself, creating a friction stop against the dial cover and binding the mechanism.
Also, when I tightened the pivot gear screw, it would turn the spring and change the tension. I had to anticipate the tension created by tightening the screw. Anyone who has done a valve adjustment knows what I am talking about here. But it was not that hard. Actually, it required just enough tension to just come up to the keeper on the pivot gear, then lifted up and over the keeper.
You would think there should be more tension, but any more and the spring would overlap and lock the mechanism up.
After you make sure the pivot gear is tensioned properly, put all of the gears in place and make sure you have enough tension on the spring gear on the bottom, and that the mechanism moves smoothly without overlapping on any of the springs.
If you cannot keep the pinion gear in place (The tiny gear) long enough to fit the faceplate, and the tensioned gear wants to unwind, then keep the tension with a small flathead screwdriver until you can fit the faceplate. Once the faceplate is fitted and screwed down, once again make sure nothing is binding.
Step 4: You Are Almost Done!
Now you are ready to fit the needles. Notice that on the dial faceplate the holes for the needle bushings are drilled too big. This is to allow you a cushion of adjustment to zero. In other words, you can physically "turn" the dial to set it to zero without changing the position of the needle. Also notice that you can not move it too much, so you must center the needles as best you can.
Notice that even a little push on the needle will seat it slightly and it will be very difficult to remove.
Cycle the action a few times, and then place the needles where they should be. Make the small needle point to the center of the zero. The large needle should face directly upward, at the zero, when the dial face needle holes are perfectly centered, allowing you adjustment either way.
You will need this leeway for the next step.
Once the needles are looking centered, tap them down with a plastic screwdriver handle. You cannot hurt the mechanism by tapping them.
Step 5: Final Step!
Now to place the plastic cover over the dial face. This is the hardest part of re assembling the unit. This is because the cover is not moveable once it is snapped down. And once it is snapped down, guess what-it moves the dial face just a little. So you must anticipate the movement to zero it.
Once you get past this, you will notice that the mechanism binds. What a bummer!
But do not despair. This fix is easy. Remember, you have just put tension in several places that has not been alleviated. How do you relieve the tension that is causing your binding? Simple.
HOLD THE UNIT IN YOUR HAND, and take the plastic handle of a screwdriver to the back of the unit. Tap it, gently. This was cause a shock that will unseat the components and cause clean, smooth movement. Don't overdo it, and do it several times if you have to to make it move freely.
If you tap the unit on a hard surface, such as a table, you will be causing undue shock and may damage the unit. Holding it in your hand absorbs a lot of the shock.
If it's still zeroed after all this, go ahead and test it out with a feeler gage.
I have one that goes down to .0015", or 15 ten thousandths of 1 inch. Or, if you take one in, and divided into ten thousand equal segments, this would equal just 15 of those ten thousand segments. Wow, that's pretty thin.
But the micrometer reads it perfectly, see the pic. The micrometer must be 25+ years old, but it is still very accurate. The oil has really smoothed the action and ensured protection from corrosion, and guarantees a smooth action another 25 years from now.
Not bad for a dollar!
Thank you for reading.