Cleaning or repair of a Mercer Dial Indicator

I am certain that at some time I have read an article either in ME or MEW on repairing/cleaning a dial indicator.

I have just become the owner of a Mercer 0.0001" indicator with a slightly 'sticky' stem - it will return, but only slowly.

Having taken the back off, it looks a lot like the inside of a watch and I am loathe to interfere without doing some research first. Hence this posting.

Any assistance would be appreciated.

Richard

Hi if you search on YouTube I very quickly found 4 clips of people making repairs to various makes of dial indicators.

This might help you understand how they are dismantled

HTH

Chris

Try wiping as much of the stem as you can over with a cotton bud and some sort of degreaser on it. I would use IPA. I have been known to use cigarette lighter fuel but take care as the fumes are surprisingly explosive and the best way of getting rid of it is to set it on fire or I suppose tip it out some where and let it evaporate.

Sometimes they have been oiled or some has got on it and gone sticky so this often works. Best to try this before messing with the mesh of the rack and pinion etc inside it. If it improves you can get at more to clean by taking the back off but don't leave any fluff behind.

I literally swilled one with lighter fuel once. Didn't work out because there was slight scoring on the plunger so threw it away. Clock oil might help with that sort of thing used very sparingly.

John

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The vital thing is not to lubricate the stem in anyway at all. It must work dry. Try wiping it with a tissue moistened with a little solvent. If you take the back off you can clean the bit of the stem inside with a cotton bud. Make sure that all traces of the solvent have evaporated or have been wiped away. The stem should now move freely. This advice was given to me many years ago by an old employee of Mercer and it has always worked for me. Normally the actual mechanism will not require any attention. Many people try to cure a stick stem be applying oil with the result that matters are made worse.

There was an article called "DialTest Indicator Restoration and Repair" in the Nov/Dec 2010 issues of EIM.

Author was called Richard Gordon.

Edited By V8Eng on 16/06/2015 19:58:56

Edited By V8Eng on 16/06/2015 20:02:13

Many thanks to all of you.

I had thought of using a solvent - not lighter fuel, but methylated spirits. Though I'm not sure about swilling it round, even though that makes sense in case its been lubricated unsuitably at some time.

Richard

Meths is not a good oil solvent, best use white spirit to get rid of oil and believe it or not dip in hot water with a hint of wash up liquid and a final rinse in hot water, then dry with a hair drier.

Given that now most ultrasonics use an aqua based cleaner with hot water after wash. I can recommend 'Micro' at a 2% solution for an ultrasonic.

Clive

I repaired many when I did an 18 mths stint in the standards room at Ferranti a long time ago.

From memory ( a long time ago ).

As stated you need a very clean, dry, score free spindle using solvents.

The only special tools other than good small screwdriver sets needed to dismantle are a couple of good sets of finger lifters. A small set for the main finger and a very small set for the revolution counter finger. These are literally miniature types of tyre levers with a small groove cut in to clear the finger spindle, 2 per set.

Depending on indicator model basic dismantle starts:

Remove Back.

Remove plastic rotating main screen either clips or screws.

Carefully lift each finger using equal pressure with lifters at 180 deg under each and lift of dial.

This usually reveals a couple of screws on the outer edge of the main gear train assembly that hold it to the indicator assembly. They allow rotational adjustment of the gear train assembly to mesh the main first contact gear with the linear spindle rack gear. Remove these screws and the gear train can be removed and further dismantling necessary of the gears and springs.

Remove the end fittings from the spindle and slide out.

Do all the cleaning and score removal necessary, check for free smooth movement in housing.

Reassembly is a reversal of above but: when you mesh the main small gear with the rack you will need to reset the preload on the main spring as follows.

Rotate the gear train so there is no mesh with spindle keeping the adjusting/locking screws lightly nipped. Very lightly refit the larger finger with the lightest tap just sufficient to rotate the gear train.

Wind about 4 complete revs to tighten the main spring and whilst then holding to prevent unwinding rotate the gear train assembly to mesh with the spindle and tighten the two rotational adjusting/securing screws. There should be minimal play twixt spindle and gear.

At this stage you need to check its operation. The spindle to be clean and smooth operation. The main finger should move promptly and cleanly and return to its zero point. You may need to play with the preload revs and meshing to get this right.

Remove finger.

Refit dial. Refit fingers by lightly tapping back down with a good small diameter flat ended punch, taking care not to bend the spindles.

Reassemble front.

Reassemble back.

No doubt there are others who may be able to correct if needed.

Do not, under any circumstances wet the whole inside of the DTI just wipe the stem with a tissue wetted with solvent. You may have to do this several times whilst moving the stem backwards and forwards gently. This action will soon draw all unwanted material out.

.Not methylated spirit ! As Clive says it is not a good solvent. I use a 3M product produced to degrease surfaces prior to using one of their adhesive tapes it apparently is isopropyl alcohol - works a treat.

No real help, because I've never got around to fixing it, but; here are a few pictures to show how nasty they can get inside ... This one felt just a little sticky.

MichaelG.

Edited By Michael Gilligan on 16/06/2015 22:54:16

IPA is IsoPropyl Alcohol by the way. It can be bought with fairly high purity of ebay. It's not bad for degreasing things in general especially when rubbing with things like cotton buds and has survived the health and safety people so far but isn't as good as what used to be about.

I think I have seen mention of people using acetone on here for degreasing. Not substance I am keen on due to fumes.

Curiously window cleaner is water, ipa and a slight amount of some detergent. That might help.

Lighter fuel is very effective but do take a bit of care with it.

John

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Edited By John W1 on 16/06/2015 22:55:24

Acetone can attack some paints and plastics as well.

Use Acetone, but not nail polish remover, that's acetone plus some sort of oil.

Ian S C

I've bought IPA in half-litre cans from CPC.

I believe the video cassette recorder head cleaner fluid that Tandy used to sell in 60 ml plastic bottles was also IPA.

Best regards,

Swarf, Mostly!

Use lighter fuel. We used it for many years and it worked well. Just squirt it down the spindle hole.

I've an old Mitutoyo service sheet that instructs to clean and lube the stem with petrol only and to never put oil on the stem. I have found it works ok on old dial gauges (One of which just happens to be an old .0001" Mercer that still is my precision "go to" in the workshop.)

Edited By Hopper on 17/06/2015 12:50:00