Test Dial indicator sticking?

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yadnom1973

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I picked up this Test Dial indicator second-hand off eBay and it’s a well made little device but from the rest position, it has a kind of sticking point before it starts moving. In practice, you’d zero the work at least a few tho in, past the sticking point so it should not affect it in operation but it concerns me. The spring is good and the needle snaps back to rest when released its just that if you gradually increase the surface contact from rest it hits a point right at the beginning, a tho in or so and then springs past it. I made this little video to show what I mean:


If they are designed like this then thats fine but if not then this may be symptomatic of a more serious problem within the mechanism. All the ones I’ve used did not stick like this but I thought I’d come here and ask if anyone has bought one that was like this by design.

Any advice welcome.
 

retailer

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A dial indicator is not designed to stick, if you elect to do nothing then it looks as if you can work around it - in normal use I always try to use a dial indicator in the mid part of its travel so I'm always sure the contact point is in good contact with the part I'm gauging. I would say your dial indicator does have some sort of issue.

You might try some sort of lubricant, I have a Russian built dial indicator that I purchased new and it lay unused for for over 10 yrs, I had occasion to use it one day and pulled it out of its case to find that the sponge foam in the top of the case had turned to goo, after a lot of effort cleaning it off I found that the needle was sticky and unreliable in operation as it would not return to the same zero point each time - I was able to access the inner working by pulling off the back cover held with three small screws and found that the lubricant had dried out, I gave it a good squirt of CRC and it was all good. If yours has a back cover and you have the confidence then you might want to have a look to see if has any grit or dirt in the gear train, youtube is good here - do a search and you may find a video in how to clean the inner workings.
 

XD351

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Take a look on the doubleboost youtube channel , he has a mate that made a few videos on fixing various types of indicators . I would take the cover off ( carefully and on a nice clean table incase something drops out you will have half a chance of finding it ) and have a look inside , sometimes a very small amount of instrument oil ( Starrett or the like ) on the pivots and sliding mechanisms can work wonders . If you don’t have instrument oil 3 in 1 will do- i can hear the clock and watch makers screaming that you need watch oil already - its not a watch its an indicator ! Trick is just a minute amount don’t flood it !
 

john_reese

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The first thing to try is solvent on the stem. That is where they usually stick. Get some naptha (paint thinner) and apply it to the stem with a Q tip. Work the stem in and out. That usually solves the problem.
 

Wizard69

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There are all sorts of potential issues here, It may take some work to zero in on the root cause.

One possibility is a slightly bent shaft that releases after a bit of pressure is applied. Surprisingly this is a common injury to dial indicators as the can get jammed into things, dropped or otherwise abused at the working end. If the shaft is actually bent how much success you would have straightening it is up to you and the techniques you can apply.

Another common problem is a gunked up mechanism. Your best bet here is to clean with a very light solvent or oil such as kerosene of very light penetrating oil. Please don't use 3in1 or other heavy oils. You want practically invisible lubrication. NEVER use WD 40 or other "lubricants" that leave residue.

At home I have a collection of dial indicators repaired from a box of broken ones bought at auction. Literally nothing new here but I was able to stock my shop with a few functional units. In this case scavenging parts from one to get another to go. Often springs are the primary issue in these units, but I saw several other issues. Now I'm limited to tooling and ability here but I must say most of these dial indicators are easier to work on than a watch, far easier really. I would most certainly take the back off to see if you can identify the cause of the problem. by the way if the shaft is sticking you should be able to feel it is the nerves in your hands are still good. The sticktion should be greater if the probe shaft is allowed to rebound hard, indicating that you have something jamming up.

In a nut shell dial indicators are pretty straight forward. A rack turns a set of gears the show deflection and the number of turns, if that function is supported. You only need to zero in on the hang up.
 

XD351

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I think this is a dti ( lever type ) not a dial gauge ( plunger type ) and there are a couple of types of mechanism depending on manufacturer , it will either have some form of gearing to convert the linear motion to rotary motion or a spiral drive mechanism like in a starrett back plunger indicator . Itcould just be the spring return tension driving everything back home to hard or a damaged stop point . If this is a dti ( lever type ) does it read in both directions ( push the lever one way needle moves clockwise push it the other way it moves anticlockwise ?
 

yadnom1973

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Thanks, everyone for taking the time. To be clear this is a Dial Test Indicator with the lever. I really hadn't realized that I'd obscured that fact in the video. This model reads in both directions without the need for flipping a lever of any kind. I don't think this is gunk of any kind, the unit is in pristine condition and it just doesn't feel like that. Sticking is misleading, I just can't think of a better term. The needle moves freely once past the one spot at the beginning and snaps back past it to zero every time. It only sticks at the start, in both directions, as if it had worn it's self into a little divet and needed the extra force to jump out of it each time it wanted to start moving but once in motion or anywhere beyond it's stat position it works perfectly.

It feels to me like it's rubbing past a point, reminiscent of when gearing is misaligned or a shaft is bent. The needle has 540 degs of rotation in both directions but it only happens at the beginning of the stroke, not when it passes the same position on its way back around and not when it returns in the other direction.

so I'm inclined to believe that something between the actuation lever on the bottom and the spring mechanism is damaged, bent or out of place. I don't know if and how these units can be damaged by overshooting their travell with to much force? Also if you look closely the needle is slightly bent. I suspect that has some story to tell, it's a very fine needle. Maybe if it was spun with too much force and brought to a sudden stop at the end of its travel, there's no damage or scratches on the body or glass, its perfect. so no drops or blows and the needle is non-ferrous so unless someones been in there.

I think something is bent as suggested by Wizard69. There are four small screws on the side and with the condition of the unit I suspect it would come apart with ease. This is the one thing I dislike about eBay, it discourages any poking around. If this behavior is not part of any recognisable design, and that seems unlikely now, I may just have to return it. Which is a shame as it's a nice little unit.
 

bobden72

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I have one that does that now and again I find a quick spray on the leg and work it a few time and it OK for another six months.
 

yadnom1973

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I opened it up.







The long arm with the partial gear on the top that rocks back and forth, I'm not sure what to call this type of gear, I think at the end of its travel when it comes to its rest position there is not enough clearance between this and the next gear causing them to jam up slightly at the begging of the stroke.

This means the jeweled bearings must be slightly out of position. It's all pretty small and delicate in there so I gave up and replaced the top plate but found that the simple act of disassembling and reassembling had improved the issue. So I went back and completely disassembled the mechanism cleaning all the parts with alcohol and even did a little deburring on one of the gears.

However, it was pretty clean in there to start with and I don't think the rough cut had any effect on the dials operation. In reality, the fix came from carefully disassembling and reassembling all the parts until they were correctly seated in place and then it worked without any problems.

I didn't lubricate as I was unsure what to use on these little jeweled bearings. I have some sewing machine oil but I suspect that something even finer may be needed, if it's wise to lubricate them at all. And it was so clean in there and most of all it worked, everything moves freely and the needle snaps back into position so I'm going with not fixing what ain't broke at this point.

I've just returned one of these DTI on eBay. I hate going through the whole return business and then you just have to buy another so I'm very pleased to have this up and working so well.
 

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