How do these work? (20-0-20 indicator)

[Highpower]

Someone educate me please. I've never used one of these short range indicators before, and need to know how they work.  
I have an old clunker here like the one below (Standard NO.228) that is filthy and frozen solid, and decided to have a go at restoring it. Thanks to Bob's previous posts (krv3000) I've managed to get it all apart without destroying anything (so far).

How are they used exactly? Are you supposed to pre-load the needle half way through its full range, and then zero the dial?
Also, I don't know how much pre-tension I need to put on the "clock spring" when going back together after I get everything cleaned up? What say you Bob?

[Sunset Machine]

Yup, pre-load it and zero the dial. I use a similar one often with my old-style vernier height gauge in place of the scribe.

[TomG]

That type of indicator is used for inspection of production parts. To use it, it is zeroed out to the nominal dimension and the flags are set for the plus and minus limits. Each part, or a sampling of parts are then checked to ensure that they fall within the tolerance specified on the print.

Tom

[Highpower]

(08-30-2015, 10:52 AM)TomG Wrote: That type of indicator is used for inspection of production parts. To use it, it is zeroed out to the nominal dimension and the flags are set for the plus and minus limits. Each part, or a sampling of parts are then checked to ensure that they fall within the tolerance specified on the print.

Tom

That part I understand. I guess the better way to phrase my question is how important is it to zero the gage in the center of the stem travel, so you have an equal amount of movement on both the + and - sides?

My plan is to replace the 1" travel dial indicator I currently have on my Sinclair rifle round concentricity gauge with this one. I don't need a 1" travel when I'm working to a .002" max run out. The .0005" divisions will come in handy here.

Another question.... The hand (indicator needle) is covered in surface rust which I will clean off. What would be the best choice for refinishing the hand? Cold blue solution, tool black solution, or just a coat of paint?

   

[f350ca]

Me putting that back together would be akin to doing brain surgery on a cat.
Had a watchmaker paint (much to his discuss) the hands on my Rolex (senility award from the company I worked for) black (gold face and gold hands, brilliant combination).

[krv3000]

hi don't panic right the spring 1 full turn shod be enough but check that it dus not over wind when you operate the plunger as for the hand the proper way to culler it is by polishing to a mirror finish then change its culler with heat but all I do is give it a good clean then go over it with a indelible ink marker don't pant as this will mack the hand bigger and heavy

[dallen]

if you want the hand blue, polish it up all nice and shiny, degrease it then lay it on a piece of steel and heat from the bottom until it gets the nice deep color on it,

WARNING it may end up anything from light blue to a deep blueish purple color.

But its easy to do, tiny watch hands can be a pain to do.

[Highpower]

Thank you Bob!    

I had a feeling that painting the hand would be detrimental to it's operation. I love your idea about using the marker. I have plenty of Sharpies around here. I spent some time cleaning up the parts in my ultrasonic cleaner today. Most of them came out clean, but the brass parts were still covered in dried up grunge and dull looking. I ran those through again using some ammoniated horology cleaning solution (for cleaning clock parts) and they came out shining like a new penny. I still need to polish up the bezel a bit and do the same with the hand now. All in good time.

One more question... Where should the pointer be when the indicator is at rest? Most of the pictures I've found on the net has it at the 9:00 position. Is that about right? I wish this thing would have moved before I had to take it apart to break everything loose. That would have answered a lot of these questions.  

The reason this thing was stuck was because someone else had been in there before me. One of the bezel retaining screws is missing (don't know where I'm going to find one of those...) and the upper brass bushing for the stem was buggered a bit and corroded. I ran a reamer through it and got it opened up again. The stem slides right through now.  

[Highpower]

(08-30-2015, 04:16 PM)dallen Wrote: if you want the hand blue, polish it up all nice and shiny, degrease it then lay it on a piece of steel and heat from the bottom until it gets the nice deep color on it,

WARNING it may end up anything from light blue to a deep blueish purple color.

But its easy to do, tiny watch hands can be a pain to do.

Thanks for the tip David, but there appears to be a fiber washer/insulator between the hand and the "hub" it's swedged on. I would be afraid of burning up the washer and then the hand would be loose and just spin. I could be wrong but that is what it looks like to me.  

I've used that method to temper small flat springs in the past though. It works a treat because you can more easily see the colors change.

I'll try to get a picture of the "washer" a little later...

Edit: Well I was wrong David.
After having a closer look under a USB "microscope" what looked like a fiber washer to my nekid eye is actually bubbled up paint or plain old built up crud. It's not a washer at all... it's a flange that is part of the hub.

   

[krv3000]

hi well where the hand sits depends on the clock ie the travel of the plunger if it has a long travel then 9 o clock is ok for preloading the clock but if it has a short travel I set them to 12 o clock but I ant come a cross a stranded place to put it as I sed you can heat it up but I don't like that as I have tried in the past and the time taken to prep the hand and so on I find the felt tip a porch much beater and all the ones I have dun are still going strong one thing you must not do is over oil it  all I use on the ones that I have dun is starret instrument oil