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Dial Caliper Reading Wrong

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charbar

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Mitutoyo 505-644-50 8" dial caliper. Trying to measure an oil pump rotor today and found out the thing is basically 19 thou off. I've never had a issue with it before but I'm pretty sure some other jackass had their hands on it last week and who knows wtf he might have done with/to it.

Anyway, with the jaws closed and the needle zeroed out if I measure anything it will read 19 thou less than what the actual measurement is. If I 'zero' it with the jaws closed and the needle at 19 thou then it will read correctly once I open it up more than 58 thou. Coincidentally when I am closing the jaws I can feel somewhat of a 'stop' at 58 thou and then it takes more effort to close it the rest of the way.

I know nothing about how to fix this or even how to take this thing apart. I would rather not just start tearing into it without an idea of what I am doing first. Any ideas/pointers?

Thanks

Here are a couple picture of it if that helps any.

dc2.JPG
dc1.JPG
 
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whateg01

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The gear jumped on the rack. Possibly debris the the rack teeth caused it. Until you clean it and reset it, just rotate the dial. You should be doing that anyway.
 
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Wolley

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The square slot on the back of the dual is how you re-zero it. You need the corresponding square wire tool to insert in the slot. It comes with the caliper. You need to get the junk out first. GL
 
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charbar

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Well boy do I feel like an idiot! :lol: Blew it out with the air gun (probably a better way?) and it works perfect now. I knew it was dirty (gets used in an auto repair shop) but I didn't think that would cause my issue!


I bought this thing second hand years back so I don't have the square tool mentioned. That would allow me to put the zero mark at the 12 o'clock position and then adjust the needle to it correct? Anything else I could use to do this? Or maybe I just better leave well enough alone. Zero has been at the 5 o'clock position for years so I'm used to it!
 
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OccupantRJ

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Basically the tool just makes the pinion gear jump relative to the rack. A sliver of shim stock can also be used to do it. Debris in the gear rack is a constant in a machine shop and it only takes a tiny particle to cause issues.
 
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charbar

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Well I got the needle close to 12 o'clock when the jaws are closed. If I turn the dial and put the zero mark to 12 o'clock then the closest I can the needle is about 95 thou, otherwise it wants to go to about 18 thou if I try to get any closer. I'm assuming this is because that is just where the gears mesh and that is the closest it is going to get? Or am I still doing something wrong?
 
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charbar

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Wrench97 said:
Can't you rotate the head?
Click to expand...


Yes, I now have the needle and the zero mark on the dial at about the 11 o'clock position, I just cant get the needle adjusted to stay at the 12 o'clock position with the jaws closed. I'm assuming there just isn't that much fine adjustment to get everything to 'zero out' at the 12'oclock position?
 
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rlitman

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charbar said:
Yes, I now have the needle and the zero mark on the dial at about the 11 o'clock position, I just cant get the needle adjusted to stay at the 12 o'clock position with the jaws closed. I'm assuming there just isn't that much fine adjustment to get everything to 'zero out' at the 12'oclock position?
Click to expand...

Note that his indicators have 200 graduations per rotation (0 at top and bottom), while yours has the better 100 graduations (0 at top only), but the concepts are the same.
 
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RoninB4

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-When the needle on dial calipers isn't at the 12 o'clock position it's usually because some crud has gotten on the rack. They're always at the 12 o'clock position when new. Sometimes it's difficult to see the offending crud with the naked eye and magnification is required. Using a fine sewing needle will usually remove whatever got in there. First symptom of crud is when the sliding jaw is run along the beam. It should be smooth and free of resistance, any perceived drag or "bump" indicates the rack probably needs inspection/cleaning. It's best to attend to this as soon as trouble is noticed before the crud gets imbedded into the rack, damages the delicate little gears in sliding jaw, or deforms the tooth profile of the rack.

If the needle is off the standard procedure for resetting is the small shim too supplied with the caliper when new. I may/may not have one because they often get lost. If the needle is only off .010-.020 I'd just loosen the dial clamp and reset to zero. What I do next is NOT recommended unless you really feel confident with your assembly skills on delicate mechanisms:

Remove the stop mounted on the beam. The Mits used a black plastic bump stop that just pressed into two holes on the beam. It comes out fairly easy and goes back in with thumb pressure. Some calipers use small screws to hold the bump stop. Take careful note of how much the needle is off from 12 o'clock. Carefully slide the entire moving jaw off the beam and note where the needle is now. The difference going in CCW rotation is how far you need to advance the needle position. This can be easily done using your cleaning needle on the tiny gears inside the moving jaw housing. Now is also a good time to inspect the gear rack under magnification. Carefully slide the moving jaw back onto the beam and examine your results. It may take another attempt or two to get the needle to the 12 o'clock position. It's nothing more than getting the sliding jaw engaged with the beam rack at the right place, the gears/rack are locked to each other. Everything should come apart and go together easily, if not you're doing something wrong and forcing it can ruin it. Calipers need periodic cleaning like anything else.

I've always preferred the Mits dial calipers because I can take the entire instrument apart (but don't recommend it). I bought one of the Browne & Sharpe dial calipers once, thinking the covered rack would be an upgrade. Got something in the rack a few months after purchase and one of the tooth profiles must have been damaged or something because I never could lose the slight "tick" it had at one location. I gave the caliper away and only buy the Mits, JMO.
 
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OccupantRJ

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bornbadbob said:
I haven’t used my dial caliper since I bought my digital 20+ years ago
Click to expand...
I machined for work for 30 years. I have a couple of digitals and three B&S dial units. I grab the dials first every time. The digitals rarely get used other than for quick metric conversion. I can measure with the dials twice in the time it takes to turn on and zero the digitals, not counting the occasional dead or loose battery.
 
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txvwnut

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I bought a Mits digital caliper back in the 80's used up until about ten years or so ago when I noticed something wasn't right about a measurement I took. Pulled a mic out and took the measurement, sure enough the digital was off by a few thou. Used my standards to check it and the larger the piece the more it read incorrectly. Pulled the battery and put it back in the drawer with the intention of sending it in for repair and calibration and haven't done it yet. Went back to my vernier caliper and never have to worry about dead batteries or the dial getting off.
 
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charbar

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dscheidt said:
You'll just have to worry where you left you magnifying glass.
Click to expand...

Yep I go cross eyed even trying to read my micrometers and dial calipers. Vernier calipers aren't happening with my eyes anymore. Been so long since I've used one I honestly don't know if I remember how to read one even if I could see it :lol:
 
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bornbadbob

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I have the original direct reading style, a couple of dial ones and a cheapie digital that is my “go to”
 
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bornbadbob

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txvwnut said:
I bought a Mits digital caliper back in the 80's used up until about ten years or so ago when I noticed something wasn't right about a measurement I took. Pulled a mic out and took the measurement, sure enough the digital was off by a few thou. Used my standards to check it and the larger the piece the more it read incorrectly. Pulled the battery and put it back in the drawer with the intention of sending it in for repair and calibration and haven't done it yet. Went back to my vernier caliper and never have to worry about dead batteries or the dial getting off.
Click to expand...
A lot of you folks use your calipers for much finer work than I do. I am using mine to check drill bit or bolt sizes, measuring a hole size that sort of thing. Not much that requires real accuracy.
 
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whateg01

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bornbadbob said:
A lot of you folks use your calipers for much finer work than I do. I am using mine to check drill bit or bolt sizes, measuring a hole size that sort of thing. Not much that requires real accuracy.
Click to expand...
I use calipers for a lot of things, for sure. Sometimes the things I'm measuring require some level of accuracy. Sometimes they require that level of precision. Sometimes they require both. Other times using a dollar bill as my measuring device is close enough.
 
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