Caliper conundrum

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BryanJohnson
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Joined: Wed Jul 23, 2008 7:45 pm

Caliper conundrum

Postby BryanJohnson » Wed Apr 08, 2009 8:56 pm

I've picked up my caliper this evening and found that when the jaws are together, the scale show 0 but the dial shows .65mm, i.e. it is at 4 o'clock instead of 12 o'clock.

Caliper S4um.jpg

I've no idea how it go to this condition, even less so how to get it back to normal. Everything else seems fine with it.

I know I could turn the dial face so that the zero was at 4 o'clock, but that wouldn't seem right.

Can any of our more experienced engineers provide a suggestion before I get the screwdriver out?
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grovenor-2685
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Re: Caliper conundrum

Postby grovenor-2685 » Wed Apr 08, 2009 9:24 pm

I know I could turn the dial face so that the zero was at 4 o'clock, but that wouldn't seem right.

Well, that is why the face is rotateable, to allow you to calibrate the zero.
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Keith
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David Knight
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Re: Caliper conundrum

Postby David Knight » Thu Apr 09, 2009 2:01 am

Bryan,

At the risk of boring you (hopefully not insulting) here are a few things to check and maybe some of this will work. 1/ Make sure the measuring surfaces are clean. A simple method is to place an ordinary sheet of paper between the jaws, close firmly, then pull out. If you get yet another reading from the .65 mm shown in the pic (hopefully smaller) then that was part of the problem. 2/ After cleaning, close the jaws and hold up to a strong light to see if any light shows through, if so this will give some indication as to possible wear. 3/ If the jaws are clean and not worn and still no joy then rotate the dial :-)

Hope this helps,

David

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BryanJohnson
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Joined: Wed Jul 23, 2008 7:45 pm

Re: Caliper conundrum

Postby BryanJohnson » Fri Apr 10, 2009 3:58 pm

Martin Wynne has kindly provided a solution, which has been proven in a few minutes.

The drive pinion has skipped a tooth on the rack, probably caused by some swarf or similar debris lodged in the rack.
Remove the strap at the far end of the arm (2 small screws) and carefully disengage the slider from the arm. Take take not to dislodge the adjusting strip under the locking screw from its recess.
Clean any debris from the rack.
Re-engage the pinion on the rack and try again. Some trial and error may be needed until the caliper closes at or near 12 o'clock.
Replace the restraining strap and zero the dial.


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