Replies

1. 
   RickL | Jul 08, 2005 07:59pm | #1

   Have you tried contacting  http://www.mitutoyo.com/

   It doesn't take much to slip the teeth on a mechanical dial caliper. I typically buy the Enco ones at $16 a pop. Good enough for metal work and I don't sweat it if the wooddust gets in there. http://www.wttool.com  is another good source for inexpensive calipers. Paid $26 dollars for a 12" dial caliper. and bought a decent import digital 6" for a real good price.

2. 
   JohnWW | Jul 08, 2005 08:15pm | #2

   Mark,

   What happened is that you have some debris in the fine gear rack that runs down the middle of the bar.  Behind the dial is a small gear, connected to the pointer, that runs in the rack.  When you the gear that moves the pointer ran into the clogged teeth, it skipped a tooth or two and was thrown off.

   Purely by luck, you got the gear to skip a few teeth again, in the proper direction, when you ran it back and forth, but this isn't a good way to reset the caliper and it won't prevent the problem from happening again.

   To properly service the caliper, start by cleaning up the gear rack with a fine brush.  A toothbrush, or a similarly sized fine brass brush, works well.  It doesn't take a lot of debris in the track to cause trouble, so look close at the track under good light and use the tip of a needle if necessary, to clean out any clogged teeth the brush doesn't clear.  After you clean the track, run the head back and forth gently, if there is still something in the teeth, you'll feel the head catch as it passes over the clogged section.

   Once the the head is moving smoothly, you may need to get the gear driving the pointer to intentionally skip some teeth on the rack to get the pointer vertical when the jaws are closed.  To do this you will need to make a small tool out of some shim stock or a soda can.  Cut a 1/16" wide by 2" long strip out of the thin metal and put a slight downward bend in the strip about 1/4 inch back from one end.

   Now move the head of the caliper down to the middle of the bar and slip the strip in behind the head just over the rack with the bent tip down so it is against the gear teeth of the rack.  Now, if you move the head toward the strip, the gear on the head will ride up on the strip and will disengage from the rack.  You won't be able to see this, but you'll feel the drag on the head as the gear runs into the strip.  Move the head a fraction of an inch further to the left so that the gear will skip a few teeth and then pull out the strip, allowing the gear to settle back into the teeth on the rack. 

   Now close the jaws on the caliper and see if the pointer is at the twelve o'clock position.  If it isn't, just repeat the procedure until the pointer finally settles into the right engagement.  Getting the adjustment right is a "hunt and peck" process that may take several attempts, but with a little practice you will be able to reset the caliper in just a couple of minutes.

   To minimize the chances of this happening in the future, try to keep the caliper away from the worst dust in the shop, and clean the track as soon as you feel the head running roughly.  I always close the caliper and check it for zero before I do any measurement, just to be sure.

   Hope this helps, John W.  

   
   

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   Edited 7/8/2005 1:17 pm ET by JohnW

1. 
   MarkRD | Jul 08, 2005 08:39pm | #3

   John, Thanks, I get your process. I'll be cutting up a coke can today... (FYI I knocked it off my router table after my previous post and bumped it out of whack again :-( Do the screw on the back of the dial and the screw that holds the dial in register (at the bottom of the dial) have anything to do with the device going in/out of calibration?MarkFYI, lots of "gunk" in the rack (geard strip)Also this device is about 20 years old. My wife bought it when she was in Engineering school. I found it in a drawer and "stole" it for the shop. (SInce she's a Nurse Practitioner now, I don't think she'll be needing it)

   Measure it with a micrometer, mark it with chalk, cut it with an ax.

1. 
   JohnWW | Jul 08, 2005 10:33pm | #4

   Mark,

   I'm not familiar with the details of your caliper, but in general the various screws that are visible don't affect the adjustment of the tool unless they become so loose that something falls off.

   John W.

   Edited 7/8/2005 4:11 pm ET by JohnW

1. 
   KeithNewton | Jul 08, 2005 10:50pm | #5

   I have made a habit of never laying mine down with the face side up. The dust is less likely to get up into the rack gears than it is getting down into the same space if it gets left laying face up.

3. 
   WillGeorge | Jul 08, 2005 11:03pm | #6

   No ZERO button..? or off after setting Zero...

   I have a China L-CHEEPO (about $25.00).. I tested it with my old Brown & Sharp inside micrometer set... It is just about perfect... BUT.. I ZERO it before I use it... EVERY TIME... AND check it once in awhile!

1. 
   MarkRD | Jul 08, 2005 11:19pm | #7

   As I said, it's 20+ years old. Still works great - just does not have all the fancy features...M
   

   Measure it with a micrometer, mark it with chalk, cut it with an ax.