Starrett Calipers ...
I calibrate gages for a shop in Houston, and new API standards state that all tools on the floor used in any part of production must be calibrated.
I ran across a pair of 0-6" Starrett Dial Calipers that have an issue. The needle rests at zero at the bottom of the dial. This is purely aesthetic as the calipers are both within tolerance and have repeatability.
Is there something I can adjust to bring zero back to the top of the dial? I was thinking slight adjustments to the track that the gear runs along, or would I have to disassemble the whole gage?
What does it matter where the Zero in on a dial????
I believe there is a way to reset the needle. Some one here knows how.
I've seen this kind of thing happen for two reasons...
First (and mainly on cheap calipers), the pointer can sometimes slip on its shaft when the caliper is closed (too) quickly.
Second, the pinion gear can skip a tooth on the rack which is normally caused by stray metal chips. If a small piece of shim-stock is placed on the rack while the caliper is being closed, it can lift the pinion off the rack. Then, just close the caliper by a small amount, remove the shim, and test the dial's position. It can take several tries to get the "reset" correct. This method might seem overly aggressive, but my Mitutoyo caliper comes with a shim-like tool and instructions for this purpose.
Thanks for the info.
The machinist is complaining about the zero being at the bottom now, making it an issue. As I said before, the calipers are accurate and within tolerance so it is purely aesthetic.
The machinist has gone on the warpath now, telling machinists to take their personal tools home so that they cannot be damaged. This is actually a big help to me, because these new API regulations are a pain in my behind.
Once again, thanks for the advice.
Tried the shim tactic. Worked great. Thanks again.
Interesting. I would guess that the pinion that rides on the rack is spring loaded to maintain intimate contact.
I have an import caliper that I dropped once. Ever since then, the zero has been off by about 5 or 6 thousanths from the top. I have checked it against my mike and other calipers and am confident it is accurate (+/-0.001") but it is puzzling. It seems to me that if it skipped a tooth, it would be off in a multiple of 0.025". So I wonder what happened here. No obvious way to disassemble or I would have done so.
Make it fit.
I have several brands of dial calipers and all of them have a moveable bezel. Just reset the bezel to zero.
I've rebuilt several calipers and they have all had 2 gears that run on the rack. The gears are spring-loaded onto their hubs so that one always pushes on the left side of the teeth and the other always pushes on the right. Basically, the springs keep torque on the gear shafts. This eliminates backlash problems and keeps the dial from jiggling left/right.
I seem to remember that I had to remove the clear, plastic dial-cover first. (I used a suction cup to pull it off) Then I pulled the dial off of the dial's shaft, followed by the knurled ring. There were a few screws under the dial's face that held the caliper together. Be careful if you decide to take a look at the gearing because it's spring-loaded. I don't remember the details about how to rewind the springs except that there was a way to use a pin/drill bit/pick/etc. to lock the springs until the cover was replaced.
For your caliper, it may suffice to remove the clear cover and then remove/reinstall the pointer on its shaft. As I mentioned in an earlier post, it seems like the pointers on import calipers tend to be a bit loose so they can shift on their shaft.
Thanks guys, it's nice to know the way in. And yes, I have simpily reset the bezel with the zero line. Since it is working, I may just leave it alone and recheck it occasionally. I'll try to go in if it becomes inaccurate.
Make it fit.