I have a pair of 6" dial calipers (Chinese) about fifteen years old. They have served me well and I hate to toss 'em. Feels like there's a bit of metal on the gear of the dial. I was able to get the two main parts apart, but I can't see the chip of metal on the gear, and I don't see how the dial face is mounted onto the slide. Turning the knurled part of the dial simply turns the graduated disk. There are no screw heads that I can see. How is the dial face removed? Does it pry off, or is there some other trick? Thanks for any input.
The quick and easy answer (which you don't want to hear) is that they are all different. Actually, a lot of the Chinese stuff is copied from more reputable American/European/Japanese stuff, but there are still a lot of different approaches. In some cases, they require special tools. In others, they are swaged together and are not intended to come apart.
In the case of Chinese DTI's, the technique is quite simple.
Turn the knob of the mag-base the wrong way, because you've got it back to front on the lathe bed in order to reach the part you were checking. Then adjust the probe by pushing it with your finger. This causes the DTI to bounce off the lathe and fly across the shop, ending up in a neat pile of bits.
If only I could work out how to put it back together...
Well ... I don't have any fifteen year old Chinese dial calipers, but one way which is used when there are no setscrews is a wavy spring wire in a groove in the backing and the bezel ring. If this is the case, there should be a small hole in the bezel ring, and you need something to push in there to depress the wave in the spring wire. There should be three bulges for the full trip around the dial. You press in through the hole (with something like your smallest jeweler's screwdriver) and that side of the bezel ring will pop up a bit. Keep that part up while you rotate the ring and hole to locate the next wave, and do the same there. One more, an it should lift off -- but be careful that you have not hooked the printed face and are trying to bend the pointer to get it off.
Thanks to Don and all. Apparently mine has a different arrangement but I was finally able to clean up the gear without disassembly, then cleaned the rack thoroughly, and reassembled it. All is well. Thanks again!
On 5 Nov 2006 11:57:10 -0800, snipped-for-privacy@hotmail.com scribed:
Hey Terry:
For future ref, as it seems like you got yours working:
Most of the bezels on current calipers are press mount, maybe with a ring, mostly not. The last caliper I remember taking apart with bezel screws was a older Helios (GERMAN) unit. They stopped making that about 30 years ago.
So for non-screwed ones you can take a couple of cheap steel screwdrivers, heat them up and bend the tips up about 30 degrees or so, as to have some lever under the bezel. Temper them so they will last.
Just use them 180 degrees apart on the rim and pop the puppy off. Once you get it off, resetting the hand/pointer can be done in the same way (albeit with smaller screwdrivers) but you risk marring the dial face. The best thing is to is to get a hand puller that will take the hand off the pinion in one quick step. They can be found at any watchmakers or jewelry supply catalog such as:
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Clean and close the caliper faces, and reset the hand to wherever you want it to be, Pop the hand on with a small brass hammer. Clean the face (with a dry rag) and drop the bezel and crystal on.
Glue mounted racks can be cleaned with Isopropyl and a sewing needle in a pin vise, to scrape out any swarf. Be careful and very gentle though as most are brass, and can crown the rack tips, resulting in a less than accurate caliper. Screwed in racks are easy to remove and can be soaked for a few hours in Iso or a Vibratory Jewelry Cleaner for great results. Screwed in rack are usually steel, and can take more abuse.
Contrary to popular belief, oiling a caliper is really not a good idea. Keep them dry, away from tool oils and never, ever oil the rack and pinion gears as they will just gum up. Keep the oil away from the beam moving surfaces too as the very tight clearance on the gibs.
Best to do is blow it out every few weeks with compressed air.
If you are worried about fingerprints, rusting, etc, just use a dab of WD40 on exposed stuff... Never in the movement!!!
And, if you do this, cover the bezel with the palm of your hand so it wont fly off across the shop....
(Guess how I know this can happen!)
All the old dial calipers I have access to have some means of re-setting the dial to 'top-zero' - one has a hole underneath the bezel locking screw and a short phosphor bronze 'stick' that goes in there.
The other three came with a thin shim about 2mm wide that is pushed down the rack. It's mostly a matter of trial and error to find the point at which to release the shim so that (when the caliper is closed) the pointer is at the top.
On Wed, 08 Nov 2006 18:51:56 +1300, with neither quill nor qualm, KewlKiwi quickly quoth:
I've lost my shim stick for my Chinese dial calipers which I've had for about 30 years now. What size are those things. I'll make another one. It's .020 off now and I'd rather it be vertical.
On Wed, 08 Nov 2006 18:51:56 +1300, KewlKiwi scribed:
Hey Bob:
Yes you are right! I have had to pickup my share of broken crystals and bezels from the blowout. It is still the best way to remove swarf from the rack IMHO.
We used to use Trichloral Ethylene as a degreaser but it was banned from use after the FDA deemed it quite toxic. TriClo was the best ever to clean stuff up with though.
I have had a very good pair of $20 Chinese 5" calipers for 8 years, but I dropped them and the zero was only repeatable within .003".
I took them apart tonight, got the dial to zero when pointed in a new direction where the gear is not worn. I zeroed them. I got out a .497" pin gauge, and I can tell it is a "+" .497" pin gauge. No, the calipers are not for sale:)
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