Bad calipers?

[eKretz]

Looking at iGaging, I see no overlap. If I put a source of light right behind the jaws, I see a thin sliver of light and moving the head a bit to the right makes that light disappear. Just a few degrees is enough.

But looking at the geometry at the top jaws, they are not ground perfectly parallel. They are ground with a slight angle so that if you position the lengthwise split line right along the diameter of the circle, the contact surface of the jaw will be closer to the circumference. I'll try to draw that.

Here is my representation of this. The angles are smaller in reality, I've shown them bigger here  for clarity.

Yeah we're running into the quality issue yet again. If there is overlap, you have a crap product. Here is my Mitutoyo 8" caliper's jaws at the I.D. jaws. The picture straight on shows no gap, but if I rotate the caliper a tiny bit you can see light in the gap. Since the jaws are offset, this is visible due to parallax. Most good calipers I've used have the measuring surface of the I.D. jaws ground with a very small flat. If they come to a full point they will wear out fast if you use them much. I own about 6 pairs of calipers from Starrett, Mitutoyo, Brown and Sharpe etc. and they all have flats on the I.D. jaws with no overlap. These flats on a round inside surface creates a small amount of error when measuring inside diameters, more so in smaller bores. It's almost unnoticeable past a certain size though since the flats are of very small width. This is something that sometimes had to be corrected for in the machine shop - it's called flat-to-round error. We had a table for size correction when measuring a flat surface to an inside diameter with micrometers based on the width of the micrometer anvil and the bore size.

[ironsniper1]

These ones do have a depth rod: https://www.ebay.com/itm/150mm-LCD-Digital-Electronic-Carbon-Fiber-Vernier-Caliper-Gauge-Micrometer/153087544602

i know this thread is a little old but are those calipers any good?

[ataradov]

i know this thread is a little old but are those calipers any good?

Define "good". They are a bit better than a ruler and provide automatic measurement reading. They are not good enough for typical machining work, of course.

But they are perfect for electronics, since you rarely need to measure anything with 0.01 mm resolution.

And as far as general operation - they are very good. They don't drain the battery when unused, they automatically wake up on movement, they keep a good 0.