Recommendation on Calipers

[JagerDog]

If your closed-jaw zero is not right with a standard in between the jaws, you might have the gib loose enough that you are getting an angular shift while you hold the jaws against the standard.
Or you are simply pushing too hard and bending the beam.
Another possibility is that you have a ding on the jaws that you need to stone out.

Try measuring a gauge pin and see if you can track that 0.001" shift to the location of the gauge pin within the jaws.
You should get more accurate measurements by being closer to the beam because that gives less leverage to make the measuring head lift off the beam from a loose gib.

What he said.

Gibs should be just loose enough to provide smooth action.

Check for nicks in the jaws and parallelism as Randall described. Doesn't need to be a specific size. Roller bearing will suffice.

Calipers aren't really the tool for discrete measurements < 0.001.

[Odd_Ball]

If your closed-jaw zero is not right with a standard in between the jaws, you might have the gib loose enough that you are getting an angular shift while you hold the jaws against the standard.
Or you are simply pushing too hard and bending the beam.
Another possibility is that you have a ding on the jaws that you need to stone out.

Try measuring a gauge pin and see if you can track that 0.001" shift to the location of the gauge pin within the jaws.
You should get more accurate measurements by being closer to the beam because that gives less leverage to make the measuring head lift off the beam from a loose gib.

What he said.

Gibs should be just loose enough to provide smooth action.

Check for nicks in the jaws and parallelism as Randall described. Doesn't need to be a specific size. Roller bearing will suffice.

Calipers aren't really the tool for discrete measurements < 0.001.

Thanks for the feedback. I'm definitely not relying on calipers down to the last thousandth, its an approximation at that level for sure. But now I am curious to understand how these work and why the zero is off like this.

I think I have the gib adjusted correctly, or close to it at least. I tightened down until there was no movement and then slowly loosened until it started to move smoothly. There is definitely no play in the jaws nor in the needle if I hold the movement firm and try to push the jaws apart. I even tightened it a bit and still the same. Don't have any gauge pins, but I do have a 0.50" ball bearings from a wheel bearing and there is no change in the measurement regardless of where along the arms I put the bearing (closer or further out). The jaw faces look good and flat. I am also using less force and even no force after closing the calipers and that is not changing anything.

So it reads consistently short by 0.001" down to 0.5" at least. Consistency is a good thing however. I might experiment with smaller items or even some the feeler gauges to see if I can find a point where a 0.001" disappears. There is no skipping, binding or notches anywhere along the movement of the caliper and I would think that a worn gear would cause a cumulative error as you measure further out.

[ar15barrels]

Thanks for the feedback. I'm definitely not relying on calipers down to the last thousandth, its an approximation at that level for sure. But now I am curious to understand how these work and why the zero is off like this.

I think I have the gib adjusted correctly, or close to it at least. I tightened down until there was no movement and then slowly loosened until it started to move smoothly. There is definitely no play in the jaws nor in the needle if I hold the movement firm and try to push the jaws apart. I even tightened it a bit and still the same. Don't have any gauge pins, but I do have a 0.50" ball bearings from a wheel bearing and there is no change in the measurement regardless of where along the arms I put the bearing (closer or further out). The jaw faces look good and flat. I am also using less force and even no force after closing the calipers and that is not changing anything.

So it reads consistently short by 0.001" down to 0.5" at least. Consistency is a good thing however. I might experiment with smaller items or even some the feeler gauges to see if I can find a point where a 0.001" disappears. There is no skipping, binding or notches anywhere along the movement of the caliper and I would think that a worn gear would cause a cumulative error as you measure further out.

A 0.001" burr along an edge of the jaws will hold the jaws 0.001" apart when you are setting your closed-jaw zero.
That will cause all readings to consistently read 0.001" low.
Look closer at the jaws.
I bet you can see light between them when they are closed.

Otherwise, just zero them on a standard and don't worry about the closed-jaw zero since you can't actually measure NOTHING between the jaws.
Everything greater than 0.001" in thickness should measure correctly.

For fun, get yourself a basic set of gauge blocks.
Even a cheap set like this would be very useful:

https://www.ebay.com/itm/81-Pc-Steel-Gage-Block-Set-Grade-B-Space-Block-Harden-Gauges-Incomplete/283717476728?hash=item420ee12178:g:M7kAAOSwjydd~Rg1

[Odd_Ball]

A 0.001" burr along an edge of the jaws will hold the jaws 0.001" apart when you are setting your closed-jaw zero.
That will cause all readings to consistently read 0.001" low.
Look closer at the jaws.
I bet you can see light between them when they are closed.

Well now that you mention it ... yes, definitely. I can see a sliver of light through the closed jaws. All along where the two faces meet except perhaps at the very tip (so it appears). This makes sense now.

So a 0.0016" feeler wont fit through the closed jaws. But opening the jaws to read roughly +0.0016", the feeler gage goes in and moves with slight resistance, until I move the gage down to the very end of the jaws at the tip. There the gage hangs up firmly. Open the jaws to about +0.002", the 0.0016 gage still hangs up at the tip. Open to about +0.0025", the 1.6 thou gage still hangs but I can force it through easily. Open to +3 thou, the 1.6 thou goes through with strong resistance (meaning that I'm not forcing it but it catches a little part way through). Open above +3.5 thou and the 1.6 thou gage goes through freely.

At the very end there must be some contact and overlap of the opposing jaw blades. Most likely they've been dropped a few too many times in their day. I like that they are functional otherwise, though.

Otherwise, just zero them on a standard and don't worry about the closed-jaw zero since you can't actually measure NOTHING between the jaws.
Everything greater than 0.001" in thickness should measure correctly.

Exactly, I just need to make sure I keep the right zero setting. And to remember to stay way from using the very ends of the jaws to measure anything since it could read up to approximately 0.0014" larger* to the pinched jaw tip. I'll tape a note on the box as a reminder.

(* The 0.003" jaw gap minus the 0.0016" gage should give the reduced clearance at the tip, correct?)

For fun, get yourself a basic set of gauge blocks.
Even a cheap set like this would be very useful:
https://www.ebay.com/itm/81-Pc-Steel...kAAOSwjydd~Rg1

Nice, thanks. That would be good to have ... while I wrote this, that auction already went up from $20 to $36.

[67Cuda]

Calipers are not micrometers. Calipers are a rough measurement compared to micrometers.
.001 isn't worth debating concerning accuracy of calipers.

[sonofeugene]

However, I can always get +/- 0.0005" with Mitutoyo.

[ar15barrels]

Well now that you mention it ... yes, definitely.
I can see a sliver of light through the closed jaws.
All along where the two faces meet except perhaps at the very tip (so it appears).

Stone the burr off the tip where there is no light and I bet the jaws close up properly.
You should be able to find the damage with your fingernail.

[JagerDog]

So the tips are a bit tighter than the mid and base? Not a bad way to be out of parallel. Loose gibs would be the opposite. Some have been known to lap the jaws.

Most reloading measurements will be with the mid or toward the base of the jaws. Just know that any measurement at the tips is relative and not discreet.

Make sure they're clean. One good way is to close them on a piece of paper and slide the paper out.

[357magnum]

I was a machinist for 24 years and used nothing but starrett for all my measuring tools.
When I started reloading 30 years ago, I wanted a set of dial calipers to leave at home for reloading.
I got a set of RCBS dial calipers and they have been flawless to this day.

[Rizzo]

Was curious after seeing it going for $114.00 on Amazon.
Not sure if this is a "knockoff" but here is a link on Ebay for $25.91

Mitutoyo 500-196-30 Advanced ONSITE Sensor (aos) Absolute Scale Digital Caliper

https://www.ebay.com/p/28026546498

[newbie1234]

Was curious after seeing it going for $114.00 on Amazon.
Not sure if this is a "knockoff" but here is a link on Ebay for $25.91

Mitutoyo 500-196-30 Advanced ONSITE Sensor (aos) Absolute Scale Digital Caliper
https://www.ebay.com/p/28026546498

$25 NIB and free shipping, too good to be true, is it a fake one ??????

[ngnrnlo]

What do you recommend for Calipers?

Stick with 9mm or 45 acp.

[ar15barrels]

Was curious after seeing it going for $114.00 on Amazon.
Not sure if this is a "knockoff" but here is a link on Ebay for $25.91

Mitutoyo 500-196-30 Advanced ONSITE Sensor (aos) Absolute Scale Digital Caliper
https://www.ebay.com/p/28026546498

That's NOT a Mitutoyo caliper.
The actual caliper pictured does not say Mitutoyo on it.
The instructions do not say Mitutoyo.
The case is not the same type as a Mitutoyo.

Only the auction TITLE says Mitutoyo.
Even at that, that's a copy of a 3 generation old Mitutoyo design.

[ar15barrels]

A matter of personal preference on the feel. But I prefer Brown & Sharpe.
I'm not a fan of Mitutoyo but that's just based on feel and not on function or reliability.
Starrett has always been good stuff but again lacking in feel.

I don't like the feel of Starrett's either.
They feel just like Chinese calipers to me.

I have been using analog Mitutoyo's for 25+ years with no complaints.
I love my Swiss made dial test indicators but never even though to seek out swiss made calipers since the Mitutoyo's served me so well.

I popped over to eBay and found these:

http://www.ebay.com/itm/174133456054

For $30 shipped, I will give them a try.

[Odd_Ball]

Was curious after seeing it going for $114.00 on Amazon.
Not sure if this is a "knockoff" but here is a link on Ebay for $25.91

Mitutoyo 500-196-30 Advanced ONSITE Sensor (aos) Absolute Scale Digital Caliper
https://www.ebay.com/p/28026546498

$25 NIB and free shipping, too good to be true, is it a fake one ??????

That's NOT a Mitutoyo caliper.
The actual caliper pictured does not say Mitutoyo on it.
The instructions do not say Mitutoyo.
The case is not the same type as a Mitutoyo.

Only the auction TITLE says Mitutoyo.
Even at that, that's a copy of a 3 generation old Mitutoyo design.

The youtuber Ave actually did a review on those ebay "Mitutoyo" calipers, though I think he picked his up from Aliexpress. Its an interesting video:

https://www.youtube.com/watch?v=KnDype-j3hk