Accuracy of dropped caliper

Dad works in a machine shop and I'm just a hobbiest and one of his trainees dropped his caliper and the company just bought him a new one rather than calibrate it. I'm wondering if I put it across a 6" ruler and zero it if that would be accurate enough for me?

Reply to
Eugene
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What kind of caliper? Unless there is serious structural damage, the linearity of a dial caliper isn't going to just magically "go out", it's all about gear ratios and pretty robust. If the jaws are impacted or sprung, the zero could be off. I'd zero it at zero; the needle might not be straight up like it used to be but that's just an annoyance. But if you're not talking a dial caliper let us know what you mean and you can get a more specific answer for your situation.

Reply to
Dave Hinz

If you got any bearings lying around you could use them to get an idea of how good the thing is. You will have to find the listed size and tol. of the bearing bore and od so you know what dia. you are measuring. That is assuming you have no mike standards or gauge blocks.

John

Reply to
John

I have a number of dial calipers that have been assembled from used and abused parts. They work well for my purposes.

In a couple cases the renovations included some fair bit of (hack) surgery with a bench grinder to remove the damaged portion of the jaw tips, in other cases the jaws were stoned to remove the burrs present and that was all they needed. Hold the jaws up to the light when they are closed, and the alignment, for good or bad, is easy to see. A quick check on some gage blocks, or against a part measured with a known good tool, and it's off to the races.

When I need calibrated tools for my work, these aint them!

I tend to be able to use the same tool to measure the work I am doing as well as the place where it will fit, so I am less concerned with calibration, than with coming up with numbers that match from measurement to measurement.

The better safe than sorry mindset gets a little too pervasive sometimes. Before I would have just bought a new tool (which would also need calibration prior to use) I would at least do some checks with known standards to see if the tool was damaged beyond repair.

Worst case, it would become a measuring tool on a chain attached to the stock rack or tethered to the cutoff saw for crude measurements.

Cheers Trevor Jones

Reply to
Trevor Jones

Its a dial, When zeroes the needle points at about 10:00. I have a 5" stainless steel ruler made by Rabone Chesterman that says standard at 20 C and when I open to caliper to 5" and measure the ruler its about 5.002" So I think its close enough for my use. I managed to find the company name that mad the ruler once on an internet search and it was an old company that made accurate machinist tools so its probably a good standard and I've had it for 20 years so its kind of my standard.

Reply to
Eugene

I'm thinking it was more of a replace his personal tool with a company owned one. They recently created the machinist position at this small company closer to his house and he got the job to shorten the drive his last few years before he retires and he's basically building up the machine shop to bring in a lot of work they used to have to send out and training a couple other to take over when he retires. He doesn't do a lot of machine work on the farm and saw that I was starting to do a little so he has some tools he's giving me that he won't need.

Reply to
Eugene

No standards but an old machinists ruler which says 'standard at 20 C' so I figure it must be pretty accurate.

Reply to
Eugene

Gauge blocks are made for this - and special stacking skill with super clean and then with a twist (rubber gloves(finger acid)) for the test stack up.

Does it zero ? - and then does it read the correct value at a high end. A ruler is a crude instrument really. Not so much it, but using it...

Martin

Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member

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Eugene wrote:

Reply to
Martin H. Eastburn

Yes, it would be. There is no need for you to have it recalibrated.

John Martin

Reply to
John Martin

According to Eugene :

O.K. The pinion gear has simply skipped a few teeth in the rack gear.

There are little bronze spring shims made for teasing the gears back into proper mesh. It can take a few tries, but once you have it, you will never know that it has been dropped -- assuming that the jaws have not been distorted by the fall.

Good Luck, DoN.

Reply to
DoN. Nichols

It would prove it's about as accurate as a ruler. That's not very. Have a look at the digital calipers on eBay. They cost about =A310 ($15) in UK.

John

Reply to
John

how about checking it on a 1-2-3 block, any machine shop should have them, they are fairly cheap and very, very handy. As the name states, one side is 1 inch, one is 2 inches and the other is 3 inches. A relatively inexpensive Brown and Sharpe should be accurate to +/-

0.0003 or so, pretty close for most stuff.

John

Reply to
CAMCOMPCO

How specifically do you propose that a drop will change how a dial caliper reads?

A dropped but re-zeroed well built caliper is at least as good as a 15 dollar junk chinese new caliper. Unless you can explain how the rack & pinion gearing can suddenly become non-linear?

Reply to
Dave Hinz

Well, I have one with a couple bent teeth on the rack, and another two that suffered some damage to one of the gears inside from the hit. One of those is almost useful, but the other has a real unliklyhood that it will hold a zero from cycle to cycle.

They work good for scribing equal lines along the edge of something, but not worth boo for accurate measuring.

That's how!

Cheers Trevor Jones

Reply to
Trevor Jones

Clean the caliper first, giving especial attention to the jaw-surfaces and rack - keep dirt and chips out of here for best results.

Step 1 Mechanical condition With the caliper held shut, the OD jaws and the ID jaws (points on top) should be an exact fit. Adjust the crown of the dial to bring the dial zero to the needle, and lock the crown with the screw. Jaws should appear clean, closed, no apparent gap. If the ID jaws are burred on the tips as is often the DAMAGE case, these can be lightly ground down, and repointed from the back if you need fine points, but repointing is not usually necessary, unless your working condition demands small, fine points to get into tight places. Small burrs of inequalities on the faces of the jaws or measuring surfaces can be dressed down with a FINE, OILED hard arkansas-type stone .

Step 2 Establishing consistency at ZERO between indicator and all four measuring points (OD jaws, ID jaws, STEP gage, and DEPTH gage.) Check ZERO of the pointer on the dial, jaws closed. On any clean surface-plate or even the side of a gage-block or a clean, undamaged

1-2-3 block, set the caliper up on its jaw-end. The gage should record both the frame and the sliding jaw-portion to be on the gage, with no movement of the pointer. (This is often referred to as a "step-gage" portion of the caliper. Then, the other end - the long end of the caliper (DEPTH gage) and the rod should both be placed perpendicular on the surface-plate, and again, zero should be with no appreciable movement of the jaw.

Step 3 Checking OD jaws, and establishing linearity of measurement (consistency of rack & pinion and indicator movement) Check the OD jaws with gage-blocks, a 1-2-3 block, even the setting standards from a 2" and a 4" OD micrometer, if you have such. They both should show, right on the ZERO of the dial (or other number - whatever such standard may be calibrated to be, though anything far from X.0000" would be highly unusual).

Step 4 ID jaws Now, you are left with only the ID jaws, (the horns) to calibrate - this would be done ideally, with a calibrated ring-gage. If you have access to such, that is most desirable. If not, there are alternatives Most easily, take any gage-block (easily .750"), and "wring" another to each end of it and measure the gap. The dial should agree with the block in the middle. ( You only need this one measurement, to check ID jaws against the indicator - linearity has already been established).

Step one establishes mechanical condition Step two shows that all gages agree with each other and the dial. Step three checks OD jaws and proves linearity of measurement of themechanism Step four proves the ID jaws agree with all the others.

There are remedies for if the pointer is at the 10 O'clock position, which procedures vary from maker to maker. That is, however, purely an aesthetic thing, if the unit works accurately otherwise.

Good luck with it,

Flash

Reply to
flash60601

Ah, OK. I'll amend my statement to say "If you can go back & forth & the zero doesn't change, it's going to be fine". I suppose if you shred the thing, yeah, it just turned into "one of them fancy wrenches with a clock on the handle".

Fair enough!

Dave

Reply to
Dave Hinz

If the pinion gear is not running true on the shaft, the readings will be nonlinear. the reading will be vary between a high and low error amount caused by the gear or gears wobbling.

John

Reply to
John

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