ttrager
Cast Iron
- Joined
- Jul 23, 2015
- Location
- East Side / Detroit
And if you are, what is the verdict? Accurate or not, repeating or not?
Thanks in advance.
Thanks in advance.
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They all measure on 2 points, the "3-point" versions are only 3-point to help self-centering.
And if you are, what is the verdict? Accurate or not, repeating or not?
Thanks in advance.
I don't understand what you mean by this. Three point bore micrometers absolutely do measure on three points.
The question was not about micrometers, it was about bore gages...
You're absolutely right, I should read more carefully...
I've got all of them from the smallest up to 12". I've never had an issue with them. They all measure on 2 points, the "3-point" versions are only 3-point to help self-centering.
Don't feel bad, I missed the "digital" part of the question until this re-read. Mine are actually all analog dials.
A bore gauge is a tool that I would never want a digital indicator on anyway. In fact I just hate digital indicators.
I am not a luddite who hates digital measuring tools - most of my measuring equipment is digital - but digital indicators just suck. For just about every possible use of an indicator, a needle and dial is easier to work with.
Anyway, I think there is some confusion here.
AFAICT, Starrett don't make a bore gauge with a digital indicator.
They do however call their pistol grip bore mics "ELECTRONIC PISTOL GRIP BORE GAGES", which is confusing, as those things use the mechanism of a three point bore mic, not a bore gauge.
I suspect OP is talking about those, and not a bore gauge at all.
As for using those for measuring +0/-.0002" tolerance, that's pretty much a hard no without a lot of qualifying statements. As a zero comparator using a qualified standard, maybe.
How are you measuring those tolerances currently?
Starrett calls them bore gages, not gauges.
A bore gauge is a tool that I would never want a digital indicator on anyway. In fact I just hate digital indicators.
I am not a luddite who hates digital measuring tools - most of my measuring equipment is digital - but digital indicators just suck. For just about every possible use of an indicator, a needle and dial is easier to work with.
Anyway, I think there is some confusion here.
AFAICT, Starrett don't make a bore gauge with a digital indicator.
They do however call their pistol grip bore mics "ELECTRONIC PISTOL GRIP BORE GAGES", which is confusing, as those things use the mechanism of a three point bore mic, not a bore gauge.
I suspect OP is talking about those, and not a bore gauge at all.
As for using those for measuring +0/-.0002" tolerance, that's pretty much a hard no without a lot of qualifying statements. As a zero comparator using a qualified standard, maybe.
How are you measuring those tolerances currently?
STARRETT Digital 3-Point Inside Micrometer, Inside Micrometer Type 3-Point Inside Micrometer - 53VE36'|'770BXTZ-2 - Grainger
Technically the naming of the product is "inside micrometer", my bad. This is an example of a non-pistol grip model.
OK, with that established, I will point back to my previous question, how are you measuring those tolerances currently?
Not Starrett, but I use three point bore micrometers extensively, I have a large number of them from various manufacturers, analogue and digital.
The Starrett you linked states an accuracy of 4µm (that's pretty much standard for these, regardless of manufacturer). Others, Sylvac for example, state that a little differently. The figure is still 4µm but the property is called "Maximum Error".
In my experience that is about right. IME they will repeat quite reliably within the resolution of the reader - you zero on a ring gauge and it will repeatably read zero at 1µm resolution on that gauge, and it will reliably measure the difference between a ring gauge calibrated at 39.998 and one calibrated at 40.002 for example. But if you zero on a 40mm ring gauge for example, and check again on a 50mm ring gauge, then you might see something in the ballpark of that 4µm error.
The 4µm "Maximum Error" is 50% of the tolerance that you need to measure, so on paper, your measurement would have a low confidence.
The reality is that these are the most accurate way to measure an internal diameter short of air gauging, and environmental conditions can feasibly impact a measurement by an order of magnitude more than the stated accuracy of the measuring instrument. Hence why I ask, how are you measuring those tolerances right now? Are you looking for an upgrade, or are you looking for an absolute?
So it was a ponder on my part, which, as these things go, is entirely gated by whether the device in question is capable of taking repeatable measurements to begin with, to the accuracy required.
Now Gregor, I don't know about you, but at this point I'm starting
to think the OP needs to word his posts more carefully. Your reading is just fine by me...
Or maybe it's Starrett we need to chase with the torches and pitchforks. Though don't they call them 3-point internal micrometer?
Horses for courses ? Assuming you are talking about the three-prong internal mics, I had several Etalon Ingages (I think) with setting rings, they were beautiful things but on an ID grinder I found that the analog indicator-type gages were faster, easier to use, and more accurate. In fact, I disliked them even for regular work, they just never felt right.The reality is that these are the most accurate way to measure an internal diameter short of air gauging, and environmental conditions can feasibly impact a measurement by an order of magnitude more than the stated accuracy of the measuring instrument.
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