Depth micrometer v depth gauge

Pete F · Jun 12, 2013

I sometimes have difficulty in getting consistent readings off a depth mic. I find it tricky to get the right "feel" for where the bottom is. Is this just me or do others at least know what I'm referring to?

Given that I have an option of using a depth indicator, is this preferred for greater accuracy and repeatability? I always feel as if I'm cheating when using it and I should simply work on my mic skills.

Pete

Greg White · Jun 12, 2013

Maybe its it all aboot watt you feel comfortable with?
Aint cheatin,,plus its also aboot watt tools you have on hand.
Some might say your nothing unless you grind your own cutters,or use a depth indicator.
I only have depth mics,so there my favorite

Gw

aerodark · Jun 12, 2013

Seems like the deeper the measurement, the more likely the rod will spin off when it contacts the surface. I have never used one for measuring more than 4 inches.

Pete F · Jun 12, 2013

aerodark said:
Seems like the deeper the measurement, the more likely the rod will spin off when it contacts the surface. I have never used one for measuring more than 4 inches.

Interesting, though it makes sense. I was measuring shallow depths however, less than an inch.

With an outside mic I find I have reasonably good feel from the barrel and sliding the tip over the part. Just thinking about it now I think it's that sliding I'm missing, or am I indeed missing something? At the moment I feel as if I just crank 'er down until it hits the bottom and hope for the best.

Pete

aerodark · Jun 12, 2013

I usually give it a few attempts and take the shallowest reading. I always use the ratchet thimble on my Starretts..........

Pete F · Jun 12, 2013

aerodark said:
I usually give it a few attempts and take the shallowest reading. I always use the ratchet thimble on my Starretts..........

Ah, I think you've just answered as to why I've suddenly become a bit frustrated using them. To be honest I hadn't actually realised there was a difference between my mics until you mentioned the ratchet. My old ones were Mitutoyo with a ratchet. However they were imperial so I'm selling them as I work exclusively in metric now. The new ones are Moore and Wright with no ratchet. Likewise I used to use the ratchet, now I use one finger straight (ie not griping the spindle) and try to feel the bottom of the hole. Maybe I'm just expecting too much. Obviously the accuracy of the instrument is the same, but what sort of repeatability can I expect off a depth mic compared to say an external mic?

Pete

Putch · Jun 12, 2013

I guess it takes getting used to, the feel of a depth mic hitting a shoulder. I always make sure I hold the base down very sturdily, set the mic a little shallow from where I am measuring to, then turn it very lightly until the thimble stops

easymike299 · Jun 12, 2013

With this and a set of gage blocks to compare you should be able to measure depth within a couple of tenths

Gene

Pete F · Jun 12, 2013

Yes that's basically the same as the Mahr I have Gene, however the depth indicator I have is damaged and needs replacing so I've been using a standard indicator with it.

Pete

christinandavid · Jun 13, 2013

You should have kept hold of your imperials, less chance of a biased measurement.

Mic or gauge, if the surface you are sitting on isn't perfectly flat and parallel, and the plungy part not perfectly perpendicular, the reading will be out. Use slip gauges and dtis wherever possible before resorting to depth mics. Witness a dti check at the machine if possible, then compare to depth mic.

DP

Gordon B. Clarke · Jun 14, 2013

Pete F said:
Obviously the accuracy of the instrument is the same, but what sort of repeatability can I expect off a depth mic compared to say an external mic?

Pete

Each type of measuring equipment is made to special standards applicable to the particular type. A depth micrometer doesn't have the same accuracy requirement as a depth gauge. Repeatability accuracy will more often than not be much better than measurement accuracy.

In most of the measuring equipment catalogues I have (and I have dozens) then most give the manufacturer's accuracy specifications for each piece of equipment but to find repeatability accuracy then as good as always the relevant manufacturing standard must be looked at. Companies like Mitutoyo often (i.e. not in all cases) give the relevant manufacuring standard for their measuring equipment.

Not wishing to start an old discussion again but it is a fact that if the instrument has any type of measurement force attachment (ratchet, spring etc.) then this is always used by the ompany when testing/calibrating their products.

Gordon

Pete F · Jun 15, 2013

Sorry, maybe I haven't had enough coffee yet, but I honestly didn't understand the last two replies at all.

David, what did you mean "Less chance of a biased measurement"? I don't use imperial at all any more, so if I use any imperial tools needed to convert to metric.

Gordon, what I meant by that is that the mitutoyo outside mics I use have a quoted accuracy of 2 um. Their depth mics are 3 um. However I find it far easier to achieve comfortably repeatable results with the outside versus depth mic.

Pete

christinandavid · Jun 15, 2013

Well for a start they have a ratchet, and if you measure before conversion you will have no expectations regarding the reading on the barrel. I prefer to use our shops imperial equipment because it is less popular with everyone else and the metric version has an extra wide base which is just asking for trouble...remember that externals contact a smaller surface area and the points of contact are in line, thats why they are more consistent.
DP

Gordon B. Clarke · Jun 16, 2013

Pete F said:
I sometimes have difficulty in getting consistent readings off a depth mic. I find it tricky to get the right "feel" for where the bottom is. Is this just me or do others at least know what I'm referring to?

Given that I have an option of using a depth indicator, is this preferred for greater accuracy and repeatability? I always feel as if I'm cheating when using it and I should simply work on my mic skills.

Pete

I'm going back to the OP to give my opinion. I always prefer thinking of depth measurement instruments as step gauges although their "name" is depth gauges.

Under normal circumstances a depth micrometer will be more accurate than a depth indicator simply because a micrometer type has greater accuracy than an indicator type.

However as an indicator usually has a very small measurement presssure (1-2N) compared to a micrometer ratchet (5-10N) then consistant reading are easier as the base doesn't have to be "forced" down as firmly. A micrometer type without a ratchet will have the tendency, with the lightest excess force try to lift up. The measurement then becomes very "touchy feely".

Both types have their advantages and disadvantages but if I could only have one type and had to choose then it's be a depth micrometer and with a ratchet

Gordon

Pete F · Jun 16, 2013

Under normal circumstances a depth micrometer will be more accurate than a depth indicator simply because a micrometer type has greater accuracy than an indicator type.

Surely that would depend on the indicator used Gordon? While a mic will certainly beat the Mahr indicator that mates with the Mahr base I use, there's no reason I can't drop any indicator with an 8 mm stem into the base, and indeed that's what I've done ... and I'm currently looking at some Heidenhain Mt 25s that I think are good for 0.2 um IIRC!

Given I mentioned my only depth mic with a ratchet is imperial, are you also advocating me going back to imperial Gordon?

Gordon B. Clarke · Jun 16, 2013

Pete F said:
Surely that would depend on the indicator used Gordon? While a mic will certainly beat the Mahr indicator that mates with the Mahr base I use, there's no reason I can't drop any indicator with an 8 mm stem into the base, and indeed that's what I've done ... and I'm currently looking at some Heidenhain Mt 25s that I think are good for 0.2 um IIRC!

Given I mentioned my only depth mic with a ratchet is imperial, are you also advocating me going back to imperial Gordon?

Yes there are very accurate indicators but they don't normally have much "travel". There are also very accurate micrometers. To the best of my knowledge a micrometer is more accurate than an indicator over the same distance.

If you prefer what you have/use to what I'd use then it won't give me sleepless nights. As to whether imperial or metric is used then I honestly don't see a difference. A measurement is a measurement. Divide or multiply by 25.4 depending which way you go

As already mentioned if what I use has some type of measurement force attachment not only would would I always use it but also prefer having something with it to something not having it.

Your OP was/is Depth micrometer v depth gauge and all I've done is give you my opinion as have others :cheers:

Gordon

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