Measuring internal diameters

[routercnc]

Now that I have my lathe I am looking into tools for accurately measuring internal diameters e.g. to press fit bearings into pockets.

I'm looking for something better than the digital calipers I have (which are not that accurate in general).

I've seen this type used (an analogue internal micrometer) ~£60:
http://www.ebay.co.uk/itm/5-30mm-Moo...-/231227465653

This quotes a resolution of 0.01 mm but no accuracy value. Could be good enough?

The digital versions are pricey ~£190:
http://www.machine-dro.co.uk/5-30mm-...80-series.html


There are telescopic bore gauges, but have never used them and there seems to be a knack to using them. How do people find these? I have an external micrometer so could mic off the gauge assuming the gauges give repeatable results:


Anyone using anything else? thanks

[komatias]

Telescopic gauges like the ones in the last photo are prone to inaccuracy. I personally avoid them in all but very special circumstances.

There are others to look at too:

3 point bore micrometer is the best but most expensive

there are also dial bore gauges

Google them up for piccies.

[m_c]

I usually buy measuring stuff from Arc Euro Trade. Not the best quality, but everything I've bought from them has worked well, and calibrates fine when tested on various gauges.

I use the internal micrometers the most, but for most work a good set of digital verniers is good enough.
Note the word good, as some are horrendous. I had one cheap set where the internal jaws were over a mm different from the external jaws! Having a couple gauge rings soon lets you know just how accurate things are.

[m_c]

Oh, and telescopic bore gauges are a skill in their self, however when you need them, they are invaluable. Short of spending a huge amount of money on lots of three point micrometers, there's no other cost effective way of measuring various diameters of deep bores.
I've got a set, however I think I've only ever used them once in the past year, and that was to measure deep enough down a worn bore to get a starting measurement for a repair.

[Boyan Silyavski]

Depends how big are the bearings. I think that the first tool you mentioned will do the job correctly. By the way, whatever method of measure you use, there is no escaping the fact that it depends on you to read correctly the measure. I can take measures with cheap stuff correctly, just because i am careful not to make a mistake and am having in mind the possible reasons to miscalculate the measure.

[routercnc]

Thanks everyone, very informative.

I asked around at work as well and they gave similar responses:
The budget/entry telescopic ones are not that nice to use unless they are high end such as Mitutoyo which are much smoother
Three point internal mics are great but expensive
Verniers were not favoured in general (nick named Very-nears)
Two point internal mics were reasonable (as per 1st photo)

But critically, and as you mention Boyan, even with reasonable tools it comes down to the operator and the feel of the gauge when taking the measurement. This is something only experience can give - i.e. when the interference fit part just falls off under gravity you know your method needs a bit of work. I'm sure I can dial myself in as per all the other tools I've got.

In all I'm homing in on the 2 point internal mic. Reasonable price, just one measurement to take, seen them used a bit (Youtube etc.) to make good parts. Maybe one for the Christmas list . . .

Thanks again

[Lee Roberts]

Thanks everyone, very informative.

I asked around at work as well and they gave similar responses:
The budget/entry telescopic ones are not that nice to use unless they are high end such as Mitutoyo which are much smoother
Three point internal mics are great but expensive
Verniers were not favoured in general (nick named Very-nears)
Two point internal mics were reasonable (as per 1st photo)

But critically, and as you mention Boyan, even with reasonable tools it comes down to the operator and the feel of the gauge when taking the measurement. This is something only experience can give - i.e. when the interference fit part just falls off under gravity you know your method needs a bit of work. I'm sure I can dial myself in as per all the other tools I've got.

In all I'm homing in on the 2 point internal mic. Reasonable price, just one measurement to take, seen them used a bit (Youtube etc.) to make good parts. Maybe one for the Christmas list . . .

Thanks again

Before you do that:

All the boys I watch on YouTube...

Use the telescopic ones to get them close, an external mic to measure the scope and get them even closer...

Then! they use there own skill to find a piston fit "pop" :)

It's normally in the flavour of Starrett though on the scopes, so yeah they do operate nicely, I can't see that a cheaper set would give you that much of an off reading that you couldn't recover from it using your learned skill on the last op.

[mekanik]

Before you spend a lot of cash try using internal calipers, i used to work as a Mechanical Inspector in a Machine Shop and used these a lot, it takes some practice but you can get a good reading.
Regards
Mike

[routercnc]

Cheers Mike, Lee, Komatias

The guy I've been watching a lot recently is Stefan Gotteswinter and he likes to use the internal mic. But yes many others use the telescopic gauges and then mic them.

In the work discussion calipers were mentioned as a very cheap way to measure bores (I already have the external mic), but takes some feel/practice. I forgot to mention that above so thanks Mike. Great to hear you worked in the inspection area - that's what I like about this forum, such a wealth of experience to tap into. So I'll most likely get an internal caliper anyway and have a play - not that expensive.

Dial bore gauges look interesting, one to think about.

I'll sleep on it and bit more . . . .

[mekanik]

Dial bore mic's are expensive and you still have to check them with gauge so in all honesty i don't think its a very good investment unless you pick up something cheap on ebay.
with spring loaded internal calipers you can get a good feel ( polish the tips to form a nice ball end) and as long as you duplicate the same touch when brushing the anvils of your external mic you will get a good reading.
Good luck
Mike