Frank

Check the distance you have between the tool end and the work, allow for the height of a rotary table if you use one, those co-axial indicators a pretty long overall, even with a short probe fitted.

If you have the space and money then go for it, they seem to be very accurate and easy to use.

Emgee

I have the one from DRO (Link) and don't rate it TBH, ok for rough clocking .002/.003" which I rarely do, I'd much rather use a finger DTI. I believe the expensive ones are very good, the jig borers where I worked used to use them but they were thousands of pounds.

They are quite long which rules out use on many model engineers machines. There isn't enough daylight. Even on a Bridgeport fitiing vice, job and indicator in can be difficult.

Judging by the colour and box the one Henry links to is the same as the one I've had for 15 (or more) years. I reckon errors under 1 thou TIR are quite realistic once you have got the technique sorted and learned your way round some price related engineering infelicities.

As always with null indicators its actually pretty tolerant of set-up and other errors. But, inevitably, being an inexpensive device it can drive you nuts when it doesn't want to play the way you think it should do.

Aligning bores is where they are most useful. If you aren't planning to do bores the money is probably better spent elsewhere. Objectively the expenditure on mine wasn't really justifiable but now I have it I use it.

For outside work its hard to beat Osborne's Manoeuvre (or whatever your oracle calls it) using a cylindrical probe in the spindle chuck or collet and a thin feeler gauge to detect contact. The force needed to pull out the feeler gauge being a very sensitive measure of contact pressure.

Clive

Hi Baz, I thought mine was ok until I checked the part I had zeroed with it and it was .003" out. I took it apart and found that it was quite crude and the scissor movement had quite a lot of sideways slop which I managed to take out with some washers made from shim which improved matters a little but I'm afraid I don't trust it now,

Old, old story I guess, you pays your money…

I got one a year ago for Amadeal which was around 80 quid.

What I found was that, if there was significant run out, then you got inaccurate results. The run out in this case was due to the chuck provided with it. The fact that there is a lot of air makes this worse.

When used with well set up equipment it decently accurate and really quick to set up.

Having said that, I'm hoping that my Xmas will include an indicator holder that attaches to the spindle of the mill as used by Joe Pie (on You Tube). This won't be quite as quick to use, but on the other hand you appear to be able to use it without swapping collets / chucks so it may end up equally quick and possibly more accurate.

Both Machine DRO and ARC sell one and they are a good deal cheaper than an coaxial indicator.

Iain

Got an American friend to bring one over from the States in his suitcase. A nice repro of the Blake by Shars.

Takes a while and a few goes to get the hang of it, but once familiar and confident with said doo-dad, the thing works very well, and very fast. I only work to a thou or a tad less, and it is much faster than a lever type indicator.

And no using a mirror or getting neck ache peering round the back of the work.

Surely the important parameter is how accurately the centre is located when the needle movement is nulled. I don't see that has anything to do with the calibration of the indicator itself? Although of course one would need to make an independent measure of the centre to get the numbers.

Andrew

The neat thing about using a rotary edge finder – and in particular along with a DRO centre function – is how the centring accuracy 'homes in' if you repeat the procedure once or twice.

Martin.

Andrew

As its a single point being swept around a rotational axis defined by the spindle all mechanical and offset errors are, supposedly, the same regardless of angular position and cancel out. So mechanically speaking null is null and, theoretically, zero error is possible.

In practice it depends on the quality of the mechanical connection between the probe and the gauge which should register the same offset for any error regardless of its angular position. Realistically anything better than within ± one of the half divisions on the gauge is down to judgement and guess. Certainly unquantifiable.

Gauge needle sweep on mine is a little speed sensitive too. Turning the spindle by hand to do point to point measurements is not effective. With a long probe side to side shifts at the business end due to drag variations can clearly be seen. Mine likes 150 to 300 rpm. Presumably this gives sufficient drag to stabilise the probe lag but is not fast enough to upset things. As the Bridgeport is varispeed a quick twiddle to fined a happy speed is easy.

Always assuming the object or bore is properly round. Egg shapes or out of round engine cylinder wear can clearly be seen with the spindle running slowly.

All sorts of hysteresis and dynamic effects getting involved not to mention surface quality and any non linearities due to imperfections in the mechanism. If nothing else a dial gauge isn't supposed to be a dynamic device at 5 to 10 Hz or thereabouts so its asking a lot of (a cheap) one to read truly centred variations.

I'm darn sure that the true zero isn't quite at the centre of the needle swing on mine. Its also quite happy to read a one or two thou ding.

But is quick and close enough for most jobs. If I really want accuracy I'll break out the mirror and tenths thou Verdict then get a bit creative with the DRO. One day I might learn to use my Hamier!

Folk tend to forget that a thou' is pretty darn small and project unreasonable expectations on what is, when all is said and done, an inexpensive device. I always approach mine in the same spirit as I would a Unique pressed tin dial gauge substitute.

Clive

What's a DRO ?

The thing you must understand about these tools is that they are NOT for measuring. The length and angle of the probe used all affect the scale divisions on the dial. They are intended for adjusting the cylindrical work into alignment with the axis of the spindle and nothing else. As long as the needle does not move that is all that is required.