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Dial Gauge resolution?

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Chris Parsons31/08/2012 10:58:49
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118 forum posts
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Thinking about buying my first dial gauge (to centre in a 4 jaw chuck)

I see a large variety that can read from 1mm to 30mm+ and have a resolution of .01mm and .001mm - logic tells me that the more accurate the better, so I should go for the 1mm range and .001mm resolution - is this assumption correct? They do cost a bit more but I am trying to go for better/higher quality etc than want to upgrade somewhere down the line?

Go for a Starrett/Moore and Wright/Mitutoyo or not worry about the branding?

Interestingly the DTI indicators all seem to be .01mm resolution though?

(I am also looking to get one of these shortly)

Thanks

Chris

Edited By Chris Parsons on 31/08/2012 10:59:43

Michael Gilligan31/08/2012 11:24:01
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20183 forum posts
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Chris,

Just a couple of points:

1. Always check the specifications carefully ... especially with digital readouts ... resolution and accuracy are easily [and sometimes conveniently?] confused.

2. Strictly speaking; all Dial Test Indicators are intended as Indicators only ... the scale is convenient, but you are using it to confirm " Zero ". [hope that makes sense ... happy to explain in more detail if you want]

Yes, we all sometimes use them for direct measuring!

My recommendation would be to get the best one you can find, with a nice clear analog dial.

... it should last a lifetime.

MichaelG.

Roderick Jenkins31/08/2012 12:24:13
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2184 forum posts
608 photos

Chris,

I have all sorts of DTIs. The one I use most for centering in a 4 jaw is Verdict lever type with a small dial reading to 0.5 thou (0.013mm). This much more versatile than the plunger type and the small diameter dial means that it is easier to get it close to the chuck in some circumstances. The plunger type has to be at right angles to the job whereas the lever type can be used in almost any orientation. As MichaelG hints, when centreing what you are really looking at is movement of the indicator hand rather than an absolute measure. I'm very happy if I can centre so that the hand moves less than half a thou with one revolution of the job. For this reason the analogue type is much easier to use than a digital one (although digital are good in other circumstances).

HTH

Rod

David Clark 131/08/2012 12:25:19
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3357 forum posts
112 photos
10 articles

Hi Chris

I would get a dial test indicator plunger type.

Something with about a 1/2 inch travel.

Resolution is not to important as you are using it as a comparator, setting the component to zero all round.

Lever indicators are quite short on travel and are only comparators at best while with the plunger indicator it is possible to direct read from it although check it with a spacer of the correct size.

Lever indicators are more liable to get damaged as well.

I expect you can get a decent one of Ebay for a few quid.

regards David

Andyf31/08/2012 12:25:39
392 forum posts

Chris, for centring in a 4-jaw, I find a finger-type DTI with a 0.01mm (that's less than half a thou) perfectly adequate. I have never used one with 0.001mm divisions, but I suspect that the main object (to adjust the 4-jaw until the DTI needle doesn't move as the chuck is rotated) might be harder to achieve because the instrument was picking up too much confusing "noise" from the surface of the work, and the effects of your hand in the chuch as you turn it.

The difficult bit with most finger DTIs is getting them positioned. My magnetic stand with articulated arms is difficult to manoeuvre on my small lathe, so I made up a holder which fits in the toolpost. This allows the finger to be brought gently into contact using the cross-slide and topslide.

Finally, the instructions on many DTIs don't mention that the angle of the finger vis-a-vis the indicator body can be adjusted. It is a friction fit to the rest of the mechanism, and (though at first you might think damage will be caused) a firm push will turn it so it is at up to an angle of 90 degrees either way. Correspondence on other forums show that a substantial minority of hobbyists don't realise this and have only ever used their DTIs with the fingers aligned as they were when first taken out of the box.

Andy;

Ady131/08/2012 12:38:50
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5091 forum posts
736 photos

If you're new to the game just get a 20 quid unit with a magnetic base

Once you get some experience you can upgrade

I doubt that a machine shop would let a trainee anywhere near a good quality DTI setup

Ian S C31/08/2012 13:04:19
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7468 forum posts
230 photos
If its for setting up the four jaw chuck, don't go to a greater accuracy than .01 mm/ .001", or you will never seem to center the chuck, .001 mm much too sensitive. Ian S C
JasonB31/08/2012 13:24:00
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22751 forum posts
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I'm with david, the plunger type works fine for me when setting work in the 4 jaw, infact I seldom find the need for the lever type on teh lathe prefering to keep that on the mill.

This is what I use, 0.001" divisions

Firefly3

The Merry Miller31/08/2012 14:04:26
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484 forum posts
97 photos

 

I've had some incredible bargains off Ebay and some also from the tool stall in Bury St Edmunds market (Saturday only).

Ignoring the unbranded versions that abound, the normal, most popular selections no doubt would be from the following:

Verdict, Mercer, Baty, Mitutoyo and Starrett. I must admit I haven't seen a Starrett version on Ebay

There are more expensive versions available but their names escape me at the moment.

Also they are available as Dial Test Indicators (DTI's -lever type) or the bog standard (sorry Bogs)

Dial gauge, (Plunger type)

Len. P.

 

Edited By The Merry Miller on 31/08/2012 14:07:58

Michael Gilligan31/08/2012 16:38:27
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20183 forum posts
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Posted by The Merry Miller on 31/08/2012 14:04:26:

...

Also they are available as Dial Test Indicators (DTI's -lever type) or the bog standard (sorry Bogs)

Dial gauge, (Plunger type)

Len. P.

 

 

Len,

I've never seen that distinction before

[and Moore and Wright seem to be with me].

I thought they were all "Test Indicators"

"Dial -", or "Digital -" according to the display type,

with various configurations of Plunger or Lever.

MichaelG.

 

Edited By Michael Gilligan on 31/08/2012 16:39:23

colin hawes31/08/2012 16:57:00
558 forum posts
18 photos

I would recommend a finger type dial inicator with 0.01mm or 0.0005" resolution because it is easier to use in a hole or slot. The main advantage of the plunger type is its longer travel; a finger type usually has only about 0.030" travel but as it is only supposed to be used as a comparator this is not a problem.A plunger type is useful only when the longer travel is an advantage e.g for a machine slide precision movement indication. A dro. often takes care of that these days. Colin

Swarf, Mostly!31/08/2012 17:02:39
668 forum posts
73 photos

Hi there, Chris and all,

Jason's photo shows his clock as having a ball end on the plunger. The end usually unscrews and a wide range of 'ends' are available (but expensive). Some makers use an American thread and some use a Metric thread.

For some situations, I've found an 'elephant's foot' end to be useful.

I would suggest that when you eventually get your clock, you unscrew the end and identify the thread, write it down and keep the paper in the box with the instrument. Then if an end comes your way at an affordable price, you'll know if it will fit your clock. Alternatively, you might make one?

Best regards,

Swarf, Mostly!

Michael Gilligan31/08/2012 17:13:37
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20183 forum posts
1053 photos

An excellent "point", Swarf [Sorry ... I couldn't resist that.]

Seriously though: Very good advice, and of course you can make "specials" for those really awkward jobs.

MichaelG.

Clive Foster31/08/2012 18:27:16
3135 forum posts
109 photos

Geo. H.Thomas says " For setting up purposes I regard the plunger type indicator as little short of an abomination". He is kinder than I.

For setting concentricity of rotation the lever type Dial Indicator is the proper device to use. Ideally with the direction of surface movement parallel to the lever. Unfortunately only possible on outside surfaces.

The proper home of the usual type of Dial Test Indicator with its plunger poking out radially sideways is on some sort of solid test stand with a component carrier beneath indicating deviations of a pile of parts from the nominal size, hopefully all within tolerance. After using slips to calibrate the relevant range of course. It also suits similar applications where the movement is inherently parallel to the plunger. The geometrical and mechanical infelicities involved in scraping a rotating surface across a tiddly ball point don't bear thinking about. Hopeless in bores too. If you use a 4 way or similar shim to centre tool post and fit an elephants foot it would be ideal for measuring the tool tip height over base off the machine so you can simply select the shims needed.

If you really must have a dial for set-up then the short travel back plunger instrument is the one to use. I have a full Starrett "Last Word" kit based around this sort of device which includes a pivoted arm especially for reaching down into bores.

Although I have a good selection of all varieties of indicators, including a triplet of Heidenhain moire fringe based probes, the shop workhorse is a basic small dial ± 15 thou Verdict. I purchased the Verdict at the first Model Engineer Exhibition I visited when a special offer price proved just within reach if I ignored trivialities like buying lunch for the rest of the month! Frankly I could probably still get by with it alone but the other toys make life so much easier.

The common terminology for these devices always seems odd to me. I was taught that the lever type was called a Dial Indicator because the dial indicates deviations from concentricity and calibration beyond a basic functional check is not needed. The plunger type was said to be called a Dial Test Indicator because its proper use is to test a deviation from standard having previously been calibrated in situ to relate the dial indications to the job. The plunger type also finds its way into various other instruments (such as bore gauges) and, so I was told, can be called Dial Gauges in such applications with the proviso that the calibration marks may not be assumed congruent with the measurement made by the instrument so prior calibration is essential. Common use often seems to be opposite but even textbooks can't agree.

Clive

Stub Mandrel31/08/2012 20:59:15
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4315 forum posts
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1 articles

Amazing how plunger vs. lever can be so polarising!

I can smugly announce that I have one of each, ancient German plunger one and an Arc Euro economy lever one.

I find I use the plunger one more often, as the lever one is very fiddly to set up, but sometimes it is the only one to use as it is more sensitive and can fit in tiny holes. I use the plunger one to tram my mill, with every satisfaction. Both work for setting work in the 4-jaw, although the plunger is easiest when trying to set up a chunky piece of work.

Neil.

Russell Eberhardt31/08/2012 21:30:39
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2737 forum posts
86 photos

I have both a plunger type with 1 thou reolution and a lever type with 1/10 thou resolution. 99% of the time the lower resolution one is used in preference and the lever one stays in the drawer.

One point that nobody has mentioned so far is that the graduations on the plunger type are reasonably accurate while those on the lever type vary with the anlge the lever makes with the work.

Russell.

Clive Foster31/08/2012 21:42:29
3135 forum posts
109 photos

Neil

I guess its what you are used to. I've never considered a plunger that easy to set-up, not least because of the extra weight relative to the small Verdict. For me longest job is sweeping off the ferrous swarf so the mag base doesn't do a porcupine imitation.

Tip:- wrap the mag base in cling film or pop in a small plastic bag before approaching the machine so that any swarf that does get attracted can easily be peeled away with the bag / cling film before putting things away.

If you have a chuck guard of the type which pivots up on a rod sticking out pretty much parallel to but above and behind the bed its well worth making an adapter to fit the adjustable arm out of the mag base set to this rod. Maybe via an intermediate arm. Can make life very easy when the job or general stuff gets in the way of plonking the mag base on the cross or top slide. Not a universal solution because you don't have the fine, accurate, screw driven positioning capability you have when fitting to a slide but there are times when it makes life far easier.

Don't forget the short slide on a spigot type carriers which let you mount up a lever type in the tail stock chuck with a useful amount of slide to side adjustment. Mine gives a couple of inches I think. When you need it you need it, Often found for chump change on Evil-Bay with an "I dunno what this is but someone does" description.

Clive

(12 gauges at the last count, I think, not counting the Heidenhains)

I.M. OUTAHERE01/09/2012 01:19:48
1468 forum posts
3 photos

For centering in a lathe i would steer away from a digital unit as a needle is easier to see.

A plunger type will give you more travel and will allow you to set things true or offset in a four jaw chuck .

You will most likely find that for the price of a name brand you could but a plunger and lever type of a cheaper brand .

I have both of these and both chineese made and they work fine but do have a feel of the mechanism particularily on the plunger type( slowly push the plunger in ) as some are a bit rough or the needle will jump ( it should be silky smooth)

There are also different dial sizes from around 1 inch upwards and the biggest i have seem was around 5 inches but i would stick with a dial size around 2 inch unit for a plunger and 1.5 inch for the lever.

Having a look at the arc eurotrade catalogue(usual disclaimer applies) i see they sell dial gauge contact point set that makes a plunger type gauge more versatile and with the bent stem fitting you could use the gauge to indicate the inside of a hole - something a lever type gauge is made for .

As for resolution .001" or .02 mm is all you will ever need as with a little experience you will be able to read down to a couple of tenths anyhow .

IAN

Bill Pudney01/09/2012 04:52:09
611 forum posts
24 photos

A couple of points, I cannot disagree with most things written so far, except that I have always called the lever type a Dial Test Indicator, and a plunger type a Dial Indicator, but whats in a name!!

I recently went through a similar exercise whilst trying to upgrade my existing kit. I have a Verdict 0.005mm DTI (lever type!) which is fairly good, and a couple of Chinese plunger types, which are both adequate-ish. I read somewhere about Long Island Indicator; google it, my browser will not allow me to insert links. They have a long and detailed critique of Indicators. Allowing for the obvious commercial interest, they are very critical of a sobering number of the available instruments. If nothing else its a very interesting web page.

For what its worth I still have not upgraded my Indicators!!

cheers

bp

Michael Gilligan01/09/2012 08:11:36
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20183 forum posts
1053 photos

Well folks ... between us we have given Chris almost every possible answer.

But at least we are all agreed on one thing

... the "Clock" needs to be Analog not Digital.

Chris: Find one or more [new or secondhand] that you can read easily, and that move smoothly [there should be absolutely NO hesitation in the movement] ... then practice using them. You will quickly discover what works for you, and can then either "trade-up" or start a collection.

MichaelG.

.

P.S.  Here is the link that Bill mentioned

... you will find lots of good information there.

 

Edited By Michael Gilligan on 01/09/2012 08:12:17

Edited By Michael Gilligan on 01/09/2012 08:17:09

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