Mercer or John Bull?

[Alan Fisher 1Participant @alanfisher1]

Hi all, might be a really silly question, but as I'm a newby, I hope you will all be gentle with me. I have acquired several plunger type dial indicator gauges. amongst them, I have a Mercer and John Bull gauges in both .0005 and .0001…..They were in a batch of spares and repairs and all four work now. Question is, do I keep the Mercers or the John Bulls? Answers please and why? Many thanks and be prepared for a lot more silly questions.

[Alan Fisher 1Participant @alanfisher1]

DTi gauges.

[Thor 🇳🇴Participant @thor]

Mercer are very good Swiss made instruments, I would keep it if it was mine. Why not keep both the Mercer and the John Bull if they are working properly?

Thor

[Jesse Hancock 1Participant @jessehancock1]

Why not keep them all? One reads to nearest 5 thou and the other 1 thou.

Use the 5 thou to rough out then if needed switch to the 1thou readout.

Most of the model plans I have don't stipulate thousands they leave it to the engineer to get as close as he feels is necessary for the job.

[John HaineParticipant @johnhaine32865]

OP said half a thou and a tenth, was that intended?

[Danny M2ZParticipant @dannym2z]

Keep them both. As you gain experience you will be glad that you did.

Decent tenth's clocks are not cheap.

Welcome to the forum,

* Danny M *

[Alan Fisher 1Participant @alanfisher1]

"OP said half a thou and a tenth, was that intended?"

Yes thats right, mercer gauges in 1/2 thou and in tenths. also John Bull in half thou and one in tenths.

Making four in all.

Also in same batch were a German make in metric with a long throw, to .02mm

a Moore and Wright finger dial , missing the finger

A Baty gauge, reading to 1/2 thou and in a box with finger conversion kit and mounting hardware

and lastly another Mercer gauge reading to 1 thou.

So I don't think I have a shortage of guages now.

[Neil WyattModerator @neilwyatt]

He has one of each in Mercer and JB, so he keeps two, but which brand?

Neil

[Jesse Hancock 1Participant @jessehancock1]

John well spotted zero blindness?

[Nigel McBurney 1Participant @nigelmcburney1]

John bull indicators were very good,though not as common as a Mercer, John Bull were the first British made dial indicator to get a British Standards Kite mark, around 1960. I would advise keep all of them its very easy to drop or damage indicators.

[MuzzerParticipant @muzzer]

But…..don't forget that he who dies with most tools wins. And I'm pretty sure DTIs count.

[martyn nutlandParticipant @martynnutland79495]

That's all very well…but could someone please help me with using a dial test indicator!

I have a Mercer (0001" reading) I bought on Ebay. When it's at rest in it's case it reads 13 increments anti-clockwise of zero. I assume this creates an initial pre-load back to zero when you start to work? I'm trying to use it to centre the spindle of my milling machine over a 23mm hole in the centre of an adaptor plate I'm trying to make for a lathe chuck.

I insert the Mercer in a Jacob's chuck in the mill quill. I know I should have it in a collet but at the moment I don't have a suitable collet only Posilock ones. I then eye things up to roughly centred by manipulating the X and Y axis of the mill and then push the stylus of the Mercer out with the tip of a scriber until it makes contact with the wall of the hole. Now when I rotate the quill/chuck/spindle by hand the stylus loses contact with the hole 'by a mile' (or at least by so much it's clearly visible to the eye).

Even if I manage to keep the stylus in contact I have wildly extreme readings of eccentricity (e.g. 170/180 increments on the Mercer dial. I try to eliminate this by 'halving the value' by manipulating the X or Y handles according to where I think the high spots are, but never get very far. Should this be done only every 90°. I.e. get the stylus lying in the same plane as the X axis and half the discrepancy, then move on 90° until it's in the plane of the Y and repeating.

And even if I can get a zero reading through most of a sweep it's usually because the stylus has lost contact with the hole altogether.

Clearly this is an incompetent mess on my part and I would be very grateful if someone could tell me how you use a dti – Mercer or otherwise! Much on the internet but, of course 'theirs' always sweeps to within a couple of 'thou' straight off.

Martyn N

PS In the case there's a flat rectangular bar about 2.5 inches long. It has an attachment at one end to house the stalk of the Mercer and I assume it considerably extends the diameter the stylus can sweep. But in what would you hold, horizontally (or vertically) such a flat bar to sweep a diameter?

[sean logieParticipant @seanlogie69385]

Posted by martyn nutland on 08/05/2015 13:34:31:

That's all very well…but could someone please help me with using a dial test indicator!

I have a Mercer (0001" reading) I bought on Ebay. When it's at rest in it's case it reads 13 increments anti-clockwise of zero. I assume this creates an initial pre-load back to zero when you start to work? I'm trying to use it to centre the spindle of my milling machine over a 23mm hole in the centre of an adaptor plate I'm trying to make for a lathe chuck.

I insert the Mercer in a Jacob's chuck in the mill quill. I know I should have it in a collet but at the moment I don't have a suitable collet only Posilock ones. I then eye things up to roughly centred by manipulating the X and Y axis of the mill and then push the stylus of the Mercer out with the tip of a scriber until it makes contact with the wall of the hole. Now when I rotate the quill/chuck/spindle by hand the stylus loses contact with the hole 'by a mile' (or at least by so much it's clearly visible to the eye).

Even if I manage to keep the stylus in contact I have wildly extreme readings of eccentricity (e.g. 170/180 increments on the Mercer dial. I try to eliminate this by 'halving the value' by manipulating the X or Y handles according to where I think the high spots are, but never get very far. Should this be done only every 90°. I.e. get the stylus lying in the same plane as the X axis and half the discrepancy, then move on 90° until it's in the plane of the Y and repeating.

And even if I can get a zero reading through most of a sweep it's usually because the stylus has lost contact with the hole altogether.

Clearly this is an incompetent mess on my part and I would be very grateful if someone could tell me how you use a dti – Mercer or otherwise! Much on the internet but, of course 'theirs' always sweeps to within a couple of 'thou' straight off.

Martyn N

PS In the case there's a flat rectangular bar about 2.5 inches long. It has an attachment at one end to house the stalk of the Mercer and I assume it considerably extends the diameter the stylus can sweep. But in what would you hold, horizontally (or vertically) such a flat bar to sweep a diameter?

You can zero your dial once you have preloaded the dial against the work piece by turning the outer ring on the gauge to zero .

Sean

[Ex contributorParticipant @mgnbuk]

I never had much success with Mercer tenth thou clocks at work. I had a couple that were bought new & used soley for final inspection checks. They were calibrated & cossetted – always stored in their original packaging in a cupboard away from the shop floor. But after a couple of uses they would start sticking and giving unreliable readings, so were sent away for looking at – almost always they were not economically viable to fix. Nobody could suggest why they appeared to be working fine when carefully packed away, but would not work reliably a few weeks later when next required. The Mercer thou clocks didn't seem to have this "issue", only the tenth thou versions. After two or three similar episodes, I changed to a Mitutoyo micron clock & never bought another !

No experience of John Bull clocks, so can't offer an opinion.

Nigel B

[mechman48Participant @mechman48]

Hi Martyn
​FWIW… As you indicate the dti reads to .0001 your 'sweep' maybe no more than .005" – .010" TIR. What is the range of your dial.. ..010" – .025" – 050" .100" – 1/4" – 1/2" ?

…'I then eye things up to roughly centred by manipulating the X and Y axis of the mill and then push the stylus of the Mercer out with the tip of a scriber until it makes contact with the wall of the hole. Now when I rotate the quill/chuck/spindle by hand the stylus loses contact with the hole 'by a mile' (or at least by so much it's clearly visible to the eye).

​…' And even if I can get a zero reading through most of a sweep it's usually because the stylus has lost contact with the hole altogether'

It looks like you're still not lined up on your X & Y axes close enough for your DTI to cover with its sweep. Although you can move the stylus forward / back ward past the vertical it still can be 'out of range' … I may be misreading your post so a pic of the DTI would be helpful.

​As you've set your 'hole' by eye in x & Y axes, push the stylus past the vertical as far as it will allow… 'carefully' .. place the tip on one edge of the hole & sweep 180* to the other side, left to right or vice versa, if you are 'in range' the stylus should give you a contact reading at both sides of the hole on the X axis, the same applies to the 'y' axis & if 'within range' you should have contact all the way round the dia. of the hole, zero to zero in one revolution, then splitting the difference should bring you on centre… if you are 'losing' contact on one side ,as you say above, something is eccentric to the spindle… or possibly that your hole dia. is simply just to large for the DTI sweep range… DTI's are really only for minute adjustments, any general set up is usually done first with a dial gauge or a co-axial centre finder.

I'm sure other members will also proffer their opinions so don't take my understanding of your post as gospel, just my tuppence worth, hope it helps.

George.

[HopperParticipant @hopper]

Posted by martyn nutland on 08/05/2015 13:34:31:

That's all very well…but could someone please help me with using a dial test indicator!

I have a Mercer (0001" reading) I bought on Ebay. When it's at rest in it's case it reads 13 increments anti-clockwise of zero. I assume this creates an initial pre-load back to zero when you start to work? I'm trying to use it to centre the spindle of my milling machine over a 23mm hole in the centre of an adaptor plate I'm trying to make for a lathe chuck.

I insert the Mercer in a Jacob's chuck in the mill quill. I know I should have it in a collet but at the moment I don't have a suitable collet only Posilock ones. I then eye things up to roughly centred by manipulating the X and Y axis of the mill and then push the stylus of the Mercer out with the tip of a scriber until it makes contact with the wall of the hole. Now when I rotate the quill/chuck/spindle by hand the stylus loses contact with the hole 'by a mile' (or at least by so much it's clearly visible to the eye).

Martyn, two things here will make your life a lot easier.

First: don't use a one-tenths dial indicator for general shop work. They are way too sensitive for general use in the amateur shop and end up reading surface flaws, flex in the mounting arrangement etc etc as much as concentricity. Try using a regular one-thou graduation DTI. For particularly accurate work, a half-thou graduation gauge works well. You can still see needle movement of a few tenths on them. A cheap alternative to this is the little metric ones graduated in hundredths of a millimetre. One hundredth of a mm is equal to about 0.4 of one thou, so close enough to half a thou for practical truing up purposes.

Second: When you push the little finger of the DTI over against the side of the hole with a scriber, you are not setting any preload on the finger, so it is almost certain to lose contact with the surface of the hole at some point. You need to lower the table of your mill, or raise the spindle/head as the case may be, and push the DTI finger over a bit past the edge of the hole, then hold the finger out the way slightly while lowering the spindle or raising the table to get the finger back inside the hole. Ideally, you want the needle to sit roughly in the middle of its range of movement at the starting point.

[not done it yetParticipant @notdoneityet]

Basically one doesn't use a micrometer to meaure large distances (the name gives it away

). Tape measures for long distances (multiple metres to parts of a metre), rulers for short (part of a metre down to millimetres), engineer's ruler for more accuracy(to half a mm), then dti's. Some dti's come in tenths of a mm, some in hundredths and some in thousandths, so you, as the operator choose the relevant measuring stick! Choice depends on accuracy or precision of the measurement required.

 

One often need measurents in two dimensions. Easy to move a tape measure for measuring sides of a rectangle, per eg, where the accuracy required is less. But setting up to measure tiny distances moved means the measuring instrument needs to remain in position during any change in length. This means that sometimes two instruments are needed at the same time. Conclusion? Keep all four!

 

Sooner or later, you will need two at the same time. They are eating nothing and only need careful storage. One may get unfortunately damaged in use, or even totalled, requiring another to be purchased before further progress. One might well be attached to a stand semi-permanently and an alternative set up is required at the time.

 

Do you only possess one tape measure?, only one page-sized ruler? Only one pen

cil to mark a line? Thought not! Keep both of each is my advice.  EDITED TO SAY PUNCTUATION, OR RATHER LACK OF, IS NOWT TO DO WITH ME,  unable to set paragrahs properly at all!

 

 

 

 

 

 

 

Edited By not done it yet on 05/02/2017 06:52:20

[Ian S CParticipant @iansc]

Don't use the .0001" DTI for setting up your 4 jaw chuck, if you try for zero run out you'll go nuts, but if you use the .001" DTI, you'll be supprised how easy it is to get to less than .0005"/ the needle hardly moving.

Ian S C

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