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Again - another whatsit

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Versaboss27/05/2022 22:40:00
490 forum posts
69 photos

A friend of mine has another colleague who does house clearings (I hope that's a understandable and correct description). Among the stuff he found lately were 2 boxes with some measuring instruments. We have no idea for what this device can be used, so I present it here to the cumulative wisdom.

As far as I can see, the Compac indicator has 0.002 mm resolution!


Kind regards,

Michael Gilligan27/05/2022 22:54:07
20182 forum posts
1053 photos

That looks like it was expensive !!

Presumably, the three shiny objects are [partial] balls


Nigel Graham 227/05/2022 22:55:52
2133 forum posts
29 photos

New to me but I wonder if it measures sphericity, e.g on bearing balls, in some way: the object at the top might be calibration or comparator spheres. (Their flat "poles" being to fit them to the instrument.)

The handle is a bit odd, but looks as if in use it is folded back to be in line with the body of the device.

Lots of adjustments on it, but not apparently fine-control ones..

It may well have been made for a very specific purpose connected with a particular manufacturer, rather than being a generic tool for measuring (e.g. spheres) anywhere. Possibly even made in that company's own tool-room. If so it's feasible it was made to be clamped to, perhaps, a particular machine-tool or inspection-department metrology rig.

No name or label on the instrument (other than on the bought-in DTI) or case?

SillyOldDuffer28/05/2022 09:58:52
8691 forum posts
1967 photos

Might be for accurately positioning a large diameter job on a giant lathe to reduce run-out?

The dial indicator and non-precision adjustments suggest it's a comparator, not required to accurately measure anything.

I think it works the same way we use a DTI to reduce run-out close to zero with a 4-jaw chuck, except this one has a roller so it can accommodate really big work, such as propeller shafts or railway wheels.




Edited By SillyOldDuffer on 28/05/2022 09:59:20

John Haine28/05/2022 10:01:38
4673 forum posts
273 photos

I had something like that I bought at a market stall for the nice indicator which was a gadget for applying a small lift at one end of a beam for calibrating sensitive spirit levels.

Howard Lewis28/05/2022 10:35:52
6104 forum posts
14 photos

If it is COMPAQ, it is expensive, and valuable!

Not long ago, I wanted to replace two extensions and an anvil for a Compaq bore gauge.

Spares were not available (Retained for repairs ) but I could buy a complete new on for upwards of $5,000 with a lead time of 6 months!

For my use, I bought a 5 x 0.5 Tap and Die and made my own. Since it is set up and Zeroed against something like a micrometer or slips, a small error will not be noticed..

Take care of it, it is high precision!


Tony Pratt 128/05/2022 10:38:50
1963 forum posts
12 photos

What a lovely bit of kit but I've never seen anything like it in my engineering career, likely made for one specific task, hopefully there are some makers marks on it?


Hopper28/05/2022 11:32:14
6393 forum posts
334 photos

,A few pics from different angles would be helpful.

It could be a "sled" as used in machine tool manufacturing and reconditioning. The two partial spheres run along a dovetail or V way and the indicator reads if the matching way or V is parallel. Connelly's book on Machine Tool Reconditioning has many examples but in a much more basic form. Used to check your scraping is parallel etc.

Pretty exotic stuff if that's what it is.

Edited By Hopper on 28/05/2022 11:33:52

Ian P28/05/2022 11:57:24
2590 forum posts
114 photos

A few observations based on the one picture.

It has an odd combination of features. Obviously the indicator and the part spherical objects are high precision but the chassis or frame of the thing do not seem to be in keeping. The indexable handle looks to be a budget diecast/painted item and the single visible hex--headed bolt looks to be the only fastening holding the narrowest ends of the slotted plates to the part carrying the handle, so the bolt would need to be very tight to prevent rotation.

I wonder what the 'tyres' of the two wheels are made from? they look more like mother of pearl than some engineering material!

How many of the part spheres are there and do their bores tie up with anything on the device (like thread or bore size)

Ian P

Hopper28/05/2022 12:33:26
6393 forum posts
334 photos

Something along the lines of this, but more deluxe


The two ground spheres run along one surface. The dial gauge reads for parallel on the other surface as the sled is slid back and forth along the way while held by the handle. But possibly this one is made for a specific job in industry or lab etc.

Edited By Hopper on 28/05/2022 12:36:03

David-Clark 128/05/2022 12:41:44
220 forum posts

Hi Howard, the indicator on it says Compaq so you may be right,.

Henry Brown28/05/2022 13:12:20
552 forum posts
117 photos

I'm wondering if its for checking large gear pitches or something similar in the field? One would select the relevant rollers, they sit in between the teeth and the dial then reads variations as its moved around the gear, it would need a stop to make sure the reading was always in the same place. If not that some other similar application.

DC31k28/05/2022 19:50:10
686 forum posts
2 photos
Posted by SillyOldDuffer on 28/05/2022 09:58:52:

Might be for accurately positioning a large diameter job on a giant lathe to reduce run-out?

Your sketch appears to require a plunge-type indicator. The one in the photo looks like a lever-type indicator.

The indicator is a little unusual in that it has a rectangular body, but the dial is on the larger side of the body rather the more usual small side.

If looked at from the right hand side, I am trying to work out if there would need to be some care taken so the two shiney bits and the indicator tip form an isosceles triangle.

Maybe someone can think this through a little and see if that is the case - perhaps if it used as a comparator against a master, the relationship does not matter.

DC31k28/05/2022 20:00:53
686 forum posts
2 photos
Posted by Ian P on 28/05/2022 11:57:24:

...the single visible hex--headed bolt looks to be the only fastening holding the narrowest ends of the slotted plates to the part carrying the handle, so the bolt would need to be very tight to prevent rotation.

What is to say that there should be no rotation about the bolt? Maybe being free-swinging about that point is an intended feature. Consider how it would feel in the hand if that joint were rigid - very unbalanced. With a free joint, holding it with the handgrip horizontal, the main body would hang reasonably vertically.

There is something hidden behind the ball of the handle, possibly a fine adjust mechanism (like on a pair of trammels or vernier caliper).

The bolts in the slots (small, horizontal holding the indicator and large vertical) might have square shanks on them stopping rotation of the parts they retain.

There is a great deal more left-right adjustment on the shiney-holding arm than on the indicator holding part.

Tony Pratt 128/05/2022 20:39:51
1963 forum posts
12 photos

In a purpose built box, there must surely be some indication of a maker or use? As mentioned more photos please.


Henry Brown28/05/2022 22:31:15
552 forum posts
117 photos

Just to add to my previous comment - I've clocked stuff up to 10' diameter and only used scriber to get it roughly correct and then used a dti for final settings. Mainly on horizontal borers but very occasionally with the work piece in the vertical plain on a conventional lathe.

Versaboss28/05/2022 22:47:37
490 forum posts
69 photos

Unfortunately, I have only this single picture, but I will see if I can put my hands (and camera) on that thing.
May need a couple of days, though.

Kind regards

Nigel Graham 229/05/2022 12:00:54
2133 forum posts
29 photos

Dave -

You could be onto something with that drawing, but surely it would need a plunger not lever type indicator?

(The jig shown by Hopper would also need a plunger indicator, and its drawing seems to give that.)

My thought though was perhaps for measuring the actual diameter to fine limits readily than by using a rather unwieldy caliper, using chord geometry to measure the radius.

The only fly-in-the suds though is that there appears in the photo to be no method for accurately measuring the ball-to-DTI centres. Unless that was done in some way on a surface-table or against a reference gauge, and then the method becomes one of change from that set datum.

So I looked back at your drawing....

... and played Whatif.

IF the handle stays in the position shown in Hans' photo, as you have drawn it, and the plate between it and the rest of the device has a ground outer face hidden in the picture....

Also, note there are two "shiny things" on the device, one each side, not just one.

Place the instrument as you have drawn, on the surface-plate with the appropriate ball pair for the size-range.

Use parallels and slips to set the ball axis at the lathe's centre-height, but from where the device will stand on the bed or saddle; not necessarily the lathe's nominal centre-height.

We already know the height to the indicator plunger, as that is constant.

Now set the balls and DTI to touch an angle-plate with the indicator reading 0.

Transfer the instrument to its predetermined place on the lathe, where with the balls just touching the work, the radius is a function of the half-chord length given by the ball to indicator centres, and the DTI deflection.

Having two spheres symmetrical about the axis automatically aligns it correctly perpendicular to the work axis.

Geometrically, the deflection is the chord's distance from its diameter intersection to the circumference.


Thinking on again, if this is all so, it use need not just be on the lathe but also on some other machine-tool types or a surface table, as long as the centre-distance from the datum plane is known. In some situations, e.g. a plano-mill, it might need clamping to an angle-plate or some other vertical, true surface.

It might also measure a large-radius sphere, since the two reference-balls will always place the instrument's axis on a diametral plane.

Given that it has a lever indicator it might have been intended as a comparator against a reference radius rather than direct measuring tool.


I don't know if this the right answer, nor if what I suggest would work: the lever DTI shown may not be the right type, and it does rely on full concentricity so is not for initial setting-up.

Worth a thought though....

.... and I'm still intrigued by that round thingamyjig with its strange numbers we saw back in, err, 2019?! (A calibrated Tuit?)


Versaboss13/06/2022 23:19:06
490 forum posts
69 photos

I promised I will come back to that problem - and here I am.
And because I have now also seen the second instrument, it became quite clear in what trade they were used.

But first some more pictures.


Instrument in the box.


Instrument standing vertically


Instrument from below


A couple of the 'Rollers'.

Now, as usual, friend SOD was not too far away from the truth with his first picture - if he had drawn a gear instead of a disk,! As it was clear after seeing the second instrument, it came from the quite well-known (but now disappeared) firm Maag Zahnräder Zürich. Not for watch gears though,but for large ones. Maybe also for the cutting tools, as they were famous for their gear cutting machines also.The rollers would go into a tooth space, and the single leg with the ball point to some point on the next tooth. The DTI would then show if the tooth on the other side is in tolerance. Naturally, the instrument would have been calibrated before, in a way unknown to me.

Now the second instrument, which shows the name on the dial and on the back side








Here, the rollers can be mounted on the central arm and on the right side, after removing the hook arm. These two parts have a constant distance, but can be moved together left/right with the small thumb wheel on the right side.
The large knob in the center clamps the slide. The measuring item is the hook on the left side. As you can see, there are a lot of different rollers small ones on the left side of the box, the large ones on the right.
I suspect it has the same purpose as the first instrument, maybe for smaller/finer gears.

Now the owner has to decide what to do wit them - I would take the DTI if he would make me a good pricesmiley

Kind regards,

Hopper14/06/2022 03:21:42
6393 forum posts
334 photos

Knowing the brand name makes it easier! It looks like they are used as a comparator to measure gear tooth pitch against a master gear or variation from one tooth to another.

Models similar to the smaller second one are listed on eBay for 500 to 800 Pounds, so still regarded as a good tool apparently.
The first one in the OP must be for some large industrial sized gears, say 6-foot diameter and upwards etc, and no idea what that would be worth.
    The MAAG gear cutter pages on are some interesting reading on the topic in general and page 3 shows a similar measuring device to the second one your friend has.

Edited By Hopper on 14/06/2022 03:25:10

Edited By Hopper on 14/06/2022 03:45:49

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