Mercer Type 40 DTi

[Andy NorthfieldParticipant @andynorthfield26059]

Hi all

I’ve acquired a Mercer DTI labelled Type 40 .0001”

Can anyone point me at any information (age, date, user guide etc.) for this device?

Does it really have a precision of .0001”?

any info much appreciated.

Thanks

[Andy NorthfieldParticipant @andynorthfield26059]

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Andy, I'm not familiar with the type 40, but Mercer were good quality gauges, so if it says it has a precision of .0001" then it most likely is.

I have a Verdict one that has a resolution of .00005" but it only has a travel of 0.28"

OK, I've found some info in this scan below, model Beta 0.0001" gauges.

Regards Nick.

Edited By Nicholas Farr on 19/07/2023 20:00:53

[not done it yetParticipant @notdoneityet]

It will not have a precision of 4 significant figures but should be far superior to one measuring to the nearest thou (which will also have a degree of accuracy and precision). Precision is merely the ability to read the same when repeat measurements are taken. A DTI is a comparative device, not providing an absolute reading with regard to accuracy.

Is it a DTI (dial test indicator) or a dial indicator (direct reading of the plunger)?

[Andy NorthfieldParticipant @andynorthfield26059]

Many thanks for that info.

It’s a Dial test indicator with a range of about 0.2”. So it looks like the Beta one. At 143 Bob (wonder why they didn’t use pounds?) it was probable an expensive price of kit in its day.

I can’t find any reference to a Type 40. It’s also labelled as Mercer St Albans, England so I guess it pre-dates the later Swiss made Mercer ones.

I’m just curious to know how old it is.

A

[SillyOldDufferModerator @sillyoldduffer]

Graces Guide say Mercer closed in 1984. Seems they were primarily a high-end mechanical clock and chronometer maker, so making DTI's would have been easy for them. I guess they were put out of business by the arrival of cheap quartz timepieces.

Don't assume the instrument is still accurate today! It's performance depends on condition, not who made it, and it may be badly worn or damaged. At best it's been knocking around for 40 years, accidents happen, and old oil gums up. Can't be trusted for precision work without testing the calibration across the full range with gauge blocks. Don't fall for what its says on the dial, test it.

That said, it's an indicator, rather than a micrometer, and most of us don't do precision work. As indicators are mostly used as comparators, the calibration may not matter. A typical use is centring work in a 4-jaw. With the DTI in contact, the chuck is rotated and adjusted until the needle barely moves. In this common application a DTI doesn't have to be calibrated. Important though that the movement isn't sticky, remember condition matters!

A possible disadvantage is that a 0.0001" dial is rather sensitive for most work. On a poor surface, the needle will bounce dramatically over minor imperfections, whilst the DTI's ability to centre to within a tenth may not be matched by your chuck! For ordinary purposes a thou or 0.01mm instrument is 'good enough' and less fussy.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 20/07/2023 10:39:06:

Graces Guide say Mercer closed in 1984. Seems they were primarily a high-end mechanical clock and chronometer maker, so making DTI's would have been easy for them. I guess they were put out of business by the arrival of cheap quartz timepieces.

]…]

.

I had the great pleasure of visiting the St Albans factory a while before that … Upstairs was a long, very traditional old wooden bench with a few ‘workstations’ for the clockmakers who were mostly servicing/restoring Chronometers.

Downstairs was a very substantial machine churning-out wheels for the DTI mechanisms.

If I recall correctly, they were first crossed-out in a press tool and then loaded, in batches of ten, onto a special arbor which located them by the crossings.

That appeared to be about the peak of their mechanisation … ‘most everything else involved craft skills.

Sorry, can’t discuss why I was there in the first place.

MichaelG.

[Andy NorthfieldParticipant @andynorthfield26059]

Thanks for your wise words guys.

MichaelG you’ve started something ….anyone reading this thread now wants to know why you might have been there…

Many Thanks

Andy

[duncan webster 1Participant @duncanwebster1]

If you find out he'll have to burn you and eat the ashes

Edited By duncan webster on 21/07/2023 01:03:59

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, here's a Mercer gauge that most people probably won't have seen, it is probably made to order by a company that some may know of. It did have a tip on the end of the plunger, which happened to fit another gauge that I have that didn't have one. This was in a box of oddments that I got off a car boot sale many years ago.

Regards Nick.

[Michael GilliganParticipant @michaelgilligan61133]

That’s rather nice, Nick

MichaelG.

.

Something to do with backlash measurement perhaps ?

Edited By Michael Gilligan on 21/07/2023 08:24:38

[Nicholas FarrParticipant @nicholasfarr14254]

Hi MichaelG, I've no idea what it was used for, but it was mounted on this 2-1/2" x 1-3/4" x 1/8" gauge plate, via two 10 BA countersunk screws, and the two large holes are 1/4" dia. for mounting onto a machine, maybe, but don't know if that was original.

I had planned on making a new plate with a lug on the back, but haven't started on that small job yet.

Its operation is really very silky smooth and the plunger travel is about 11mm, which gives eight full turns of the pointer. The upper plunger bearing though is blind at the top, so can only be operated from the bottom. The dial can be rotated, but the locking tab and screw are missing.

It could be used for comparing sizes of two different things I suppose, if nothing else, but would help to set up a vice squarely on a milling machine.

Regards Nick.

[Michael GilliganParticipant @michaelgilligan61133]

The reason for asking is that Leslie Hartridge patented clever stuff to do with backlash, and I’m assuming that your indicator scale is conveniently calibrated in minutes-of-arc [when installed].

MichaelG.

.

Ref. https://worldwide.espacenet.com/patent/search?q=pn%3DUS4601601A

Edited By Michael Gilligan on 21/07/2023 10:36:15

[Nicholas FarrParticipant @nicholasfarr14254]

Hi MichaelG, yes it was the fact that the scale is calibrated in minutes-of-arc, that made me think it was of interest. I did look up Leslie Hartridge Ltd. and read about the anti-backlash device, but not having any experience of fuel injection pumps of how they are driven, I couldn't see how the gauge would have been used for these. I think you have found the answer, and I think I have a little understanding now, thanks to your link.

Regards Nick.

[Howard LewisParticipant @howardlewis46836]

Rotary fuel injection pumps are more sensitive to the drive that they receive, than in line injection pumps..

The Bosch test machine has a flywheel that could grace a fairly substantial diesel engine.

Quite sensiblke, if you think of the torsionals produced in driving an injection pump, and the reversals when on the back of the cam.

We used to modify our Hartridge machines with flywheels and anti backlash drives.

In thi way, we obtained far more consistent and accurate results.

Howard

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