dti repair ???

[picclock]

Hi

My favourite dti seems to have developed a mind of its own.Can anyone help with its disassembly ? Its my favourite because the dial face shows both metric and imperial - a shame more gauges don't.
 
Tuesday I noticed the hand going round whilst on my lathe. I even video'd it for entertainment.

Having removed the brass mechanism I find the problem is weirdly with the spindle from the pointer to the interior gear. If I rotate it it springs back to a random position. However I can't remove or examine the spindle without removing the dial face.

Any help with disassembly much appreciated.

I suspect the culprit is possibly a magnetised piece of swarf.

Many Thanks

picclock

[BillTodd]

I've seen a variety of method used to hold the things together; screws from the back, clips and, most awkward, three or four screws around the periphery accessible only one at a time through a hole in the bezel.

If you cant work it out, it sounds like it's an another awkward one

A few pictures might help us.

Bill

[picclock]

Hi Bill

Videos uploading now. Movement on



Springy needle on



FWIW I've never seen anything like it  

Best Regards

picclock

[Joules]

I would be tempted to dismantle and drop components into an ultrasonic bath, or if nothing to loose drop it in as is and it may dismantle itself.  Drying is another issue !!!


Joules

[andyf]

That's really weird! After the first video, I thought the needle might be loose on its shaft, but the springiness displayed in the second vid was very unexpected. It can't have got really heavily magnetised, can it?

As to the dial face, my guess is that it's stuck on, and is covering the heads of the two fixing screws visible when you showed the pinion. I suppose all you can do is to pull the needle off and then very gently try to peel the dial away, though maybe a long soak in lighter fluid or some other solvent to loosen whatever glue is holding it down would help, as long as it didn't dissolve the dial markings.

Andy

[jim]

i've never managed to fix one properly yet!!

trouble is trusting them again!!

[MaceT]

On the Brown and Sharpe brands, there is a fragile watch spring just under the dial face. This keeps pressure on the pinion, so there is no backlash in the mechanism. Have you held the pinion and tried to move the needle?

[BillTodd]

Is it possible that the little gear is spinning on the needle shaft, or the needle is loose on the shaft?

However, I've got a horrible feeling the tiny clock spring, which removes the backlash in the mechanism, has either broken, and is just holding its position by friction, or (hopefully) has come un-hooked. The spring normally has to be wound up a few turns to act as a pre-load on the internal gears.

It looks from the video, like the circular dial part is held to the body by a couple of screws inside the body. Removing those might allow the dial part to be removed and give you a better understanding of how the bezel & dial comes apart.

If there is no obvious way to remove the bezel & dial (which almost certainly comes off from the front, after removing the needle), then it might require a thin steel shim to be inserted between the bezel and dial body to push back any spring clips that might be under there.

Bill

[lordedmond]

I fear for the long term outcome of a dear friend, it may have to be laid to rest in file 13 if the open internal surgery fails 

if you get it working will you trust it ?




Stuart

[picclock]

@ Lordedmund

I fear it's had it.   

It's passed on! This dti is no more! It has ceased to be! It's expired and gone to meet it's maker! It's a stiff! (Apologies to Monty Python)

I tried heating it in an oven to release any adhesive used. Its now developed a severe case of suntan.

And despite my efforts it still springs to any random position 

Thanks for your help and suggestions

I will disassemble with a grinder and see if I can figure out how it should have been taken apart.

Best Regards

picclock

[DaveH]

RIP dti

DaveH

[Bogstandard]

Picclock,

Keep the sensor tip arm off the end as a spare, they are almost impossible to get hold of for reasonable money if you ever break one. Nearly as much as a new cheapo DTI.

The ball has just fallen off mine, but mine is an easy fix, because it is only used on the lathe for 'clocking', I will just superglue a tiny glass bead on the end of the arm.


Bogs

[picclock]

As the final word on this - for the curious. I cut through the case ring with a dremel to find that it had been pressed onto the backplate. If I'd known I could have used a puller but it would have been pointless. Underneath the scale is a small brass plate removed with two screws. The top of the brass plate acts as the bearing for the needle spindle. The spindle is attached to a very fine hairspring - which in my case had broken. This biased the needle to eliminate the backlash of the gearing, however with one end free it was acting like a free-wheel system, overriding the centring spring in the other part of the mechanism and causing the random pointer positions.
Note the broken piece of spring under the brass plate.

Best Regards

picclock