Author Topic: DTI Challenge 2022  (Read 2390 times)

Offline vtsteam

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DTI Challenge 2022
« on: January 25, 2022, 12:33:14 PM »
I've had this DTI sitting in a drawer for easily 5 years. I got it at a flea market. Hard to read even what the dial says under the yellowed glass, Federal and then Model C21, and .0001".

From the overall condition, long storage and, now I see, missing screws, I'm worried the insides aren't in great shape....

Guess I'm going to try taking it apart. Maybe Bob is watching ....... I hope!  :borg:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #1 on: January 25, 2022, 01:55:01 PM »
Three screws held the bezel on. I didn't want to bend the hands by lifting it straight off, because the numbers ring would have interfered. But I was able to lift it at the short end of the pointer, then shift the whole bezel up and off the hand, and free of the body.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #2 on: January 25, 2022, 02:06:17 PM »
I removed the large pointer by slipping a pair of tweezers under it, closing them lightly, then lifting up so that each arm of the tweezers was lifting flat against it. It came loose with a little pressure, and I was glad the hand wasn't bent in the process.

The small hand was a little more difficult to figure out. I couldn't fit the tweezers under it. But two miniature flat bladed screwdrivers did fit under, and luckily, it was an easy sliding fit on its shaft.

I then took off the zero adjust cap at the top of the gauge, and removed the back of the DTI. There were only 2 screws of 4 in the back. The mechanism cage is brass, but the instrument case itself seems to be zinc die-cast.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #3 on: January 25, 2022, 02:23:29 PM »
The works looked better than I had feared. But the screw holding the brass plate on in the upper left corner was corroded some. It is located where the two missing screws in the outer case rim were. you can just see one of the resulting holes in the case, above it.

I was able to turn the other three screws without a problem. But I couldn't budge the corroded screw. I haven't applied too much force, as I don't want to strip the slot or twist off the screw. Not sure what to do here exactly. Maybe some kerosene (paraffin, UK) applied with a toothpick on the screw post joint under the brass plate....?

The movement seems to be pretty good, and from what I can see, undamaged. But it is slightly noisy -- and occasionally tends to not return to zero perfectly without a little help, so I think it needs cleaning.

I am a little nervous about opening it up further. I have visions of parts springing out all over the place, and/or not being able to replace everything exactly where it goes, and in proper relation/orientation.

I might give it a pause here, in case Bob chimes in.......... :scratch:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: DTI Challenge 2022
« Reply #4 on: January 25, 2022, 05:05:12 PM »
Were it me, at this point Id pop it in my ultrasonic cleaner to dislodge any gunge then rinse in distilled water or IPA and gently blow dry. With any luck it will also loosen the stuck screw.

Im assuming at this point the dial with its printed overlay is off as that should not go in the tank.

(My ultrasonic cleaner these days mostly gets used for cleaning my glasses on which it does a splendid job!)
Andrew Mawson
East Sussex

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #5 on: January 25, 2022, 05:08:14 PM »
Avoiding the problem of the stuck screw temporarily, I got some toothpaste (old fashioned Crest Regular -- the type with abrasive in it, not "gel) and started polishing the plastic bezel.

(I also did add a couple toothpicks worth of kerosene to the stuck screw, hoping it will penetrate.)
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #6 on: January 25, 2022, 05:09:21 PM »
I don't have an ultrasonic cleaner, Andrew.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline RussellT

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Re: DTI Challenge 2022
« Reply #7 on: January 25, 2022, 05:35:44 PM »
Warm the screw up with a soldering iron?

Russell
Common sense is unfortunately not as common as its name suggests.

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #8 on: January 25, 2022, 06:21:49 PM »
Russell!! We think alike. Exactly what I did, except I used a solder sucker, which puts out more heat than my pencil iron. I also tapped the screwdriver lightly with a tack hammer twice. And the screw finally released.  :ddb:

Sproing.......
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #9 on: January 25, 2022, 06:26:50 PM »
The pieces and parts. I washed everything in warm water and dish soap, using an old toothbrush as a scrubber.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #10 on: January 25, 2022, 06:32:06 PM »
Hmmm......... Despite the fact that the dial said "Full Jeweled" uhhhhh, I didn't see any. Maybe I don't know what I'm looking at, but those just appear to be holes in the brass plates. There were no bushings of any kind, jeweled or otherwise.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #11 on: January 25, 2022, 06:33:34 PM »
I've been watching John and Bob on clocks:

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: DTI Challenge 2022
« Reply #12 on: January 26, 2022, 04:27:38 AM »
'Fully Jewelled' refers to the lying salesman who marketed it - they were on his fingers  :clap:


Nowadays in the UK we have something called the 'Trades Description Act' that prevents that sort of lying but no doubt the dial gauge pre-dates that by many a year. Is there anything similar in the States Steve?

Andrew Mawson
East Sussex

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #13 on: January 26, 2022, 09:03:44 AM »
Federal Trade Commission Act, Andrew. In this case it would have been the manufacturer since it's marked on the dial. Or it could have been a repairer somewhere along the line if this was a mix and match Frankengauge.

Anyway it's back together, cleaned and carefully oiled (lightly as per Bob's video -- though only with 3-in 1 since I don't have instrument oil).

Results, it is much easier to read, it sounds "proper", and smooth.
Problems: still yellowed bezel, return to zero is not consistent.

On the return to zero -- it was losing about a tenth of a thou, every time it was pushed to full reading and released. This, I believe turned out to be the plunger end screw, located at the top of the clock. It's housed inside a removable cap. It sets the zero limit. It was turning itself loose ever so slightly every time the DTI was cycled. That is easily remedied with a tiny dab of paper cement on the screw threads. I don't believe this screw is supposed to be bottomed out tight, but allowed to float and provide that zero adjustment. But I might be wrong......Bob, any idea?

Second problem with the return to zero: once the screw setting was remedied, if pushed to full limit, the pointers would return to zero fairly consistently, but if turned to say a quarter rev of the pointer, would not return all the way.

I'm not sure of the cause here -- could be friction/wear, or weak return string, or mis-assembly.

For wear/friction, I'd guess that the most likely suspect is the tiny pointer pinion. It seemed a little worn, by eye. It revolves the most of any shaft in the movement. It gets a lot of end pressure also, when the clock hand is pressed on, or pulled off. Or maybe its bearing hole was supposed to have a jewel in it....??? The pinion shaft fits into a brass block bearing that looks to be hand made. Is this block original?

For mis-assembly, i'm not completely sure how to set the backlash spring to "2 revolutions" or where on the rack I'm supposed to start engaging its pinion -- fitting this part up is tricky -- you have to rotate the rack clear of the pinion to get the spring post screwed into it, and attach the spring. Then push and rotate it back to engage the pinion. It doesn't always engage in the same place on the rack (invisible, done by feel) so the range of motion varies, as does the amount of pre-tension on the backlash spring. Maybe I haven't got that all proper -- and maybe the zero position is varying because of it.

I do wonder how important the insistent zero is -- is the gauge useful even if it never gets figured out? I guess I could only tell by using it on a gauge block to see if I get consistency past zero....

Well, of course I'd like to get it working perfectly to begin with, but if that tiny pinion is the cause -- there's no way I can make another, or if the movement is really missing a jewel there, nothing I can do about that either....
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: DTI Challenge 2022
« Reply #14 on: January 26, 2022, 09:22:13 AM »
"but if that tiny pinion is the cause -- there's no way I can make another"


Of course you can make another - you just haven't worked out how  :lol:
Andrew Mawson
East Sussex

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #15 on: January 26, 2022, 12:38:43 PM »
I took it apart again and checked out the pinion with calipers. It actually doesn't seem worn to me, it's simply reduced at the top and then splined. I think also I may not have pressed the pointer on far enough to keep the pinion gear from having end play.

The bronze bushing on the clock face does have a fair amount of wear, however..... (photo below) or at least it isn't a close sliding fit on the pinion shaft. A much easier job to replace if I decide to in future.

I also felt that I may not have properly lubed the plunger rack and the plunger rack guide -- which is a flat slotted brass piece (photo below). A rod slides in the slot to keep the plunger from rotating. When I tried those parts in place while the mechanism was out of the case and the pinion removed (no gears meshing with the rack) I could hear a slight squeek and feel a little resistance to moving the plunger.

I had previously tried putting a tiny amount of oil on the guide rod that slides in the brass guide. This also carries a spring and it's very fiddly to screw into the plunger, twist and then engage in the slide. When I did that previously, I don't believe the oil actually made it to the guide brass by the time it was installed.

I also hadn't understood earlier how to engage or disengage the plunger rack from the mechanism gears. I now realize that you can rotate the assembled mechanism inside the case before fastening it down to disengage or engage the rack. I thought the adjustment was only to center the pointer spindles in the face, but it has a mechanical assembly purpose as well.

This made assembling the plunger much easier this time, and I also was able to oil the slotted brass guide instead of the guide rod.


Here are some pics of the indicator showing the parts I mentioned above:

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #16 on: January 26, 2022, 12:42:06 PM »
Reassembly went better all around, and this time, the indicator does return to zero most of the time, though it's a little lazy if you move it less than .002 from zero. It then returns to about .0004. Otherwise it zeroes well. I think it's probably usable, assuming you want readings anywhere else.

The range is to 90 thou. Technically it should be 100 thou, and I could unscrew the zero adjust screw to add another 10, but with the wear and spring strength as it is, that reduces return force, and makes zero less certain.

Ideally the pinion bushing should be replaced, and maybe a stronger (or shorter) return spring would make zeroing perfect, and give the full range, but I think it should be good to try as is.

Another interesting fact, only two of the case holes have threaded bosses under, so only two screws can be fitted -- which was probably the original configuration.

Here's the indicator after cleaning, and oiling, polishing the lens and reassembly.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: DTI Challenge 2022
« Reply #17 on: January 26, 2022, 01:26:47 PM »
Bob will be proud of you Steve, it's a great improvement on what you presented us with initially  :thumbup:
Andrew Mawson
East Sussex

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #18 on: January 26, 2022, 02:57:33 PM »
I hope so Andrew.  :beer:

But if I did anything wrong or could have been improved, I hope he lets me know!
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline jiihoo

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Re: DTI Challenge 2022
« Reply #19 on: January 27, 2022, 07:11:58 AM »
Thank you Steve for this writeup, very interesting. And the link to Doubleboost videos where Bob teaches how to fix a DI/DTI was pure gold!

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #20 on: January 27, 2022, 10:09:09 PM »
Thanks Jiihoo  :beer:   

The indicator seems to be zeroing even better today. Seems very smooth and quiet compared to before surgery. 

Maybe it's working better today because it's warmer. It was -10F last night. When you're dealing with a tenths of a thou indicator, maybe temps matter. Or maybe it's just working itself in after years of disuse. Anyway, it's even better today.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline PekkaNF

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Re: DTI Challenge 2022
« Reply #21 on: January 28, 2022, 03:31:08 AM »
Good job Steve.

I don't think that return to exact zero is that important on that kind of unidirectional indicator. You need to offset the scale anyways to allow negative reading when doing real life measurements.

Pekka

Offline BillTodd

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Re: DTI Challenge 2022
« Reply #22 on: January 28, 2022, 05:45:27 AM »
Good job Steve.

I don't think that return to exact zero is that important on that kind of unidirectional indicator. You need to offset the scale anyways to allow negative reading when doing real life measurements.

Pekka

Yes exactly right  :-)

 Nice fix, vtstream   :clap:
Bill

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #23 on: January 28, 2022, 06:40:09 PM »
Thanks Bill!  :beer:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline krv3000

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Re: DTI Challenge 2022
« Reply #24 on: February 03, 2022, 05:18:49 PM »
hi well dune  :D  well as to not returning back to 0 comen problems may be at hand 1 to much oil on the rack  the bush that the spindle runs in may still be needing a good clean the way I do it is  with a pace of wood made to be a snug fit in to  the hole DO NOT use sand paper or a file to make the wood fit use a knife then once a nice fit is at hand just rotate the wood and keep doing that till the wood comes out clean.  not enough tension  on the back lash spring all D.T.I's have different No of turns on this spring so its by trial and era to get it right as for the screw on top of the spindle shude be screwed all the way in and the big mistake people do move the plunger to fast the plunger only moves slow in use and the one big factor in its acracy is its age and haw badly its worn   its quite conmen to see on the face juled   movement when their are non fitted   the  more you do the better you will get at it regards bob

Offline vtsteam

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Re: DTI Challenge 2022
« Reply #25 on: February 04, 2022, 02:05:08 PM »
Thanks Bob!  :beer:

I'll try the wood in the spindle bush ckeaning trick -- I think you're right that may be the problem. The stop is a screw that goes into the end of the spindle under the cap at the top of the indicator. I also have been thinking that some corrosion or dirt above the bush under the screw head may be preventing it from sliding positively to a stop .

Thanks for letting me know about the non-existent jewels. Glad to know I'm not crazy, or didn't lose something when opening the clock!

Thanks for the good advice, too: I will be careful not to push the movement too fast when trying it, though I have to admit I probably did sometimes already. :wack:

As a side note, I just also took apart and cleaned my old dial caliper. I'd never have done either of these two things without your posts here and encouragement. I hadn't used the caliper for a few years, and the glass had got cracked. There was dirt in the rack. I made a new glass out of a seltzer bottle plastic (I think that was a tip from you years back) and got the movement pivots clean and lubricated, and the rack cleaned. Works beautifully again. I'm going back to using that with my Gingery lathe. I built the lathe with that caliper 20 years ago, so I feel like they go together. I actually like it better than the digitals I have. Just feels better to use. The digital calipers I'll use elsewhere -- just not with the Gingery. I know.....tool sentiment..... :loco:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline krv3000

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Re: DTI Challenge 2022
« Reply #26 on: February 12, 2022, 05:41:55 PM »
their is nothing more satisfying than fixing sum thing once broken

Offline russ57

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Re: DTI Challenge 2022
« Reply #27 on: February 12, 2022, 08:02:49 PM »
their is nothing more satisfying than fixing sum thing once broken
Absolutely..

-russ


Offline vtsteam

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Re: DTI Challenge 2022
« Reply #28 on: February 13, 2022, 07:05:49 PM »
Nice to have things working again!  :proj:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg