DTI vs DI

[earlgo]

Re: centering on a 4 jaw chuck. I looked at the 1958 Atlas catalog and it shows that the ATLAS 6" 4 jaw chuck has concentric circles on the face to help in centering. (I thought my Dad might have done this.)

The grooves are 1/4" apart and by interpolation one can hit center close enough to use a DTI right at the get go. Grooves might be useful on those chucks with out them.
(This past winter was terrible on the machines in the garage. They sweat profusely at every up and down in the temp, and I must have missed this chuck in the cleanup.)
--earlgo

[Mr Ron]

Which is the preferred tool for measuring runout on round stock mounted in a lathe chuck? a dial test indicator or a plunger style dial indicator. It would appear that either one works and although I do possess both types, I always use the DI because it is always handy and the DTI is in it's case and requires assembly before I can use it.

I may have expressed myself wrong in my original post. I didn't intend to be "measuring" runout (quantity), but to indicate concentricity of round items held in an independent lathe chuck. Coax indicators were never considered, but I thank Harold for voicing his opinion of such. It just adds a bit more good information to my mental database and to others as well.

[GlennW]

For those who may use their DTI and turn it upside down as in indicating their tailstock, keep this in mind.

The DTI itself is usually good, but the holding device is where it goes bad.

As rigid as a holding devise may seem, it probably isn't when inverted.

[tornitore45]

Yap, mean old gravity.

[Harold_V]

> Once you understand how easily one of the Last Word indicators can be wrong...

Could you explain? Until recently a Gem DTI (a Last Word clone) was the only indicator I had and it has never lead me astray since I figured out how to use it (which didn't take long).

That it has "never lead you astray" may or may not be true. Because it's the only thing you have at your disposal, you can't know that bit of information. I will also note that it could be that while your indicator may have provided erroneous information, the end result was still acceptable. You don't always enjoy that if your work is inspected by others.

I'll provide the single experience that taught me my lesson.

When I was working in precision grinding, I had need to dial in a part to less then two tenths. I figured my Last Word wasn't up to the task, but that's how I started. When I had the needle motionless, I then switched to an electronic indicator. I was shocked to discover I not only wasn't running true, but I was well out of tolerance and would have scrapped the work had I trusted the Last Word.

When new, they tend to work reasonably well. However, once the jeweled lever arm is bumped from the spiral shaft (not all that hard to do, and happens quite frequently), the indicator, for what ever reason, tends to lose sensitivity. Even after having mine serviced by Starrett, it would not perform acceptably, and it took very little time for it to misbehave.

Of all indicators I've ever used, there's only one that has my attention, and it's the B&S TesTest. I own three of them and have never had a problem with them, assuming you don't consider a loose crystal as being a problem. That's a pretty damned good comment, considering I've used two of them for more than 50 years.

H

[SteveM]

Yap, mean old gravity.

Gravity, it's not just a good idea, IT'S THE LAW!

[John Hasler]

The Gem was my only indicator, not my only instrument.

[warmstrong1955]

I use what suits the job....as in the precision for the job.
Just like micrometer work, or caliper work. Need to get close...DTI. What's a thou or two among friends....a DI.

As far as coax indicators, I have one, and use it for roughing things in, but mostly for centering on things that are rough. Nasty rough. I make a lot of finished parts, from burned parts. I like the coaxial indicator for getting somewhat centered on those to bore & turn 'em. Some, are ugly burns, not mine mind you...as I'm nicer to myself when I burn my own parts. A coaxial indicator makes it easy to split the difference between ugliness of ID & OD, so I can get a complete finish on both, without welding.

The writing on the part ain't lyin', and...this is a goodun....relatively speaking.
Still...a little pre-machine welding required. Nice that they drew an arrow to the location....one of 'em anyway.

Bill

[BadDog]

When I first started working on this skill, I heard great things about Last Word being, well, the last word (as Starrett would seem to believe). I acquired one, but even in my ignorance I could tell it wasn't reliable, it all to often wouldn't even repeat. I tried to figure out the apparent nonsense within the context of my less than stellar equipment, but eventually I realized it was the indicator. Fair enough, it was quite old and used, sometimes that's how it goes. I then happened onto a bulk lot of a bunch of metrology gear for a once in a lifetime cash price. I bought it. That's where I got a couple of very nice Last Words (I think there were 5 total, but 2 "like new"), and my first B&S BesTest (a few to be exact). I figured I would sell stuff I didn't need and duplicates and come out with the rest for near nothing. It took me quite a while to check out the treasure trove, but I found that even the Last Words that came with calibration stickers (only about 2 years out, but still) were not nearly as good as the BesTest. Limited mounting, tiny dials, having to flip a lever to apply the opposing side, and a significant penchant for "sticking" (maybe more like binding?). Perhaps it was improper lube or something, but the BesTests worked flawlessly, smooth and repeating every time. I eventually sold all the Last Words, and the couple I've acquired since then as well. I just don't like them in general, though they have a cool steam punk appearance. I'm only just functional, maybe best described as "machiner "(more than machine operator, but not deserving the name "machinist", maybe a decent "apprentice level"?). But I've been very underwhelmed by my exposure to Last Words. But I've got friends who can't imagine my displeasure, and who have been only too happy to buy my nicer examples, and they still call me a friend (at least I think they do).

My current crop consists of a standard BesTest in 0.001, 0.0005, and 0.0001 that all get lots of use. I've got a big faced jeweled Swiss Tesa of the same design as the BesTest that is "as new" and works beautifully, but it usually stays put away. And I Mitutoyo BesTest clone that is the only thing from Mitutoyo that I've ever been dissatisfied with. It's consistent, but just "rough" in every way. It sits out on the head of the lathe pretty much all the time, convenient to grab any time, but not something I have any real concern about. Then there is that Interapid I mentioned. It's very well made, and I really want to like it, but I just can't get past it's operation reverse to everything else I've got. For a while I seem to have gotten dialed into the flow of such things in the Phoenix area, though that's largely dried up now. So I've had a few others that worked just fine that also got sold, I've got more than enough to do what I need. But if I lost it all today, tomorrow I would be looking for a BesTest standard body 0.0005 DTI before much of anything else along those lines.

[John Hasler]

Harold writes:
> Of all indicators I've ever used, there's only one that has my attention, and it's the B&S TesTest.

I thought you were down on *all* DTIs but now I see that the BesTest is a DTI so it's just the Last Word you hate?

[Harold_V]

Correct, although hate is likely a little strong.
The Last Word isn't. It doesn't tell the truth, and a DTI that lies to you is virtually valueless. The amount of error I can not say, and I suspect it's not consistent, indicator to indicator.

In regards to DTI's, I have no quarrels, especially with the B&S BesTest. I rely on mine and wouldn't have it any other way (that's why I'm not impressed with the coax concept).

I made mention that I use my Last Word for removing taper. Works a treat for that purpose. Once it's set up on the grinder, it does nothing more than indicate movement. Removing taper is a hit and miss proposition at best, so it seems to work adequately for that purpose. It was exceptionally nice applied to the old #2 Cincinnati centerless grinder I used to operate. Seemed a real good fit, and was up to the task. For that reason, hate is a bit strong. I'd hate it if I had to rely on it for other functions, though (based on real life experiences).

Interesting observation by BadDog in regards to the Interapid. They were the indicator of choice for QA when I worked at Sperry. Every inspection station was equipped with a surface plate, knee, height gauge, Interapid DTI and a Cadillac PlaChek.

Oh, yeah! And a (not so) trusty 6" vernier caliper.

H

[Mr Ron]

Based on comments made about "last word" DTI's (the only DTI I have is a Gems), I must conclude I will have to use my DI for centering until I can afford a B&S, BesTest.