What you need is a Noga arm. The one I have has a plain shank end which goes into the drill chuck or collet or whatever. Or as shown, adapted to a quill clamp so you don't have to disturb any mounted parts or in-situ tooling to do indicating. This clamp was a prototype to allow the shank to be placed vertically or horizontally, but I want to make one more like the open C shape with a single tightener. Anyways, it takes about 3 seconds to have the DTI ball on a surface ready to rotate. I would argue the DTI can go places the Blake cannot because the Blake indicator arms are bent a certain way & limited in span. This is the short Noga, my vise is 5" for reference.
I bought mine for re-boring pulleys. I was rebuilding several machines, and I had to bore out some pulleys. These were used pulleys, and the bore wasn't very pretty. I could reach all the way to the bottom of the pulley to find good parts of the bore.
It is also a lot faster to use, if you get the hang of it. You aren't craning your neck or using a mirror to see the dial when it is facing away from the operator.
One other way it shines is when you are indicating on the outside of a large circular object. It can be done with a DTI and a flexible arm, but there is quite a range the coax is faster and more convenient. But only once or twice a year (for me, anyway)
- This sounds like I'm a big fan. I'm not, really. The few times it is needed it is a blessing. Otherwise I reach for my Mit DTI (I'm not an animal!) - I got mine for 75$ and for that price it is well worth it.
Too funny @PeterT. I don't need anything. You wanted a photo of a DTI. I assumed you wanted to clarify what @Dabbler was talking about. You said you would post a photo and then didn't. So I figured you just forgot.
I think you just know that lots of folks on here confuse DTIs with DIs (plunge indicators). So I helped you out with a photo. Nothing more, nothing less. LOL!
This sounds like I'm a big fan. I'm not, really. The few times it is needed it is a blessing. Otherwise I reach for my Mit DTI (I'm not an animal!) - I got mine for 75$ and for that price it is well worth it.
I am the same. I have all sorts of indicators. My CoAx indicator mostly gathers dust. My favorite is a mitutoyo DTI AND I AM AN ANIMAL!
One of the features of the Co-ax indicator that nobody has mentioned is that they will indicate in both plus and minus directions from a zero point. So will most DTIs, but you have to flip a lever to do it while the co-ax will just do it all the time. I've never used this feature but I did note that it's there.
The other thing about them is the way they are designed to be chucked in a spindle. You can chuck a regular DTI too, but good luck reading it while the chuck turns. The coax indicator body stays in one place while it's axis spins co-axially (hence its name) with the spindle. In this way it's sort of like the difference between a mill and a lathe - in one case the work spins and in the other the tools spin. This has its uses too.
My advice to most is that a co-ax indicator is not an essential piece of instrumentation. I'd only buy one if I got a really good deal cuz it will mostly gather dust.
It's probably one of those things where both devices have their pros & cons & overlap. The best solution is for us to have both available in the cabinet! More tools! Bwa-ha-ha-haaa
No its not spinning obviously, mill is in neutral drive & you are controlling the measurement position with your hand. You position it & read the dial, takes longer to type than to do it
BTW there are top facing dials, I have one, I just keep forgetting to use it because I'm used to my regular one.
Actually thing brings up another point about the dial facing away &/or requirement for a mirror etc. I rarely if ever use a mirror for most part. I focus on Left, Right & Facing me (3 quadrants) until the needle is same position. I do shift myself a bit to see Left or Right facing but I also find it easier to make precise handwheel adjustments to converge needle position anyway. Rarely does it take more than 3 divide-the-difference iterations & needle should be entirely static. Which, if you had a tenths DTI, means you are accurate to tenth (COAX are 0.001"). What WILL drive you nuts with a DTI is if you are off center by a large amount & needle is swinging wildly. Don't do that. I'm lucky & have a DRO so I can use practically anything including the DTI ball itself & DRO half function so the whole exercise is converging the last 0.002" or so.
Anyways, if the measurement feature (typically a ID hole or OD boss) is truly circular, the 4th rear facing will indicate same as front facing once the 3 quadrants are dialed. But always wise to do a sanity check. If feature is not truly circular, that's a different issue & neither instrument will tell you center, or at least without a bit more elaboration of the non-circular feature. Think of simple deviation like an elliptical hole. The COAX will settle to some kind of minimal spread needle blur vs DTI will say something like +0.001 left, -0.001 right, 0.000 center face (0.000 rear face). Tomatoes, tomahtoes. If the ellipse axis is angled, its kind of the same but the measurements don't represent quadrants anymore.
I like that the machine is not running and I am free to sweep & examine any position of the circumference. Example if the hole has a negative nick or positive burr on the wall, DTI can clearly see that with a hand held sweep & work around / re-adjust measurement positions accordingly. But COAX will always blindly run over that obstruction & its needle registers it as a deviation indistinguishable from a centering issue. If I recall my COAX also had an arm sticking out the side which had to be be static. So that either requires hand holding or mag base stop post or whatever. Now as I type this, maybe that is a 'feature' in that rotating the handle to examine needle blur in another axis (elliptical hole example).
Here’s a simple and excellent use for a coaxial indicator. Have you moved the lathe tailstock to turn a taper? Chuck the coaxial in your three-jaw, put a dead center in the tailstock, indicate against the dead center. Voila, tailstock alignment in seconds without a test bar.
Hmm, I wonder. Would the COAX also be subject to gravity DTI / holder upside-down-itis as the arm rotates? The COAX needles are typically much heavier stock & the mechanisms are not exactly Swiss watch. I really don't know the answer. Field test with independent measurement required, I vote you haha. (This is my Noga mini mag base test but I've seen the same test with a very solid locked down holder & seem to recall the discussion was on DTI's with holder eliminated).
Yes, it actually can be spinning! I know cuz I've done it! Albeit at low speed but it certainly works just fine at low speeds. It's something to see! Someplace I remember reading not to exceed 750 rpm. There is a handle that you hold (or block) to stop the indicator from spinning while the spindle spins.
I sold my COAX long time ago, so alas, I cannot be a tailstock test pilot contender. But I will break out my top reading DTI for a photo op.
But it would be interesting for someone to do the inverted (gravity) test like my post #28 pictures with a COAX. I'm struggling to remember if the drift issue was with the arm or the DTI or a bit of each.
I sold my COAX long time ago, so alas, I cannot be a tailstock test pilot contender. But I will break out my top reading DTI for a photo op.
But it would be interesting for someone to do the inverted (gravity) test like my post #28 pictures with a COAX. I'm struggling to remember if the drift issue was with the arm or the DTI or a bit of each.
It's easy to see what you are doing with the DTI. Again, I don't think it matters unless you are comparing the two readings in the two cases - which I wouldn't do. But it's not obvious to me what you want to evaluate with the Coax. Can you describe the test you want to do in more detail?
Hmm, I wonder. Would the COAX also be subject to gravity DTI / holder upside-down-itis as the arm rotates? The COAX needles are typically much heavier stock & the mechanisms are not exactly Swiss watch. I really don't know the answer. Field test with independent measurement required
Just the 'inverted test' with an indicator arm screwed in. (Left) chuck the coax on its stem in the lathe, zero the dial. Then (right) rotate chuck 180-deg & record any needle movement, likely require a mirror.
My memory isn't that bad on this one. I surprised myself! I had said 750. The Blake website for their coax indicator says max rpm is 700 - 800 rpm. I think much less than that is better but for some machines I suppose that may not be possible. The relevant part starts just before 3 min in their video where they show how to use it with the spindle turning. In fact they imply that this is the way it is supposed to be used.
The Blake Manufacturing coaxial indicator is a precision centering instrument for locating a workpiece in a Horizontal or Vertical machine. We´re at CA, USA.
blakemanufacturing.com
A question for anyone here. Blake says to preset their device to the midrange of the small scale to maximize the coaxial range.
No place do they mention moving the needle the opposite way. I assume one way is for inside alignment and the other way is for outside alignment. Does anyone have other ideas about why it's like that?
FWIW, the device also seems quite contiguous between one direction and the other. If there is any hysteresis there, it isn't obvious to me. This makes me wonder if it might also be used in a push/pull configuration.
Just the 'inverted test' with an indicator arm screwed in. (Left) chuck the coax on its stem in the lathe, zero the dial. Then (right) rotate chuck 180-deg & record any needle movement, likely require a mirror.
Blue = tailstock arbor or blank looking head on. Orange = indicator ball positions
Of course, whether the COAX or DTI sees gravity effect, it doesn't really matter for lathe TS realignment because we are only after any deviation on the left & right positions (3:00 & 9:00). Any gravity effects here should be the same & cancel one another. Even if measurement device was perfect, the up-down is controlled by the height of TS casting which is useful to know but something we don't change often.
Anyways, the issue is if gravity can pull the arm down for reasons @thestelster elaborated on & as shown in my post #28 with DTI on Noga arm, then indicator ball drifts slightly (red dot) & gives false vertical center. What I can't recall on coax is if the stationary arm has any influence on where the primary reference plane is if there is such a thing.
Blue = tailstock arbor or blank looking head on. Orange = indicator ball positions
Of course, whether the COAX or DTI sees gravity effect, it doesn't really matter for lathe TS realignment because we are only after any deviation on the left & right positions (3:00 & 9:00). Any gravity effects here should be the same & cancel one another. Even if measurement device was perfect, the up-down is controlled by the height of TS casting which is useful to know but something we don't change often.
Anyways, the issue is if gravity can pull the arm down for reasons @thestelster elaborated on & as shown in my post #28 with DTI on Noga arm, then indicator ball drifts slightly (red dot) & gives false vertical center. What I can't recall on coax is if the stationary arm has any influence on where the primary reference plane is if there is such a thing.
Well, yes and no. The height of the tailstock won't effect the tapering during turning greatly, but if we need to ream or drill a hole with a tailstock that's too low or high, it could create an oversize hole. (Of course extending the quill of the tailstock has to travel in the same plane (parallel) as the spindle). In the book I referenced, Schlesinger suggests a height difference between head and tail of no more than 0.0008".
- I got mine for 75$ and for that price it is well worth it.
