Test indicator question

jonesturf · Nov 10, 2012

Okay, I feel like a noob. Kind of am I guess. Been around machines for a while but have mostly used dial indicators. Now that I have a SB lathe at home and a Rockwell mill I have gotten more involved. I purchased a few dial test indicators. I noticed (because I dropped one the other day) that the point moves. I am very delicate when it comes to precision instruments because my dad is a surveyor. I know if I knock it out of whack I can put it back but if I am trying to indicate something can I move that to get a better angle? I would have thought it would be better to leave it alone.

I also see some used one's for sale on ebay with the contact points out of whack. Emailed the one guy and he said his intrepid is that way because they move. Wondering what everyone thoughts is on this. If I spend $300 on something I wouldn't want to break it because I am lazy. Looking at either grabbing an interapid, compac, tesatest or bestest in .0001 for final indicating when doing barrels for chambering.

jonesturf · Nov 10, 2012

Also how many guys use metric dials? Any reason why I shouldn't? I kind of wish we were metric.

Glenn Wegman · Nov 11, 2012

The point is adjustable and should be positioned to the least possible deviation to the calibrated angle. The calibrated angle can differ with manufacture. B&S are calibrated with the point parallel to the surface being checked whereas Interapid is calibrated at 12 degrees from the surface being checked. A trip to the Long Island Indicator site should disclose which brands use which angle. Mainly DTI's are used as comarative indicators due to the sine error introduced by the small radius that the point travels in as it is deflected. By "comparative" the object of the game is usually zero or minimal needle deflection when the surface is swept or rotated or compared to a master. Can be used for small increments of measure though keeping possible error in mind.

Dropping them is not a good idea. I have dropped two and both landed on the point. Both are no longer used and were replaced with new ones. They just never seem the same after they hit the ground...

The real Leigh · Nov 11, 2012

DTIs are comparators. The only really valid measurement is at the zero position, which can be changed as desired (the tips are movable).
The manufacturers go to great lengths to make you think the off-zero calibration is valid, and it is sort of, but not to any level of precision.

I think Interapids are best, for repeatability, smooth movements, and robust construction. I have a couple of them.

- Leigh

opscimc · Nov 11, 2012

jonesturf said:
Okay, I feel like a noob. Kind of am I guess. ... Looking at either grabbing an interapid, compac, tesatest or bestest in .0001 for final indicating when doing barrels for chambering.

Having never chambered a barrel myself, a 0.0001" indicator might be what you need for the purpose you describe. However, although a more sensitive indicator gives you, well, more sensitivity, it comes at the price of a reduced total travel. That's a disadvantage when trying to center something that starts out more than 0.008" off center. And, high sensitivity itself isn't necessarily an advantage. If the part you are measuring is rough or out of round by only ~0.002", the fluctuations/variations of the needle will make using the indicator much more difficult.

At least 90% of the time I reach for my 0.0005" Interapid which, for my uses, is an excellent compromise between travel and senstivity. I actually have three of them; two "standard" horizontal dials (one with a 1" dial, which I don't recommend, and the other with 1.5") and one of the less common vertical. The latter is a lot easier to use when tramming my mill or centering the tailstock on my lathe. Having said that, just yesterday I needed the sensitivity of my 0.0001' B&S Bestest.
.

daredo222 · Nov 11, 2012

jonesturf,
Nobody seems to have answered your question exactly - the point or stylus can be moved by simply pushing it gently but firmly with your fingers. It is clamped by miniature friction clutch which overrides. Re your “.0001 for final indicating”, I would be surprised if the average gun chamber was round to .0001" and a total indicator reading of .0005", (eccentricity of .0025") is good work.

Ray

The real Leigh · Nov 11, 2012

daredo222 said:
I would be surprised if the average gun chamber was round to .0001"

Hm... Haven't encountered many bench rest rifles, have you?

Lousy alignment can find you at the wrong end of the target range. :eek:

- Leigh

jonesturf · Nov 11, 2012

Thanks everyone. I should have added I already have two .0005" test indicators. Actually three if you count a cheapo. One is a Mahr Puppitast i got for under $30 on ebay and the other is a bestest. Haven't really ogt to use them much yet as I have been rebuilding my lathe. I know some people mention being able to indicate close to a couple tenths on a .0005" and once I get around to using them I may find that all I need.

I guess my initial question was a little more general in seeing if anyone moves the contact point to a desired angle to facilitate easier setup. I didn't want to be doing something that is gonna hurt the inidcator. I know the point moves and manufacturers recommend certain angles, usually close to 0 except for interapid's 12 degree, for accurate measurements, but is that in relation to the workpiece (from the indicators neutral point) or is that the angle of the contact point? For instance if I moved a contact point 45 degrees on way so I could see the dial better would that throw the measurement off as long as the workpiece was close to the angle of the point?

Hopefully that makes things more clear. On another note when I get to chambering (which will be the accurate thing I do on my lathe) I want to make sure its as close to perfect as can be. Hence the possibilty of using the .0001" inidcator. Looking at the tesatest .0001" and .00005", which is the same with grads in between, and an interapid vertical. We'll see. BTW Tesatests are a pretty good deal from Amazon and so some of the Interapids.

jonesturf · Nov 11, 2012

Also how is the vertical indicator easier for centering a tailstock? Curious on that operation. Thanks again for the help everyone.

Glenn Wegman · Nov 11, 2012

In relation to the work piece.

The position of the body of the indicator is irrelevant, as long as the contact point angle is correct in relation to the work piece. That's why the point is adjustable, so you can always have it at the correct position. Or as correct as you can get it!

Glenn Wegman · Nov 11, 2012

watch out how you hold your indicator when sweeping a tailstock or similar operation. Using an arm of any length can introduce error when inverted. The shortest most rigid setup is the way to go. Gravity, it's the law...

This is with a very short Noga base.

Just the indicator itself.

jonesturf · Nov 11, 2012

Good to know. I was thinking that moving them would around all the time would throw them off. I guess they are not as delicate as I thought.

The real Leigh · Nov 11, 2012

They're pretty rugged, but not baseball bats.

- Leigh

opscimc · Nov 11, 2012

jonesturf said:
Also how is the vertical indicator easier for centering a tailstock? Curious on that operation.

With the more common horizontal dial you can see it fine when indicating a center in the tailstock when you're in front of the lathe, but the dial disappears when you rotate it by 180 deg. So, you either have to use a mirror (and figure out whether ithe indicator rotated CW or CCW so you know which way to adjust the tailstock), or walk around behind the lathe to look at it. The vertical dial never disappears. For the same reason it's easier to use for tramming a mill.

Glenn Wegman · Nov 11, 2012

Or you can orient a horizontal to a position so it can be viewed with the face in a similar orientation to a vertical.

The real Leigh · Nov 12, 2012

Well, zero can be a relative term. I've known people with zero relatives.

- Leigh

opscimc · Nov 12, 2012

Glenn Wegman said:
Or you can orient a horizontal to a position so it can be viewed with the face in a similar orientation to a vertical.

Reorienting the lever by 90-deg. as you've done has made the movement parallel to the face, as it is on the vertical style indicator. However, it also made the movement parallel to the length of the body, whereas on the vertical style it is perpendicular. So, reorienting the lever does not make the two styles of DTI equivalent.

Also, from the point of view of mounting it, both dovetails are now "hidden" from the front of the face,and a long distance from the lever, so any arrangment for mounting it on the lathe's chuck that would have the DTI rotate in a small dia. circle near the lever, and not interfere with the tailstock, wouldn't be a simple one.

Glenn Wegman · Nov 12, 2012

opscimc said:
So, reorienting the lever does not make the two styles of DTI equivalent.

Agreed

I was not trying to say that they were in fact equivalent, just showing that there may be applications where a horizontal style could be set up so that the face would be visible through full rotation.

opscimc · Nov 12, 2012

Glenn Wegman said:
just showing that there may be applications where a vertical style could be set up so that the face would be visible through full rotation.

For the record, for years I got along just fine having only horizontal stye DTIs. It's not like I tram the mill or recenter the tailstock all that often and, even then, for these functions the horizontal style is fine. It's just that the vertical style makes the jobs easier.

winger · Nov 12, 2012

I've been trying to talk myself into one of these.
Inventor's Corner: Wireless test indicator measures blind holes | Machine Design
Would really help tramming in dies.
I saw an add for it, so it is on the market. I didn't bookmark it though.

Dave

found the site for it
http://www.measure-all.com/images/products/Vyndicator-sell-sheet.pdf
I have no connection to this company but did see the prototye in use.

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