HEIGHT Gauge question

[GlennW]

Google "Height Master" and then look at the images.

[pete]

For my Google image search I just used Cadillac type height gauge and multiple types by various manufacturer's showed up. I'm unsure of what the Cadillac designation means though.

[GlennW]

I'm unsure of what the Cadillac designation means though.

"Cadillac Gauge Company" was the manufacturer of "Pla-Check" height gauges.

Just like "Mitutoyo" being the manufacturer of "Height Master" gauges.

[TomB]

Thank you all for the answers

[BadDog]

For this type of gauge, the name "Cadillac" seems more or less like "Kleenex". A case where in common usage the brand name has become (almost) synonymous with the thing itself. Seems like I once knew a proper name for the thing, but whatever it may be escapes me now.

[wally318]

Ok so I've finally had a bit of time to look at and play with this for a bit.
And I'm a bit confused as to the readings I'm getting.
Am I looking at this the wrong way?
Here's what I see. The spacer rings are all .500 thick and .500 space between.
Except the bottom 1. It's .175 thick.
When the bottom ring is touching the granite I get a reading of .184 using
a digital height gage. Picture 1.
When the micrometer is opened to the 1.0000" mark on the top ring I get
a reading of 12.114" . Picture 2.
If I understand this correctly, it needs some calibration. The thimble needs to
be adjusted upward by aprox. .114", so that I get an actual height of 12.0000
when the micrometer is at the 1.0000" point.
And if thats the case. Then its impossible to get all the way down to a 0.0000"
reading, because of the .175" thick bottom ring. Unless you had a surface plate
with a recess. Or raise the height micrometer with parallels, and then subtract their
thickness from the reading? I'm going to try this when I get down to work in a bit.

On a second note, I noticed when taking readings that sometimes when pulled the height
gage finger off the height micrometer rings I would hear a little plink.
Indicating a bit too much preload on the finger or too low a reading.
So my second query is this. Once I know how to take the readings from the correct place
and know that the height mic is reasonably calibrated and or what the error is, then what would
be the proper technique to take/get accurate readings off of parts and the micrometer. So that
I was confident that not too much error would creep into the measurements?

I need a bit of help to wrap my head around/understand this.
Can we deal with 1 issue at a time? I bring this up like this
so hopefully all interested can learn something.

[GlennW]

.200" would be the minimum reading. With the thimble zeroed on .2 the bottom ring should be .200" above the surface plate.

Don't forget to always rotate the thimble in the proper direction. Don't back it up.

[pete]

Many thanks for clearing that up about the Cadillac gauge company Glenn.

Since I've never used one of the Cadillac type gauges this could be wrong. While they could be used to preset your scribeing point to a certain elevation I'd think just how accurate that method would be is subject to a lot of "feel" or that preload you mentioned for exactly when the tip starts to touch. I'm only going by what I've read of course, but I believe there more of a transfer type gauge and mostly used to pre set the elevation zero point on high accuracy DTI's etc. Once that's done then accurate measurements on anything sitting on the surface plate can be done. The rings obviously give you whole number settings, and the super micrometer head allows an accurate setting between those whole numbers. That said attaching a dti type indicator alongside your scribeing point and zeroing it's tip out to the bottom of the scribe when both are touching the surface plate would remove that "feel" or preload issue.

There's usually a few thou + - built in inaccuracy on most of the more common height gauges. Checking the allowable + - on most of them when I bought mine was eye opening. Have you got a set of trust worthy gauge blocks and a 10ths or better dti? If it were me that's what I'd use to check and re-calibrate if needed your new height gauge. I doubt any standard type of height gauge is even 1/10th accurate enough to double check one of these Cadillac style of height gauges. What some of the high end calibration labs use today I'm not sure of, it could be laser measurement now. But in the not too distant past most would have used a lab grade of probably ceramic gauge blocks on a inspection grade surface plate and + - 68 degrees single digit temperature and humidity control to calibrate that gauge. We can't get nearly as well as a proper calibration lab could of course, but you can get fairly close if your careful about surgical cleanliness and watch how much hand heat gets transferred to anything your checking. I've added a $40 but what seems to be fairly accurate digital indoor / outdoor weather station in my shop recently just to have a general idea of what I can expect for room temperatures. Little of what I do would ever need that, but it's giving me a rough estimate just in case.

[wally318]

OK. so I think I have this figured out.
You can tell me if I have it figured out right.
By loosening the screw at the end of the thimble,
I could turn the thimble up by about 4-1/2 revs. or .114 aprox.
So that when I turned the thimble down by that amount I was
very close to 12.0000".
And yes Glenn .200 is about as low as you can measure.
But I tried using some 1.5" high I beam parallels that I could use if ever needed
they are very close to .0001" tol. and it will take you down to 0.0
But thats probably moot. You could probably get those measurements with a
regular micrometer.
Next I scrubbed both upper and lower surfaces on the rings with WD40 and
a scotchbrite pad. A nice dust cover will prevent the need for that too often.
Later when I have some time, I'll stack up some gage blocks and transfer the
height/measurement to the micrometer and use that to dial in the thimble.
I'll use a few different height samplings to check several rings.
I figure if I can get it to a tenth-good enough and call it a day.

As for the finger preloading, thanks for the input Pete.
So my instincts were correct that by hand/feel its very difficult to get
a consistent accurate reading both with the height gage touching off at a
given height on something you need to measure and then transferring that
height to the micrometer to get the height reading.
So ... by using a dial indicator on the height gage to measure something
and transferring that to the micrometer, that takes the feel out of the
equasion?
My height gage came with a indicator adaptor bar.
I had to do a bit of adapting to clamps to make it work.
But look at pic.1 is that what you had in mind?
Pic.2 is that a suitable indicator for the job?
Maybe a longer or angled/curved indicator point
to create a bit more room?

[pete]

Yep your on the right track, but you'd really need a finger type 10ths reading dti style to get the best results. Add that along side the scribeing point and have it's ball tip maybe a thou below the flat bottom of the point. Zero the indicator when both it's tip and the scribes tip are touching the surface plate. A plunger type indicator has to be as close to 90 degrees to the measurement surface in both X and Y as you can eyeball it to or the actual linear travel of the indicator tip will give an incorrect measurement. How your using it there it probably doesn't much matter since your only looking for movement past the initial zero setting. Custom machining a quick attachment to mount a dti along side and with it's tip just a little behind the scribeing point is probably the only way you can get the dti to play nice with your height gauge. But a dti would be a lot smaller and easier to use for what your wanting. Maybe make that adapter so you can position that dti in two positions? One as I said just behind the scribes tip and another so it's positioned well in front of the scribes tip so you can then get dual use out of it when transferring height measurements with the dti from the Cadillac gauge while checking parts? At least that's probably how I'd do it. Afaik most or maybe all of these types of gauges came with a proper fitted wooden storage box. That protected the gauge while not in use and also kept the usual airborne dust from collecting exactly where you had to clean.

Again it's only information I've managed to pick up from various sources, but it's my understanding the micrometer heads and internals on these Cadillac type gauges are built much much better than any standard micrometer for there very high accuracy ability. If you use Google images with the term Super Micrometer or Bench Micrometer you'll see what I mean. Most of those are the bench type horizontal models, but I believe the same heads were used on this type of height gauge to get that required accuracy level. They obviously have much larger and easier to read thimbles, the micrometer screws and nut were much more accurately made, lapped and checked etc, etc. "If" that Cadillac gauge was never abused or dropped and as long as the gauge's internals doesn't have excessive wear you should be able to do a whole lot better than getting it within a 10th. The tough part even using gauge blocks to check it's readings is you don't actually know where or even if it was mostly used at only a few height settings. If so it could have localized wear in those areas. You may already know this, but when checking a gauge or micrometer against gauge blocks you also want to chose your gauge stack height in the top and bottom of the 1 inch increment but also chose 3-4 stack heights that check the gauge with it's micrometer thread and it's thimble in different positions of rotation. Odd numbers for example. Given it's apparent age I'd also best guess it as probably needing a real cleaning and flushing out of the old congealed oil and any dust that's gotten inside. To do that I'd proceed very cautiously, even to asking on the PM Metrology forum if anyone has had one of these apart and if so is there any tricks or anything to watch for. Re-lubrication of equipment like this is fussy work, hardly any oil is used at all. Less than a drop applied with just the very tip of something like a wooden tooth pick on each turn of the micrometer thread would likely be almost too much. You could also check with some place like Long Island Dial Indicator Repair and ask how much just to clean and lube the internals but not re-calibrate it. That might be reasonable, but I can't say for sure if it would be or not. Also since I've never used one of these types of height gauges it's possible the factory used what's called "dampening grease" in the thimble area. Not many have heard of it but it's in more items than we think. Cameras, binoculars, rifle scopes and some metrology equipment. It's used for multiple reasons, one is operational feel while using the instrument since it provides a light but consistent drag on anything that's rotated in fine increments. It's also used to take up minor but required clearances. So if you do take it apart and find something like a light grease I'd bet on that being what it is. It's also a very special and bit hard to find grease. Google has a bit of information about it for anyone that's interested.

[Harold_V]

A word of caution.
The discs on those gauges are high precision. Using a Scrotchbright, which contains an abrasive, is akin to using sandpaper to dust a piano. If you must clean the instrument, in order to preserve the degree of remaining precision, never use an abrasive. If the instrument is so badly degraded that one is required to make it clean, it most likely has already suffered considerable damage. Clean Stoddard solvent (paint thinner or mineral spirits) should be more than adequate.

H

[GlennW]

You'd have some pretty significant cosine error with the gauge set up like you have it in the first pic.