How to correctly use a height gauge

Graham,

I posted this link in a previous thread

... just increment the last digit to get to the next page.

Cover picture shows the blade nicely.

MichaelG.

I have a Shardlow vernier height gauge a contempory of the Rabone gauges, they were both supplied with a setting piece to check the calibration. The scribers are made to a specified height which is usually engraved on the side, the top and bottom faces should never be ground the only part that should be ground is the top of the chisel point. The attachment finger has a specified height so the scribers can be fixed above or below but only the top face is direct reading to the scale, any other mounting will require a clear head to cope with the calculation of the actual height. The dropped point scribers are useful to reach down to scribe lines below the normal range of the standard scriber but require some calculation. The height gauge can also be used with other devices like vernier protractors and dial gauges.

Mike

Looking at your one Graham I can see where you get the "radius" from. Looks like yours has been sharpened away and the angle has become far too steep as confirmed by Michaels link and the corners do look soft and rounded rather than a nice crisp arris.

Like Bogs I tend to only use mine now for initial setting out and then use the DRO

Just to confirm my staged photo was as I said correcting a blade that pointed upwards and to one side, subsequaent sharpening on the slanting face

It looks to me like Graham's blade has been replaced by something with a brazed-on tip.

MichaelG.

Most tend to have a carbide tip, but it could have been replaced at sometime with a homemade tip

Just as an aside; I don't think the Chesterman 369 was "intended" for scribing ... The booklet only makes reference to its use as a gauge.

Of course, we are free to use our tools as we wish.

MichaelG.

Michael have a look under "standard equipment" and it lists a hardened scriber.

Edited By JasonB on 09/01/2015 10:09:54

Before I go along the "I'll make one" route, does anyone know a source for replacement straight scribers for height gauges? I've managed to find a few cranked ones, but no straight ones.

Graham

.

Thanks, Jason

I had missed that ... I was just reading the body text.

MichaelG.

I have got myself thoroughly confused using my height gauge and ask if someone my help. I am trying to measure a hole size and position. In order that I can 'feel' the hole edge I have used a 'finger DTI' mounted to the arm of a digital height gauge. I zero the DTI and readout on a gauge block on the surface table. Move the height and touch the bottom of the hole, adjust the height gauge to zero the clock, measurement 1.(18.25 mm) Now move gauge arm up so the stylis of the DTI finger touches the top of the and adjust the height gauge to zero the clock, measurement 2. (26.28 mm) The dia of the stylis is 2.00 mm.. 26.28 - 18.25 = 8.03 mm. Adding the stylis dia gives 10.03 mm. I check the hole dia with a caliper and it measures 9.05 mm. So I am 1.00 mm adrift with my height gauge measurement and for the life of be I cannot see my error. There has to be a simple explanation and someone has been through it all before. Help please!!!

Regards Gary

The stylus of the dial gauge is likely to be getting pushed up for the first reading so would have moved clockwise from the no contact position.

When you touch the top of the hole the stylus gets pushed down and the needle moves anti clockwise from the no contact position.

I suspect your 1mm difference is one full turn of the dial.

Edited By JasonB on 05/05/2023 11:51:33

If the scriber meeds sharpening, do not abrade the under side. Doing this will upset the Zerom point.

Sharpeming should be done by on the upper sloping surface.

If you want a cranked scriber, such that when flat on the surface plate, the height gauge reads 1" o0r 2", make one from some gauge plate.

Make the flat underside first, to use as a datum. From there, the vital dimension is from that datum surface to the arm on the gauge, set to, and locked at 1" or 2" (Depending on the gauge. Both my Shardlow and Chesterman gauges use 2" as the Zero point with a cranked scriber )

Obviously the accuracy of the dimension from the underside of the scriber to the surcae which clamps to the arm of the Height gauge determines the accuracy of future measurements.. Very fine emery, finishinbg with fine wet n dry is the way to go..

Howard

The other way to use a Height gauge dor measurement is to fit a DTI and Zero that on the datum surface, noting the Height Gauge reading.

The datum surface could be on the component being measured, or Gauge Blocks (Slips ) ensuring thet the two protective slips are used, to prevent wear or damage to the gauge blocks proper.

The Height Gauge is then adjusted until the DTI iagain reads Zero on the surface being measured.

The difference between the two readings is the dimension beinbg measured.

HTH

Howard

Note there is a new post to this old thread to save anyone else like Howard replying to the original question

The thread contains references to calibrating the gauge.

If the original test-pieces are missing, suitable alternatives for our purposes are unworn milling-cutter shanks (mind the cutting edges don't touch the instrument), bearing-races and similar. These are all finish-ground to very high tolerances.

Four factors together define how good a measuring instrument is, or not! They are:

• Resolution - how finely the instrument's display reads. The display can be a plain scale, a vernier scale, or a digital display. None of them are trustworthy, for example digital calipers usually display to 0.01mm, when they only measure to about 0.02mm. Resolution can be wrong either way : digital displays imply better than reality, and analogue scales suffer multiple error problems, such as parallax,
• Accuracy - how close to actuality the measurement is. Unusual for any measurement to be spot on - the result is normally a scatter of answers hopefully near the truth.
• Precision - it's common for measurements to cluster together at some distance from the truth, Imagine a gun firing six shots at a bulls eye, and all of them miss but land together a foot to the right. The gun is precise, but not accurate. Conversely inaccurate guns can never be precise.
• Repeatability - this is a measure of how close successive measurements are to each other. Expensive digital calipers are often more repeatable than cheaper models of the same accuracy and precision.

Height gauges have many limitations. With a microscope, even a sharp scriber is blunt, and so is a new razor blade Even less precise and accurate are the lines scratched by the scriber. A line has to be about 0.1mm (4 thou) wide to be seen with the human eye, and this limits what can be done by scribing. Wouldn't want to make it worse with a blunt rounded scriber, but it's not a major problem.

My digital height gauge has the usual screw adjusters, and I expect it's OK to about the same range as a digital caliper, that is ±0.02mm (±1thou). It can pick up a feature to about that, but a scribed line transferred to that height could be 4 times worse.

I don't think too much should be expected of a 40 year year old vernier gauge - wear always reduces precision, accuracy, and repeatability. Resolution too, if the scales aren't in good order. Verniers place an additional burden on the operator that causes errors too. They depend on eyesight, correct head position, and brain getting the right answer.

How accurate does a height gauge need to be in a home workshop? I think anything that gets within about 0.03mm is 'good enough' unless the owner is doing something special.

Plenty of practice needed too. Micrometers come with a clutch to help eliminate pressure errors, but many claim developing a 'feel' is better.

Dave

Edited By SillyOldDuffer on 05/05/2023 13:28:25

This thread (and using the thing this morning) reminded me of something I don't understand about my height gauge, so I took a photo to enquire here:

The vernier subdivides each millimetre so you can read to hundredths, but the scale is calibrated 0 to 50, so you have to double whatever the reading is. Why?

(The vernier scale is labelled "Ver 1/50mm"

Andy I think you will find it reads 50 x 0.02 which is 1mm. 0.02 of a mm is eight tenths of a thou.

Hi Andy, Baz is correct, and it means the scale has a resolution of 0.02mm. i. e. 25 Vernier divisions X 0.02 = 0.5mm. Therefore, if you were to make a measurement of 50 + 40 Vernier divisions, it will also = 2"

Regards Nick.

Edited By Nicholas Farr on 07/05/2023 21:00:14

A good illustration of why I cough up for batteries: a digital readout removes the stress of reading this type of vernier gauge and eliminates interpretation mistakes.

Now then analogue lovers, what height is Andy's gauge reading? And for extra points, what's the thickness of the ratchet-pulley object he's measuring?

Dave

Edited By SillyOldDuffer on 07/05/2023 21:00:27