Metrology Monday: Height Gauge

The first measuring tool I want to cover is the one depicted in my teaser photo, the height gauge. I expect that things will get a bit more consistently structured as I progress in this series but I aim to cover what the tool is for, features and what the options are and any alternatives.

What Is A Height Gauge For?

This may surprise everyone but the basic use of a height gauge is used to measure height. More specifically, the height of a point above the surface the gauge is sitting on, ideally a flat surface. (Next week, surface plates!) The gauge has some sort of linear scale and a probe. You move the probe to the point to be measured and take a reading. This is also probably the least useful use of a height gauge.

The pointy probe is called a scriber and, again those machinists with their tricky obscure names, can be used for scribing a line at a specific height. This seems to me to the most useful function. My gauge’s scriber has a sharp silicon carbide tip so I imagine it can put a scratch in any material I am planning to work with. I have visions of getting all the handrails at the same height or marking cut lines for kit bashing.

The third use of a height gauge is as a stand for a dial test indicator to use for checking the parallelism of a surface with the surface the gauge is sitting on or the flatness of that surface. This is more of a machinist thing where you are attempting to judge how reliably parallel machined surfaces are as reference points. I suppose you could check wheelsets for concentricity.

Lastly, the dial test indicator/gauge combination can be used to check multiple parts for conformance to a specific height. You set it up to a standard and then pass multiple instances of a part under the indicator probe to see how far out they are from the standard.

Options

My height gauge is a Mitutoyo 18″ Vernier Height Gauge. It is graduated in both imperial and metric and reads down to .001″ and .01mm respectively. It is a good quality model but way taller than I am likely to need but was available used for an excellent price. If I was buying one new, I would get a 12″ or even a 6″ one. I don’t inticipate the need to mark a lot of truncation lines on O scale rolling stock.

Like almost any took, height gauges are available in a range of qualities from plastic maybe junk up to ludicrously accurate and breathtakingly expensive models. In fact, machinists usually talk about toolroom versus inspection grades in terms of metrology tools. Inspection grade is for when they start talking millionths of an inch and not what I need.

In addition to Vernier models, you can buy gauges in dial and digital models with escalating price levels for each type. Digital models are handy in that you can zero the display at any point. My model can be zeroed only at base surface level or thereabouts.

Alternatives

The common economical alternative to a height gauge is a surface gauge. It is more or less the scriber on a stand without the measuring capability. Presumably you can also hang an indicator off of it as well. You can buy surface gauges but shop made ones are a common beginner project.

Next week I plan to cover the surface you set you gauge on.

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