Metrology Monday: Gauge Blocks

What Are Gauge Blocks For

Just like surface plates are a standard for flatness, gauge blocks are the machinist’s standard for length. And also like surface plates, they are less simple than they appear.

Created from well conditioned steel and polished to a very find degree, gauge blocks come in sets of different sizes that are combined to get whatever length is required. An imperial set is typically 81 blocks and covers ranges from .001-12.000″ in .001 increments and .2000-12.0000 in .0001 increments. The odd starting point for the ten thousands is because the first block is .1001 or such since nobody can make a durable block .0001 thick. Making up the required combination may count as playing with blocks. ๐Ÿ™‚

The assembled length is used to compare or calibrate whatever you are trying to evaluate against the standard. My singular “real” usage so far has been checking the accuracy of various used instruments I have purchased. As I mentioned somewhere previously, one can mount a dial test indicator on a height gauge, zero it out on the gauge block(s) and use it to check parts for expected length.

A fun feature of gauge blocks is that you can “wring” them together. The highly polished surfaces allow a close enough fit that they will stick to each other. Very handy when you need to move a pile of four blocks.


If you don’t have a gauge block set, you can start with a micrometer and measure some object, take the result and compare it to the resulting measurement from other instruments to see if they agree. Some higher end micrometers come with a block usually called a “standard” which is used to check the mic. This is effectively a single gauge block.


Cheap gauge block sets go for about $180CDN new and things go up from there. In my case, I opted for a used set of some personal and historical interest which I will now enthuse about:

In the 1800’s, New England was a center of industrial excellence with the precision manufacturing aspect perhaps most famously represented by the Waltham Watch Co. Where you have machinists, the tool manufacturers follow and so it was with Massachusetts. That industrial sector is a shadow of its glory days but the shadow is a long one with the L.S. Starrett Company still in business. I have more than one Starrett measuring tool but my gauge block set is a product of a less well know competitor, Van Keuren.

The Van Keuren Company still exists as a brand but no longer operates out of its building in Waltham, MA. (As an aside, I worked in the Waltham area for about six years, love those brick mills) I know they still were there in 1942 because that is when my block set was manufactured. The three digit serial number suggests either an early product or one that didn’t sell a lot.

The set sill contains the inspection certificate with the deviation from labelled size in millionths! for each block. I do wonder if they still conform to those results but am unlikely to need to care. ๐Ÿ™‚

Metrology Monday: Indicators

What Are Indicators For?

Next to calipers, the most common measuring tools used by machinists are dial indicators and dial test indicators. These precision instruments are used to precisely measure changes of dimension over relatively small ranges. They consist of a graduated dial with a movable face and a “hand” driven by some sort of probe that one applies to a surface. They are used while held in some sort of holder rather than in one’s hand. Here is a typical holder setup:

I am lumping the two indicator types together since it makes it easier to explain how they differ. The major distinction is one of range. The big one in the photo is a dial indictor: it has a plunger probe with an overall travel range of 1″ with each revolution of the hand covering .1″ or 100 thousandths which are the smallest units on the dial. I use my indicator for “rough” measurement such as getting a milling vise aligned or centering stock in a chuck.

The other is a dial test indicator. It has an overall range of only .030 inches and is graduated in .0001″ increments. Test indicator dials also tend to be marked counting up from zero in both directions and, like this one, have a lever probe instead of a plunger. Test indicators are typically used for really precise measurement such as checking the parallelism of two surfaces. Here is a setup I used to see how parallel my 1-2-3 block was :

I moved the block around under the probe and got at most about half a tenth movement. I may be detecting fingerprints on the polished surface. I am calling it good enough. ๐Ÿ™‚


Indicators do come in digital versions but the vast majority are still analog dials. They come in both metric and imperial versions although in North America the vast majority available seem to still be imperial.

Indicators also come in a wide array of price levels. My dial indicator is a cheap one that cost maybe $50CDN with the stand. My dial indicator was purchased used and is not a cheap one, being made in Switzerland. You can easily spend several hundred dollars on an indicator but if you don’t have a pressing need it is probably not worth it. (I just liked the idea of measuring things in .0001″ increments. I have no other excuse)


There aren’t really genuine alternatives to indicators but cheap ones are readily available that seem to be quite good enough for most work. If you aren’t doing machining, you probably don’t need on unless you want to check the runout on your drill press or assess the flatness of machined objects.

Metrology Monday: Surface Plate

This week I am talking about the humble block of stone known as a surface plate.

What Is A Surface Plate For?

When evaluating the dimensional properties of various machining related items, one quickly arrives at the need for something to compare to. A standard or reference as it were. One of the basic results one hopes machine tools produce is straightness and it’s two dimensional version, flatness. The surface plate is the general standard upon which evaluations of flatness rest. For what is basically a simple block of rock, there are some details I find fascinating.

As I mentioned last week, you can set things on a surface plate and evaluate how parallel a top surface is with the side resting on the plate. With additional tools, you can also check for squareness.

There is also a way to check for flatness of a surface. One applies a marking fluid (ink/paint) to the plate and rubs the surface to be evaluated around on it. The result is paint on the high spots. What you do with that is whole other post but basically you can scrape, grind or machine things to improve flatness. Scraping is the basic manual way of getting something really flat and a skill I hope to acquire eventually.


Modern surface plates are commonly made of granite although cast iron and glass ones are also made. (I have never seen either for sale by vendors I frequent). Granite plates are produced and serviced! by a variety of vendors big and small. The history of surface plates is an inversion of the usual progression of technology because they were originally made from cast iron and granite took over when wartime metal shortages made trying alternatives such as glass and granite attractive. It turned out that granite was good enough for most uses. Cast iron is apparently preferred for really high end work.

Plates come in an assortment of sizes from 6″x 12″-ish up to huge multi-ton monsters. As you would expect, with greater size comes greater weight and things quickly get out of reasonable reach of the hobbyist. My plate is 12×18 and 3 inches thick and weighs 72lbs. I would have gotten a smaller one but this was on sale.

Speaking of on sale, plates come in a variety of grades with increasing levels of flatness. Mine is alleged to be flat within .0001″ which is quite good for an inexpensive (~$60CDN) but I have my doubts. Plates come with inspection certificates but the vendor didn’t bother to actually fill it out… I am not too worried because it is flat enough that I can’t detect any variation using the best methods I have available, a dial test indicator. (Teaser for next week!)


Unless you are aspiring to finicky levels of accuracy, a surface plate could be overkill. A 70lb block of granite is not something you just whip out of a drawer for a quick measurement. The best alternative I have used in the past is a piece of plate glass, in my case a discarded glass shelf. It still sits handy to my workbench for use as a reliably flat assembly surface.

I have also seen at least one Youtuber using a piece of granite counter top. I have no idea how flat that is relative to an official plate but with modern processes, probably close enough for many. Actual granite surface plate manufacture involves leaving the blanks in temperature controlled rooms for months for the internal temperature to even out to avoid the minute distortions it causes. I doubt countertop companies do that except by accident.

Weekend Reading: How To Build a Model Railway – Ultimate guide to making buildings

Sometime around the Christmas holidays during one of those bits in Ontario where we ventured into bookstores carefully bemasked, I picked up the Model Rail annual How to Build a Model Railway: Ultimate guide to making buildings. It definitely provided some enjoyable reading.

While I think “ultimate guide” is a bit of hyperbole, this volume is structure build articles and structure build adjacent articles from cover to cover. (Save the few front and back pages of on-topic adverts I so greatly prefer to the North American interstitial approach). As the cover says, over 30 build articles. There are also a couple of how to research your prototype and a bit extolling the merits of scratch building.

The subjects are entirely UK based but other than making me wistful for thatched roofs and castles, the techniques covered are generally applicable and run the gamut of all media, card, clay, resin, plastic, wood and plaster. No whole etched metal kits covered but metal is in there too!

There is probably limited merit in reviewing an ephemeral publication such as this but I wanted to take note of the good work the Model Rail staff produces. I enjoy the regular Model Rail when I can get it and this was more and denser than that.

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.


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.


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.

Some Pending Verticality

This is the current main loading dock side of Griffiths Foods, one of the few remaining rail served customers on the CN GECO spur. The view is facing west with the real Comstock Road is directly to the right. In the absence of any 1970’s photographs, I am going to take this and run with it, or at least what will fit.

The building front will be a maximum of 38 scale feet wide and mirrored to what is here. Main truck docks to the left will be implied to be in the off layout space in front.

Things I like about this and hope to capture:

  • Side by side truck and rail doors with the truck dock ramped down.
  • Despite a lack of any windows, there is a lot of things going on.
  • Clear progression of additions at different heights/widths.
  • Whatever that machinery on a plinth is to the right.
  • I have a big pile of 1:48 embossed brick sheet!

Things I am reasonably sure don’t belong in the 1970’s:

  • That metal siding at upper left. Covered windows perhaps?
  • Security camera on corner of building.
  • Gas bottle storage with exchangeable 20lb propane tank.

My current plan is a foamcore shell with brick sheets applied thereon. I will do the foamcore as a mockup to see how it looks.

Metrology Monday: Introduction

Formally, metrology is the scientific study of measurement. Machinists typically use the term to refer to actual measuring. This is an aspect of metal working that I find fascinating, probably because there are all sorts of wonderful tools involved. To predict that I will be overkilling this particular aspect of the hobby takes no special foresight. ๐Ÿ™‚ I have resolved to share this enthusiasm through a series of posts.

There are various aspects to the subject I intend to explore besides the tools themselves. I briefly touched on engineering fit in my roller gauge design. That is a way of establishing one required measurement. There are also techniques I need to learn more about; I see machinists on Youtube taking measurements in clearly deliberate motions I don’t yet understand the point of.

Depicted in the photo are my new surface plate and height gauge. Next two series topics sorted!

About That Foam Scenery

During some of my scheduled shop time, I have been working towards getting all of the spaces between the tracks filled in with foam. The first priority to is relieve my anxiety about any derailments involving rolling stock making a fast trip to the concrete. Nothing even close to that has happened and I am generally well pleased with operational performance so far but it is still something I worry about.

Getting all those non regular shapes cut and fitted is time consuming and got me thinking about what I might do differently next time. I haven’t really settled on anything but I did want to share what I have learned about this approach. Queue the list.

  • Retrofitting foam is fiddly and time consuming. No matter what methodyou chose it will take time and probably involve a mess somewhere.
  • I have tried tracing the shapes onto the underside of the foam from below. This is awkward and not as accurate as I hoped. I always have to trim things down.
  • I have tried “routing” the shapes by tracing the edges from above using hot wire tools. This produces closer shape matches but has the various drawbacks of hot wire tools. Ironically, the Hot Wire Foam Factory router tool doesn’t work as well as the “knife” tool. The router is too short and too thick.
  • Foam board aka extruded polystyrene rigid insulation is very slow to cut with hot wire tools. The Hot Wire demo videos all depict white foam “bead board” and are clearly the intended material. I will consider using that instead for future projects if I don’t need the structural feature of the rigid foam.
  • Polyurethane glue works a treat but squeezing the bottle (LePage 200ml) for long beads is hard on the hands. I have resorted to using a quick grip clamp as a squeezer.
  • T-pins are great for holding foam bits together while the glue cures. T-pin use number eleventy-one.
  • Fumes from hot wire foam cutting are unpleasant. duh.
  • Getting the pictured foam in along the back edge strongly validates the removable backdrop design. It would be a real bother to do from the front.
  • Ditto having the layout lighting working.
  • Glue instructions say to dampen surfaces prior. Choose a stable container for your water supply. Just sayin’…

I expect to have everything roughed in sometime next week and will probably roll straight into some final contouring with additional layers of foam and sundry coatings. I have a jar of Foamcoat I intend to try out in addition to the traditional Sculptamold.

Not a New Year Resolution

I have been struggling with hobby inertia in the last couple of months. It is just easier to sit down at the computer(upstairs) rather than descend the stairs to the shop and figure out what to do next. And the longer you are away, the harder it is to remember what that was and where you were at in it.

Late in December, I decided that I needed to reform the habit of regular effort. (Just ask be about workout routines, I am a master of starting those…) I have scheduled a daily block of time merely labelled “shop”. I am using Google Calendar so that it goes ping on my phone so I have less excuse to “forget”. The intent is to be in the shop or doing shop related things for at least that long.

I have taken the approach that anything done is good (barring fire and flood caused, of course) and that it will eventually produce results through accumulation. So far, so good. I have done a bunch of cleaning and reorganization, done some planning for the developing machine shop and made, at long last, some progress on foam scenery base for Comstock Road. The lighting update is one identifiable result.

I have more or less stuck to the routine and it feels like I am getting some forward progress. Hopefully I will have more discretely identifiable things to share in the near future.


Part of my recent experimentation with milling on the lathe involved cutting some steel bar stock roughly to length with a hacksaw. 1/8 x 3/4 bar wasn’t too strenuous but 1 1/2 x 3/4 was way too much like exercise. After considering the alternatives to just quitting, I settled on as cheap a horizontal/vertical bandsaw as can be got the imported 4×6, in my case, the Craftex CX122. Back-ordered during the “Black Friday” echo sales we get in Canada due to proximity to the US, I picked it up on the afternoon of New Year’s Eve.

Assembly was a bit of a challenge due to less than stellar documentation but I think I have it together correctly. I say think because the instructions included a list of required tools and a reference to a loose parts list but neither actual assembly instructions nor the aforementioned loose parts list. </rant>

Anyway, after a fair bit of squinting at the tiny exploded parts diagram and replacement parts list (all the parts of the entire machine, not just those to be assembled) I had a saw and no leftover parts. This, of course, required something to be sawn.

I chose a round bar of mystery steel offcut the metal vendor threw in with my first order because it was bent over part of its’ length. (I don’t want to be there when 1 inch steel bar gets accidentally bent!) Cutting off the bent bit is a useful thing and low commitment if things went pear shaped. I set it up and fired up the saw. After a good while, I had two pieces of steel and no catastrophe. I did realize belatedly that the drive belt was insufficiently tensioned and did correct that. That bit was in the instructions so was entirely my fault.

The cut is nice and smooth and reasonably straight and best of all, my arms do not feel as if they are going to catch fire or fall off. Metal working is looking more enticing already.