Making a Marking Gauge
Above: Gauges made by Ian Wilkie. Left: pin gauge made from sheoak, right, cutting gauge made from ringed gidgee.
Words and photos: Ian Wilkie
A marking gauge doesn’t have to be pretty or particularly sophisticated to do its job. the essential features are that the beam locks firmly and squarely in the stock, and the pin or cutter is sharp enough to set accurately and scribe a fine line. However, if it happens to be made of some beautiful wood, and is resplendent with polished brass, who is likely to complain?
1. The author’s early model gauges made from sheoak with brass strips in the stock faces and wooden thumbscrews.
The brass work is functional as much as decorative, and very early in my marking gauge career, I tried inlaying some brass wear strips on the face of the stock. As my guide, I had a cheap beech example which had two strips of brass about 6mm wide dovetailed into the face of the stock as on the sheoak (Allocasaurina torulosa) gauges in photo 1, which, apart from the wooden thumbscrews (the original was plastic) are close copies.
A small dovetail bit can be used to make the slots. I hacksawed out a couple of strips of 1/8” brass and went to work on them with a file, judging the slope by eye, and testing for fit as I went. In minutes I had each piece sliding neatly into its slot. these were pinned with a single screw through the centre, and after sanding to level wood and brass, the edges were all seamless. I was pleasantly surprised at how easy it was.
One problem any would-be maker faces is how to lock the beam in the stock. Ways to do this include low-tech wedge systems, cammed beams which lock when twisted, and thumbscrews. For my earliest gauges I used wooden thumbscrews. these have the advantage of not needing a protective shoe when bearing against hard woods. Despite years of use, the gauges in photo 1 have virtually no marks on their beams, unlike beech examples I’ve seen, which had deep grooves worn in the beams by their thumbscrews.
Stocks on commercial gauges are usually 24–28mm thick with a 50mm or so square face. this gives the stock enough width to bear against the reference edge, without making it too bulky. However a little more width in the bearing surface, and a little more depth below the beam are helpful.
2. Ian Wilkie with gauges of various sizes that he has made.
My preferred dimensions for daily users are around 66mm wide x 55mm high for stocks, with beams about 16–18mm square and 200mm long. I also make the stocks a little thicker (around 30mm), partly to keep it in proportion, and partly to have a deep mortise to hold the beam firmly. this seems a good size, and makes a comfortable handful. I have some handy smaller gauges and I’ve also made a couple of monsters for when I need lots of reach, such as the panel gauges in photo 2.
3. The metal patch glued on the end of the beam protects against wear.
On my early gauges I glued a metal patch on the end of the beam to protect it against wear caused by rubbing on the workpiece (photo 3). pin gauges present no problem, just drill a pin-sized hole through the metal, then a slightly undersized hole in the wood and drive the pin far enough in to hold it firmly.
Cutting gauges require a bit more work, depending on how you make the cutter. A flat cutter like the one illustrated (a piece of recycled hacksaw blade) requires a flat surface to bear against. that means drilling, chiselling, and filing, to make a tapered, flat-sided slot in the end of the beam. It works well enough, provided the slope of the wedge is shallow enough to hold firmly, but it takes some fussing and fettling to get everything right.
4. On the left a grub screw holds the cutter, while on the right a thumbscrew secures a pencil.
A neater solution is to fix a brass end on the beam by means of a stub tenon (photo 4). I made one like this to hold a pencil, but the same principle works for pins and cutters, if the cutters are made from a rod with the cutting blade formed on one end. the pencil gauge uses a small thumbscrew, because the pencil needs pretty constant attention, while pins and cutters are retained by a slotted grub screw (left in photo 4).
This system works well, the only downside is you need to make the brass caps. If you don’t have access to a metal lathe with a 4-jaw chuck, you could fabricate the ends with a piece of square bar and some brass thread rod.
Making a gauge
I will go through the steps of making two gauges, excluding the turning of the metal parts. one gauge will be fitted with a cutter, and the other with a point. I’m using two different arrangements for the thumbscrews.
5. The ring gidgee parts on the left will be a cutting gauge while a pin gauge will be made from the sheoak parts on the right.
The ring gidgee (Acacia aneura) gauge on the left in photo 5 will have my ‘standard’ 10mm brass insert for its thumbscrew fitted to the top of the stock, and a cutting blade. The sheoak and parts on the right are for the pin gauge. Instead of a double-threaded insert, the brass dowel sitting on the stock has been threaded for the thumbscrew. the end-caps for the beams have a half-dozen turns of thread on the 6mm stubs to help lock them in place. there are also two pieces of 3.2mm plate for the wear strips, and some 1mm thick plate to make the ‘shoes’ to protect the beams from the brass thumbscrews.
Having the thumbscrew on the top of the stock is convenient, and if the grain of the stock runs lengthwise, you have the best orientation for holding the threaded brass insert solidly. The threaded insert isn’t absolutely necessary in hardwoods like these, because they will accept very good internal threads across the grain, but the brass inserts should never wear out. the threaded dowel is necessary on the sheoak gauge, because the thumbscrew will be on the side (not enough room above the beam). Any threads tapped directly into the wood here, would be into endgrain, which results in very poor threads in wood.
6. Ian’s screws are made from 16mm bar with M6 threads. The matching inserts have M10 outerthread. Thecross-dowel screw on the right is easier to make but harder to fit.
Small thumbscrews and matching brass inserts can be bought but are not ideal. the small 1/2” diameter head makes it difficult to tighten firmly, and the coarse 20tpi thread does not lock easily. I prefer to make my own screws from 16mm bar with M6 threads,
and matching inserts with M10 outer thread (left, photo 6).
The finer M6 thread (25tpi) and larger knurled head give a screw that locks firmly. I am trying the cross-dowel method (right, photo 6) because it is marginally easier to make than the insert, though it will require me to drill two perfectly intersecting holes.
I do as much to the wooden parts as I can, before committing to glue-ups.
7. The hole in the beam for the end cap has to be centred and perpendicular.
I first drill the centre hole in the beam for its end cap. I leave the beam over-long, sothatifImessuptheendhole,Ican cut a bit off and do it again. The centre of one end is marked very carefully before the beam is set up in a vice on the drill press taking care the hole is centred and perpendicular (photo 7).
8. The end-cap should fit snugly and squarely.
The beams start out about 1.5mm oversize, leaving room for any small error in centring the hole, but not too much to trim down after the glue has set up. The end-cap should fit snugly and squarely (photo 8).
9. Drilling a hole through the stock where the beam will be placed.
After routing the channel for the wear- strip, the next job is to fit the screw insert. To make this easier drill a hole through the stock where the beam will be placed (photo 9). This allows the taps to clear and cut very clean threads. Get rid of as much waste as possible, without getting too close to the eventual edges of the mortise.
10. The insert top of the insert is left proud then levelled with a file and sandpaper
The stock is set up in a vice, so drilling and tapping can be completed without moving it. Drill a hole for the tap and then use the drill-press to start the tap straight and square. I found that using a No.2 starter tap, followed by just a couple of full turns with the full-size tap gives a thread that starts easily, and tightens as the insert is screwed home, needing no glue. The top of the insert is left a teeny bit proud so it can be neatly levelled with a file and sandpaper (photo 10).
11. Threaded dowel fitted in the sheoak stock.
Fitting the threaded dowel in the sheoak stock is straightforward. To give the screw some clearance, I used a 1/4” bit (6.35mm), which allowed for slight mismatch of the two holes (photo 11). This gave an easy fit, without being sloppy. The dowel was made to be slightly proud of the faces, and will be sanded flush along with the wear strip later.
Fitting the wear strips
12. Cut the wear-strips the width of the channel, then draw-file a bevel on each side.
Cut them close to the width of the widest part of the channel, then draw-file a bevel on each side, testing frequently, until they slide in without excessive force (photo 12). Because it is so narrow (less than 3.5mm), you can be several degrees off with the bevel and still not have any visible gaps. If you cut the strips accurately, you’ll only need to bevel the sides. It took literally less than a minute each to fit these strips.
13. The tiny gap in one corner will disappear after sanding.
Photo 13 shows a tiny gap in one corner where the file slipped off the edge, but after sanding smooth that will disappear. With the fitting now done, I glued in the wear strips and the end caps on the beams with an epoxy glue.
Pins and cutters are made from 1/16” and 1/8” bright steel rod or you could use the ends of broken drill bits. Most drill bit shanks are soft compared with the cutting end, but usually not soft enough to file, whereas bright steel is easy to deal with. It comes annealed and is easily worked with a file. to form the ‘blade’ on the cutter, I first file a flat on one end, then bevel the back to form two rounded knife edges coming together in a flat point. once roughed out, I heat the ‘working’ half to bright red with a MAPP torch and quench in water.
I don’t bother trying to temper the hardened steel, it doesn’t seem to be too brittle. After hardening, the oxide is cleaned off with fine emery cloth, and the cutting edges sharpened with stones and a very fine diamond file. to make a pin, chuck a short piece of 1/16 rod in a battery drill, and file the point while spinning it.
14. Finished pin and cutters, one polished and sharpened, one straight from the torch.
Photo 14 shows a finished pin and a pair of cutters, one polished and sharpened, the other straight from the torch. Once the glue for the metal parts has cured, I file any excess metal from the wear strip and insert, and prepare the beam. I cut the beam about 1.5mm larger than the 16mm square brass caps, so there’s a smidgin of wood to clean off each side, bringing the beam to an exact match with the brass.
15. Plane the beam close to the brass, then carefully sand off the excess.
I plane the wood as close to the brass as I dare (photo 15), then carefully sand off the rest. the simplest way to do that is to stretch a couple of grades of coarse paper over a flat surface. I use a piece of cast-off counter-top, with a cleat screwed on each end to hold the paper.
16. While planing keep checking the beam is square and the sides parallel.
Wearing a rubber glove makes it easy to hold the wood without slipping. I constantly check the beam remains square and the sides parallel (photo 16).
17. The brass cap quickly shows if you are sanding too much off one side.
The brass cap is a guide, and quickly shows if you are sanding too much off one side (photo 17). The beam sides must also be parallel, or it will not slide smoothly in use. I round the corners over to make the beam hand-friendly, and sand to the finest grit, because it needs to be at its finished dimensions for the next step.
Fitting the beam
18. Make sure the sides, top and bottom of the stock are parallel and square to the face.
This is the crucial element in making a gauge that works well — aim for a beam that is perfectly square to the stock, slides firmly without binding, and sits rock-solid when the thumbscrew is tightened. First make sure the sides, top and bottom of the stock are parallel and square to the face (photo 18). there is no need to finish-sand yet, just get them flat and square at this stage.
19. Marking gauges are handy for marking out the stock mortises.
Marking out the mortises on the stock (photo 19), is a job where a couple of my small marking gauges come in handy. Depending on where you place the thumbscrew, allow an extra millimetre for the protective shoe. the width is the critical dimension for a top screw gauge, you don’t want the stock wobbling from side to side when you use it. I mark out about a millimetre under-size for that dimension. this gives me a tiny bit of wood to file away so I can clean up any chisel marks, and sneak up on a perfect fit.
The mortise for the sheoak gauge was marked out to accommodate the shoe on the side, not the top. I mark both sides so I can attack the mortise from both faces, reducing the risk of splits at the edges. the waste is chiselled out to the lines, and then the file comes into play. I use a 150mm double-cut bastard file with its edges ground off so it won’t cut into the sides.
20. Bend a small lip on some 1mm brass plate for the ‘shoes’.
Before test-fitting the beam with the thumbscrew, I made up the protective brass shoes. these need to be kept in position when the beam is slid back and forth. the simplest solution is to bend a small lip on the ends of some 1mm brass plate (photo 20).
21. On this gauge the top of the stock was treated a little more decoratively.
If shaped and polished, the lips look neat, and have a bonus effect of covering the slight gap above the beam when the screw is tightened. Another way is to attach a small spigot that engages the inner end of the thumbscrew hole, as I have done for the sheoak gauge. the groove in the front of the lipped shoe allows the cutter to close up to the stock face. Once the beam is fitted, the top of the stock is shaped. You could let your imagination run wild, but I generally don’t, preferring a simple rounding-over though I occasionally try different shapes (photo 21).
The stock is now ready for final sanding, followed by a rub-down with 0000 steel wool and the application of a suitable finish.
the brass can be left with a flat sheen off the steel wool, or buffed to a gloss. Use a thin shellac-based finish, or perhaps a penetrating oil, so you don’t alter the fit of the beam. I use a coat or two of Ubeaut Shellawax, then buff it off with a cloth wheel. the inside of the mortise gets a good waxing.
Ian Wilkie is a retired veterinary pathologist and academic who makes furniture and hand tools. His interest in wood and tools goes back to growing up on a farm where fixing and making things was part of everyday life. In issue 99 he wrote about making an infill shoulder plane.