01 April 2015

Remaking a Chinese Made Marking Gauge

This project started out with a no-name marking gauge. It's not a branded tool which is an indication of its origin and a marketing ploy. It can be bought through a well established retail chain in the USA under its own label, but it originates from this factory. The same tool can also be bought in other countries putatively under different brands.

This establishes this tool as a commodity and with that in mind I set about to refining it suit my needs better with some modifications. A user review can be read here, which is overall positive. The positives that I note of the marking gauge are its substantial cutterhead which is held in place with a flush screw to the beam and which can be fully retracted into the headstock. This makes transferring measurements easy and accurate, much better than having to use a rule to set the cutter distance from the headstock. There are, however, two grating shortcomings of this tool.

The first is that the thumbscrew sits so close to the headstock that it can be difficult to get enough purchase with fingertips to tighten to the beam. This is compounded by a general problem with all marking gauges: slippage. The end of the thumbscrew has a small surface that presses against a polished rod's curvature, making the thumbscrew in this arrangement a very flawed design feature.

I set about tackling these problems by reducing some of the metal. The trick is figuring out how to do so safely and with precision. I thought I recalled another weblogger mounting a beam in a jig so it could be placed against a grinding wheel in a controlled manner. I did some searching but came up empty. I decided to go for broke. Even though the graduations on the beam are nearly illegible and without a reference point on headstock are also useless, I decided to be prudent, nonetheless, and to file a flat off the beam on the opposite side.

I didn't have any blue layout dye so I use a black permanent marker and then drew two closely spaced parallel lines, using a knife and a straightedge. I then made up two blocks of pine with vee channels to hold and protect the beam in the vise jaws. I set the beam in the blocks firmly with the scribed lines as upright as I could and began filing. The permanent marker proved to be not so permanent when I flipped the beam end for end but just enough of the reference lines remained. I filed down long enough to create what I think will be a sufficiently wide flat for the thumbscrew to bear against. I thought it better to not polish the flat since the filed surface would make it easier to line up the flattened surface with the thumbscrew. I then went ahead to work on the headstock.
Filing applied to one half
A flat filed along the full length

I tried the same permanent marker on the headstock but this proved to be even less effective. I planned to use a grinder with the face of the headstock against the toolrest. This made it necessary to scribe a straight line perpendicular to the axis of the thumbscrew over a contoured surface. There was no way to establish such a line so I ground down slowly and replaced the thumbscrew occasionally in order to check that the edge was square to the top of it.

I learned that the brass of the headstock is very soft, almost too soft to be an effective tool. Perhaps not surprisingly the manufacturer's website refers to headstock metal as copper. This doesn't appear to simply be a bad translation. I didn't so much grind off the metal as rub it off. There were no sparks and when the alloy heated up, I learned how the wooden handle is attached. A set of left handed threads squeezes it in place. It would be a simple matter to make a replacement of a preferred wood or with different contours if a user is so inclined.
Left handed threads on the butt of the headstock

There is also an accessory for this marking gauge, a double cutter for marking mortises. I advise against it. The small face on this gauge makes transferring two marks even more likely to create inaccuracies. It also requires the use of multiple brass washers as shims to establish the width. Other manufacturers have devised much better solutions for this function.

I am satisfied with the results. I would not suggest that somebody buy this marking gauge simply in order to go through what I did unless he is in China and Taobao is the best local source for handtools. Dating myself, I come across so many better made handtools today than when I began this craft. It's manifestly better to support those manufacturers or to delve into toolmaking oneself by making one or a few from scratch and scraps.