Surface Gauge scribe material ?

[jcfx]

I got an old General Tool surface gauge that I'd like to make a scribe for, it's got an odd sized clamp that takes
a .093" diameter scribe, I'd like to make one that has a straight and 90º point. Researching
it seems tool steels don't like to be bent, looking around McMaster the only thing the right
diameter is spring wire which can be bent, what else would be a decent steel to use that
would be bendable and hold a point to work as a scribe ?

[Steggy]

Get a piece of C1144, grind your point, form your bend using heat (you may be able to cold-work the steel, but carefully examine it for cracks) and then heat-treat it. C1144 generally hardens to Rockwell 25C after a quench in oil from 1550°F, followed by drawing at 1000°F. The resulting piece will be hard enough to scribe most metals, but not brittle to the point when the point will be easily damaged.

An alternative would be to make your piece from hot-rolled C1045, which can be cold-formed. Use the same heat-treat regimen as for C1144, but quench in water. Final hardness will be Rockwell 20C or thereabouts.

Hot-rolled and annealed alloys such as 4130, 4140, 4340 or 8620 could be used if you can get a small quantity at a reasonable price. Heat to 1550°F and oil-quench. Drawing is not a requirement. Finished hardness will be Rockwell 50C or better.

[Harold_V]

Make life easier. Use a drill blank. Already hardened and sized to your needs. HSS is difficult to anneal, so heating for bending won't alter the hardness significantly, if at all. Just make sure to let it air cool after shaping. If you insist on quenching, make it oil, not water.

You can shape the scriber by inserting the drill blank in a drill motor, which you would then hold against a belt sander. With the drill motor running, a nice, uniform shape can be generated easily.

H

[Kay_B]

And what is the best way to heat the metal? A gas burner provides heating in one zone, and yet, at the place of heating, the properties of the metal can change. Very often, the metal becomes more brittle after heating. Although, a lot still depends on the quality of the metal. But I prefer to think about all such moments in advance.

[Wolfgang]

Of course one could use the old stand-by material, O-1 or W-1 tool steel, which should be easy to obtain in the required diameter.
File ends to a point, then heat treat by heating the pointed end with a propane torch. Play the torch over the steel to prevent local overheating. Stop heating when a magnet will no longer attract the steel, and plunge the embryo scriber into warm oil (salad oil is OK) in the case of O-1 steel, or into warm water in the case of W-1 steel. Carefully polish the hardened end and reheat it with a small and gentle flame until you see a straw colour appearing on the steel. Stop heating and let air cool.
Sharpen the pointed end on a grinder, dipping the tool often into water to keep it cool.
Voila, a perfect scriber at Rc 60 - 62 which will last a long time before re-sharpening is required.
BTW, the curved end of the typical surface gauge scriber is a touch probe. It is used to touch off a surface, the height of which may then be measured with a scale held vertically up against the scriber curved point. This feature is from the days before height gauges were common shop tools.
One more thing. When grinding a scriber point, or centre punch, be sure that the grinding marks run axially with the tool, NOT circumferentially.

Wolfgang

[jcfx]

All good steel suggestions, unfortunately McMaster only has .093" sized rods which are W1 steel
which is what I thought of using, I'll give that a try, it's cheap enough from McMaster if I group other stuff with it
otherwise the shipping would nuts for a $300 item.

Wolfgang, you got me confused over axially vs circumferentially, I would be grinding a round rod wouldn't that be the same ?

[armscor 1]

As Harold suggested drill blank is an excellent choice, used it on my home made surface gauge and holds up well.

[jcfx]

Normal drill blanks aren't long enough in small diameters, the W1 and O1 I found on McMaster is described as a drill blank .

[Bill Shields]

Drill rod as opposed to drill blank is what is probably being described by Harold. I used his recommended trick in an electric drill to make the points prior to bending

I had a surface gauge of that size and drilled the clamp out to handle .125 drill rod.

I heated it with my old stand by the oxy torch and formed it around a piece of round stock.

Typical blacksmith but been using it for best part of 40 years.

[pete]

Axially just means the grinding marks run the long way on a shaft. You'd present the shaft being ground in line with the wheels face but be grinding on the wheels normally used edge. Spin your part and hold it at the half angle of the point taper on the wheels edge. I didn't know it for years, but when resharpening prick and center punch points, that axially ground method is the one recommended. The grinding marks running that way help to displace the material being punched and flow a bit better. A small detail, but one still worth knowing about.

[Harold_V]

Drill rod as opposed to drill blank is what is probably being described by Harold.

No, I meant drill blank, as they are heat treated, unlike drill rod. They are also HSS (or cobalt), very unlike drill rod.

I used his recommended trick in an electric drill to make the points prior to bending

Works a treat, doesn't it? I made a replacement point from a 1/8" drill blank for my Starrett scriber using that technique. I happen to have a lot of extra drill blanks, including the 1/8" diameter needed for the scriber.

To be clear, just as long drills are available, so, too, are long drill blanks. The difference between drill rod and drill blanks makes it worth the effort to obtain the blanks. That may not be true for others, however. We each dance to the music we hear.

H

[Kay_B]

Of course one could use the old stand-by material, O-1 or W-1 tool steel, which should be easy to obtain in the required diameter.
File ends to a point, then heat treat by heating the pointed end with a propane torch. Play the torch over the steel to prevent local overheating. Stop heating when a magnet will no longer attract the steel, and plunge the embryo scriber into warm oil (salad oil is OK) in the case of O-1 steel, or into warm water in the case of W-1 steel. Carefully polish the hardened end and reheat it with a small and gentle flame until you see a straw colour appearing on the steel. Stop heating and let air cool.
Sharpen the pointed end on a grinder, dipping the tool often into water to keep it cool.
Voila, a perfect scriber at Rc 60 - 62 which will last a long time before re-sharpening is required.
BTW, the curved end of the typical surface gauge scriber is a touch probe. It is used to touch off a surface, the height of which may then be measured with a scale held vertically up against the scriber curved point. This feature is from the days before height gauges were common shop tools.
One more thing. When grinding a scriber point, or centre punch, be sure that the grinding marks run axially with the tool, NOT circumferentially.

Wolfgang

Thank! Described in great detail and sensibly. And it really makes sense to heat up gradually. I just do not have much experience in working with metal (namely with heating and subsequent change in shape), so I didn’t guess it myself. Do you think it is worth trying such repeated heating first on some unnecessary piece of metal? To try out the technique and fill my hand.