Restoring Engraved Lines

[Franko]

I've owned this wonderful old brass and wood caliper for decades.
The engraved lines on part of the scale are almost worn off.

I'd like to restore the lines, but I'm not sure how to go about it.
I could use a very small ball burr in my mill, or a graver or lathe tool by hand.
I have a carbide scribe, but I don't think I can match the other lines with it.
Any suggestions?

 

[RJSakowski]

I while back, I bought some carbide engraving bits on eBay for engraving a brass plaque. I used the 45 deg. (22.5 deg. each side) bit but you can get them down to a 10 deg. total included angle. They worked very well in my Tormach. I ran at 10,000rpm.

http://www.ebay.com/sch/i.html?_sacat=0&_nkw=engraving+bits&_frs=1

I wouldn't use a carbide scribe as it displaces the metal rather than cutting it.

Tormach makes a drag type engraver which would be closer to the original method of engraving.

If yu are thinking about it as an antique, modifyiong, sprucing up, and cleaning detract from its value. Personally, I do all that stuff as I am more interested in usable antiques but Antiques Roadshow cares.

Nice tool!

Bob

 

[Franko]

Thanks, Bob. I have some similar bits that are part of my Dremel tool collection. I would like to use the mill because of the control and precision it expedites.

I think I picked this tool up in the late 60's when I was working for a heavy hardware store, so I guess that makes it about 45 years old. I'm not sure about it's antique value, but it is a tool I like to use. I'll never sell it. It is very handy to stick in my pocket when I go to the metal supermarket or hardware store for stock and screws.

I think enough of it that don't want to make new marks that don't match the originals.

 

[Rex Walters]

Those fine little engraving bits really want high RPMs. I've been toying with the idea of mounting a dremel tool or router to the quill of my lathe so I get X-Y-Z table control (and DRO) but can still use higher RPMs (my mill tops out at about 2500 RPM).

I've also got access to an Epilog laser cutter, so I've been considering using that to etch some lines for a completely different project. I don't think it would etch very deep into brass though, and accurate fixturing/alignment would be tricky for refurb vs. cutting all new lines.

Not having to clean up any of the numbers was a nice bit of luck. The lines should be easier to repair. My project needs both (on a round rather than rectilinear part no less).

The hardest part about this kind of thing is not being able to experiment with techniques (tooling/speed/feed/doc/etc.). You've kinda got to get it right the first time.

It looks like the only worn places are by the nub where your thumb goes (which makes sense). For that half inch or so, if there's any groove left at all, I'd be tempted to just try my luck with an ink-pen (a technical draftsman's pen) and cover it with clear fingernail varnish for protection. At least that would be reversible if it all went to hell.

Regards,
-
Rex

 

[Andre]

I would use a small hand graver to cut some deeper lines then tarnish the surface with acid, to darken it then sand the brass with a sanding block to remove the tarnish from the top surface so the dark color is only on the line.

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[Rex Walters]

I would use a small hand graver to cut some deeper lines then tarnish the surface with acid, to darken it then sand the brass with a sanding block to remove the tarnish from the top surface so the dark color is only on the line.

That definitely seems like the safest way to engrave a few lines. My few attempts at engraving with a hand graver weren't terribly promising, but maybe Franko has a better hand. A hand graver takes skill (which I most definitely lack).

How would you make the lines straight and parallel? I guess you could use a straightedge, but I've never tried anything but freehand. Also, does acid darken non-ferrous metals? (Serious question, I've no idea.) For traditional engraving and inlay work, I think using a filler is more common.

I bought some hand gravers and engraving filler (a glorified crayon) from Luthiers Mercantile International. Maybe you will have more luck than I did with engraving. Soft brass might be easier than the mother-of-pearl I was attempting to engrave. It wasn't a complete disaster, but looks pretty amateurish to my eye. Fortunately it's only about the size of a quarter so most people don't notice!

 

[Andre]

Brass tarnished really easy with say citric acid from a lemon. Then let time do the rest of the darkening.

You could also use a sprig loaded center in your mill and use the machine ways to scratch a perfect line. Then use the graver or even a file to deepen the line.

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[hman]

There's a product called "liver of sulfur" that will blacken brass and copper quickly and easily. Originally, it was a solid, consisting of of sodium and potassium sulfides. I'm not sure what the currently available stuff has in it, but you can still get a liquid product that does an OK job.

 

[Franko]

I like the idea of tarnishing it and polishing it. That would make the other lines better, too.
I wonder if cold black would work?

I have some brass to practice with. I'll try one of the Dremel burs to see if it works.

I don't have a graver. I looked them up and they are out there, I just don't know what size and they aren't cheap. In the pictures, they all look the same. They look like they have a pie shape profile.

I could grind one using 1/4" tool steel. I've never hardened anything. Does it have to soak in heat, or can you just bring it to yellow or red hot and dip it in oil? (I have oil hardening rod)

I have some 3/8" high speed blanks and I imagine the corner would be about the right profile, but making a knob or handle would be more difficult than using the 1/4" rod.

I guess it would be possible to grind one from an old file.

 

[Rex Walters]

You should definitely try making a tool — I bought my graver before I got into metal working. It wouldn't be hard to manufacture something usable.

I wouldn't worry about hardening for such a small project on such soft material, but oil hardening a tool like this is trivial. Just heat it until the tip is cherry read, then dunk it in a can of oil (then polish away the black scale).

The acid/liver-of-sulphur on brass thing is something I absolutely am going to try. Thanks for the tips! I'm getting all sorts of wild ideas for my next inlay.

I've got liver of sulphur, but a better grade of bourbon might fix it.
--
Rex