caliber to mark metal

[Eloy Workshop]

[DIYer]

Thanks Eloy Workshop! We've added your Caliper Modification to our Scribes, Awls, and Marking Knives category,
as well as to your builder page: Eloy Workshop's Homemade Tools. Your receipt:

Caliper Modification by Eloy Workshop

tags: scribe, adjustable

[ACinSV]

So - note that it's not a video about how to modify a caliper, it's a demo video showing a product you can buy that's a modified caliper - still cool! :-) It's also in Spanish, that is, Spain Spanish, and the link is to Amazon.es, and the product's not shippable to the US, nor is it sold on Amazon here by that mfg. HOWEVER -- with a little searching, I found the identical tool on Amazon from another mfg. It's obviously European, and thus in metric only, but I LOVE this idea -- seeing as how I keep my old cheaper caliper for scribing metal so I don't thrash my nicer one doing that (I make knives and scribing hardened steel is a good way to wear off the outer point real fast and make it lousy inaccurate.

Link (no, it's not one of those where I make money off it, shoulda thoughta that, although I just realized it does donate a little cut to a kids' charity - but doesn't cost you any more :-))

https://smile.amazon.com/Betfandeful...gateway&sr=8-3

[Masterjuggler]

I imagine if you wanted to make this, a regular HSS bit wouldn't be enough to cut through if it's properly hardened steel. Which is actually pretty likely, I've had trouble drilling through a horrible freight caliper. Probably the easiest thing would be EDM if you have access to such a machine.

Short of trying to do something like that, it would probably just be easier to grind down the outside of the top jaw some to bring the tip back, to make it parallel when marking like the image with the green check mark. Also probably lightly smooth the edges on the inside of the slide jaw so it doesn't scrape against the work as much.

Guess that's another small project on my list lol.

[Tuomas]

Yep. Its a demo video.
I have that kind of similar marking skribe... and many times i have answered to comments like " you shouldn't use caliber for marking ".

Here those are very common tools.

[Tuomas]

I imagine if you wanted to make this, a regular HSS bit wouldn't be enough to cut through if it's properly hardened steel. Which is actually pretty likely, I've had trouble drilling through a horrible freight caliper. Probably the easiest thing would be EDM if you have access to such a machine.

Short of trying to do something like that, it would probably just be easier to grind down the outside of the top jaw some to bring the tip back, to make it parallel when marking like the image with the green check mark. Also probably lightly smooth the edges on the inside of the slide jaw so it doesn't scrape against the work as much.

Guess that's another small project on my list lol.

You don't need to make a hole. Grinded / filed groove on the backside and a screw with washer to hold the scriber would work as well.

[Masterjuggler]

You don't need to make a hole. Grinded / filed groove on the backside and a screw with washer to hold the scriber would work as well.

Wouldn't you then still need to tap threads into the hardened steel? At the very least, my cheap taps can't do that.

[Tuomas]

Wouldn't you then still need to tap threads into the hardened steel? At the very least, my cheap taps can't do that.

Yep. But its doable with quality taps. I have fixed one by making bigger hole and re-threaded it.

Backside of my marker looks like this:


Those marking scribes are about 10-20$ here in hw-stores, good ones. Of course there is "premium" models too.

[ACinSV]

I imagine if you wanted to make this, a regular HSS bit wouldn't be enough to cut through if it's properly hardened steel. Which is actually pretty likely, I've had trouble drilling through a horrible freight caliper. Probably the easiest thing would be EDM if you have access to such a machine.

Short of trying to do something like that, it would probably just be easier to grind down the outside of the top jaw some to bring the tip back, to make it parallel when marking like the image with the green check mark. Also probably lightly smooth the edges on the inside of the slide jaw so it doesn't scrape against the work as much.

Guess that's another small project on my list lol.

Tuomas points out lower down that grinding a slot and using a retaining clip is a better idea than drilling a hole, and I agree for several reasons - more in a sec. But I do want to point out that drilling a hole in hardened steel isn't all that difficult with a good, preferably stub-length, cobalt bit. You also must have the workpiece held securely, use cutting/tapping fluid, use the right cutting speed for the drill diameter, and drill at the right rate (which is not only not too fast but not too slowly). It's actually not that (ahem) hard, you just need to use good technique. Cobalt bits are very brittle and will break easily if the workpiece is not held very securely, or if there's not good lubrication. I do it somewhat often on hardened knife steel (usually 80CrV2, sometimes 52100) with very good results.

The reason the groove is a better idea - well, there are several. First of all - in hardened steel, the above notwithstanding, never drill, i.e. try to cut it with another hardened steel, when you can grind, i.e. use a much harder abrasive. Second, if you're drilling, you have to get the hole exactly right, or figure out some way to adjust/calibrate the caliper, or the whole (ahem) point of using a caliper to get the measurement right is gone. Or you'll have to add/subtract an 'offset' error amount every time you use it, or transfer a measurement from a rule :-(. Or have an oversize hole and/or undersize scribing bit with a set-screw of some type, and that's got its own potential problems.

The advantages of the slot are several, the greatest of which is its adjustability, particularly for calibration, not just up and down, but in and out, to get the measurement exact. Note: you'll want a scribing point that's flat-ground offset to the "inside", so that it exactly meets the inner jaw, as in the pictures, not centered like a pin-punch. Easy to make from a drill bit, piano wire, or other precision-size piece of tool steel. Note 2: you can also use a pencil lead for marking! :-)

As to the inner jaw - I'd be cautious about 'bringing it back' / rounding it - you want to think very carefully about the implications for accuracy. I'd - and this is only my initial thought/one solution - put some Sharpie/blue marking dye on the blade and make sure not to grind off the middle material, only round off the edges. I'd also try to be careful to keep that grinding 'vertical', i.e. remove a very uniform amount from top to bottom of the blade - can't quite think of why that matters right now, but seems like a good idea for some reason other than just neatness.

[Masterjuggler]

If cobalt works well on already hardened steel then I'll have to pick up a set. That's a good point about trying to get the hole in the right spot though, I also imagine it'd be easier trying to grind a precise slot. If you were to grind a slot and widen/shim it to tweak the distance, you'd need some way of pushing the scribe bit up against the side of the slot so it doesn't seat at an angle. Really that should be done anyway, but in a slot ground to just the right width it's less of an issue.

In a pinch, the edge of the scribe could also be beveled slightly on the inside to account for it being too close to the jaw, but that wouldn't last between sharpenings.

As far as rounding the jaw, I really just meant breaking the edges so they aren't sharp and scratchy. You'd still need to keep the caliper perpendicular to the edge of the work anyway, or you'd be scribing to the distance times the sin of the angle, so I'd think it doesn't need to be a round jaw like in the OP.