Does watching YT scribing make you cringe?

The line is not the final mark...

It is a reference.

If you are cutting to length one will cnfirm by measuring the work.

Drill bits wonder more than the scratch error.

For hobby level work the error in method is far less than the tolerance of most hobby work for the specific task.

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@rwm Ergonomically it is easier to stay perpenticular to the sides with a hermaphrodite caliper, but that's jus a nit. Either way, using one caliper or the other will yield similar results. I'd use the really cheap ones to make my marks, but 1) I don't have a set, 2) cheap ones a very soft, and then damages is inevitable. As I stated before, after hundreds of scribe marks, no damage to my Mit vernier, nothing visible, even under a microscope.
 
higgite said:
I saw an Amazon ad for some Mitutoyo hermaphrodite calipers that actually says “Measures in both inch and metric units for versatility of use.”
https://www.amazon.com/Mitutoyo-950...=hermaphrodite+caliper&qid=1615216058&sr=8-29

I almost bought them, but I’m holding out for some that only measure in inches so as I don’t get too confused.

Tom
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My vernier version of hermaphrodite caliper manages to offer both inches and centimetres. :)
The possibilities for confusion do, to some extent, remain.
vernier scriber.jpg

Notice the inches scale is divided 1/128" instead of 1/1000", or 1/500", which is maybe sensible given scribe line thickness.
The metric 0.05mm is about 0.002". The imperial 1/128" is nearly 0.008"
I guess it more easily suits fractiony stuff in inches.
@tq60 is right in that the scribe line is to guide the eye when cutting. After that, you measure on the work directly as you go.
 
higgite said:
I saw an Amazon ad for some Mitutoyo hermaphrodite calipers that actually says “Measures in both inch and metric units for versatility of use.”
https://www.amazon.com/Mitutoyo-950...=hermaphrodite+caliper&qid=1615216058&sr=8-29

I almost bought them, but I’m holding out for some that only measure in inches so as I don’t get too confused.

Tom
Click to expand...
While checking the advert, I noticed that there was an associated scale (ruler) that was also calibrated for Imperial and Metric. Metric must have been on the backside, I can't figure out how they got the point four of 25.4 out of /64ths. In any case, by buying the scale along with the calipers, you could get measurements in inches without confusion. Unless, of course, you had the scale turned over by mistake.

I had a buddy who had some insight into such measuring. He would measure with a micrometer, mark the cut with chalk, and cut with an axe. I personally would have used a torch, but such differences is what makes the world go 'round.

.
 
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OK, just for giggles to see what the error actually is. I figured using the caliper set to 2 inches and used a 1/16 hook over the edge.
The distance of the scribed line from the edge would be 1.999. Only an error of 0.001 inch. If you are machining to that scribed line or center punching for a hole it is dependent on how good you are at eyeballing that line. I am betting that spending an hour to lay it our "correctly" (Clear off the granite, clean it, get out the tools, set up and scribe the line, put the tools back away, cover up the granite) and then eyeballing the final machining will not get you any closer to the desired result. If you are not eyeballing the the final machining then why did you need the line in the first place?

The more you hang over the edge the more the error, the shorter the caliper set distance the greater the error, so everything is variable.
So even with the hermefrodite caliper, if your overhang varies 1/16" over the length of the scribed line, then you still have the same error as the veneer did. And with either letting the tool drift to not being perfectly perpendicular to the scribed line and the edge of the part will also add even more error.

I am now convinced that error is not a valid concern for whether or not to use a calipers for scribing a line in ink. As many have also pointed out that even under magnification there is no detectable wear to the calipers after many many years.
 
In our world, there is nothing absolute. As has been well pointed out, when we have to get it running, we will do what it takes. I have done things with my tools that I would normally never think of but in production, time is money. It isn't just the loss of product but all the workers standing around and the bills continue.

It all depends on where you are and what you are doing. Would I misuse a device that is for making precision tooling or doing measuring to confirm spec, no. Would I have one of those tools out on the floor for maintenance work, probably not.

Now for the home shop, I don't see the need to abuse precision tools. That said one has to define "precision tool". It is a term used pretty loosely.
 
Flyinfool said:
OK, just for giggles to see what the error actually is. I figured using the caliper set to 2 inches and used a 1/16 hook over the edge.
The distance of the scribed line from the edge would be 1.999. Only an error of 0.001 inch. If you are machining to that scribed line or center punching for a hole it is dependent on how good you are at eyeballing that line. I am betting that spending an hour to lay it our "correctly" (Clear off the granite, clean it, get out the tools, set up and scribe the line, put the tools back away, cover up the granite) and then eyeballing the final machining will not get you any closer to the desired result. If you are not eyeballing the the final machining then why did you need the line in the first place?

The more you hang over the edge the more the error, the shorter the caliper set distance the greater the error, so everything is variable.
So even with the hermefrodite caliper, if your overhang varies 1/16" over the length of the scribed line, then you still have the same error as the veneer did. And with either letting the tool drift to not being perfectly perpendicular to the scribed line and the edge of the part will also add even more error.

I am now convinced that error is not a valid concern for whether or not to use a calipers for scribing a line in ink. As many have also pointed out that even under magnification there is no detectable wear to the calipers after many many years.
Click to expand...
Tilt sine error, while theoretically there, was always so tiny it was never the issue.
It was the pressure under sharp points grinding away on a measuring instrument. Maybe unreasonable, but it rucks up my psychology.
Not nearly so bad as seeing the caliper as a handy adjustable spanner, which would be so gross, it would provoke more than a cringe that nobody would question. Umm - has anything like that been tried? Noooo - you kiddin'me!
 
I am sure that calipers have been used as an adjustable wrench, just like micrometers have been used as a C-CLAMP. :face slap:

Scribing a line in ink is nowhere near the other possible abuses that can happen. I am guessing the the pressure used to scribe a line in ink is less than the pressure used making a measurement as the tool is designed for. especially as you slide it around with finger pressure to get it all square for the most accurate possible measurement.
 
Papa Charlie said:
In our world, there is nothing absolute.
Click to expand...
I used to think that - but now?
After the struggles with knowing that even now, placing anything on this planet was always a matter of knowing the exact time (Longitude), we now have it that no fundamental units depend on any physical artifact any more, and our standard for length is based on the speed of light.

That being a speed, requires then we have a pretty good standard for what is a second. The clock makers have finally won! It used to be the NIST standard was good to one part in 10^15. They eventually got a second accurate to one in 300 million years. Now this has been surpassed, and nobody is really sure how accurate it is, but may well be less than a second in a time that exceeds the known age of the Universe!

With what I have, I still try to make it as good as I can get it. I have some stuff that is unnecessarily more precise than it needs to be :(
 
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