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ACME
04-13-2006, 03:07 AM
hi,
pls tell me where can find "digital gear tooth caliper" or "Gear Tooth Vernier"(metric version) from internet shop, i want to get one...


thanks

Tel
04-13-2006, 04:44 AM
http://www.cvtech.com.au/estore/

John Stevenson
04-13-2006, 09:51 AM
If you want digital try here.

http://www.pj-tooling.co.uk/

.

JCHannum
04-13-2006, 10:07 AM
It appears that vernier is becoming the term for slide calipers.

I see that the link by Sir John sells digital verniers. I find it somewhat annoying when a vendor does not use the proper terminology for the items they sell. It tends to make you doubt their knowledge of their wares, and question any statements they might make about them.

Lew Hartswick
04-13-2006, 10:13 AM
A-men to JCHs comment about a manufacturer not using proper terminalogy.
Nothing will kill my acceptance of a product quicker.
...lew...

Rex
04-13-2006, 01:06 PM
I think most such terminolgy is to maximize hits from search engines. It catches people who know what they want (calipers, digital) as well as those who do not (digital vernier).
And sometimes it's a translation issue.

Evan
04-13-2006, 02:07 PM
Digital calipers operate on the vernier principle internally. They use two strips of capacitive "fingers" that have a very slightly different spacing on the moving strip vs the stationary one on the beam. This produces the signal that is counted by the electronics. They really are digital vernier calipers.

Wirecutter
04-14-2006, 12:18 PM
Evan, you're such a smarty-pants. :D

Actually, that's interesting info. It figures you'd be the one to come up with an archane tidbit such as that.

Paul Alciatore
04-15-2006, 04:46 PM
I love to disagree with Evan.

The Vernier principle is based on two scales that have a slightly different spacing. So far, so good. But they are used differently in a true Vernier caliper and in a digital caliper where they are used to generate electronic signals. The digital caliper does not look for the best alignment, it just interpolates the distance based on two or more different signals from multiple sensors.

In this sense, it is ultimately an ANALOG device at it's heart.

Of course I also insist that standard household Voltage (220VAC) is TWO phase, not single phase.

Break out the gloves, Evan.

Evan
04-15-2006, 10:28 PM
"In this sense, it is ultimately an ANALOG device at it's heart.

Of course I also insist that standard household Voltage (220VAC) is TWO phase, not single phase. "

Split phase, not two phase.

My explanation was terse but correct. The row of capacitor fingers on the beam could be revealed and compared visually with the shorter and slightly different spaced row in the read head. They would appear to function in exactly the same way that a plain vernier caliper does, because they do.

In particular, it isn't practical to make an encoder with discrete elements that produce a discrete impulse for every .0005" the head moves if it were to count a single element at a time as is done in many rotary encoders.

Instead it uses the vernier principle to produce numerous counts for a small movement as subsequent slightly out of line elements line up, just the same as a visual vernier caliper. If you were to count the alignments of the marks on a regular vernier caliper as it is slowly moved you would be doing the exact same thing that the digital vernier does.

This can be visualized by using two gratings with a slightly different line spacing. As they are moved relative to each other a rapidly moving moire pattern is seen. This principle is used in some optical measuring devices and is a variation of the vernier principle.

gmatov
04-16-2006, 04:42 AM
Evan,

I am not going to investigate this, but is it still a version of the Farand scale, or Farrand scale, as used on many larger, older, machines?

120 inch lathe, 60 foot centers, accurate to a thou or less. Horizontal mills, 18 foot column, 40 foot horizontal travel, accurate to a thou or less?

Vertical Boring Mills, 14 to 20 foot between columns, accurate to within a thou?

Actually, with an operator with some experience, I would say they were more accurate than the "set and forget" machines of today. A MACHINIST made a piece, checked it, went to the IE and told him he screwed up on his calculations.

I've seen a tape NC machine tear the turret off an 84 inch NC VTL because the programmers told the operator that they were right, he was wrong. He said, "OK, there's a 67 inch 2 ton forging on the table, you got it going to "Home", center of the table, with it spinning a hundred or more RPM, I'll punch the "Start" button, but I'm out of here!"

Man, that was a spectacular crash. Couple months to repair. IEs come up with numbers out their asses. You can't do the job, with average aptitude, in the time they calculate, they increase feeds and speeds, willy nilly.

Time study guys, IEs, suck. They can't get the job done in their calculated time, it's the bums on the machine who are to blame.

NC also hides operator error. The tape says this, the operator drills that, almost always a 1/4 inch off, not .013, but exactly .250, a turn of the dial, "I didn't do it, it's the tape, or the program."

I knew lots of operators who insisted that running any type of NC machine was harder than using the dials and indicators. They never ran manual machines. But, they knew their job was harder. Set and forget. It beeped for a tool change, man, this is a pain in the ass.

I hate to say that some of the posters, here, should buy a manual machine, learn to run it, then consider buying any NC machine.

Some of the pieces you have posted are beautiful, the "Cassowary", (I know, that's a bird, not a type of scope, that's Cassograin, or some such.)

Anyhow, some of you post very nice project pics. I am not in your class. I fixed these things, only ran them for about 10 years. What I do now, with the machines I have, or have bought, is for my own satisfaction.

Actually, were I good enough, and, should I use the word, "greedy" enough, (I am on SSDI and soon to take retirement, so greed would come in if I tried to make money while I was on SSDI, as well as being illegal, or, at least I would have to reimburse the SS for anything over XXX dollars per year, hell, might even get kicked off.

And, in my situation, I am not as some of you are, trying to make a living at this. Good luck to any of you who are. It is a cutthroat business. As much the buyer looking for a penny per piece less as for you trying to get a contract for a penny per piece less.

Good Greif!!!!

Cheers,

George

gmatov
04-16-2006, 04:54 AM
Ah, I should have mentioned that there was a 2 phase alternating current.

Tesla had all the phases covered. Actually, with Westinghouse's engineers, it is remarkable that Edison and DC didn't overcome. Inferior, but AC wouldn't work.

The Westinghouse "brains" insisted on 133 cycle, Tesla said 60, it did not work till they came down to his criteria. And then, GW killed Edison on the "War of the Currents"

I forget how many phases there were in his original stipulations, more than 3, I know. That's why it's called "polyphase.

220 is 2 110 volt lines, in synch, not 2 phase.

Cheers,

George