Gear Caliper

I picked up a starret one of these, I think on ebay - but I watched for a long time before one went cheaply enough to just have around. Now, truth be told, I haven't needed to use it yet...

It depends on what you want to measure.

The only thing that they are good for is measuring the thickness of the tooth at the pitch diameter.

What it does is it allows you to set a stop precisely to control how deep the jaws go prior to measuring the width -- so you do it at the pitch diameter.

But to do this, you need to know what the pitch of the gear is to start with. I guess that you could try different depth settings and keep trying until you get a tooth thickness which matches the depth for a known pitch diameter.

The only ones which I know are available in two different sizes, and unless you are making gers for machines which you can't move by hand (and likely can't even move the gear by hand), you want the smaller size.

And if you are getting them from eBay, you almost certainly will wind up with an inch set, not a metric one, though Starrett makes both styles.

The sizes in inch units which Starrett offers are for 20-2 DP and 10-1 DP

And the metric ones are for 1-1/4 - 12 Module and 2-1/2 - 25 Module.

You want the smaller one (larger DP or smaller module), and IIRC you found your lathe's gears were 1 module, so they are too fine for even the smaller of the two metric ones.

The new prices back in January 1998 ranged from $759.00 to $944.00 depending on size and whether supplied with case.

It appears to not be listed at all in the current on-line Starrett catalog. You should watch eBay for a copy of their Catalog #29s -- which has advice on how to use the gear tooth calipers.

Good Luck, DoN.

564

+1

They'll tell you what circular tooth thickness at the depth you set it for. ... Presumably (properly) at the Pitch Diameter...

You'll get more use, for less money (and less monkeying around) with some standard tenths reading mics, some proper wires, and a disc mic. Arguably, you could use a caliper in lieu of the disc mic. ... and if you do get a disc mic, get a non-rotating spindle one to keep your life easier...

I cut a LOT of gears, and inspect almost as many while making them... I inspect most by hand, and some at intervals on a gear inspection machine.

For my money I'd buy a disk anvil micrometer as others have advised here, and become familiar with chordal gear measurements as amply described in Machinerys Handbook.

Methinks this method of gear measurement beats the others "hands down".

Wolfgang

[ ... ]

Not of that specific piece of information. The question is mostly whether you truly need that specific piece of information.

Hmm ... the price is attractive, and it is in metric units, which matches your needs for making gears for the lathe.

Certainly not a plain micrometer -- unless you mill off the teeth adjacent to the one which you are trying to measure. :-)

And the disc micrometer, while it can reach in there, has nothing to set how deep you are measuring.

Do you have a copy of _Machinery's Handbook_ yet?

If so -- look up "gear -- tooth caliper, vernier" in the index, and turn to the first page listed (1938 in the 25th edition, elsewhere in other editions).

Look at the drawing, showing the gear tooth vernier in use. Look in particular at the fact that it is measuring at the "pitch circle" of the gear, which is a point along the curved face of the gear. The end of the vertical scale of the gear tooth vernier rests on the top of the tooth, and limits how far down the measuring jaws go. Without that, there is no way to be sure that you are measuring at the proper point on the tooth. Too high, and you get a narrower tooth reading than you should have -- too low, and you get a wider reading. So -- *if* (and only if) you need the correct reading of this datum, you need the gear tooth vernier. Based on a quick reading of this section, the gear tooth vernier and its measurement is used mostly when cutting a gear with a hobbing machine -- not something you will have available (nor could you get one up to your apartment if you had one -- they are big and *heavy*. You use it for adjusting the hobber to produce the needed clearance on large gear teeth by setting the hobber just a little deeper than normal.

So -- if you *want* a gear tooth vernier just to have one (as I did), then go for this. The price is a lot better than you are likely to find on a used Starrett or B&S one.

However, you don't really *need* it.

Enjoy, DoN.

Sure you can. That's one of the beautiful things about gears - EVERYTHING is related. With a relatively few parameters, you can get to everything else you need or want.

That's why one uses Van Keuren wires to get in there. (:>)

But you can use it to measure the span across the tangencies, and back track that to get other information.

Van Keuren wires* and mic will tell you what you need, here. Preferably a tenths mic.

• - I have, in a pinch, used gauge pins some times...

I hob at work, and at home, and have never had necessity for one yet, but instead rely on wires and other measurements. Besides, if you need to thin (or thicken) the Circular Tooth Thickness while hobbing a gear, it is not a 1:1 relation anyway, so you still need to do the math. In other words, if you need to alter the tooth thickness .001", you do not adjust the hob's cutting depth by .001" There's a relationship...

For instance, for a 40 Tooth gear of 20 degree Pressure Angle - To alter the Circular Tooth Thickness by .001", you would change the hob's cutting depth by .0014" For a 40 Tooth gear of 14.5 degree Pressure Angle, it would be .

00155".

... certainly haven't yet... (:>)

They certainly *are* cool looking though, and I'd be forced to buy one if I tripped across one in person, for relatively little money!

But not limited to the tools which he listed.

There is where you are going beyond his listed tools. :-)

I presume that a specific diameter of pin is needed for at least each pitch diameter -- and if the tooth has been thinned, you will need a slightly larger wire.

O.K. With more math, of course.

Again -- how critical is the diameter of the pins? Can you adjust for wrong diameter pins by cranking through some math -- as you can for thread pitch three-wire measurement?

O.K. You have the wires. How much would a set of appropriate wires cost him, compared to that gear tooth vernier? (And, of course, they could be used for other measurements, which the G.T. vernier could not.

Of course -- so for the math challenged, the gear tooth vernier gives the quick and dirty way of verifying that the extra depth will do it.

Since the hob is providing a pure trapezoidal shape (and depending on the multiple cuts to generate the needed involute shape), yes. If using a set of involute gear tooth mills, however, the calculations are likely to be a bit more complex.

Exactly! I think that I got mine (in a nice plush-lined leather covered fitted box) for something about the range of the import one which he is looking at. This was after watching many go for much more on eBay -- I just lucked into mine at the right time, I think.

Enjoy, DoN.

To get the proper size wires, divide 1.728 by Diametral Pitch. Wires will most often check a fairly large range of Circular Tooth Thicknesses, too, for a given DP.

As critical as one wants to be, or not... (:>) Yes, one can calculate for over/under wire sizes.

Wires are relatively cheap. One could buy individual Gage Pins for about $2.50 USD, each, I believe... (more or less, depending on quality and origin...)

No more complex. Just different. (:>)

Machinery's Handbook has all of this in it.

Did I mention that bevel gears are on my project list.(Providing I can figure out how to cut them without a dividing head). :-)

(But I assume it doesn't change anything, and I can still accurately measure those type gears without a GTV, correct?).

Thanks.

Darren Harris Staten Island, New York.

[ ... ]

I have *no* idea. Open your copy of _Machinery's Handbook_ (you

*do* have one by now, don't you?) and read all about gears and gear tooth cutting. I've never considered making a bevel gear so I haven't bothered reading about them. I'm not even sure that a Gear Tooth Vernier would be usable on a bevel gear, because the shape and dimensions of the tooth vary as you move from the major diameter to the minor diameter.

And you *will* need at least some form of dividing head, along with special sets of gear tooth cutters for the Bevel gears. You can't use the standard involute cutters for straight tooth gears.

Enjoy, DoN.

========== If you are going to make or think about making gears I highly recommend Law's book "Gears and Gear Cutting." It is one of the workshop series and stresses home made gears including bevel/miter gears.

see

?productId=243&categoryId=-1

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

I've been told probably 1/2 dozen times that that is the book to get and I've been trying to get that book along with a few other "Workshop Practice" titles. (And I see that in the link you posted Amazon is only selling it for one grand. :-)

This is what I'm waiting for:

But apparently there is a shipping problem. (See below)...

---------------------------------------------------------------------------=

----------------------------------------------------------------- "Dear Darren,

I am very sorry for the delay and not returning your emails untill now.

The Publishers of Gears and Gear Cutting have just told us that a shipment is due from Malta on the 4th August 2010. The books have been stuck in Malta after reprinting waiting for enough other books for shipping. We will get our shipment a few days after that.

If you can wait we will send your book straight out when it arrives, if not we will refund you in full.

There is no problem with your other book Workholding in the lathe except we were hoping to send them together as 1 package.

Sorry once again,

Thank you for your extreme patience so far,"

---------------------------------------------------------------------------=

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I guess that's what I get for ordering from outside of the country.

So I'm still waiting. But as for measuring gears, this auction win I received is proving to be interesting:

So with my Machinery's Handbook(27th Edition), which I've temporarily misplaced in a room full of "stuff", that should tie me over until I get the Ivan Law book. :-)

I really want to get into the tool making aspects of machining and was wondering if making my own cutters would be plausible. (But without a surface grinder I guess this would be difficult).

And I'm still searching for a mini dividing head. :-)

Thanks everyone.

Darren Harris Staten Island, New York.

[ ... ]

Oh good -- you *do* have _Machinery's Handbook_.

You can make the cutters with a bench grinder a magnifier and patience. (Something like an optical comparator will help to check a tool against a scaled-up drawing of what it should be -- but you can grind by hand and check against a gear of near the same number of teeth (given DP and PA the same, of course, or metric equivalents).

There are small ones for the Unimat and the Emco-Maier C5 mill which will handle certain fixed numbers of divisions. IIRC, 32, 36,

40, and 48 divisions -- and subsets of those. But if you need an odd number of teeth you will have problems for many of those.

Good Luck, DoN.

Actually, you can. The process is described in Law's book, mentioned below.

It's a good book to have. One of the nice things is that it is written from the perspective of actually *doing* things, and getting things done.

I'm a bit of a freak about gears, kind of obsessive/compulsive, having a love of them, the design process, the manufacturing process, and tooling. As such, I think that Dudley's book is a mandatory possession.

Another one you might want to look at is Edgar's which is available on Gooogle books.

There are many others, and others will likely chime in with the old standards and links to them.

Personally, I seem to gain more from the tooling (hobs and shaper cutter) design texts, and have found the technical handbooks and texts from Barber Colman to have been INVALUABLE.

Ironically enough, after diving in and dedicating so much time and effort to the subject and the texts mentioned, I have found (in retrospect) that Machinery's Handbook has

90% of everything you will ever need.