What "parameter" describes whether two unknown gears from the surplus bucket will work together? Is there a number that describes how the teeth mesh? I've googled "pitch circle", etc but I seem to have a mental vapour lock.
TIA, Chris
The term is Diametral Pitch.
TIA, Chris
Diametrical pitch and pitch angle. In metric it is the pitch rather than DP.
snipped-for-privacy@my-deja.com wrote:
=============== Metric gears are generally speced as "module" Module = 1/ diametrical pitch. You will occassionally see the inch module specified, but general module usage is metric. 1 m/m module =
25.4 DP[inch], 0.5 m/m module = 50.8 DP[inch], etc.If you are getting into gears a good reference is Law, Ivan "Gears and Gear Cutting" ISBN 0-85242911-9 While written for the person who wants to make their own gears in the home workshop it has very good information on the nomenclature and identification of all types of gears. One source in the US is
Unka' George [George McDuffee]
------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
Pitch and pressure angle, assuming that they're "ordinary" involute (is that the right term?) gears.
George sez:
If you are getting into gears a good reference is Law, Ivan "Gears and Gear Cutting" ISBN 0-85242911-9 While written for the person who wants to make their own gears in the home workshop it has very good information on the nomenclature and identification of all types of gears. One source in the US is
Bob Swinney
You got it.
Take a look at the Bost> >>> snip The right keywords make searching much easier!!
Spelled "Diametrical Pitch" if you're going to use it in search engines. (They can be picky. :-)
And "Pressure Angle" comes into it as well. Typically either 14 degrees or 20 degrees for inch dimensioned gears.
Enjoy, DoN.
*Diametrical* Pitch and "Pressure Angle".
Assuming that you aren't talking about helical gears, in which case the helix angle also needs to match in some way corresponding to the angle at which the two shafts cross. (The same angle for both if the shafts are the usual parallel.)
Enjoy, DoN.
I think the common term is diametral pitch, Don.
Right. You can derive some gear dimensions from others, but the ones that should be the same on matching gears, to keep it simple, are diametral pitch (so the spacing between gear teeth is conformal, and the gears don't "jump" from one tooth to the next) and pressure angle. The pressure angle (usually the standards, except for plastic gears: 14.5 deg, 20 deg, or sometimes 25 deg) should be the same for both gears to get uniform velocities and to minimize sliding. Lower angles run quieter; higher angles are stronger. The
14.5 deg angle is becoming less common on commercial gear applications today.These are just the tip of the iceberg in gear dimensions but they should be all you need for an ordinary application. Oh -- you'll want to know the pitch circle to get proper axial spacing, too.
-- Ed Huntress
DP and PA are hard to measure when buying surplus . For inch gears the diametral pitch should equal (number of teeth + 2) / (measured outside diameter) rounded to the nearest whole number. An example from my lathe is (80 + 2) / 5.110 =3D 16.047. That's a 16 DP, 80 tooth gear I bought to replace the broken idler. The nominal outside diameter is ( 80 + 2) / 16 =3D 5.125".
You can measure PA with a protractor on large gears probably close enough to tell 14.5 from 20. I measured ~42 degrees between the inner flanks of adjacent teeth on the tractor steering sector and assumed
20PA:Jim Wilkins
DP and PA are hard to measure when buying surplus . For inch gears the diametral pitch should equal (number of teeth + 2) / (measured outside diameter) rounded to the nearest whole number. An example from my lathe is (80 + 2) / 5.110 = 16.047. That's a 16 DP, 80 tooth gear I bought to replace the broken idler. The nominal outside diameter is ( 80 + 2) / 16 = 5.125".
You can measure PA with a protractor on large gears probably close enough to tell 14.5 from 20. I measured ~42 degrees between the inner flanks of adjacent teeth on the tractor steering sector and assumed
20PA:Jim Wilkins
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Right. It's one thing to specify a gear that you want; it's another thing entirely to measure those parameters on a gear that you have. There are some shop-level methods but I've long forgotten them, if I ever knew them at all.
-- Ed Huntress
Especially when it's damaged enough to need replacement, and you are rummaging through a junk pile to match it with only tools you can carry in a pocket and don't mind losing.
I used the 80 tooth gear for the example because I bought it new and am sure of its size. The clerk at Bearing Specialty Co in Nashua told me they enounter a lot of custom sizes they can't match from stock, such as my tractor's steering sector.
They are nice people who have been very helpful with my strange requests -- although the last time I was in there an alternate-energy designer bought some 2.000" ID bearings to go on 2" water pipe. Maybe mine aren't so bad. I did clean the gear before plopping it on the counter.
I need to find a local inventor with great ideas who needs an electronic + mechanical tech to build them, and pays regularly. I've worked for quite a few of them, the trouble is that a place like DaVinci makes them a great offer and they leave.
Jim Wilkins
You're right! I've been reading it as "diametrical pitch" all this time -- given the derivation of the term.
====================================================================== diametral pitch The number of teeth given per inch of a gear's pitch diameter. Diametral pitch is the most common method of classifying gears. ======================================================================
I wonder how that spelling became the standard? And why?
And my spelling checker complains about it when I use the correct term. :-)
Hmm ... I did not know about 25 degrees. New information for me.
Hmm ... don't they (the higher angles) put more lateral stress on the bearings in which the gears are running?
I think that is what my 12x24" Clausing lathe has -- 16 DP 14.5 PA.
Yep.
Enjoy, DoN.
There are portable gauges which are useful for the DP for standard sizes at least. A round piece of either sheet metal or Bakelite, usually with a hole to hang from a key chain. I have one. It is not small enough for instrument gears, but reasonable for machine tool gears.
The gauge is quicker -- even if you have a good calculator with you, since you don't have to do a precise tooth count first. :-)
A rack gear is pretty much a trapezoidal tooth shape and easy to measure if it is large enough -- or if you have an optical comparator. The complex shapes come from making gears of differing tooth counts which will smoothly roll in mesh with the rack gear -- and thus with all others of the same DP and PA.
Of course. :-)
Enjoy, DoN.
'Dunno, but it was spelled that way in the 1909 edition of the _American Machinist's Handbook_.
I suppose so. But the bases of the teeth are broader, so the teeth are stronger. The trend is toward higher pressure angles except for timing gears, like lathe change gears, where the loads are relatively light.
Plastic gears are another story; the high-performance ones are often non-standard in every way, with stub teeth and high pressure angles. They can do anything they want when they inject-mold the gears in wirecut-EDMed cavities.
I have found that many gears found in high volume applications are neither standard DP nor pressure angle. I have also noticed that what seems like a majority of the hobs and a lot of the milling cutters offered for sale are non-standard as well. Automotive gears seem to always be specialized.
Don Young
The 14° P.A. is more tolerant of sloppy gear center spacing--hence it's use on change gears on lathes
>What I've read is that 14.5 PA was easy for the foundry pattern maker because the sine of 14.5 is 1/4. 20 PA came from early automotive transmission designers who first ran tests to prove that the extra lateral bearing pressure wasn't a problem.
The first gear cutting bit I made was for a broach to fit a pulley to a hydraulic pump drive shaft. It's a 30 degree ANSI involute spline:
Jim Wilkins
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