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  • Gear cutting and end mills

    Can anyone recommend a brand/type of end mill, half inch diameter and smaller, that will stand up to steel and cast iron? Just a benchtop hobbiest so they will see relatively light use. Is there a spacing formula for
    cutting a gear rack? If it's in Machinery's Handbook I can't find it. Finally, the term module, as I understand it, refers to metric pitches. Why are they given in module and not as mm? Does module have a bearing on
    anything other than pitch? Thanks guys.

  • #2
    I'm a hobbiest as well and a like the prices at online-carbide, they're just a little cheaper than the "brand names" but seem to have great quality still, and their shipping is reasonable. I get the variable helix end mills with a corner radius. The corners are the most fragile part and you rarely really need or want a really sharp corner. I've bought some from amazon as well if I can get them with Prime.

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    • #3
      I believe the module is in mm and is the pitch dia per tooth for a metric gear. As for end mills, any endmill should be fine with steel or cast iron. Better brands last longer but are expensive. Where are you? There is no location in your profile, its easier suggest suggest sources if we knew where you were.
      Last edited by Mcgyver; 05-07-2019, 08:52 PM.
      .

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      • #4
        I'm on eastern side of West By God Virginia. What I was curious about was why the term module is used. Why not millimeter?

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        • #5
          A module is in millimeters. It's 25.4 of them.

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          • #6
            The Module is "Metric". It has to do with the pitch circle of the gear. Example: A gear with 30 teeth with a module of 1 would have a pitch circle of 30 mm. A module 1 rack would be Pi x module for the distance on the pitch line. This also means it is Pi x module for the distance between the same point on two adjacent teeth.

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            • #7
              So you are in the US. That means that you will need to be familiar with both English and metric gears - sooner or later anyway.

              Gears made to English measure (inches) are usually specified in terms of Diametral Pitch. By definition, Diametral Pitch is the number of teeth PER inch of diameter as measured at the Pitch Circle. So a 16 DP gear would have a one inch diameter Pitch Circle. The formula is:

              P = N/D

              Where P is the Diametral Pitch.
              N is the number of teeth.
              D is the diameter of the Pitch Circle.

              If you want the spacing between the same point on adjacent teeth the math is also simple. This is the Circular Pitch and is usually represented by a small p.

              p = Circular Pitch

              Now since you have P teeth on a one inch Pitch Circle, that means that you have P teeth in 1 x pi inches. The circumference of a circle (the Pitch Circle) is pi times the diameter. So the Circular Pitch (the tooth to tooth distance) would be that circumference divided by the number of teeth. To convert from P (Diametral Pitch) to p (Circular Pitch) the formula is:

              p = pi/P

              or

              p = 3.141/P

              These formulae are in Machinery Handbook in the chapter on gears. In my edition of MH (26) they are in Table 1 on page 2004, but your page number may differ.

              The term Module can be applied to both English and metric gears and it means the same thing for both, BUT the UNITS of measure are different. The Module is defined as the diameter as measured at the Pitch Circle divided by the number of teeth. So the formula is:

              M = D/N

              You may notice that P and M are simply reciprocals of each other: N/D and D/N. I do not like the way that MH explains this, "Module is an actual dimension, whereas diametral pitch is only a ratio." That is not strictly true. In physics most physical quantities have an associated unit. Length is associated with inches and meters. Weight with pounds and grams, etc. Speed or velocity is measured in distance per unit of time or meters per second, miles per hour, etc. Now, Module is a distance (the diameter of the Pitch Circle) divided by a pure number (N - the number of teeth) so it's associated units are distance/1 or just distance. P is the reciprocal of that or a pure number (N) divided by a distance (the diameter of the Pitch Circle) so it's associated units are 1/distance or "per inch" or "per mm", etc.

              These are real units and any true equation in all of physics and engineering will hold true for both the numeric quantities and the units associated with them. If the units in an equation do not come out right, then the equation is WRONG. I passed many a physics test using that simple fact: knowing the units involved enabled me to work out the CORRECT equations which I then used to solve the problems.

              Also I used the small p for Circular Pitch and the M for Module. These are the same measure but Circular Pitch is usually the term used for English gears while Module is used for metric ones. The formulae are the same, only the units (inches and mm) are different.

              As to why the usage of the terms differs in English and metric gears, I can only offer a suggestion. English gears are measured in inches and one inch is 25.4 times bigger than one mm. For most, common gear sizes measurements in inches, Diametral Pitch (P) numbers simply work out better: whole number Diametral Pitch values represent sizes of gear teeth that are useful in the real world. A 16 Diametral Pitch gear would be Module 0.0625. Both are correct, but we prefer the whole number over the decimal. On the other hand, a Module 10 metric gear would be 0.1 Diametral Pitch in metric units. In both cases the numbers used are chosen based on what is easier for the human mind to comprehend.

              Again, from MH, "The diametral pitch system is applied to most of the gearing produced in the United States. If gear teeth are larger than about one diametral pitch, it is common practice to use the circular pitch system." Notice that the dividing line between using P and p is at the numeric value of one. Thus, if this rule if followed, all gears would be specified with numbers greater than one. I do not know if the same practice is true for metric gears but it seems to make sense in answer to your "why".



              Originally posted by Proudpappy View Post
              Can anyone recommend a brand/type of end mill, half inch diameter and smaller, that will stand up to steel and cast iron? Just a benchtop hobbiest so they will see relatively light use. Is there a spacing formula for
              cutting a gear rack? If it's in Machinery's Handbook I can't find it. Finally, the term module, as I understand it, refers to metric pitches. Why are they given in module and not as mm? Does module have a bearing on
              anything other than pitch? Thanks guys.
              Paul A.

              Make it fit.
              You can't win and there is a penalty for trying!

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              • #8
                What is the rack for ? Easy and fairly cheap to by from Browning, Boston Gear.. those type places.
                And the cheapo standby, get a ring gear and flatten it out..

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                • #9
                  My Weiler Matador lathe is capable of producing 30 Diametral threads from 6 to 60 DP and 20 Module from 0.1 to 4 mod (as well as 48 English threads and 30 metric), so what would I be making with these selections? Just dreaming because I have a hard time making 1/4"-20 threads.

                  http://www.lathes.co.uk/weilermatador/

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                  • #10
                    Here's a pretty understandable description of the term module:

                    The module is typically quoted in standardized gear sizing charts with implied units of length, either (mm) for SI units or (in) for BG units. In a sense, it’s a measure of the unit size of the gear on the basis of the number of teeth present on the gear. A useful analogy is that the module defines the “size” of each tooth as a portion of the pitch diameter “pie.” This really means that each tooth possesses a “module” unit of the portion of the total pitch diameter. For example, a gear that possesses a module of 10 (quoted in SI units) quite literally means that that each tooth “uses” 10 (mm) of the total pitch diameter.

                    If you want to read it in the original context that copy/paste was from this site: https://blog.misumiusa.com/understan...d-gear-module/

                    (added)
                    It also helps to keep in mind the definition of the word module:

                    mod·ule
                    /ˈmنjo͞ol/
                    noun
                    noun: module; plural noun: modules

                    each of a set of standardized parts or independent units that can be used to construct a more complex structure, such as an item of furniture or a building.
                    an independent self-contained unit of a spacecraft.
                    Computing
                    any of a number of distinct but interrelated units from which a program may be built up or into which a complex activity may be analyzed.
                    Last edited by lynnl; 05-08-2019, 07:51 AM.

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