A Handy Dovetail Measuring Calculator For The Home Machinist

This isn’t anything I am going to be needing right away as cutting Dovetails is still quite a bit above my skill level but a friend sent me a link to this and I thought I would share it for those of you who may need to cut some in your adventures of making metal chips.

The actual math involved is Trigonometry and I can barely spell it, let alone do it.

This calculator does all that for you. So instead of this,

You go HERE, and punch in a few numbers after you have done the measuring.

Could be very handy for numerically illiterate Joes like me or just a quick and easy method to save time for those who do know advanced math.

I can make change for a dollar easy enough but anything past fairly basic math has me pulling off my shoes and socks so I can count my toes.

Never was good at Math and was told by my 9th grade teacher That after his class I would never have to take another math class.

Way cool I thought, so I didn’t.

He was very wrong about that I found out the hard way later.

I was in the very first year of mandatory competency testing. Lo and behold when I finally go back to school as a Senior I am informed that I have passed zero competency tests in math.

I had to start at the very beginning in remedial math and take multiple classes so that I could take 4 years worth of competency tests in one year.

When you try and cram all that in your head you resort to survival mode. Study for the coming test so you can pass it, then immediately forget what you just studied so that you can concentrate on studying for what is coming up on the next test.

Rinse and repeat.

I made it.

Just barely.

13 thoughts on “A Handy Dovetail Measuring Calculator For The Home Machinist

  1. I remember geometry from hs and I can almost count the times & places I used it since then.

    Figuring out how much gravel I’ll need to fill a spot this long, that wide and so deep.
    Which put more pizza in my oven, the rectangle pan I had or the round one?
    And much later when the kids came home from school and needed help with the home work.

    For the last one they had to bring the school book with them so i could read up and see if I remembered what they needed help with… FWIW I was able to help them and that surprised the heck out of me!


  2. My first algebra class almost sunk me, then in the middle of a test, the word problem just made sense. My teacher accused me of cheating… Ha, I didn’t Mr. Rubin, you were just a great teacher.

    Geometry teacher in HS said, we wouldn’t need it, so one day of Geometry, and 4 of “computer science”. He was a prophet in computer science. But I went hard science, so Trig, Analytical Geometry,The Caluculus x 5 semesters, Strength of Materials, Statics, Dynamics, Physics, Chemistry, Electronics, Rotating Machinery, the works. I used to be able to map out trans and cis organic compounds (not much of that in cereal anymore!!). It’s not scary, but a spreadsheet makes it quick, easy and repeatable.

    I have to have a reason to use it though. Just doing the math for fun isn’t as much fun as it used to be. I like to make things now, math makes it possible.


    • You and I are kindred spirits! I also took the same paths as you did, and I actually put that math knowledge to use. DON’T ask me to use it now, my brain is ossified.

      Interestingly, in Circuit Theory the Prof would explain the inner workings/math of a particular circuit, then he would look at ME and ask, “Mr. Igor, how is this circuit used in the Real World??” It was a cold day in Hell if I could not tell the class at least ONE use of the circuit – the prof *knew* I had extensive troubleshooting experience with circuitry and therefore knew real-world applications. The class was tough – lots of math! – but it was also quite fun. I have lots of “war stories” on some of the profs and classes I experienced in college. Heh.
      (In case you are wondering, I went back to college when I got out of the Military and graduated with three degrees at the age of 29. It was tough but I lived…)


      • I went for two semesters, got married, went back for one (dean’s list!! wohooo!) Apprenticed as an electrician until the bust in mid 80’s, back to school for real, and graduated at 28 with 6 1/2 years of credits. Married with two kids.

        I’m buying lunch next time you come this way. I’d like to visit.


  3. This is a useful place-old time books on all sorts of technical things.

    Being completely confounded on how to achieve accurate work, a guy on Practical Machinist forum recommended this book-
    “Accurate Tool Work”, Goodrich and Stanley, 1908. found at the Old Time books place.

    This book has a clear description and examples of using trigonometry, as well as many other cool things.
    The name always threw me till I realized it just meant Tri-geometry, the math of measuring triangles.
    For example- you need to cut an exact taper on a part. Say, 8 degrees for an ER collet.
    Look at the trig function tables for 8 degrees, go to the tangent. It is 0.14054″ These are all based on a 1″ base leg of a triangle.
    The tangent is the 90 degree offset distance from the base- if it was a framing square, it would be 1″ on the long side, and .14054″ on the short side. A line between those two points is 8 degrees.
    So to set this up, all you need is an indicator to measure 1″ of travel, and another to measure the .14054 off set- move the part 1″, and check the tangent measurement and adjust to .14054″.

    I have used this to make an ER collet holder for a obsolete mill spindle taper. Being a dropout, this felt like my daughter yelling with excitement when she first learned to tie her shoelaces unaided.
    “DADDY!!! I DID IT!!!!

    Liked by 1 person

  4. I think you’re a smart guy. Just curious… how did you do in high school, especially English? No disrespect intended. Were you a challenge to the grown ups?

    Liked by 1 person

    • I have been crazy busy but I remembered this question and came back to it.
      Yes, I guess you could use “Challenge”. My mother taught me to read before I ever started school. That turned out to be a double edged sword.
      While I was ahead of everyone else at first, the teachers quickly shut me down and tried to make me conform to the grade levels.and abilities of everyone else.
      I had a very rough and unstable childhood. I went to 12 different schools, 3 in the second grade alone. By the fourth grade I was spelling college level vocabulary words out loud in front of the class.
      I had very little interest in school, even back then I found it to be a glorified baby sitting service and refused to apply myself. This frustrated the shit out of all of my teachers because they knew I was pretty smart.
      I was a trouble maker and got my ass beat at home and at school.
      This doubly reinforced my orneriness.
      The short answer to your question is yes, I was a challenge to my teachers.
      I ran away from the abuse at home when I was 15, dropped out of my Junior year and wound up living with one set of Grandparents, That Grandmother died when I was 18, My Grandfather couldn’t handle me and bailed out back to Tennessee. I wound up at my other Grandmothers who convinced me to go back to school. I was into drinking and smoking pot heavily by then.
      I just barely managed to graduate high school with a 1.2 GPA. My Mom lived long enough to see me graduate at age 19 and the finished drinking herself to death 5 days before my 20th birthday.
      Just so you know, in my final year at High school, I was reading up on Particle Physics on my own in my spare time.
      I went to College at age 29, graduated from a two year college after being there 3 years because I started with general automotive and got invited to join a FORD motor co exclusive training program that only opened up every other year. I graduated from that with a 3.73 GPA, With honors, PHI THETA KAPPA.
      All while drinking like a fish the whole time.
      I’m no dummy by any stretch of the imagination. I just suck at math.


      • Thank you for your answer. I had a stable home life, but I feel the same way about the glorified baby sitting that goes on in the school system. If you ask me, the teachers wreck as many as they help. Maybe more.

        Liked by 1 person

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