Help with my math? Going crazy.

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jeporter02

jeporter02

Member
Joined
Feb 1, 2022
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Location
London, UK
I'm turning my first nib section and I feel like I can't do simple math. The threads connecting the section to the body are 9mm x 0.75. In order for the convertor to fit into the section, I need a 7mm hole. That seems like it will be fine because I'll have a 2mm tenon, and after the threads are cut, there would still be 1.25mm of material between the hole and the minor pitch of the threads connecting the section to the body, right? I realize you have to account for some runout, but something isn't adding up. See the pics below. My outside diameter is 8.87 mm. My inside diameter is 6.97 mm. That should mean that the wall of the tenon should be 1.9 mm thick, right? But it's only 1 mm. thick. I've taken the measurements a hundred times and the results are the same, within a couple thousands of a mm. I don't think it's an "off" reading. My calipers seem to be working fine.

I'm worried that if my threaded tenon is 1mm thick, then that means it's as little as 0.25mm thick at the bottom of the thread, right? What am I doing wrong?

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Nothing is obvious. I have math brain clouds all the time when working on pens and dealing with metric and imperial.

Good luck!
 
It's funny how when I was in school I thought I'd never need what they were teaching. Now with hobbies I need math, geometry and chemistry. I remember when calculators came out and we were told we couldn't use them because we might not have one when we needed it. I must admit that I'm almost passed all that because now I can't remember things I need to. Ha Ha.
 
Kenny Durrant said:
It's funny how when I was in school I thought I'd never need what they were teaching. Now with hobbies I need math, geometry and chemistry. I remember when calculators came out and we were told we couldn't use them because we might not have one when we needed it. I must admit that I'm almost passed all that because now I can't remember things I need to. Ha Ha.
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It was kinda the opposite for me. I loved algebra, geometry and more and thought I will never forget this! Now, I have to ask my high school teacher daughters how to do those formulas! I do need them every once in a while. I still prefer working out basic math functions on paper of in my head than using a calculator for addition/subtraction on 10 to 12 items or less.

Back around 2003 (I think) my oldest grandson who was 5 and living in Arkansas got on the phone with me. His mom called us (we were in Japan) - "My grandson said, Pappaw, do you know what the square root of 35 is?"

Me: "Don't you mean to ask me the square root of 36?"
Him: "No Pappaw, 35!"
Me: "I don't have a clue except it will be somewhere around 5 something."
Him: "5.916079
Me: "How do you know THAT at 5 years old?" (We were told at his birth that a region of the brain that indicates intelligence was highly active in him, so we have had high expectations, but not that much. ) "Did your mom teach you how to figure out square roots?" (I didn't know what a "Square Root" was until I was in the 6th grade!)
Him:" I did it on a calculator!"
 
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I feel like the older I get the more I'm overthinking things. I had run all the calculations on subtracting major and minor pitches on threads and drawn out diagrams and had drill bit charts out. I had figured out precise calculations on tap sizes, and then I got stumped on (literally) 1+1 = 2.
 
jeporter02 said:
I'm turning my first nib section and I feel like I can't do simple math. The threads connecting the section to the body are 9mm x 0.75. In order for the convertor to fit into the section, I need a 7mm hole. That seems like it will be fine because I'll have a 2mm tenon, and after the threads are cut, there would still be 1.25mm of material between the hole and the minor pitch of the threads connecting the section to the body, right? I realize you have to account for some runout, but something isn't adding up. See the pics below. My outside diameter is 8.87 mm. My inside diameter is 6.97 mm. That should mean that the wall of the tenon should be 1.9 mm thick, right? But it's only 1 mm. thick. I've taken the measurements a hundred times and the results are the same, within a couple thousands of a mm. I don't think it's an "off" reading. My calipers seem to be working fine.

I'm worried that if my threaded tenon is 1mm thick, then that means it's as little as 0.25mm thick at the bottom of the thread, right? What am I doing wrong?

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I am generally surprised how people calculate something using formulas. I always had problems with mathematics at school and university. And not only with mathematics, I often asked do my assignment, and https://ca.edubirdie.com/do-my-assignment helped me with this. We cannot know everything and often make mistakes or do not notice something. This is normal, everyone learns from mistakes, or does not learn.
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Such a stupid mistake can happen to anyone. Sometimes the mistake is right under our noses, but we don't notice. That's what forums like this are for.
 
My mom always says "if it was a snake, it would have bit you." And let me tell you, I would have a lot of snake bites.
 
Calculators are a great thing. I have basics on my phone. Now the are under $25 and do just about any kind of math or science calculation.
I struggled with most math. That is the only thing that kept me from a degree in mechanical engineering. My son is the genius- when he graduated, he discovered he had a double major- math and ME. Many ME classes had a math prerequisite. His wife was a math major.
 
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