Design Large Spur Gear - 44in CNC Shop Bot

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Discussion Overview

The discussion revolves around the design of a large spur gear, specifically a 44-inch gear intended for cutting on a CNC machine. Participants are exploring calculations related to gear dimensions, including the number of teeth and diametral pitch, while addressing challenges in achieving the desired tooth size.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant is attempting to design a spur gear with large teeth but is struggling with calculations that result in smaller teeth than desired.
  • Another participant questions the specific calculations being performed and seeks clarification on what is meant by "tiny teeth."
  • A participant outlines the relationship between pitch diameter, number of teeth, and diametral pitch, expressing uncertainty about how to determine the appropriate number of teeth for the gear.
  • Concerns are raised about the radius used for the sides of the teeth, with a mention of needing a reference from The Machinery Handbook.
  • One participant introduces a discussion about the implications of irrational numbers, specifically pi, in real-world calculations, though this is met with confusion from others.
  • Another participant recalls that The Machinery Handbook contains formulas relevant to gear cutter setup, indicating a potential resource for resolving some of the design issues.
  • A link to a gear calculation resource is provided, suggesting that spur gear calculations are universal and may aid in the design process.

Areas of Agreement / Disagreement

The discussion reflects a lack of consensus on the appropriate number of teeth for the gear and how to achieve the desired tooth size. Participants express differing levels of understanding and approaches to the calculations involved.

Contextual Notes

Participants mention the need for specific references, such as The Machinery Handbook, to clarify calculations and design considerations. There is also an acknowledgment of the complexities introduced by irrational numbers in practical applications.

ssakcaj77
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Hi, I am new to this forum so forgive if i am mis posting or multi posting. I am in the process of designing a 44 inch gear to cut on my shop bot cnc machine. I have been up and down calculations but i end up with tiny teeth and can not find the right formulae to calculate an oversize spur gear. Any thoughts ?
 
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What exactly are you trying to calculate? What do you mean by "tiny teeth"?
 
pantaz said:
What exactly are you trying to calculate? What do you mean by "tiny teeth"?

I am trying to build an oversize gear with large teeth. Given a Pitch Diameter(D) of 44" I am trying to find how to base the number of teeth (N) in order to calculate Diametral pitch(P)

Pitch Diameter is D=N/P

Number of teeth is N=D x P

Diametral Pitch is P= N/D

Based on that, we have D but I am not sure what to do about knowing what the propper amount of teeth would be or do you just pick em and go with it.

I picked a number and went with it for fun and when i was done calculateing addendum, dedendum etc I ended up with teeth that were around 1/2 big. It would work, but i need larger teeth for this project.

I also need to check to see about the radius used to make the sides of the teeth. I read that there is a chart of info on this . Need to find my machneries handbook!
 
Pi is irrational, where do the left over digits go?
 
Doug Huffman said:
Pi is irrational, where do the left over digits go?

doug, what the hell you want me to do with that statement ?
 
I am traveling at the moment and for the week. I don't have my library handy. ISTR I seem to recall that there are formulas in The Machinery Handbook for setting up gear cutters. The extra digits of irrational numbers are a typical problem for real world problems.
 
Doug Huffman said:
I am traveling at the moment and for the week. I don't have my library handy. ISTR I seem to recall that there are formulas in The Machinery Handbook for setting up gear cutters. The extra digits of irrational numbers are a typical problem for real world problems.

im just trying to find my copy of MHB right now
 
QTC has their http://www.qtcgears.com/Q410/Q410Cat.htm" . The spur gear calculations are universal.
http://www.qtcgears.com/Q410/Q410Cat.htm
 
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