Using 2 bolts M12 or 4 bolts M6?

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In summary, the question is about the strength of using either 2 M12x1.5 bolts with a length of 30mm or 4 M6x1 bolts with a length of 25mm, placed equidistant in a circle, to bear force. The conversation also touches on the use of 3D thinking and the importance of considering moments in addition to force when designing a joint. The individual asking the question tested both options on Inventor software and found that the M12 bolts could withstand more axial force. Another contributor explains that the strength of a bolt is based on its shank's cross-sectional area and suggests that 2 M12 bolts may be stronger due to having more cross-sectional area than 4 M
  • #1
cherish
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Hi there,

I'm not sure that using the same type of 2 bolts M12x1.5 (L=30mm) or 4 bolts M6x1 (L=25mm) & place equidistant in a circle as picture below, which can bear force better & why?

Thanks many in advanced!

[PLAIN]http://img824.imageshack.us/img824/7971/123ok.jpg
 
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  • #2
Is this coursework?

If so, here's a hint.
Think about what is acting on the joint besides force. Think in 3D.
 
  • #3
Studiot said:
Is this coursework?

If so, here's a hint.
Think about what is acting on the joint besides force. Think in 3D.

hi Studiot, certainly this's not coursework, just a small problem that i design it for a gearbox. First time i try to use 4 M6 as mentioned above & my boss agreed with solution but later i found a guide from catalogue they using 2 M12 in stead as picture attached, just a bit wondering that the total diameter of these two solutions is almost the same but not sure which is stronger :grumpy:

While looking for an answer i made a test on Inventor software & the result is that: M6 appeared in failure with axial force 750N but M12 is compliance with 1500 N axial force (even if 2500N is still fine). by the way not understand essence of situations.
P/S: one more test
one M12 can bear an axial force P = 2500N & 7 bolts M6 can bear an approximately axial force (P = 2500N)

Thanks many in advanced & have nice weekend!
 
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  • #4
OK what I am talking about is moment.

A single bolt cannot cope with moments due to forces applied across the joint or slight angular misalignments.

Two bolts can cope with moments in one plane ie along one axis

3 or more bolts can cope with moments applied in two planes at right angles and therefore all such moments.

Does this help?
 
  • #5
Think about it this way- a bolt's strength is based on it's shank's cross-sectional area (not diameter)... so what has more cross-sectional area, 2 12mm bolts, or 4 6mm bolts?
 

1. What is the difference between using 2 bolts M12 or 4 bolts M6?

The main difference is the size and strength of the bolts. M12 bolts have a diameter of 12mm and are generally stronger and able to withstand heavier loads compared to M6 bolts, which have a diameter of 6mm. Using 4 M6 bolts may provide more even distribution of the load compared to 2 M12 bolts.

2. Which option is more cost-effective?

This depends on the specific application and the cost of the bolts. In general, M6 bolts are smaller and thus may be less expensive than M12 bolts. However, using 4 M6 bolts may ultimately cost more than using 2 M12 bolts due to the increased quantity needed.

3. Can I substitute M12 bolts for M6 bolts or vice versa?

No, it is not recommended to substitute bolts of different sizes, as this can compromise the structural integrity and safety of the project. It is important to use the specified bolt size for the intended application.

4. What factors should I consider when choosing between 2 M12 bolts or 4 M6 bolts?

The factors to consider include the weight and load of the object being secured, the type of material the bolts are being fastened to, and the desired level of strength and stability. Consulting with an engineer or following engineering guidelines is recommended to determine the appropriate bolt size and quantity for a specific project.

5. Are there any specific safety precautions I should take when using bolts?

Yes, it is important to ensure that the bolts are of high quality and suitable for the intended use. It is also important to properly tighten the bolts to the recommended torque and regularly inspect them for any signs of wear or damage. Additionally, following proper safety measures and wearing protective gear when handling and using bolts is crucial.

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