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Quick bolt Reserve Factor Calculator

A program to see if your bolts are up to it.

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richardandtracy19/09/2020 22:24:18
943 forum posts
10 photos

This is a little 32 bit windows program to see what the reserve factors are in the heavily loaded bolts you're using are.

It's a tool I knocked up to speed writing stress reports at work, but it's simple enough to use as a design what-if tool, and may have wider application, which is why it's available for download on my website.

The program looks like this:

Program description page and download is available through the link.

The program input is on the left, output on the right. The program uses a table of British/ISO metric screw thread sizes, also standard materials used in bolts (plain grade 4.6, high tensile 8.8, cap heads 10.9 and several types of stainless) and permits you to specify the loads in Newton's, acceleration/duty factors in gravities as well as design factors. The results then are presented in the right half of the window. A reserve factor factor of less than 1 is highlighted in red as this is bad. The pdf help file suggests the acceleration/duty factors that may be sensible to consider. The bolt loads used in the input can be calculated by hand or in the bolt loads calculator that may be downloaded from my website. The help file also shows the formulae used to calculate the reserve factors to verify for yourself that it's telling the truth. The program can screenshot itself to provide an entry for a report should you need to keep one on record. (You won't believe how much time this saves a stress engineer with a 300 page report to compile, typically it can take 45 minutes to type up bolt calculations, and double check each line in them. This is a single button press and then a paste. Imagine this saving 50 times in a report...)

If you have materials not on the material list, or sizes not on the size list, both lists can be edited in accordance with the help file to add the new properties.

The program is in metric. Only metric. I wrote the program for use at work in a modern engineering business. Imperial units have not been used there for 30 years. I am not going to risk breaking the program/ reducing simplicity for obsolete measurement units.

Hope you find it useful. It has saved me hours since I wrote it earlier this year, and I wonder why I didn't do it years ago. I have had another stress engineer verify the output, so provided the input is correct, you can rely on the output.



Frances IoM19/09/2020 23:27:51
827 forum posts
26 photos
seems to be happy under WINE on Linux though most of my use is at M3-M6 level!
Thor20/09/2020 05:24:53
1273 forum posts
39 photos

Thanks Richard

richardandtracy20/09/2020 07:12:17
943 forum posts
10 photos

Most of my usage has been M6-M16 but I have recently had cause to specify up to M63 for a little 6 tonne spacecraft turnover and transport trolley.



SillyOldDuffer20/09/2020 09:11:56
6309 forum posts
1380 photos

Another Linux success ( wine 5.0 on Ubuntu 20.04 ).

Thanks for sharing,


richardandtracy20/09/2020 10:25:05
943 forum posts
10 photos

I'm pleased it works for you, and it's nice to hear it works on Linux too.



ega20/09/2020 11:17:43
1811 forum posts
153 photos


Someone (whose name I don't remember) said that his life's ambition was to write a piece of software that would benefit others, and put it into the public domain.

richardandtracy21/09/2020 14:49:47
943 forum posts
10 photos

In response to requests for smaller size threads, I have dug out data on M1.4 to M3.5 threads.

If you have already downloaded the program, there is no need to do so again, just open BoltData.csv in Notepad or a suitable text editor and append the following data:

M1.4 x 0.3,0.907
M1.6 x 0.35,1.171
M1.8 x 0.35,1.586
M2.0 x 0.4,1.929
M2.2 x 0.45,2.305
M2.5 x 0.45,3.183
M3.0 x 0.5,4.749
M3.5 x 0.6,6.379

Then save the file as a UTF-8 text file (normal old-fashioned DOS text before extended character sets were invented).

This will add the data for the smaller metric threads. In these small sizes I have specified the pitch because not all taps & dies conform to the 'ISO Coarse' thread standard pitch by default.

The additional thread sizes are now included as standard in the download from my web site.



richardandtracy21/09/2020 14:52:36
943 forum posts
10 photos
Posted by ega on 20/09/2020 11:17:43:


Someone (whose name I don't remember) said that his life's ambition was to write a piece of software that would benefit others, and put it into the public domain.

Not a bad aim in life. Always good to be able to offer up something useful by way of a thank-you for help received.



Thor21/09/2020 16:06:46
1273 forum posts
39 photos

Hi Richard,

Thank you for the data on the smaller sizes.


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