Q&A forum: Screw Thread Strength Calculator
(size and capacity)

Yes our calculators are limited, exactly to the provisions described on our website

I believe your problem was that you have a thread the OD of which has been reduced from that required by a full thread dimensions and you wish to know whether or not it was still serviceable.

If I have understood the problem correctly, we at CalQlata would indeed use both Threads and Threads+ to answer the question as follows:
1) Select the correct thread from Threads and extract the necessary input data for Threads+
2) Enter the data into Threads+ for the fit class to which your thread has been machined and extract the strength of a standard screw (i.e. ‘S’)
3) If you have a standard thread on a non-standard root diameter, then the strength (of the thread, not the shaft) will increase or decrease linearly with diametral cross-sectional area. E.g. if you have twice the theoretical cross-section area of a full thread you will have twice the strength (2 x S)
4) You then compare the diametral cross-sectional contact area of your under-machined thread and reduce the strength accordingly. E.g. if your contact cross-sectional area is 80% of the design thread then your strength will reduce to 1.6 x S
5) If the root of your thread has also been machined smaller, reducing thread thickness at the theoretical pitch diameter then your thread will capacity will reduced still further. E.g. if the tooth thickness is 80% of the required thickness at the theoretical pitch diameter then your thread capacity will now be 1.28 x S

It is then up to you to decide whether or not 1.28 x S is satisfactory for your purposes.

We performed this calculation in a little over 5 minutes