In previous articles on the subject of fasteners, we have dwelt very little on the subject of female threads, other than in the article talking of bespoke nuts. The other main situation where we will find female threads is where these have been machined into castings or into machined parts. Unless the rules forbid their use, it is likely that we will have chosen an aluminium block, or where we are designing bespoke parts, aluminium is a very popular material, either in its cast or wrought forms, owing to its low density. Where Read more…

There are a plethora of different kinds of nuts on the market, and many are aimed at the racing market. Most of these will have been designed originally for the aerospace sector, and here we benefit from the exceptional quality control that the aerospace industry demands. Despite this range of good quality proprietary parts being available to us, there are also a considerable number of racing engine manufacturers who have bespoke nuts manufactured to their own designs. These might be to fit into a particularly confined space, maybe to minimise the height of the nut, or perhaps to Read more…

In the recent Race Engine Technology magazine article on the subject of fasteners, Wayne Ward touched on the subject of locking nuts and locking thread inserts. There are a great many applications where the loss of a fastener is not critical to the operation of the system as a whole; indeed it is common to build in a certain level of redundancy into a bolted or riveted joint for loss or failure of fasteners and the accompanying loss of pre-load. Again, even in this situation, the physical loss of the fastener is again rarely critical. In this article we shall look at some of the implications of losing a fastener. Read more…

After having calculated bolt stiffness, or measured the load-deflection curve directly, the best way to calculate pre-load is to measure the extension of the bolt directly. This method is preferred for con rod bolts and all con rod and bolt suppliers generally recommend this method. The fasteners require design features to allow measurement with a special micrometer. This method is impossible for fasteners in blind holes. For large fasteners in blind holes the extension can be measured directly if there is sufficient access for other measuring equipment.

Ultrasonic methods are very accurate but don’t seem to Read more…

In previous articles we have looked at how to calculate fastener and joint stiffness, and seen how these values of stiffness can affect the proportion of the working load experienced by the fastener by calculating the ‘load coefficient’.
See http://www.ret-monitor.com/articles/401/back-to-basics-part-2/

The forthcoming article in Race Engine Technology on the subject presents some simple examples of how variations in fastener stiffness can affect the levels of stress Read more…

Last month, we looked at some basic calculations regarding cyclic loading of fasteners. We must apologise for the recurring errors in printing symbols. The questions marks last month should have been ‘delta’ symbols. For example strain was given as:

e = ?L/L

This month we shall look at the calculation of joint stiffness, and the good news is that the methods and the basic calculations are the same. The combination Read more…

Last month, we looked at some basic calculations regarding cyclic loading of fasteners. Engine design engineers need a good understanding of the subject in order to correctly design the optimised fasteners required, but also those whose business is in improving the performance of engines need to be able to calculate when the standard equipment just isn’t going to be good enough.

We examined the concept of load coefficients and looked at a very simple example of how the load coefficient Read more…

In the previous article, we looked at the relationship between tightening torque and axial force developed, and a formula was given which included the effects of those parameters which, as engine designers, you are most likely to want to change. In this article, we shall look at the effects of cyclic loading – it is necessary to understand this in order to determine the proper pre-load. This process of doing fatigue calculations and checking that the pre-load is sufficient is an iterative process, and may involve changing materials, fastener geometry

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I have little doubt that, for many of you reading it, much of this short article and those that follow will be a case of ‘teaching Granny to suck eggs’. However, for those who are involved in engine design, possibly as beginners, an understanding of how a fastener develops load via the application of torque is a useful lesson. These articles don’t pretend to be a full guide to fastener and joint design (there are some very authoritative books on the subject), but will help give a basic understanding. This month’s article looks at the relationship between force and torque.

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A leading race engine manufacturer ran into fastener problems recently when out of the blue they suffered two separate incidents of flywheel bolt failure, each on a different specification of engine, during the same test. One failure had occurred on a standard specification engine and the other on one which had been given an increase in torque of 30%.

The manufacturer found themselves with a difficult engineering problem to solve and one which needed fixing very quickly. Read more…