My machines are mostly fixed together with hex head screws or bolts with
plain washers and spring washers.
I was talking to a machine builder today who suggested I call up conical
washers or belleville washers instead.
What is other peoples opinion on this?
If heat is not an issue why not look at looking at nylock nuts.
They have a nylon insert that "jams" the threads - preventing the
loosening of the nut.
Doesn't require special tools, can be reused numerous times, and
dispenses with the requirement for additional lock type washer.
Cam Jacks> My machines are mostly fixed together with hex head screws or bolts with
One advantage for using Belleville washers in place of either flat or lock
washers is they tend to maintain the preload exerted on the joint system so
long as the bolt and joint deformations are relatively small. Better yet,
increase the fasteners length to diameter ratio to reduce stress, fatigue
failure and loss of preload.
When it comes to properly designed highly stressed threaded bolts, the
first year mechanical engineering "Statics and Strength of Materials"
books and courses go over the theory of how to size a bolt very well
for the range of forces a bolt must endure, and also how much torque
must be used to pre-stress the bolt correctly.
I don't design highly stressed machinery, so I have forgotten much of
what I read, but if I had to design those things again, I would reread
my old stuff and search out new articles to be sure I did it right.
It's a really thorny issue, making bolted joints that won't vibrate undone.
One thing to note, is that some people feel (backed up by test results) that
spring washers actually make things worse. If you look at catalogues for
slewing ring bearings, they usually say they will not necessarily honour the
guarantee if spring washers are used, and you must use solid, hardened
I think the Nordlock type of serrated/cam-action type seem well thought of,
and my other recommendation would to use an appropriate grade of Loctite
Otherwise, the correct size/number/length/torque of bolts will do the job in
Actually, washers are supposed to make the torquing of bolts more
consistent by providing a hard consistent surface to put load against.
Variable bolting surfaces like castings and varying amounts of
corrosion make for totally unknown torque loads to get the desired