When we calculate fastening torques for bolts in inserts, we calculate the torque based on the bolt going into a female thread with no insert in the first instance. The manufacturer then advises how much extra torque we should add to overcome resistance in the insert. This could be 0.1 Nm for an M3 and 0.4 Nm for an M6.
Do you have any information for Clinserts in M10?
other question:
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We wish to install a M10 x 1.4 D Keensert into a EN485-6082-T6 component. We will probably use a Grade 12.9 fastener. I have calculated a fastening torque of 59 Nm based on the fastener securing to Aluminium alloy threads. Do you have a list of recommended fastening torques? If not, can you advise me of an additional torque imposed by the insert on the fastener which must be overcome before 59 Nm's worth of pre-load is developed? |
Answer:
The tightening torque of a clinsert is not a value that can be determined by us, as it is dependant on the quality of the thread of the bolt that is being used. Most clinserts are made to military spec, which means that the tolerances of the thread are tighter then standard threaded bolts. The class of the bolt will not influence the friction, it's the tolerance of the thread of the bolt that will create more or less friction.
basically the inside thread of an insert is class 3B ,this means that it is used for close tolerance fasteners. These fasteners are intended for service where safety is a critical design consideration. This class of fit has restrictive tolerances and no allowance.
(The higher the class number, the tighter the fit) (B designates as an internal thread)
example:
3/4-10 thread has a basic pitch diameter of 0.6850 ; here you see the tolerances:
you have to bear in account the plating of the bolt, which might create interference caused by thread galling from the plating. You might then think the fastener is fixed correctly, but it is not sitting tight. The connection is underloaded and becomes suseptible to metal fatigue. Also the quality of the thread can be verified with a go-no go gage with a specified maximum torque. This measure the maximum amount of damages such as dents, scrapes, nicks or gouges.
now the confusion comes, since these inserts have been originally designed to the American standard, unified thread system, nobody bothered to change the tolerance 3B to the metric system: which would be class 4H or 5H.
so in the case you need to use below table:
M10 falls falls between 5.6 and 11.2 ; which and comes with a pitch of 1.5, below you see the tolerances:
