Torquing bolts

[goboatingnow]

Originally Posted by tkeithlu

goboatingnow, one of my fond memories of engineering school was our field trip to Standard Pressed Steel (now SPS) in Allentown. They were among the first to roll threads into fasteners rather than cutting threads, hence the name of "Pressed". Rolled threads are much stronger than cut ones, for reasons I could still explain given enough time.

Actually while this is true , Re rolled threads , the origins of SPS go back to making brackets out of pressed steel rather the forged. The original pressing hut was maintained as a sort of museum on the site in Jenkintown . Fastener manufacture came later. Hence the “ pressed steel “ moniker refers to that period rather then rolled fastener manufacture

[Newf1]

A bit off topic but I used to work for an oilseeds mining company and one troubling area was bolts loosening off on a large piece of equipment called a vibrating screen. The bolts were 3/4" and about 12' long. Torquing down screen cloths to a specific value was the fastest and easiest method and was the least reliable. They then went to a bolt that had a built in dial indicator in the head of the bolt. It was torqued to a value/position on the indicator specified by the engineer. It was left for "X" number of hours and then checked and adjusted as required. Better results from a reliability standpoint. A third and most reliable method was performed in the shop during major rebuilds. The end of all bolts were machined flat and each bolt was measured using ultrasonics. The length was recorded on each bolt. Engineering provided a value for the amount of stretch they wanted and a probe was placed on the end of the bolt to measure stretch/elongation while the bolt was torqued. This provided the best reliability by far but was hard to duplicate in the field when worn out screen cloths had to be replaced because of the not so clean conditions in the field. Also very slow and tedious and not conducive to field outages where time was of the utmost importance. Sorry for the derail but shows the amount of effort some industries go through to keep things tight.

[Tetepare]

In most cases you’ll be torquing multiple bolts, and often there is an order in which they must be done. Also, some bolts need to settle and be re torqued after a short period.

Finally for the non mechanical, when using multiple screws or bolts, put them all in a bit, then hand tighten, then crank to final position. NEVER put one bolt/ screw in, crank it all the way in, then start the next one.

[tkeithlu]

Newf1, there are various ways to keep bolts from loosening once torqued, as you know. Lock washers, bent tags, nylon inserts, tight threads, and cotter pins come to mind. I'm surprised that they weren't on your list.

A dealer mechanic once failed to bend up the locking tabs on the rear wheel of a dirt bike of mine. The hub cracked in multiple places when the bolts loosened slightly and I hit the ground rather hard after a jump.

[goboatingnow]

Originally Posted by tkeithlu

Newf1, there are various ways to keep bolts from loosening once torqued, as you know. Lock washers, bent tags, nylon inserts, tight threads, and cotter pins come to mind. I'm surprised that they weren't on your list.

A dealer mechanic once failed to bend up the locking tabs on the rear wheel of a dirt bike of mine. The hub cracked in multiple places when the bolts loosened slightly and I hit the ground rather hard after a jump.

Mechanically restricting a bolt is a very coarse way of ensuring optimum fatigue life and retaining clamp load

The key to clamp load is to tighten well into the elastic region of the bolt without straying into the plastic region. This is actually very difficult to detect reliably using torque. The elastic region allows the bolt to accommodate certain joint relaxation while retaining clamp load.