Originally Posted by
Andrew R Stewart
"
lock washers work by DIGGING INTO the contact surface... they can and do ruin aluminum parts they get smashed into" maddog34
Not completely correct. Lock washers also provide a spring like aspect to the fastener to handle the slight loosening that stresses and vibration produce in the installed bolt.
"Lock washers are special types of washers that prevent fastened parts such as nuts and bolts from loosening due to vibration and rotational forces12345. They provide a spring force or friction between the fastener and the assembled part, thereby maintaining tension and keeping the fastener tight." some quote from a online search so must be correct
Andy
I should have offered an answer for the OP's question- I do like to add flat washers (not locking ones) to my accessory fasteners when possible. Especially when the accessory is Al (and this is when maddog34 is correct) the flat washer reduces the wear on the accessory bolt hole's surface and makes tightening the bolt a bit easier to do. I have seen far too many split and star lock washers that are deformed, pried open or broken on the M5 and M5 bolts that most bikes use for these functions. What i dislike about thread locker is that so many people want to just forget about doing the periodic maintenance that keeps a well assembled bike working trouble free, and they believe thread lockers are the best "head in the sand" solution. Andy
Reality time... i regularly see Over-torqued screws on racks... i have, on many occasions, seen BMX rear axle nuts and split Lock Washers tightened to the point of pulling threads.. the dropouts are sometimes totally eroded by the split washers... i also see non-flanged nuts tightened onto aluminum dropouts... i've scrapped a couple alu. frames because of such erosions...
Flat washers indeed help distribute the forces involved, but most bike owners forget them or don't re-install them... sad but true.
Cross threaded American nuts show up on Metric axles occasionally... the axle and nuts need replaced... i keep a big plastic Skippy jar of rear axle nuts here, and about 30-40 solid rear axles, many with complete hardware and cones..... 100 serrated flat washers sit at the ready in one of the small parts organizers drawers... the serrations always face towards the nuts, NOT the frame
most walmart bikes come with no washers, just a serrated flange nut... many show ample indication of Vise Grip use... sigh.
split washers are for more or less permanent installs... they are metal-ripping destructors as the nuts are removed.
a large burr typically forms, that then needs removed.
the spring force you mentioned forces the face of the cut into the metal... twisting the nut to remove it causes the destruction to begin.
star lock washers tend to dig in less, in multiple spots.
they get used as ground point improvement aides around here, mostly... with a smear of Di-lectric grease.
old car revivals, car stereo and acc. lights come to mind....