I think, for what I read, that when you use a washer with a bolt, the weight that it is supossed to carry will get better distributed.
My question is: I am assembling the x-carve, and, in the gantry step (step 4), they instruct us to use washers for attaching the makerslides to the side plates only in the bolts that go into a slot that is wider. That makes sense. But why do we not use washers in the bolts that go trough normal holes? Wouldn’t it be better? Or is there a mechanical/functional reason why sometimes it is better not to use washers?
Thanks in advance!
For applications like this where the hole is circular and not slotted, and the torque is relatively low, it’s easy to get away without using a washer. It can’t hurt, but it’s approaching the point of diminishing returns.
However, high torque applications absolutely need a washer to distribute the force down over a larger area and to help reduce the under-head friction. In those instances, you’re generally oiling the threads AND the bottom side of the bolt head to let you get the most preload that you can.
Makes sense about the cost.
When you say it’s easy to get away, you mean that it can work ok and have no problems at all, but that it would still be always good to use a washer?
(What I mean is, is there any application where a washer is not only not necessary, but counterproductive?)
I can’t think of any time off-hand where a washer would be counterproductive if you’re using typical bolts, unless your clearances are so tight that using the washers would cause the bolts and/or nuts to rub against something. They’d be bad for screws and bolts with tapered heads, like drywall screws, but hopefully that’s not applicable here.
A lot of the time the force of the tightened fasteners is not enough to cause yielding (permanent damage) of the fastened material. This means that the bolt isn’t pressing in hard enough to whatever your fastening for it to do any harm. In the case of the plate with the slot using a washer for the bolt, the slot takes a way the side material that the fastener would typically use as a support. However, I’m sure the washer here isn’t necessary either because of the plate material being used.