How can I increase the resistance in an adjustable scissor-lift?

Question

Recently I built a scissor-style laptop raiser and book lectern. It works fine, but the weighty laptop requires much tightening of the wingnuts, making me fear that over time the wood will crack (they're some simple pine scraps and I already remember hearing some cracking, although not much).

The logical way forward seems to be increasing the friction between the arms at the contact points by gluing some material (or something like Nordlock nuts) to both parts, thus increasing the friction coefficient between the surfaces. That would enable me to get more force of friction per unit of normal (~tightening) force, reducing sliding and the need for drastic tightening.

I have researched about the best materials for increasing friction, and thought that the best options would be either two pieces of rubber on both sides or something like anti-slip tape, or perhaps the aforementioned expensive Nord-lock type nuts.

I also want to avoid wood abrasion.

What is the simplest, quickest and least expensive way to increase the overall strength and/or decrease the need for tightening per unit of "strength"?

Answer 1

I suspect a combination approach is the way to go here, so that you're not hanging your hopes on one potential fix that might not do quite enough (especially over time).

The compression of the wood under the washers is unsightly and obviously you want to minimise this, but just to mention there is a limit to how far this will progress, and eventually the wood reaches its maximum compression.

So the first thing I would suggest doing is installing fender washers¹ under each wingnut. These will spread the load as the nuts are tightened and reduce the compression. You can install the fender washers under the existing washers or in place of them.

But I suspect the thing that will make the most difference is to fit something at each hinging location that provides much more friction than wood on wood. So I would make washers from something like thin rubber sheeting (old bicycle inner tube works if you happen to have a source) or a cork-rubber composite, e.g. Crubber². Both of these materials are used to line woodworking vice jaws and reduce slippage, and both can be cut easily using scissors so you don't need a set of punches or anything.

Since you clearly already have a drill, I would sandwich the washer material between two scraps, clamp tightly, drill a series of holes a sufficient distance apart, unclamp and then simply hand cut washers with the holes as centred as your OCD demands :-) ³

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¹ Large washers with a small hole.

² No endorsement, it's just the only brand I know.

³ For anyone who ever needs to make something like this as perfect as possible without a punch, here's one neat trick. Start with a template made by drilling through thin plywood, MDF or hardboard with a sharp flat bit/spade bit or Forstner. The resultant hole can be placed over the pre-drilled central hole with surprising accuracy purely by eye; not every one will be perfect, but if you take your time you shouldn't be out by more than 0.5mm every time.