I've been standing at my desk instead of sitting. It has really helped my back. Enough that I can concentrate on work. Now my legs and feet ache. I'm able to move the keyboard/mouse and sit, but the monitors are too far away. I've ordered a new chair that I know will work so I should be ok sitting. However, I still think standing is good too.
You can see in the previous post, I have a laptop & 2 monitors. I could adjust the stand I made, but not with everything on it. It's time for a stand that can adjust with everything on it. And to make it wider (13") so nothing hangs off the ledge.
I've seen some DIY lifts that use an X with 1 side fixed and the other moving. Unless all the weight is on one side, it won't work for something distributed across the whole thing. I decided to go with a scissor jack, like for a car. The base is fixed, the top is fixed and a screw adjusts it.
By using 2 crosses, I can have a wide stance to support across the whole 56". The middle pivots are 12.5" apart. And front to back are about the same.
I want to raise & lower about 20". To make the crosses, I cut 8 pieces of wood to 22". So, we have 8 links.
I found the center, drilled a hole and then drilled another hole just a bit in from the end (1/2"?).
I used those holes to drill another piece with matching holes. Then, with a bolt in the center, I rotated the bottom piece to its undrilled end & drilled through. Using this, the distance from center to the either end will match. And then I drilled all the rest to match.
For the base, I have a long piece of 1x3. I purchased v grooved wheels with bearings to roll along it. It's important the the bolts through the wheels are the same height as the fixed bolts.
I'm using 1/4" 20tpi bolts everywhere. I have washers between pieces of wood to reduce friction. The wheel bearing is recessed so I stack 2 washers and the fender washer prevents the wheel from rubbing wood.
I have a strip of 1/4" oak nailed to the base that works as a rail for the V. Just lightly planed square off the bandsaw.
The crossed links are separated by a small block of wood and washers. The total thickness should be the same as the 1x3 used for the base & top.
Looking at the end with the top & base. You can see the oak strip is offset.
Here is my initial assembly. I have 3 horizontals fixed with dowels to the 2 56" long base pieces. The front top rail is screwed to the desktop left right & center. The back top rail is only screwed in the center.
With everything tightened down, it moves smoothly up & down. If you look at the cross bolts, you can see the crossbars I bolted between. This adds strength & some stability front to back.
I used insert nuts in the end of the crossbar. It's bolt -> washer -> wood link -> washer -> wood spacer block -> washer -> wood link -> washer -> insert nut -> crossbar. The cross bars are oak. Because I have lots of it. And this is the part to raise & lower the desk stand.
I drilled holes in the center of the crossbars. In one crossbar, I put a threaded insert.
I screwed a piece of 1/4"-20 rod through the insert and through the hole in the other crossbar. On the end of the rod on the other side of the hole I put 2 fender washers with paste wax between and then 2 nuts that I jammed together. I also put paste wax on the threaded rod to help lubricate it.

There is lots of tension in the mechanism. Enough to bow the 1x3s upward 1/4" in the middle when fully raised. When moving, there can be a shift front to back that is easy to steady with a hand.
In the raised position, you can see the drill I'm using to move it. It stays in that position, not moving left or right. It's quick and I can't imagine how long it would take otherwise.
I'm pleased with this. When seated or standing, everything is at the right height.
I'll have to add something to hold the keyboard & track when standing. Perhaps something I can remove when sitting.
I might eventually wear the holes the bolts go through, but I can make the holes bigger and put some kind of bushing in if it matters. They're only pine.
The 1/4-20 rod might not hold up. I think the paste wax lubricating it will keep it from overheating. The tension might fatigue it. I'm going to put a rope around the crossbars as a safety when it's raised. That will give be time to look for a thicker rod with coarser threads that will move quicker.