I had the same problem as a reader who needed to raise and lower his benchtop planer, so I went to a scrap car yard and got a car jack for $2.50. I brought two square tubes with one to fit inside the other (not a sloppy fit; it must be a good fit), welded a plate across the top of the large tube and drilled screw holes to be able to screw it to a shelf. I fitted this inside the bench and welded a bolt on the lower part to fit over the car jack. This will raise the outer tube fitted to the shelf. The smaller tube (inside tube ) has two struts welded across the bottom end to be bolted to the base of the bench. As you can see in the photos, it can be raised and lowered by a cordless drill. The top of the bench can be removed when you need to use the planer.
– Edward Honan