Types of Scissor Jacks Used in Workbench

adjustable-workbench-scissor-jacksThroughout the workbench design process I experimented with several different scissor car jacks. I bought a scissors lift that was intended to be a transmission jack. This looked perfect; it was very wide and it had plenty of lift. But there were two problems with this jack. First of all, it did not have enough mechanical advantage and almost as bad was that it was of such poor quality that it just would not work. Next I tried an RV stabilizer jack. This was a huge scissor jack with an amazing 24” lift. However, I learned that these oversize scissor jacks actually have less mechanical advantage than the ones for automotive use.

I then bought a scissor car jack at a salvage yard from a mid-90’s Chevy Blazer. This has 16” of lift and it works great! I recommend getting a scissor jack from a pick-up truck or full size SUV for the primary jack to raise and lower the workbench height.

So as it turned out, automotive jacks worked best for this application. A secondary benefit to using automotive jacks is that they are very inexpensive and readily available at any salvage yard.

Jack Handle Observations

Workbench Mobile Base Motorcycle JackOne important thing you want to watch for with the automotive or truck jacks is how the jack handle attaches to the jack. Some jack handles have a hook on the end and the jack has a corresponding hole for the hook to go in to. Others are driven by a nut, or something else. The one I had the best luck with is the style that requires a hook on the end of the jack handle. It will probably be easier if you find this style of scissor car jack. Fortunately, this is the most common style for automotive use.

The lower scissor jack is used to raise the bench up onto the mobile base. For this I recommend a motorcycle jack. you can see by the picture on the left that the motorcycle jacks have a large stable platform that the bench can rest on when you are moving it around. On motorcycle jacks the handle typically attaches to a nut, but these are still far and away the best choice for the mobile base.

I also learned a few special characteristics about automotive type scissor jacks.

  • First, and most importantly, is that the higher a scissor jack goes, the greater the mechanical advantage. So, when it is near the top it has an unbelievable amount of leverage! However, when it is collapsed is has very poor mechanical advantage. This is why the RV stabilizer jack was unsuccessful.
  • Another thing I learned is that scissor car jacks move! What I mean by this is that as a scissor jack raises up, the screw also moves up with it. And the screw moves horizontally through the jack as well… It is probably easier to explain visually.

automotive-jack-zero-turnsIn this first photo you see a scissor jack from a Honda Civic. The jack is fully collapsed with zero turns on the screw. The top of the jack is 2-1/2″ from the floor and the screw is even closer to the floor. Also, the screw is centered inside the jack.

automotive-jack-four-turnsIn the second photo you see the same jack only now the screw has 4 turns on it and the top of the jack is 4-3/4″ from the floor. Note that the screw itself has also moved up off of the floor.

automotive-jack-89-turnsIn the last photo you see the same jack again. This time the jack is fully extended with 89 turns on it, and the top of the jack is 12-1/2″ from the floor. Note that the screw is now 6″ off of the floor. Also note that the drive end of the screw actually moved toward the centerline of the jack and the other end of the screw moved several inches to the left.

This is important to keep in mind because you need to fit two of these inside of your bench while also accounting for their movements. The jack you select might look just fine when you install it, but cause problems when you actually try to use it.

Fortunately, as I said at the top of this page; it is easy to find a scissor car jack that will work for this application!