Creating a Lift Desk #4: The MECHANISM

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Blog entry by Underdog posted 12-04-2015 07:31 PM 985 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 3: Part Cutout and Base Assembly Part 4 of Creating a Lift Desk series Part 5: Re-finishing Unused Trim - A Cautionary Tale »

When I first got this drafting table, I had to think of how I was going to incorporate it into the desk I wanted to build. Several design decisions were made simply because of the size of my office, and the size of this mechanism.

I couldn’t go any larger than 70” wide, and 30” deep simply because the office just isn’t big enough for it.
I couldn’t go much smaller than that because this mechanism is just that big. As it was, I needed to remove the legs from the base, and the top, and decide if I was going to keep the tilt mechanism….

I agonized over the loss of the tilt ability for a week or two, but finally decided in order to have the storage and aesthetic qualities I was after, that the tilt had to go, and the arms had to be shortened.

So I removed the top, the tilt mechanism, and the legs. That’s the state you see in the first photo.

I finally worked up the courage to get out the Saws-all and shortened the arms, leaving enough tab on the top surface to bend down and weld into the ends of the arm tubes. Point of NO RETURN! I figured there was no going back anyway, because I’d already bought and cut up the plywood.. I took the mechanism over to my mechanic for welding. The price? Two biscuits from the local Golden Pantry. Good Deal! (Unfortunately, no pix of this either!)

Later on, after assembling the pieces of the desk and bolting this to the bases, I discovered that the right side arm was higher by 3/8”. I had to remove the mechanism and cut a slice into the bottom of the right arm and then reweld it to the same height as the left side. The price? Well. I still need to bring the boys some biscuits. Better do that before the next welding project, huh?

So.. when I got this thing all fixed up and ready to install, I started thinking about a couple other things. Like, how much metal debris got down in the lead screw?
Turns out, quite a bit.

Also, when testing it out without the top attached, I heard it go “thump thump” on the way down. I wondered about it til I took it apart. It’s got a kind of clutch mechanism, so that if the limit switch doesn’t work, or it hits something immovable, it won’t burn the motor up. So if you have enough weight on the clutch (from a tilting top, for instance), then it doesn’t slip like that.

The other thing was that I needed to move the electrical receptacles on the back, to the top of the base so I could get to it. So, I cut new holes in the top of the base, and moved the receptacles, then placed an insulator strip (old plastic oil can) to prevent shorting.

I then proceeded to take it all apart to clean all the grit out, and re-lubricate it. So hence the pix of the wiring and the lead screw. I didn’t want to forget how it all went back together.

Speaking of getting it back together…. when I got everything properly cleaned out and lubricated, and these spring loaded orange plastic slides (count: 4 each) on each corner, I tried to re-assemble it.

So…. imagine the base column sitting there with the motor and lead screw installed, and grease in each inside corner, and me holding the top column with the spring loaded slides, also greased, trying to lower this into the bottom column.

And then realizing after several tries, springs and slides falling off, and no small amount of blue streak incantations, that those springs on the slides have to be compressed before they will go down into the bottom column. Grease everywhere, temper frayed…

Finally, many wraps of electrical tape later, the whole mess slid down in place. Thankfully, I didn’t get any of the greased parts dirty so that I had to take it all apart and clean it. But boy what a pain!

Anyway, the mechanism worked flawlessly after adjusting the limit switches. Hummmmmm….. Up and down no problem. Only needs some weight on it to keep the clutch nut from spinning.

Ahhhh! Ready to bolt into the assembly!

-- Jim, Georgia, USA

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