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I've designed a table with an adjustable shelf. I feel as if I've researched the names and techniques for what kind of gear system to implement, but I need the experience of someone with knowledge of the subject to help me finalize my decisions.

Here is my design: Adjustable Shelf Desk, closed.

Adjustable shelf desk, opened

My questions pertain to the gear and crank system.

1 -The shaft in the design is 56" long. The shelf will hold approximately 30 pounds of equipment. What thickness should the shaft be?

2 - For mounting the shaft, I'm currently looking at these: Hub City FB260URX1/2 Flange Block Mounted Bearing - *can't post more that 2 links yet...

I'm just looking for verification that this is appropraite for my needs.

3 - Based on my research, the gear system is called a Rack and Pinion, but I'm having trouble figuring out what specifically the size and type of gear I should buy. Can someone provide a reference of something that would work for this set up?

4- Lastly, I need advice on how to mount and secure the crank and gears to the shaft. Will some sort of locking collar work? Or do I need something else? I am currently looking at these: Climax Metal 1C-100 Steel One-Piece Clamping Collar - *can't post more that 2 links yet.

That's it for now. I'll edit if clarification is needed.

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  • you will probably want some gears to make it easier to turn the crank and make it easier to lock.
    – ratchet freak
    Sep 26, 2016 at 10:27
  • Are you making the gears and shaft out of wood? If metal, just a piece of random hollow conduit is more than enough (this is very little force), and the gear size depends only on how much you want to turn the crank to move stuff. Figure out how many times you'd like to turn the crank to move your thing and use that to calculate gear size (1 rotation = 1 circumference of gear that the rack moves). Figure out how hard / easy you want it to be to turn and use that to calculate the size of the handle that you're turning (e.g. 30 lbs * gear radius / handle radius = force at edge of handle).
    – Jason C
    Sep 26, 2016 at 18:50
  • Originally, I played around with the idea of making everything out of wood (shaft and gears), but I wasn't confident that it would be smooth and structurally sound, especially because this is my first project using those sorts of equipment. I do, however, like the idea of being able to make everything myself, and I've found several good resources on making your own gears. I'll have to ponder some more on this! Thanks for the suggestions.
    – GreenWire
    Sep 26, 2016 at 19:02
  • Have you seen woodgears.ca
    – Jason C
    Sep 26, 2016 at 19:06

2 Answers 2

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I am by far not experienced with this. So I have little to say. I am sure you have gears on either side so lets start there.

1) I would say for the shaft maybe a good 1-1/2 in to 2 in would be a good thickness if it is a stronger wood. That would last very long. I would even consider thicker for pine. All it would take is to much weight and the grain can give anyplace in the shaft. Unless your using metal.

2) Any bearing the shaft fits into would work fine. Make it flush with the wood and have pressure so it does not fall out. You can also just place the shaft directly in the wood. I would make the hole in the wood ever so slightly bigger and use oil as a lubricant. Of coarse that would things a little harder but possible.

3) Something I can give a fairly good answer to. It is call rack and pinion, I am sure. The basic rule I have with gears is small gears will give more torque. Like on a drill, making it easier to rise the shelf but slower. A big gear will be faster, but harder to lift. I recommend smaller Maybe 10 teeth will work for you. I have a website you can use http://geargenerator.com. You can download the gear selected and print it. It is fairly accurate in size. So if you have a band saw you will be able to make a gear. cut the gear out (not perfect) and glue it to a piece of wood. Once dried use a drill bit and cut in between the teeth at bottom edge to make things easier. Then if you have a band saw you can cut it out. There is a gear without buying a gear. But this simple website does not help with the rack. But you can cut it out as well. As long as the teeth can line up and move you are set.

4) oh man... I will try my best. You can make a locking collar pretty easily. again a band saw may be best. I will be adding a rough picture of what I am thinking below. But use a bearing in the wood* and slide the shaft through for the handle to attach a locking collar. And do the same on the other side. It can not move at the point but can be loosen to move. The shaft should then reach over to the gear. I consider gluing the gear when it is on the shaft. Also put a bearing in the wood* on the other side, having the shaft sticking out the side. Locking collar there and on the inside. That should really work good. * Cut a hole from the inside and do not cut all the way through. Just so the bearing is flush to the wood. But have a hole cut bigger than the inner-diameter so that the shaft goes through the wood easy, but the bearing does not fall out. and have a locking collar on the inside against the bearing so it also has no problems falling out of place, but not so it is harder to turn.

Cut in half at the red line. The screws will tighten as you tighten on each side. This would be good for each end of the wood to keep the shaft from moving.

Here is a sample gear from the website. I showed were you should drill before cutting out the gear

I am hoping this answered the question very well. If not comment and I will do my best.

P.S. welcome to the club!

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  • This information was incredibly useful! I will be working to finalize my designs soon. Thanks for taking the time to add the pictures as well!
    – GreenWire
    Sep 26, 2016 at 18:56
  • no problem, willing to keep helping. Would love to see how it turns out!
    – Ljk2000
    Sep 27, 2016 at 2:56
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Not sure if this is the answer you are looking for, but I would consider, instead of gears, using a pulley system.

If you used a pulley setup, you could make used of any number of pre-made and readily available hardware systems (I would start with garage door hardware). This way you are working in tension, instead of compression, which requires much less material, and if you run a cable from the bottom of your lift hardware, up over a pulley, and back down to the rod where your gears would have been, then your crank simply has to wind and unwind the cables to operate.

Rough example sketch

Something else I would recommend would be to use full extension side mount drawer slides for runners. This would allow it to slide up and down smoothly, they are simple to install, and using two each side as shown, would prevent racking, or leaning of the shelf front to back.

In addition, I would mount then so that they are contracted with the unit up, and extended in the down position, this way you don't have to see them at all above the desk height.

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  • That's a great idea with the shelf runners. I was thinking about how best to keep the shelf unit aligned while ascending and descending, and I feel this is probably the best workable solution. Thanks for the input!
    – GreenWire
    Sep 26, 2016 at 18:56
  • @GreenWire You may also want to consider an additional locking mechanism that holds the shelf itself, rather than just e.g. a ratchet on the gears / pulleys. That way if your lift mechanism breaks, the shelf doesn't fall. Perhaps something as simple as holes at regular intervals on the shelf sides with pins you pop into place. Either that or make sure there's a bit of clearance between the shelf and the rest of the surface (or that the shelf can't fall all the way flush) to protect your fingers in case of an accident.
    – Jason C
    Sep 26, 2016 at 19:02
  • Yes! I was planning on having some sort of simple peg, or even having another full on shaft to help lock it in position. I'll have to play around with it more once I finalize.
    – GreenWire
    Sep 26, 2016 at 19:05
  • If you use a 'touch release' drawer slide, that may be enough to hole the shelf in the up position. Accuride 3832TR has a catch that is spring loaded, so when the slide is in the closed position it hold the drawer closed, and a slight touch will release it. In you case, the closed position would be up, and the open position would be down. accuride.com/en-us/products/3832tr-touch-release
    – Jacob Edmond
    Sep 27, 2016 at 12:20

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