Table Mechanism Development

While working on the computer models of how to make the table height adjustable (in concept), I started thinking about different ways to change the height of the table and looked into what types of solutions were already on the market.

There are four main ways the height-adjustable tables work are designed (Knighton, 2018);

• Crank, including;
  • Traditional cast iron crank tables (the first type of height adjustable table invented)
  • Simple modern crank tables – as a cheaper alternative to electric
• Electric (very common)
• Counterbalance, including;
  • Single leg pneumatic counterbalance
  • Two-leg pneumatic counterbalance
  • Two-leg spring counterbalance
• Gas Cylinder

The main problem with most of these methods in their traditional form is that they have a range limited by the mechanism. Most of these rely on one shaft piece sliding into or alongside a second one. The highest setting is the length of these two pieces and the lowest is only half the total height. As I want the table to go from lounge up to standing, a more creative option would be necessary (although you could engineer something to do this range in a straight line, but where’s the fun in that?).

Working on computer models

In my user feedback post (read more here), I spoke about how the triangle shape inspired me to create a table lifting motion by using two triangles passing each other to go from low, medium, and high settings. I used computer modelling to test this out. As you can see below there are some parts of this initial design idea that worked and some that didn’t. The video clip shows the two bars crossing over each other, which wouldn’t work using real materials.

There are some things that I did learn from this exercise. For example, the two rails under the table top work quite effectively. It appears the two triangles push the table top slightly higher than the final ‘standing’ height when they cross over each other. To account for this I planed on exploring using a compression spring to provide some give in at this point, or alternatively having a thicker table top and creating a small arch cut out underneath to accommodate this motion. I would discover through building a proof of concept mechanism later that this was not needed (see more below).

Initially, I thought that whatever solution I designed for the adjustment mechanism/system, should be enclosed in a casing. This is standard across office desks marketed to commercial office spaces. However, after looking into different methods, combined with feedback from Samantha (user) and their curiosity about how it would work, I felt like a blend of modern and industrial aesthetic suit the design direction. This aesthetic also supports the idea of work in a post-pandemic society. Why go to an office with plain white desks with metal t-shapes legs spanning across a large office space. People are now looking to be in the office less, and have a higher quality experience. Going back to an industrial aesthetic and a more homely trendy vibe. It is also suitable for smaller more eclectic-styled offices which we will likely see more of in the future.

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Settling on a crank table, and researching types of gears

I learnt a lot working on my CAD modelling and playing how the components would work together and if the table motion was possible, but still wasn’t answering the question of how the user would get the table to move. Would they simply lift it themselves and then lock it in place? Not ideal if you have a variety of able-bodies. Perhaps a counterbalance or spring-loaded mechanism, where the table wants to be in the top position, and the user uses force to push the table into a lower position and then lock it in place. I have owned an old architectural drafting table that worked like this, and the plus points were that it was quite smooth, simple and you could set it to any height (not preset lock locations). There were some occasions where I would go to unlock the mechanism and forget to apply the correct amount of pressure to the top and it would spring up very quickly (not ideal).

For my design, there is two points where motion could be applied and it would translate into lift.

First, if you rotated the pinpoint where the triangle meets the base, this rotation motion would push the tabletop up. The main issue with this would be having a crank quite low down to the ground (similar to Image 6 of the traditional tables).

The second is if the tops of the triangles slide across the rail under the table, one in one direction and the other opposite. A simple solution to this would be a handle through the top of the table to slide them across each other, but again, not ideal for the user.

After considering the benefits of different types of table lifting mechanisms, and that the motion required for the top to move using a slider motion, I decided this could be solved by using a crank. Similar to how old industrial tables worked (and playing into that aesthetic), but instead of moving up and down, it would be moving components back and forth. This of course presented me with a new challenge. How to adapt an old method to marry with my design intent?

Crank with a break tool

Standard crank tables work like a pully system, and require a breaking system to prevent them from dropping, as seen in the examples below.

Types of gears (that could be used to crank the table top)

There are a variety of gear systems I looked into while researching how to create a height adjustment mechanism, these inlcuded:

Name	Image	Description / Function
Spur Gears (or Toothed Wheels)	Image reference: (Ryan 2017)	Spur gears are the simplest type of gear. They are known as cylindrical gears and have spurs, or teeth that interact with a chain (such as a bicycle) or with another gear. (KHK Stock Gears 2021). These types of gears are extremely reliable but some drawbacks to this type are; they can produce noise and they cannot transfer power between nonparallel axes or over long distances.
Helical Gears	Image reference : (CRL 2021)	Helical gears are gears with angled teeth cut around the perimeter of the gear body. These gears are smoother than standard spur gears and allow for smoother operation. (CRL 2021)
Rack and Pinion	Image reference: (Budmir 2017)	Rack and Pinion systems are made up of a rack (sometimes referred to as a linear gear) and a spur or helical gear. These are ideal for providing linear drive over long distances. These systems can sometimes have backlash issues, but when using high-quality helical gear, the backlash is a rare occurrence. (Budmir 2017) When using metal on metal construction, lubrication is important, and often an automatic lubrication system is used. When designed correctly, pre-lubricated rack and pinion systems can be used for several years before maintenance is required. (Anselmo 2012)
Worm Wheels	Image reference: (Collins 2017)	This mechanism is made up of constructed of a v-thread ‘worm’ and a spur gear, made of dissimilar metals. Their shafts are oriented at 90 degrees to each other. The worm is typically used as the driving component as its threads activate the gear’s spurs. The resulting action is a mixture of sliding and rolling. Worm wheels ideal for quiet operation. Worm gears are also self-locking making them ideal for lifting/ hoisting weight-bearing applications. (Collins 2017)
Bevel Gears	Image reference: (Ryan 2017)	Bevel gears are used when you want to change the force direction by 90 degrees. (Ryan 2017)

Creating a proof-of-concept prototype with ‘found’ components

To supplement my design process, I ordered a variety of parts I could find on Amazon that I could use to explore the idea of a crank system. With the ongoing covid-19 pandemic the workshop was on restricted access, we were not able to access for extended periods of time to experiment, test, or play with our design ideas. They were available on a click and collect only, so completing as much of the process at home was a requirement due to the situation.

Items ordered from Amazon:

• Foam Core Board
• Single Speed Freewheel Cassette Cog Sprocket x2
• Large Split Pins
• Single Speed Bike Chain
• Compression Springs
• 3D Printer Timing Belt Pulley

Images of experiment process

The video below shows the final product of my experiments. It is constructed upside-down due to the weight of the chain vs the foam core. Also, this method makes it easier to see what is happening. In the end I didn’t need to use the compression springs as this experiment proves my crank style concept for raising the table using the leg style designed. There was some resistance between two pieces of board when sliding, so the final design will benefit from the incorporation of a rail / slide component incorporated.

I did press on the legs to see if they were locked in place and they did seem that way – if I use worm wheels then the mechanism will be self locking.

I also used the timing belt to show how with one gear being moved, it would transfer the motion across the table and to the other set of table legs. This design could be adapted to work with a handle crank or with a small electric motor.

A more robust prototype will be needed to test strength, force required to move with weight, and to further refine the table details. For the purposes of this project, and due to time and resource constraints, I proceeded to create computer designs for my final presentation renderings.

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References

Anselmo, M. 2012. Lubricating rack-and-pinion sets for long life [Online]
Available at: https://www.machinedesign.com/motors-drives/article/21831619/lubricating-rackandpinion-sets-for-long-life
[Accessed 22 April 2021]

Budmir, M., 2017. Rack and Pinion Drive System: What Is It? [Online]
Available at: https://www.motioncontroltips.com/what-is-a-rack-and-pinion/
[Accessed 22 April 2021]

Collins, S., 2017. Worm gears: What are they and where are they used? [Online]
Available at: https://www.motioncontroltips.com/worm-gears-what-are-they-and-where-are-they-used
Accessed: 22 April 2021

CRL (Compañía Levantina de Reductores S.L.), 2021. Helical gears or spur gears? [Online]
Available at: https://clr.es/blog/en/spur-gears-helical-gears
[Accessed 22 April 2021]

KHK Stock Gears, 2021. What is a spur gear? [Online]
Available at: https://khkgears.net/new/spur_gears.html
[Accessed 22 April 2021]

Knighton, B., 2018. Do You Know How A Counterbalance Standing Desk Works?. [Online]
Available at: https://worldinteriors.com/blogs/austin-furniture-roots/the-crank-table-guide-background-maintenance-and-common-fixes
[Accessed 22 April 2021].

Knoll, 2021. Height-Adjustable Tables & Desks. [Online]
Available at: https://www.knoll.com/design-plan/products/by-category/tables/height-adjustable-tables
[Accessed 22 April 2021]

Ryan V., 2016. Gears and Gear Systems. [Online]
Available at: https://technologystudent.com/gears1/gears1.htm
[Accessed 22 April 2021]

Ryan V., 2016. Bevel Gears. [Online]
Available at: https://technologystudent.com/gears1/bevel1.htm
[Accessed 22 April 2021]

Schultz, C. 2018. Back to Basics: Helical Gears [Online]
Available at: https://www.geartechnology.com/blog/back-to-basics-helical-gears/

World Interiors, 2021. The Crank Table Guide. [Online]
Available at: https://worldinteriors.com/blogs/austin-furniture-roots/the-crank-table-guide-background-maintenance-and-common-fixes
[Accessed 22 April 2021].