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Shop Furniture #1: Assembly Table - Design

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Blog entry by mawilsonWCR posted 03-06-2021 04:34 AM 538 reads 0 times favorited 0 comments Add to Favorites Watch
no previous part Part 1 of Shop Furniture series Part 2: Outfeed Table - Design »

Filling the time waiting for the new building shopping for machinery and designing shop furniture. First up: an assembly table. Okay, actually it was an outfeed table, but that is really pretty simple. A good learning exercise for Fusion 360, though. The table and Fusion 360 may be the subject of a future post.

My assembly table is hardly unique. Seriously, how many ways can you build a table. That said, every design needs to start with some requirements.

Features

  • Lots of room. Top will be approximately 4’x8’.
  • Dead flat top. Torsion box is the winner here. 1/2” plywood bottom skin, 3/4” top skin and 1/4” hardboard sacrificial top.
  • Mobile. About the only things in the shop that won’t have wheels will be a desk/worktable and the miter saw station.
  • Adjustable height. Powered. Read on.

Actuator Selection

There are probably as many ways to adjust the height of an assembly table as there are adjustable height tables. Well, maybe not quite that many. Probably the most frequently used method involves using scissor jacks, though why most use car jacks is lost on me. RV stabilizer jacks are scissors with a flat top for welding to trailer frames – no awkward vehicle interface to deal with. Some implement some variation of linear actuator. I’m opting to use an actual linear actuator.

So many choices. Capacity is all over the map, but it’s a relatively easy choice; pick the highest capacity that fits in the budget. Basically, the actuator need to be able to lift the top and optionally whatever might be on it. Since I have to be able to move assemblies afterward, a 300# lift capacity should be sufficient and fit in the budget.

The major choice is throw length. Too short and the table won’t get tall enough. Too long results in a table won’t get low enough. So I loaded a spreadsheet with data on each length to generate the minimum and maximum height. A 12” throw resulted in a minimum of about 26.5” and a maximum of 38.25”. That seems to be the sweet spot in range.

Leg Design

A single actuator won’t hold the table steady. Four could, but there’s a problem. Lacking a servo control system, there is no way to ensure they will move in unison or stop at the same point. So, borrowing from another design, I plan on a scheme of fixed legs attached to the top fitting into a box attached to the base. This is a draft section at minimum and maximum:

Also borrowing from yet another design, I plan to include a pin to lock the legs at the selected height with a 2” interval.

The remaining question is: will the 7” overlap be sufficient for stability?

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