Automated Draughting Table

Updated 23 Sept 2021

Now this project can easily be described as overkill, but I had an old draughting board and tee-square (stored behind a desk in a corner of the house) and a stepper motor that I’d bought for a client project that didn’t eventuate. All my drawing is done on CAD now, but every now and then I wish I had a nice big flat surface to work on that isn’t the dining-room table. I also had a spare section of wall.

So I came up with this.

Yes, I know – the old drawing board needs a bit of a clean up… Behind the board is the mechanism to lift it, together with the controls. The motion is controlled by a rotary encoder, which is mounted on the shelf holding the board (grey box with knob).

Here it is in the up position, held in place by the linear actuator I made.

At the base of the linear actuator is the (NEMA 23 size) stepper motor. I had to recess it into the cavity wall to get the right angle for lifting. The actuator is fitted with limit switches at the top and bottom extremes of movement.

The controls are a Arduino Nano with a Funduino expansion board. The stepper motor driver is a DM542 unit, and the power supply came from an old Lenovo laptop.

The mechanical components are a piece of M10x1.5 threaded rod, a couple of sections of PVC pipe that neatly slide inside one another, a coupling a nut and a bearing turned from delrin, and a few screws and 3-D printed components.

The DM542 stepper motor controller is very flexible. You can adjust the number of micro-steps the motor can do, and limit the motor torque. This last item means that you can protect it from overload if it jams. If I push on the board as it is lifting, the motor stops.

A sectioned view of the actuator:

I wrote the Nano program so that the rotary encoder can change the speed of the motor in steps in either direction up to an adjustable maximum. Clicking the knob ramps the speed back to zero. Encountering either of the limit switches stops the motor instantly, but allows motion away from the switch.

My wife has just claimed the new device for her 1000-piece jigsaw.