**LINK**

A timing belt, a strip of metal, and some super glue.

I always use HPC for anything to do with gears, good products and excellent service.

Dave W

An alternative way of doing the job might be to re-work one of the inexpensive 12 V electric linear actuators that can be found on E-Bay et al for £25 – £30 if 2 to 4 inches of travel will do. Basic idea is to replace the existing telescopic tube guide system with an external rail with a nut block running up and down it. Screw needs to be far longer. Either replace with standard threaded rod or trapezoidal thread lead screws aren't silly expensive. Maybe £10 – £15 per metre and as much again for nuts.

Looked into similar some years ago for a friend and planned to use a 3/4 square tube as the guide for a nylon sliding block with the original nut converted into an insert to take a longer version of the old screw. Plan A was to re-machine the end of the screw to sit into the standard gearbox. Plan B was to simply chop the original screw and couple it to the new one via UJ or similar coupling.

Darned if I know why the job was never done. Got some drawings based on re-working a Hiwin brand actuator on the computer. Used a 3 mm pitch by 11 mm Ø screw according to my drawings.

Clive

Something like this perhaps?

linear actuator

I meter of threaded rod. 1 nut welded to a bracket some swivelling allowance. I electric screwdriver. All cheap as chips.

Just hold the driver to stop it turning?

You will have side load issues with a rack.

Perhaps a bike chain and sprocket, could even be motorized with a wiper motor, extend the worm wheel shaft so that you can fit a sprocket.

On a similar line to Jon Lawes, I have tacked a chain around a steel disc to mesh with a sprocket. A rough and ready rack could be made with a bit of square tube with a row of suitable spaced holes, and a small sprocket from a bike, the holes could be drilled about 5 mm and squared.

Ian S C

There's a few racks on ebay from old lathes about the size you are after. Might be worth a look. 👍