I looked at buying a Linear actuator but they are too expensive for the project i wanted to do so I thought i would make one and document it for Instructables so that others can follow what i do for their project or improve on it.
I have 2 options for you guys here, the frist option I tried and a slightly improved model.
Step 1: What you will need
You will need the following materials and tools
Welder - Optional
Hacksaw - a junior hacksaw is fine
flat head screw driver
vice - i used a hobby vice which was fine
a metal file
Materials : -
Epoxy Resin - Araldite is what i used
threaded rod - M10
Nuts - M10
piece of clothes rail
clothes rail holder
DC Motor or a Cordless Drill with forward and reverse
Step 2: Picking your drive method
You need to choose your drive method well, my original plan was to use a sewing machine motor to drive my actuator figuring i could reverse to polarity to reverse the motor. it turns out a sewing machine motor uses AC current and a AC motor will only spin one way regardless of which way round the polarity is. to get it to reverse you would have to use gears which i wasnt prepared to do.
However a DC motor will spin the opposite way when the polarity is reversed, so i broke up a cordless circular saw for the motor, it wasnt very good as a saw anyway, i cut the cashing up and kept the gears that are in it in place.
Your other option is what i have ended up choosing which is a cordless drill, the advantage of this is that it has a chuck so what ever you put in it will be centered.
Step 3: Inner rod
the inner rod of the actuator is basically a threaded rod
now if you are using a cordless drill as i have decided to do in the end then you could just cut it to the correct length with enough to fit in the chuck of the drill extra.
if your using a DC motor its a little more involved you need to attach the rod to the shaft of the motor.
using the drive wheel from the sewing machine motor you need to weld a nut on the end of it making sure its as central as possible.
then just thread in the rod in to the nut as tight as possible and weld that to the nut, put a spot of expoxy resin on the nut to hold it to the pully centralised let it set, then put it all on a screwdriver to hold it while you weld it.
now you could use a long bolt instead of the nut and rod but i couldnt find one long enough as i wanted at least 20cm of travel in the rod.
now that its all welded together its not going to come appart and you can used the sewing machine pully to attach it to the shaft of the motor as it had a little screw in the side of it which you can tighten on to the rod of the motor.
Step 4: Outer Casing
the outer casing is the same no matter which method your using, basically a nut inside the rail.
cut the rail to the same length as the threaded rod using the mitre block to keep the cut as straight as you can.
the nut was a tiny bit larger than the rail was but thats ok because it would mean it would be tight in there.
i cut the rail to length then i cut slits in the end, about 6 of them so the rail would open as i hammered the nut in to it.
hammer the nut in to the rail, make sure the nut is level before you carry on.
put the rail in the vice with the nut facing up and mix up some epoxy resin, paste this around the nut and in the slits being careful not to get any inside the nut where the thread is as this will mess the actuator up. You need to let this set for about half an hour before you can work on the other end, and leave it for at least 24 hours before you use it to make sure its gone off properly.
now you can put epoxy resin inside the rail holder and put the other end of the rail in to it, not the nut end, put it in the vice and clamp it so it pushes the rail holder tight to the rail, now put epoxy resin around the edges filling in the gaps and let this set.
Step 5: Put it together and your done
all you have to do now is to thread the outer casing on the the inner road and your done.
i have pictures of the threaded rod on its own in the casing which then can be put in to the chuck of the drill and used that way, but also of the one that can be used with the DC motor.
Some of you are saying to your selves "where does the petroleum jelly come in to it then" well i use this as a cheap grease, best thing i have found is to mount the rod on your motor or in the drill and get some petroleum jelly on your fingers and use the motor to spin the shaft slowly while you grease the rod, this will provide less friction on the rod when its spinning up and down on the nut and hopefully make it last longer and it wont squeak when its turning ;-)