Lead Screw Design

Why wouldn't you just buy one?

Gordie.

If you mean ordinary metric thread, I'm not sure there is an M40. Standard sizes are M36, M39 and M42, and M39 is non-preferred.

But for that sort of diameter bolt stress is not a problem, only about 0.3 MPa.

Have a look at isel.com, they have such lead screws in M16 and M25 and I think thats more than enough for your 30kg - if you dont want to lift them over meters in milliseconds ...

regards uweka

Take in count the power that you will apply to the screw, not just the static load. In how much time do you need to move it? Or, whats the power of your motor?

How high do you want to lift the 30kgs? I suspect you want a very long lead screw and therefore the large diameter (M40) It will be costly to have it machined... . I would suggest the following... Take a lenght of steel tubing with a 5mm wall thickness and a 40mm dia. Use 6-8mm solid rod and coil it around the tubing. This will be the thread. If you use 8mm, leave 8.5mm gap between windings. Weld it to the tubing every 20mm (short welds-not too much heat, you don't want to distort the tubing..) as you wind, you weld because the rod will be under tention and will spring back if you don't weld it as you go along. To make the lead nut, take a short piece (about 200mm) of tubing that fits easely over the newly made screw. On the end of your screw, spot-weld the end and wind a lenght of rod in between the gaps, using a oxy-acetelene cutting torch to heat the rod as you go along- red hot, in order to take the spring out of it. Cut the spot-weld off and unscrew the 200mm long "spring" , make sure it turns easy enough. Insert the "spring" in the 200mm pipe.Carefully mark on the outside where the "spring" touches the inside wall of the tubing. Drill 8mm holes (at least 10 holes will do) along your markings spaced out over the lenght of the tubing. (obviously remove the "spring" when drilling) Then weld the "spring" securely in place from the outside through the holes. The reason for this is you can't afford any weld blobs and "bird poo" to be on the inside of the nut. You can install a grease nipple on the nut to make it easy to lubricate. Remember to leave space on both ends of your screw for the bearings...

Interesting approach on how to build a lead screw. But, if you 're not concerned about long term reliability, what about using threaded bars and conventional nuts? Its cheap, and reasonable if you're thinking about slow movement. If you're going fast, use ball screws ($$.$$$,$$!).

What if you need a leadscrew 6meters long? From the sound of the post I think this guy is an engineering student that got his first assignment. I agree to buy a threaded bar would be the cheapest option. But why does he need to DESIGN a lead screw? Assignment maybe? He probably has to design to travel a certailn speed and lift 30kgs with a certain type of drive... I am out of here..

the design is tricky and the optimum result will only be achieved by trial and error.

isel.com may assist. Another helpful organization is Gallil -