Lead Screw or Linear Motion Source

[evolution]

Our team is looking for a Lead Screw that is atleast 45 inches long. We found one with Grainger, but with the complementary nut and shipping, it comes to almost $100. Anyone know a cheaper source for lead screws of this length?

Also, do y'all have any thoughts on other ways to achieve linear, powered motion? We've considered a linear slide with chain running the length of the slide, but this too is quite expensive.

Any thoughts or help apppreciated!

[Rick TYler]

The only other mechanism that leaps to mind is a drum-and-cable setup. I'm guessing you want a lot of precision, right? It might be time to get out and sell candy bars or hit up parents for $10 apiece or sell some blood or another quick-and-dirty mini-fundraiser.

[Madison]

What is it that you're hoping to accomplish and with what precision? There are many options for linear motion -- some expensive, some not; some more precise than others.

[Greg Perkins]

Look into "Rohlix" linear motion...they dont use lead screws, just ball bearings at opposing angles, they work amazingly, and are extremely safe, anymore than 20lbs of force to the external area of it will stop it from moving...look into i

[Kirk]

McMaster has 1.5', 3', and 6' lead screws. Search for screw and its the first one on the right (Acme Threaded Rods and Studs). They are still expensive but they have a lot more variety that Grainger.

Kirk

[Rick TYler]

I thought the idea of four AM planetary transmissions with matching omni wheels was expensive until I started pricing linear actuators and fully-equipped lead screw systems. *Boggle* We are now considering imprisoning a squirrel in a cage to move our aiming mechanism. (Check it out -- animals are not against the rules.)

[Andy A.]

Long rack and pinions have worked for teams before. They can be bought in 6' lengths or so from mcmaster. It's fairly easy to put two racks end to end and create a longer rack, or cut one down to size. So racks have the advantage of being a little more flexible in length. Be careful, as steel racks get very heavy very fast.

They also appear to be cheaper.

-Andy A.

[evolution]

I'm looking at page 3019 of the McMaster-Carr catalog. We're looking for a 10-pitch lead screw that offers sufficient strength, minimizes weight, and that is as cheap as possible.

I'm currently between a "Grade B7 Alloy Steel 3/8 inch - 10 pitch" lead screw or a "zinc-plated steel 1/2 inch - 10 pitch" lead screw (in a 6 foot length, they both come to below $30). The B7 alloy offers a mininmum tensile strength of 125,000 PSI, while the zinc-plated steel offers a minimum tensile strenfth of 65,000 PSI. What's more important for overall stiffness - material type or diameter?

Also, B7 alloy has a plain finish, while other has a zinc finish. The zinc finish is supposed to prevent rust, but will this also increase the short term efficiency of the lead screw?

Thanks!

[sanddrag]

Maybe you could spin it a bit faster and get by with plain ol threaded rod. I'd try to get grade 5 or 8 rod and nut though.

[Dillon Compton]

Last year my team ran the first stage of our arm extension (about 50 inches, I believe) on a "lead screw" that was just a piece of 5/8 threaded rod. We used a nut with an inch outer diameter, and tied it into a home-made bracket(I forget how). Driven by a CIM motor, this lead screw was used for the entire competition season, and still works today. Other than a single design modification we made on the first day of philly regional and the occaisonal(read: twice since we built the thing) application of a lubricant, we have not touched the thing since we installed it in mid-january 2005. The screw runs to full extension in under 4 seconds.


That was really just a convoluted way to say that threaded rod works fine, just use a hardy nut and I suggest coupling the motor shaft directly to the rod (mcmaster sells shaft couplings that will stage the sizes for you).

Good luck!

Dillon Compton
Team 1394

[Dick Linn]

If it suits your purpose, you can get acme screws and nuts from ENCO. 1/2" x 10 tpi x 6 ft is about $13. They are often on sale. www.use-enco.com