the most inexpensive lead screw needed

I am on a very tight budget and so I need the most inexpensive lead screw I can find. Not only that, but I only need the screw to bear a
load of at most 15 pounds. I have done considerable searching, but cannot find any suited for my very small scale project at a reasonable price. The following link is for the least expensive I have found so far, but it still has a capacity of 240 pounds for a plastic nut:
http://www.roton.com/Mating_Components.aspx?familyp60762
Is there anything less expensive than that?
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On Sun, 29 Jul 2007 21:47:57 -0000, snipped-for-privacy@keenebroadband.com wrote:

========Much depends on what you are using it for and how durable it must be [and under what conditions]. More info = better advice.
4 lead anything will be expensive.
Can you use a larger piece of allthread with a coarse pitch, and a nut clamped in place? If back lash is excessive, you could use two nuts with a spring between them clamped against the slide. This will reduce backlash and allow adjustment for wear. Stronger spring = less backlash but harder to turn.
See http://www.use-enco.com/CGI/INSRIT?PMAKAa9-1523&PMPXNO719279&PARTPG=INLMK32 if you have to have acme see http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2 if you have to have 4 tpi action http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2
These are examples only and your local mill supply / fastener shop will most likely have something suitable in stock.
7/16X20 and 1/2X20 (UNF) make a nice lead screw in that it is easy to calibrate for movement, i.e. 1 turn = 0.050 inches.
Unka' George [George McDuffee] ===========Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.
Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.
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On Jul 29, 5:13 pm, F. George McDuffee <gmcduf...@mcduffee- associates.us> wrote:

This is for a rather ambitious robotics project. I need the lead screw to lift a small platform about 4 inches, weighing no more than 10 or 15 pounds. I also need a lead screw mechanism to slide a platform in a horizontal direction mounted on a rail or track. That platform would also be about 10 pounds, and I need it to slide at least 3 feet. Both of these would be connected to rotary motors. According to my research, it seemed like a lead screw was the least expensive screw mechanism available. If there is something less expensive, I would much rather use that. Also I need a moderate degree of precision so I can move the platforms in increments of a millimeter at a time, and it must be able to hold its position and not "drift" when the motor is not pushing it along.
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.5 in / .25 in threaded rod from the local hardware store. Chuck it in a drill press at a low speed and gently sand the sharp apex from the threads. Even cheaper?... steal the rod.
Hul
snipped-for-privacy@keenebroadband.com wrote:

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I think it's worth asking - what is the actual purpose for the lead screw? Often, I've found that if something I want isn't available, it's because I'm trying to do something the hard way, and something better/easier exists.
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On Sun, 29 Jul 2007 22:26:38 -0000, snipped-for-privacy@keenebroadband.com wrote:

<snip>
====Sounds like a natural for allthread and some nuts.
Unless you have space/weight limitations use 1/2X20 or 7/16 X20. Given your accuracy requirements, you can simply tap a hole to the same thread size. 1/4X20 should be adequate is you can keep the screws under tension.
These will wear out in fairly short order (a few thousand to 10s of thousands of cycles depending on lube and nut material], but should be adequate for your needs, i.e. proof of concept. Self lubricating material such as nylon, delrin and HDPE with relatively long threads [c. 1 inch] will last longer. A one inch [2X] "depth of thread" in a polymer should eliminate any backlash until wear become evident.
FWIW -- with a depth of thread engagement equal to the major diameter, most screw materials will fail before the threads strip. With a 1 inch depth of thread [2X diameter], a 7/16 or 1/2 screw *WILL* fail before the threads do until the wear becomes totally excessive.
Allthread [or Redithread] typically comes in 2, 3, and 6 foot lengths in the US. For example click on http://www.barnhillbolt.com /
http://www.fastfixdirect.co.uk/code/navigation.asp?fType steners&MainCategoryID=4 http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2 http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2
FWIW -- lead screws are generally very high accuracy [like micrometer threads] and are used on lathes to generate the threads. Very much over-kill for what your are to do. Term you need to search on is "linear actuator." for some examples click on http://www.trossenrobotics.com/store/c/3103-Linear-Actuators.aspx http://www.surpluscenter.com/sort.asp?UID 07072309213746&catname=electric&keywordLD http://www.surpluscenter.com/sort.asp?UID 07072309213746&catname=electric&keywordLA
remember that you can trade speed for power and accuracy by gearing the stepper motors down to the threaded rods. Small cog [timing] belts are generally used. click on http://www.sdp-si.com/D265/D265Cat.htm http://www.sdp-si.com/D785/D785Cat.htm
*************** Welcome to the world of engineering/design where the criteria are
*strong *light *cheap
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Good luck on your project, and please feel free to ask if you have more questions.
Where are you located? Your use of "millimeter at a time" indicates you may not be a US resident.
Unka' George [George McDuffee] ===========Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.
Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.
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On Sun, 29 Jul 2007 22:26:38 -0000, snipped-for-privacy@keenebroadband.com wrote:

All thread and a do it yourself split nut.
Gunner
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snipped-for-privacy@keenebroadband.com wrote in

Acme screw and nut from McMaster-Carr would be my suggestion.
--
Anthony

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