I've been looking through the interweb and found a few nice miniature ball screw assemblies from the likes of Bosch-Rexroth, NSK, and Specialty Motions Inc, but I'm not sure what the next step would be, or even if they're affordable for the average hobbyist like me.
On Monday I'm going to start calling some local distributors to see what the process is of getting some prices.
So far the only item that I've found with a price is a miniature ball screw assembly at McMaster-Carr which goes for $150 each, which is really out of my price range.
For cheaper than $150 you're going to need to go surplus. By their nature reciprocating ball screws are precision mechanics, and that's where the price comes in.
Does your application absolutely require ball screws? Would a lead screw work as well? They make fairly affordable anti-backlash lead screw assemblies in all varieties of sizes. McMaster-Carr is one source; I prefer Reid Tool & Supply.
Firstly thank you all for your help and suggestions.
To recap:
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Miniature Ball Screw Assemblies will run about $150-$170
5/8" ball screws and ball nuts are a from 1/5 to 1/10 the price of other sizes 5/8" ball nuts are between $20-$30 each 5/8" ball screws are about 1/2 the cost of other sizes
mcmaster stocks a 3/8" ball nut for $60 which passes for miniature mcmaster stocks 3/8" ball screw material for $1.79 per inch.
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Robin G Hewitt: Thanks for your tip about MSC Industrial. I've been looking through their catalog and verified that there is a specific size ball nut that sells for 1/5 to 1/10 the prices of the others in MSC and McMaster. I'm thinking strongly about adapting my design around that specific size. I also noticed that McMaster stocks a 3/8 inch ball nut for $60 that has the approximate proportions of a "miniature" ball screw.
Gordon McComb: Yeah, I've pretty much come to the same conclusion that the Miniature Ball Screw assemblies are going to be in the $150 range, but luckily I've found a 3/8" ball nut and screw in McMaster-Carr @ $60 per nut. It's still more than I'd like to pay, but it's definitely better than $150.
I've been trying to recreate a "poor-mans" version of MIT's frameless linear actuator. I built my first prototype with a lead screw, and I'm losing most of my torque to friction. Everything I've seen so far suggests that peak efficiency of a lead screw is only %20-%30 effecient, and ballscrews should be about %90 percent efficient, which suggests about 3x the force output. So for prototype #2 I'm going to try a ball screw and pay closer attention to sources of friction.
Robin's catch of #28 for a 5/8" ballscrew is a good one, though frankly I can't fathom why that size and pitch is SO much less than the others. I guess it's not a typo. Maybe as 5/8" is so common for small machines they make so many they can afford the volume discount. 3/8" is a bit more compact than 5/8", though that isn't quite as "miniature" as I was imagining!
I would think that in addition to the screw mechanism a fairly hefty source of friction is the guide (or guides). I would agree that a
*quality* ballscrew would be important, but the linear bearings and absolute precision in construction would be too.
Let us know how this thing works out for you!
-- Gord> Firstly thank you all for your help and suggestions.
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