Inexpensive Linear Slide Assemblies?

[Homl]

Where can one find inexpensive turn-key linear slide assemblies ready for control motors? Maybe in foot increment lengths. Something that can be easily bolt together for a router table.

Originally I was planing to build my own. By the time I added up all the cost of the linear bearings, lead screws and other component, man was it expensive. On top of that, I have to put in lots of hours designing and building the slide assembly.

I found some fully assembled slides by Techno and a few others, but they are way too expensive.

Inexpensive is what I am looking for. Something reasonably accurate, lightweight and rigid, nothing fancy.

Thanks for the help!

[Sanghera]

What about some inexpensive bushings?

[vacpress]

ebay - theres lots of stuff like that.. gonna be a long wait to get matching componenets tho

[buscht]

http://cgi.ebay.com/ws/eBayISAPI.dll...e=STRK:MEBI:IT

[Homl]

Thanks, but they are too short. For the Z axis, one of the assemblies would work fine. I am looking for something 48" or larger. Are there inexpensive supplier for linear asseblies where you can purchase off the shelf, rather than to hope to get lucky on ebay?

Thanks again.

[DDM]

I don't know how good they are but 8020 and Tslots have a linear bushing setup for their extrued aluminum. I know it's not THK but when I talked to the guy at 8020 it seems that you could probably keep things within 5 or so thou. If you could figure out some kind of pre load to get the slop out of there you would be set. Assuming that you don't get anything too abrasive on the aluminum the anodizing shouldn't wear that much and most of the wear would be on the plastic(not sure what type off hand they use, but you could make your own from modernplastics.com) If that doesn't do it for you there's always gas pipe and roller skate bearings.

[Homl]

Yeah, something close to that kind of simplicity but with a little more precision. Maybe something in the line of a simple aluminum extrusion with a couple of basic guide rods with a decent ACME screw. A thick delrin plate that act as the bearings, the screw nut and the mounting platform.

[DDM]

Yeah other than guide rods could run some money if you went with a precision ground hardened shaft. I know you can get the rod for hydraulic cylinders for a decent price and with using like a uhmw, bronze impregnated teflon or a oiled broze bushing. You could get real trick with the oiled bronze bushing by adding an oil pump to your setup so that the rod and bushing is lubricated all the time and the only thing you would have to check is the oil in the resiviour. Any one else have any comments?

Carl

[pminmo]

McMasterCarr www.mcmaster.com 6061K75 1"OD 48" $58 Look at page 952 of their online catalog.

For 36" and under www.use-enco.com drill rod on sale is pretty good. Just according to how precise you want to be.

[chuckknigh]

Drill rod and even gas pipe work amazingly well, but there's another "off the shelf" option that you may be overlooking. Window frame extrusions. Add some plastic slides, and they should work quite well.

I found a glass supplier in my area, and went into their shop. They have so much of the stuff, even as "offcuts," that it's amazing. That, and some plastic slides, fully supported of course, and they'd make GREAT linear slides.

There is one extrusion I have my eyes on...nearly 4x6" in cross section, and reminds me of a capital letter "E" made out of 8020. I don't know how it works for glass, but it'd be perfect for slides. Stiff, strong, and it would have a minimal contact area.

Thank you, John Kleinbauer, for the original idea.

-- Chuck Knight

[DDM]

When talking about using extruded aluminum products for linear slides having a good cross section is good but when everything is build rock solid it is the straigtness factor that would concern me. You are looking at a max of .012" of straigtness. Sure I could put it on the mill and a dial indicator to see what kind of straigtness I have and then put it in a press and see what I can do to make it as straigt as possilbe. Also If you have 4 different rails that you are using as linear guides they should more or less cancel themselves out if you have a nice tight system which would involve some kind of preload system. From there what kind of wear are you going to encouter. 8020 and Tslots I think both use uhmw for their bushings. If you were to make your own and make them say 10" long you would have greater amount of cancelation of the different straightnesses. But over time you're going to get wear. That's the thing I haven't figured out yet. I don't feel like replacing bushings after say 300 hours of run time because the slop has got too great. If you you could do some kind of preload on them so that over time as it wears it keeps the same characteristics as when it was freshly installed. Maybe some kind of spring setup or air pressure to push the bushings into the extruded aluminum. Ok well I'll shut up now. I've got all of these ideas in my head and not enough time on solidworks to work all of them out.

Carl

[chuckknigh]

Let me ask you this, Carl. You're talking about a deviance from straight, of barely over 1/100th of an inch. That's better than most people can do on hand tools, and wood can move more than that with a change in humidity.

It's wonderful to plan for super precision, but unless you intend to use something like a LASER inteferometer for measuring deviation, a few thousandths is a realistic goal. .01 is just 10 thousandths, which while not perfect, is still pretty darned good. Holding accuracy of a few thousandths, over a span of 4 feet or more, is EXTREMELY difficult, especially for a first time builder.

Throwing money at it can help (i.e. high grade linear components) but you asked about inexpensive options. BTW, UHMW is surprisingly tough and long lived. And, thread wander in anything short of a precision ground screw can throw off your measurements, too...it's not just the straightness of the linear slides.

I'm not saying this level of precision can't be done...just that trying for this level of precision, for a first time homebuilt tool, is probably overkill.

What is your intended use? You've got me curious...

-- Chuck Knight

P.S. Have you considered a parallel kinematic system, rather than a simple X-Y-Z table? More complicated, but errors are not cumulative, like they are on a more traditional table.