SBR16 linear rails

I've been on the lookout for cheap, rigid linear motion for a while. This appears to fit the bill.

Two 500mm rails and four blocks for $57.34 shipped. The rails are 16mm ground steel rod, supported with aluminum extrusion. The bearing blocks have openings matching the rod.

To be clear, I know that Aliexpress rail won't be as good quality as "proper" rail off Misumi or something. But between the massive diameter and the aluminum support, it should be far, far more rigid than any ground rod.

So, what gives? Has anyone tried this stuff? Is it likely to have play or friction? According to some spec sheets I've found, it's rated for 7,700 N dynamic load! Is that realistic?

Thanks!

That looks like a great price - definitely worth giving it a go. Bear in mind that the bigger diameter bearing blocks start to get quite heavy, so you don't want to go unnecessarily large. I've been looking at SBR12 supported and also just plain old 10mm rods and bearings.

Good luck!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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the_digital_dentist
Good luck!

You think it's too good to be true? It's a little below average on AliExpress, but not wildly so, and the vendor has a 99.3 rating (with reasonable feedback count). I've had very good luck with parts from AliExpress, so I'm perhaps overly positive. It's true that if you get a lemon you're going to be stuck as the shipping cost to return anything is almost certainly more than the entire purchase cost.

I think you get what you pay for and you don't get what you don't pay for.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Certainly can't argue with that in general, but I think this class of general purpose, widely used engineering components is exactly the sort of thing where the Chinese manufacturing capabilities have transformed the market. It reminds me in a lot of ways of Russian manufacturing in the 70s and 80s - wonderful parts made with a very direct approach, heavy and strong. The difference is that it was a real struggle to find and get hold of their products in the pre-internet days, where as now we have unbelievable choice and access!

Side note: does anyone else with Russian gear remember the rather strange lubes that would often be used? I have a Russian microscope from my teens where the lube appeared to go off over the years, and it stank to high heaven. I have no idea what it was, but I like to imagine it was rendered from some large animal that previously roamed the steppes...

Edited 1 time(s). Last edit at 04/06/2016 06:31AM by JamesK.

Perhaps this would help reduce moving weight?

Or just use SBR12's, which are still certainly strong enough and would be much lighter.

Yes, although it puts the pressure on you to design a carrier to hold them accurately. I suspect that once you go supported you can bring the diameter right back down, but for some reason they don't seem to make sbr8, and even sbr10 seems difficult to get good deals on. Strange world.

How well do MGN9 rails hold up? Is that large enough?

Wish I knew

This is oversized for a printer unless its big

It would be nice to know "How to use a linear rail".

How to mount them?

Best way to load the guide blocks?

Hang the load?
Put load on top?
How much side load can be used?

Which mounting affords the best precision.

Difference between round rod rails and others

I have a couple of MGN 12 (Hiwin dovetail profile type with circulating balls) rails to use
The SBR rails are round rods and round bearings with ball bearings inside

The manufacturer's data on the linear guides specifies the loads/torques they can tolerate. Google is your friend...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

the_digital_dentist: Yes, but it's hard to tell exactly how much force the printer will exert on the rails, or exactly how the rails behave as they approach their limits, without some testing.

If you're building a printer to extrude concrete and build houses, you'd better worry about the linear guide specs, otherwise, it's unlikely to be an issue. If you look at the specs of the linear guides you'll see they are capable of handling very large loads that are probably a couple orders of magnitude beyond anything they'll might possibly see in a desktop 3D printer. Unless you're buying very tiny linear guides, you'll never be able to push them anywhere near their limits.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

That's what I was thinking, but 9mm is pretty damn tiny. I feel like if they were enough, people wouldn't use the 12mm rails as much as they do.

I'm not so concerned about making things as compact as possible, so I buy whatever size used linear guides I can get inexpensively via ebay. They are typically 12-24 mm wide rails, I suspect because that's the most common size range used for industrial machines. I rarely see the really small ones.

The loading isn't going to be an issue with the 9 mm linear guides. The problem with small ones is that if you are using them to try to minimize moving mass by using them end-supported for the X axis in a coreXY machine, they'll flex almost as much as the 8mm round rails. You're using only one to support the extruder carriage, so it will flex more than the typical pair of 8mm round rails. I think that's why people are using bigger linear guides for the X axis. You might be able to get away with a single, end supported 9 mm linear guide for a bowden set-up, depending on the span.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

You know you have too big a guide rail for your 3D printer when:

the bearing blocks have grease fitting installed

Hiwin CNC Linear Rail & (2) LG25 Ball Bearings/Slides/Blocks 500mm L x 25mm W
[www.ebay.com]

The 12mm linear guide bearing blocks on my printer have grease fittings. The 24 mm guides I'll be using to make the next machine don't.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

the_digital_dentist:

The reason I might use 9mm rails is price, they seem cheaper than 12mm. I would bolt them to a support, probably a 1" square aluminum tube, so the strength of the rail itself isn't a huge issue.

I prefer to get used Japanese made linear guides, for probably about the same price as the new Chinese stuff. The last three I bought were 24mm wide rails, about 500 mm long, and cost about $35 each shipped. One was actually new-old-stock. Each rail came with one bearing block. You have to comb through the ebay listings for a while to find deals like this.

Here's a new old stock 15mm rail with bearing block for $31.50 shipped: [www.ebay.com]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

While that's a good deal, this is still half the price, for (almost) the same length. While I appreciate well-made hardware, I don't want to use a Japanese 15mm rail if a Chinese 9mm will do.

Well, good luck to you, then.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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epicepee
While that's a good deal, this is still half the price, for (almost) the same length. While I appreciate well-made hardware, I don't want to use a Japanese 15mm rail if a Chinese 9mm will do.

I think at the small end of the linear rails I'd be inclined to use them in pairs and avoid the torque loads. But using them in this way negates the primary advantage of linear rails which is exactly that they can handle torque loads and so you have the option of using a single (suitably sized) rail and avoiding all of the parallel alignment issues that you get with pairs of smooth rods.

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epicepee
While that's a good deal, this is still half the price, for (almost) the same length. While I appreciate well-made hardware, I don't want to use a Japanese 15mm rail if a Chinese 9mm will do.

The 15mm Japanese will do the job a the two 9mm Chinese that you will need and without the hassle of installing them perfectly //.
And linear rails call for perfectly built and rigid structure. If most 3D printers I see here work eventually, it is because the smooth rods, bearings used and structure flex to adapt to each other and even take care of some play without too much binding.
People are doing "preloading" without knowing
Anyway, why don't you LEARN from engineering books and mfg publications instead of trying blindly ?

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MKSA

The 15mm Japanese will do the job a the two 9mm Chinese that you will need and without the hassle of installing them perfectly //.

Very true. That's the best argument I've heard for the larger rails. A Chinese 12mm or 15mm rail might still be cheaper, though; I'll have to do some searching.

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MKSA

Anyway, why don't you LEARN from engineering books and mfg publications instead of trying blindly ?

Two reasons. First, I'm not in this to become a mechanical engineer -- that's what college is for. I'm in this to have fun, get some experience messing with materials, and hopefully make some nice tools.

Second, it's all but impossible to get the actual specifications of this Chinese hardware. That's part of why it's so cheap, and it's (part of) why I made this thread. (I would absolutely look to mfg papers on the Japanese rail, if I didn't know already that it's easily up to the task.) This lack of documentation is complemented by the fact that I don't know exactly how much torque I'll be putting on the carriage.

If you built a car from a random collection of the cheapest parts you could find, what are the chances that you'd end up with a Ferrari?

I suggest you just buy a cheap printer kit. You'll get a collection of very cheap parts with no specs, selected with a bare minimum of effort, you won't have to learn anything, you'll end up with something that looks a lot like a printer in the end, and if you're lucky, it'll be "a nice tool", whatever that is. Nothing but fun!

Stop reading now if you don't want to learn anything.







If there are no specs, there is no quality.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Anyone have experience with supported rail in a 3d printer enclosure? Gut instinct is that steel rail bonded to an aluminum strip forms a bimetallic strip that will curl as it warms up due to the difference in CTE. Depends how the two pieces were attached, I suppose, which most listings don't specify.

There are many ways of learning, social sharing, learning by trial and error and/or studying the science behind it all. Don't degrade someone for wanting to explore and experiment on a tight budget. I believe there historically have been plenty of incredible discoveries that have happened on accident? or with extremely tight budgets?

All parties here have valid perspectives, I just disagree with tossing one another down over it. I've learned a lot with my own modest experiences in FDM printing. Does the fact that I've attempted to do so as cheaply as possible make it less worthwhile? I don't think so.

epicepee,

You have some design decisions to make here. I too have had some positive experience ordering off of alibaba, yes I did not get good datasheets for the hardware I purchsed (5-row 12mm linear bearings) but they have certainly done well. I'd guess ordering the cheap chinese stuff is kind of like rolling the dice. Make your own Judgement call.

In regards to the initial question in the topic, I think you're going for extreme overkill. I'd scale down the diameter to 12mm as tolerances (or lack thereof) may be more noticeable on a cheap 9mm rail. If moving mass is of concern to you consider taking a chance on a smaller diameter rail for your x-axis.

Edited 1 time(s). Last edit at 12/20/2016 10:39PM by obelisk79.