Using SBR12 Linear Rail for X Axis

[marcll]

I was wondering if anyone has tried using low-cost SBR12 Linear Rail for their machine. A pair of rails 600mm long with 2 carriage blocks per rail is only around $50. I'm planning to make a machine with a working area around 45 x 40 x 8 cm (18 x 16 x 3 in) that will be able to rout aluminum sheet stock up to 1/4" thick. Here is a draft CAD of the machine, showing how there will be SBR12 mounted to steel square tubing, for the x axis http://i.imgur.com/PLxqJ20.png. Any feedback would be greatly appreciated!

Rail on ebay - 2pcs SBR12 600mm 12MM Support Linear Rail Shaft Rod + 4pcs SBR12UU Block CNC Set | eBay

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[gregoose]

I used sbr12 on my machine, on all axis, I have had no real issues yet other than the adjustment set screws on the bearing blocks vibrating loose, then the blocks lose their rigidity, but I think that goes for any supported round rail. They are very rigid and loading was more than sufficient for my machine, 20-30 lb steel gantry. I haven't tried aluminum yet and probably have less than a hundred hours on it so far but I am very pleased. My machine is 28" x 18" x 8" or 650x440x200.

Here is link to my build thread if you want to see it.
http://www.cnczone.com/forums/cnc-wo...16384-cnc.html

[marcll]

In your build thread you mentioned you wish you had bought the SBR16 instead of 12. Think 16 would be worth the extra money if the machine has to cut aluminum?

[A_Camera]

I was wondering if anyone has tried using low-cost SBR12 Linear Rail for their machine. A pair of rails 600mm long with 2 carriage blocks per rail is only around $50. I'm planning to make a machine with a working area around 45 x 40 x 8 cm (18 x 16 x 3 in) that will be able to rout aluminum sheet stock up to 1/4" thick. Here is a draft CAD of the machine, showing how there will be SBR12 mounted to steel square tubing, for the x axis http://i.imgur.com/PLxqJ20.png. Any feedback would be greatly appreciated!

I think it's a mistake to use SBR12 for anything other then very soft material. I use SBR16 and on my next machine, if I ever build one, I will use something even stronger and more rigid. On another note, if you plan to build machine you might as well increase the Z because you will regret rather sooner than later that 8 cm you are planning for now. Let me show you what I mean.



Ny CNC has a 160mm Z clearance. The vice in the picture takes away 70mm and the spindle with that short cutter takes another 45mm, leaving me with about 45mm clearance. Of course, a longer cutter will leave even less clearance. ...and I don't even have a sacrificial board on top of the table now...

So, consider the above before deciding for Z clearance. But if you only plan to mill sheet material than it may be OK, though I still think it is going to be the first thing you'd regret, just like I did. My first build had about that little also, and it didn't take a long time for me to realize that it was not going to be enough in the long run. Fixture + sacrificial board + tool takes up more space than many can imagine.

[gregoose]

From what I've read around here, bigger is always better with the round rails. I was under the assumption that I wouldn't be able to do aluminum without larger rails. Now that my machine is complete, it feels very rigid with 12mm. I imagine a larger machine might require larger rails while smaller mains do ok with them. I Haven't tried aluminum yet but I think it will have no problem. I have to figure the speeds and feeds first. I have a piece of T6 that I was going to test with. It may be a couple of weeks before I can get to it though. If anything I'll just have to limit my depth of cut. I've got a cheap speeds and feeds calc that says I should be able to go up to 0.125" depth per pass.

Structural rigidity of your gantry plays a big part also, I would have used bigger bolts and thicker gantry arms. The steel is very rigid to but still has flex.

[Biggs427]

I don't know the prices of SBR12 or SBR16, but when I planned my current build I checked for SBR20 (1000mm for X, 700mm for Y) and the price difference with shipping between SBR20 and 15mm profile rails was not that big.

I ordered on Aliexpress, but I contacted the seller once I had all my component listed and ordered in one big order so I saved on shipment costs and received it in less than 7 days.

Ask for price quotes, you never know.

[wizard]

I was wondering if anyone has tried using low-cost SBR12 Linear Rail for their machine. A pair of rails 600mm long with 2 carriage blocks per rail is only around $50. I'm planning to make a machine with a working area around 45 x 40 x 8 cm (18 x 16 x 3 in) that will be able to rout aluminum sheet stock up to 1/4" thick. Here is a draft CAD of the machine, showing how there will be SBR12 mounted to steel square tubing, for the x axis http://i.imgur.com/PLxqJ20.png. Any feedback would be greatly appreciated!

For some reason I can't read your *.png file, just get a blank page in my browser, so take everything I say with a grain of salt.

First off you have to define your expectations with respect to what you mean by machining aluminum. The one thing that is obvious here is that what I might consider to be minimally acceptable for machining aluminum would be overkill for what others will accept.

So what I will say outright here is that 12 mm round rails will not be good enough for machining aluminum. For me that means being able to cut to a depth of half the end mills diameter with end mills in the 3/8" to 1/2" range. Technically you can get just about any router to cut aluminum given enough time and a small diameter cutter but you might not like the results.

If the machine is to be focused on machining aluminum I'd most certainly consider profile rails. Being a smaller machine the cost will be reasonable and frankly there are many opportunities for shorter linear rails at discount on E-Bay. I'm not dead set against round rails but by the time you buy something large enough and stiff enough for use on a router you might as well buy profile rails.

Sadly without a picture I can't see what you have in mind for a mechanical design. Given that I will point out that no matter what you go with, the rails need to be well supported with a stiff structure. The lack of well supported linear bearings have had a very negative impact on many DIY designs.

[ger21]

So what I will say outright here is that 12 mm round rails will not be good enough for machining aluminum. For me that means being able to cut to a depth of half the end mills diameter with end mills in the 3/8" to 1/2" range.

Most routers can't do this, even with THK rails.

[wizard]

Most routers can't do this, even with THK rails.

This is very true but that is as much an issue of simply not being able to make a large DIY machine stiff enough. The original poster is looking at a smallish machine which has a much higher potential of achieving results close to this.

This brings up an interesting point, people looking to machine aluminum would likely be far better off building a short span machine vs something with a 4 foot span. At least if they want to keep costs reasonable for a DIY machine.