[nekidfrog]

Looking on ebay for linear rails and seeing a variety of 10-25mm diameter. Wondering what the minimum size for a supported rail I should go with for a 24x24in cnc frame?

These are the ones I'm looking at
http://stores.ebay.com/econvenience1...=p4634.c0.m322

[Walky]

16mm would be fine even for most steel (heavy) machine designs, even better if you can go with 20mm.

12mm bearings (at least those on the SBR12 blocks) have less bearing races (3, while the 16mm and 20mm bearings have 4) and IIRC smaller balls, so they don't have such a good fit and can't take as much load as the bigger ones.

[nekidfrog]

Sweet!

That is the ones specifically I'm looking at. Rails

Another question I have is about this Gecko G540, It's listed with 640oz steppers... Would this be to much for the gecko considering it can only source 50v? They have another option for 300oz steppers. Or would this kit Gecko g540 be better?

[Walky]

Those 640 ozin motors ideal voltage is around 80V. I'd go with the 380 oz-in kit in your case, for most machines that size it should get you better speed than the bigger motors, especially with screw drive. What drive system (screws, R&P, belts) are you going to use and what material will the machine be built of?. What do you expect from your machine?

I don't know the seller from the first link, but CNC Router Parts (from the second link) sells good stuff and their support is generally praised.

CNCRouterParts

[dmalicky]

16mm and below are ok for push loads, but weak for pull-off as the opening angle is 80 deg, instead of 60 or 50 for 20mm and above.
Open Single Bearing Blocks

[nekidfrog]

I'm mostly using this for acrylic/polycarb with light aluminum work. I'm going to go with acme lead screws just not sure what tpi/start I should go with. Still doing my research on that.

[Catmandu13]

16mm would be fine even for most steel (heavy) machine designs, even better if you can go with 20mm.

12mm bearings (at least those on the SBR12 blocks) have less bearing races (3, while the 16mm and 20mm bearings have 4) and IIRC smaller balls, so they don't have such a good fit and can't take as much load as the bigger ones.

Not sure if this is out of the ordinary, but I originally(before deciding to go 20mm) bought a set of SBR12 blocks, they all had 4 bearing races.

[victorofga]

very generally under 24 inches machine you can use 12mm rails..

about 30 inch wide you can use the 16mm yet..

over these sizes, like 48x48 or 49x96 use atleast 20mm rails.. on z you migth use 16mm yet..

do you know automation4less selling hiwin rails close same price?

AGW20CB1TxxxxZ0H, Combo, 20mm T Rail, 4 Bolt Flange Block, Specify Length, Hiwin AG 20 Combos - automation products from Automation 4 Less

they also have everything what could need for building a machine..

[Walky]

Not sure if this is out of the ordinary, but I originally(before deciding to go 20mm) bought a set of SBR12 blocks, they all had 4 bearing races.

I've just checked again and can confirm that my chinese blocks have 4 races for 16mm and 3 for 12mm. The specific bearings inside the blocks are LM12UUOP and LM16UUOP. Maybe yours use different bearings, or you're confusing them with the closed bearings?.

Here is the bearing info (UU and UUAJ are closed bearings and won't work with supported rails):