0-90 or 45-45 for roller bearings

[Ninjak2k]

I've seen a few machines those use roller blade bearings with them positioned at 0-90 (one on top of the pipe and the other on the side) and a few at 45-45, like Jgro's. Been a while since I did took statics, but does the 45-45 arrangement put the weight of the gantry on both bearings while the 0-90 puts it all on the top bearing? Are there any benefits of one arrangment over the other? It seems easier to support the pipe with the 0-90 setup as you can just put boards under the pipe and not worry about hitting the bearing. Seems like it would also be easier to mount the angle to the platform. Example here: http://www.cnczone.com/forums/attach...&stc=1&thumb=1

Lacking many power tools, getting the nice slots for the angle to sit in for a 45-45 arrangement may be difficult for me, but the 0-90 arrangment just bolts it flush to the bottom and side of the bed. I guess for the Y (gantry) and Z axis, I'd still have to use the 45-45 arrangment, though.

~Dan

[WP1]

I'm not sure there are any particular advantages mechanically. It's probably more a function of the materials and tools you have at your disposal. If you have a good budget you simply use pre-fab NSK or similar linear rails.

The CNC router I'm currently finishing uses a combination of designs. The Y and Z axis both use and arrangment of bearings spaced in what you would probably call 45-45 clamping in from the outsides of two round rails.

The X axis uses square steel tubing for the rails and the two gantry support trucks use a 0-90-180-270 bearing configuration, i.e. bearings on all four sides. The sides and bottom of each truck have two bearings each and the top that bears the load of the gantry has four bearings in two pairs.

That's 10 bearing per X truck for 20 total on the X axis, and 8 bearings total on each of the Y and Z axes.

Pete C.

[Ninjak2k]

Pete, that's some serious support you have there. Thanks for the feedback.

As for myself, some quality linear rails and bearings are out of the question - student's budget with a tinkering bug. Not looking for production quality work.... yet.

~Dan

[kywoodwrkr]

Pete,
What size square tubing did you use and how much deflection did it have?
Do you think a round piece fitted to the inside would make it any more rigid or stronger?
Thanks.
DaveP

[WP1]

I used 1" square steel tube, I think it's about 14ga wall thickness. There is nothing inside the tube because I built it into a truss type structure using 1/2" sguare tube in the truss.

The way I have it trussed and the way the entire truss sits on the table I don't think there could be any detectable deflection from the gantry weight.

Attached are an overall shot of the not quite finished router, and an upside-down closeup of one of the X axis trucks.

You can't really see it in the pic, but the truck is built with preload adjustments in each direction.

Pete C.

PS: For those who've seen me posting and wondered if I was really building anything, here is a glimpse at it

[andy_ck87028]

Hi

I have used roller bearings and have an arrangement which I have found to be both simple and sophisticated.

Imagine three rollers set at 1) 270 deg (side) , 2) 0/360 deg (top) and 3) 90 deg (side). That will clearly stop lateral movement in two directions using 1) and 3) and stop downward movement using 2). I.e., all weight is on 2). No upward movement is stopped meaning that an additonal bearing is required or you run the risk of bucking.

By rotating 45deg, (for this example assume clockwise, then 1) becomes 315 deg, 2) becomes 45 deg and 3) becomes 135 deg. The effect of that is that 1) stops lateral movement right and 2) and 3) stop lateral movement left. Also weight is jointly supported by 1) and 2) and now additionally upward movement has also been stopped by 3). Net effect fewer bearings with additional functionality just by spinning assembly by 45 deg.

I have found that approach to be really neat and easy and I have employed it on x and y with the piping being 304 stainless.

If anyone needs pictures, I'm more than happy to provide.


Andy

[joecnc2006]

Originally Posted by andy_ck87028 Hi I have used roller bearings and have an arrangement which I have found to be both simple and sophisticated. Imagine three rollers set at 1) 270 deg (side) , 2) 0/360 deg (top) and 3) 90 deg (side). That will clearly stop lateral movement in two directions using 1) and 3) and stop downward movement using 2). I.e., all weight is on 2). No upward movement is stopped meaning that an additonal bearing is required or you run the risk of bucking. By rotating 45deg, (for this example assume clockwise, then 1) becomes 315 deg, 2) becomes 45 deg and 3) becomes 135 deg. The effect of that is that 1) stops lateral movement right and 2) and 3) stop lateral movement left. Also weight is jointly supported by 1) and 2) and now additionally upward movement has also been stopped by 3). Net effect fewer bearings with additional functionality just by spinning assembly by 45 deg. I have found that approach to be really neat and easy and I have employed it on x and y with the piping being 304 stainless. If anyone needs pictures, I'm more than happy to provide. Andy

Maybe a diagram would be handy and make it easier to understand.

[Ninjak2k]

Thanks for describing your arrangment. Pictures and or a diagram would be great!

~Dan

[andy_ck87028]

Hi

I have taken two pictures. One shows the assembly from end on and the other from side on. The assembly is nothing more than two angle irons bolted together with two roller bearing between (cannot be seen in either picture) and four roller bearings bolted on the underside. The whole assembly is then rotated by 45 degrees and attached to two more angle irons which constitute the y axis.

Effectively the assembly therefore locks itself onto the stainless tubing.

I wish I could get better pictures but can't seem to improve on the quality.

Andy

[Apples]

Have a look at my post it is for a plasma table under the "plasma laser edm " forum. Then it is in the log section at the top. I have used bearings at left right and one on the top of the bar. Works brilliantly, slides and slides and rolles for ever.

Apples

[Ninjak2k]

Thanks!

~Dan