Linear rail & slides or "V" bearing & track

[CNCCajun]

Planning an all steel 4'X8' plasma table . . . maybe extruded 80/20 for the X on the gantry . . .

Looking for pluses and minuses of both linear rail & slides and "V" bearing & track. . .

I know cost difference is tremendous . . .

Do "V" bearing really jump track?

Can you mount linear rails & slides on side or on top . . .?

Do linear rails & slides get damaged by plasma dust whether mounted top or sides?

I just hate to invest over a $1000.00 rails and have one demolished by a bump from a piece of material . . .

Has anyone ever built a continuous guard over them like a piece of angle turned downward?

I have noticed that the linear bearings and rail on most of the plasma tables I have seen from the turn key builders and individuals are mounted in a vertical plane for the "X & Y" axis.

Is there any reason not to design a table mounting these in a horizontal plane. I can see where this may make things more difficult on the"X" axis.

I can't see where they would be any safer from damage running along the side of the table . . .

Just trying to get all this lined out before I start detail design . . .



Thanks ,
Steve

[ger21]

Originally Posted by CNCCajun Do "V" bearing really jump track?

I don't think they'd have sold thousands of ShopBots if they did.

[CNCCajun]

Originally Posted by ger21 I don't think they'd have sold thousands of ShopBots if they did.

If force required for a router/spindle to operate doesn't derail the gantry. . .

I think my suspicion that "V" bearings & machined track on a plasma cutter will survive . . .

Thanks again . . .
Steve

[LeeWay]

For such a large machine that doesn't even require that great of accuracy, V-bearings would be what I would use.
I actually started building my own similar sized plasma cutter mounted on a trailler. I used roller skate bearings and Unistrut. It has been sitting out in the weather and still just as smooth as the day I quit working on it. I have hauled many loads with it as well.
V bearings are cheaper, much easier to keep clean and replace very cheaply should they fail.
Linear way are just the opposite. They are, however more precise and a lot more costly.
Several ways to go other than linear rails that are actually more prudent for such a build. The bearing truck design though can mean the difference between pass or fail.
Many proven designs on the Zone.

[raynorj]

Hi, Have been lurking around forums and amazed by all the material there but unlikely to ever spot it all so maybe here is as good a place as any to ask a query about my own "current" proposal for X axis.
The machine for plastics and thin ply cutting out and routing 5mm absolute max (model building) is planned at around 1200mm x 600mm.
For X axis ways I am looking at using 65 x 12mm stainless flat bar on edge ie vertical with bolts and spacers onto main steel side member at maybe 150 mm centres. Then I plan to have profiled wheels running on the flat bar with two on top for each side of the moving gantry and one (adjustable) underneath. The groove in the wheels (nylon with bearings) would have a slight taper either side but not enough to allow significant sideways displacement. The yoke under the table joining both gantry ends would be roughly the same vertical size of the top and bottom wheel centres ~70mm and would have a central ball screw 16mm.
Y axis would be linear SBE20 ball bushings on 20 mm stainless cross shafts (2 off).
Has anyone any comments on that proposal .
many thanks
Ray: