Quick question about gantry width..

[planekrazie]

Just a quick question about a new machine I am gonna build. What would be a good width ( to reduce racking ) for the gantry? I am talking about how far to space the bearings for the gantry to ride on. Is 6" too little?
I am gonna try to build the cnc about 36"x48" cut area.
Steve

[wcarrothers1]

all depends on the drive, 2 screws, one center screw, rack/pinion on each side ect..

Typicaly you need less bearing space (I'd say) for 2 screws vs center screw.

I think the vbearings I have setup are only maybe 9" apart but I have racks/and pinion driving on either side connected by a shaft that keep it from racking..hehe

b.

[planekrazie]

I think I am gonna go with the screw in the center. So does 8 inches sound good for bearing spaceing?
Steve

[widgitmaster]

If you use a TDK style rail with recirculating ball trucks, or round supported linear rails and ball bushings, or even roller skate bearings on a stationary rail, one screw in the middle will work fine. The distance between bearing slides is not an issue, but the parallel and horizontal alignment are. Any gantry tracking loosely or on an improperly aligned slide, will bind jump and chatter doing heavy cuts.

From the side view of the gantry, the front and rear bearings should be equal to half the height of the gantry. Making this too narrow will reduce the strength at the top of the gantry, or when the cutter is at max height. Think of it as a triangle, wider at the base, makes the top very stable and strong.

For a wide distance between gantry sides, I would suggest a dual set of round linear rails set parallel to each side of the gantry end plates. this set of four slides will allow for an extremely rigid and inexpensive tracking system. The y-axis should also be a dual slide, to ensure squareness and rigidity.

My two cents.

Widgit

[planekrazie]

This is a great Tip. Thanks widgit.
Steve

Originally Posted by widgitmaster From the side view of the gantry, the front and rear bearings should be equal to half the height of the gantry. Making this too narrow will reduce the strength at the top of the gantry, or when the cutter is at max height. Think of it as a triangle, wider at the base, makes the top very stable and strong. My two cents. Widgit

[High Seas]

Hey Steve - I used 8020 and the cut size on the System2 would be that if my linear rails were long enough! The spacing on my Bridge (vice Gantry) is pretty close to 8 - 10 inches. I've experienced no racking of the bridge and only drive from one side of the X axis (not both).
Any help there? See Pics in my gallery.
Jim