I am somewhat new the CNC routers. Well, I recently built a nice little CNC router out of MDF, plywood and I used Arduino as the motion control with a dremel hooked up to it. It works very well, but is too small and slow to be useful for larger items. As such, I am making a larger CNC from steel and have a few questions about getting the rails and ball screws straight and square. Both the X and Y will be using 1500mm fully supported linear rails with ball screws driving both (20mm diameter on both). I have already bought the parts, so changing is not an option at this point (if I had to do over again, I might do R&P as ball screws could whip at higher speeds, but I cant change now).
Here are my questions:
The base that the gantry will ride on will be made of 4"x2" steel rectangular tube that is about 5' long. Welded together by by 3 rectangular tubes running perpendicular to both sides - basically a box that is make of rectangular tube. This frame will sit on a very sturdy table that I am making. The 1500mm fully supported linear rails will be on top of the rectangular tube with ball screw on the side of the tube. My question is, when I am drilling the holes for the fully supported linear rails to attach them to the rectangular tube do I make the holes slightly elongated so there is some play and once I get the rails perfectly straight then tighten them up? Or do I ensure the holes are absolutely perfect and have no adjustablity for the rail? If I make elongated holes, when I tighten the bolts, will that be enough to ensure they don't move?
The machine will be all steel and running NEMA 34's (I know 23's would have been better, but I have 34's) and will be used 75% for woodworking and 25% for aluminum. None of this was an issue with my MDF as there was some natural play and that was more of a prototype anyway.
Any help would be greatly appreciated. Thanks so much.
You might concider drilling the holes for normal clearance, 1/32 or more oversize for adjustment. Then once the rails are aligned, pin them in place with role pins or dowel pins. That will prevent any movement once the machine is in use.
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Elongated Holes?
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