New to forum so hello everyone. Hope I am in the right place. I am building a manual cnc for lack of better terms. Size is 1500m x 1500m. No stepper motion. My gantry is built out of solid maple for the risers, the x axis is 20/80 v-slot with a very nice cbeam z axis attached. I am using a heavy router 2hp. My problem is flex on the y axis movement. When I push the gantry down the rails by hand from one side. There is noticeable flex along the gantry to the other side. Any thoughts on how to stiffen all this up and not get heavy? New to this type of build. Plan to use the machine to plane large slabs, and joinery work. Long term woodworker. Any advice is appreciated.
Welcome to the forum Posting some pictures would definitely help the community in identifying problems and giving advice
Flex? Or Twist? With a 2080 I would expect it twisting about the long axis Also see How to calculate V-Slot® deflection Going to C-Beam should help, or even doubling it up like the High Z mod: High Z Mod for Lead CNC to further prevent twisting
I do have a small amount of twist top to bottom which is reflected in my router cuts. Does seem to be the 20/80. Do you feel the cbeam will remove that, cost wise it’s not much more than the 20/80. the flex left to right is troubling. Seems to feel like its at the wheels or is it the wooden support running parallel with the 80/20 on the gantry. I was thinking of building a plywood beam to replace that board. But not convinced that is the source of the flex.
here is an arrangement of cables and pulleys that will prevent the left/right twist. you can put this under the frame with a stiff vertical connector from the gantry down to the cable on each side.
David, this looks very promising. Much better than a dual belt I was thinking about with an axis across to turn each simultaneously. Thanks For the advice with drawing.
Do you actually need wheels for this kind of machine? I suspect a well designed wooden sliding carriage, maybe with PTFE inserts, maybe some kind of light oil or graphite powder, would work much better over these distances and cutting powers than a few small wheels. The additional friction may also help keep things under control since you can only really control one axis at a time anyway. (Some hand-cranked ACME lead screws to make it a "real" manual mill would be helpful and super cool) Mounting the gantry extrusion directly to the wood would allow you to design a much higher rigidity torsion box for the gantry and use its strength by screwing the rail directly to it. If you're not using wheels, you don't need a floating rail, and its attendant reduction in rigidity. The pulley system for reducing racking is a very good one, though I'd probably go with the conjoined timing belt option even though it would be a little more expensive; purely because it would allow you to throw a handcrank on the axle any time you wanted.
New Question. Since I am using this setup without motors I need a way to lock the rotation of the z axis lead screw. Any thoughts?
New Question. Since I am using this setup without motors I need a way to lock the rotation of the z axis lead screw. Any thoughts? Do you offer a self locking lead screw or acme rod with nut block? View attachment 49050
Would suggest just a simple clamp block around the neck of the knob. I.e. a block of wood with a hole in it slightly larger than the diameter of the neck of the knob with a 1/8” slot cut from the hole to one edge and a transverse screw to tighten down that gap. Fix the block to the top plate using the available screw holes.
Really need to lock the carriage, not the screw. Locking the screw still leaves you with whatever backlash is available as permissible movement.
Any suggestions on how to lock the carriage? I did try a clamp on the knob earlier but it takes a lot of force and can slip.
Some kind of pinch-clamp setup on a piece of steel angle screwed to the side of the z axis rail is how I'd do it.
