This being my first post, Ill probably sound absurd. I am building my third CNC machine. I am trying to use a LEAD machine as a base. I am adding a tool changer (120mm addition to Z axis) I also will be adding A axis rotation (150mm addition to Z axis) now using a 500mm Z axis V-slot does not sound stiff enough, further all the torque will be at the top. I was wondering if anyone has even tried a 500mm tall LEAD machine.
There is no reason to be any taller than your longest end mill. For a 1/4" end mill, that's no more than 4". With a palm router, you'll end up killing bushings very quickly unless you restrict it to cutting super light materials like foam and balsa. That's only if the runnout doesn't destroy it first. If you are using larger end mills, you are more than likely using larger spindles. Going this route, your gantry will flex long before you get to use that tool stick out. 4" is 100mm. 500mm just won't work unless you are either 5 axis or super shallow slopes.
Sounds like its not a palm router since he is wanting a tool changer. Every tool changer spindle I've seen will be way too heavy for the C-Beam anyways, regardless of height.
Thank for your responses. I though that having a single Z axis would be to weak at the extreme limits of the movement. The final machine will be 5 axis with coolant and tool changer. I do mill aluminum pieces and got tired of changing tools and flipping the parts. some of the Parts than can be tall as 6" and 3/8 thick. The big problem I see is milling PCB , the end mill are .3mm to 1mm I am afraid that the vibration on a single Z axis would be to great, Has anyone build one with 2 Z-C-beam axis attached to the Y plates instead of the V-Slot?
What you are talking about is a rising gantry. The more parts you have, the more room there is for error to develop. If you really want to go with a 5 axis, you would be better off having a dropping Z axis than two separate rising axi for the gantry. Miss a step on one side and you now have A and B skewed.
Yes I should have been a little more clear. I need to have enough clearance bellow the end-mill to spin the part which is about 200mm wide 180 degrees to work on the other side, this would have to be at least 220mm of the table this is compounded by the fact that my x axis will 1000mm in length. The B axis is at the tool head, it will swing 90 degrees left and right, The A axis would be installed as needed. The final machine will be 750mm deep, 1000mm wide and 500mm high.
What you probably want is a drop down z axis with the gantry sitting directly on elevatet y axis rails
I have to agree with what Kevon said, lower the base rather than raising the Z-axis. Raising the Z-axis just adds flexibility into the system which reduces cut quality especially in harder materials. Lowering the base board and setting the X-axis just above the Y-axis is a much more rigid solution (assuming you build a fairly rigid box beneath the frame of course). OpenBuilds did do a video of a raised Z-axis system that does offer some insight into what you seek though. The double X-axis gantry would help with an increased spindle weight. The one modification I would offer would be to put the drive motor on the lower X-axis rail where the drive force is closer to the resistance. Less leverage on the system that way. Adding a bit more space between the X-axis rails would also help.
Thank, this video is what gave me the idea to use c-beams for the gantry risers, and even if a lowered the base I still need the clearance for the A axis. Correct me if I completely off but wouldn't the weights and moments transfer from the X axis to the risers on a lateral motion? The rigidity of the V-slot is less then the rigidity of the Z-axis. In the C-beam machine there is additional support on the risers which helps with the lateral motion, A related question would be can the lead screw handle the additional weight it needs to push around?
The issue here is frame sway and while using C-Beams for the verticals will lessen the amount of the sway it's really not the best way to solve it. The best way is to reduce the amount of the eccentricity, the distance between the opposing forces and the supports of the system. To explain further, the diagram below shows what I mean by "frame sway". And while the diagram is shown greatly exaggerated so the effect is visible the reality is that sways of as little as 0.1mm can have an effect on the quality of the outcome when milling hard materials. The X-axis drive is pushing the Z-axis through the material which is putting up a resistance and the lateral force created by the X-axis drive is causing sway in the gantry frame. By reducing the distance between drive stepper and the supporting Y-axis rails, the sway is reduced. How all this ties together with what we are suggesting would look something like this... Basically mount your system on a 2x8 frame and then mount the A-axis down within the wooden framework. You might also consider mounting some blocking along the side rails in order to be able to drop in a platform for regular flat sheet routing. As for the followup question about the stepper moving the weight, the more important question would be does it have the strength to push the cutter head through the material. If you're worried, go up to the higher torque steppers.
Attached is a section of what I intend to build I am trying to get the clearance between the work surface and the bottom of the end mill of roughly 220mm. In watching the video again at TI 14.31 I notice that the bottom of the rail on the z axis is still about 2" from the work table. does the axis get any higher?
They are just simple block drawings in autocad, really nothing special. Compare what you see in the video with the main picture in OpenBuilds LEAD CNC. In the video you'll note the Z-axis beam is fixed to the X-axis carriages and only the Z-axis carriage/spindle mount moves up and down. In the original design the entire Z-axis beam moves up and down relative to the X-axis and this is how you create lots of separation between the cutting tip and the work surface. The differing methods both have their benefits and limitations and have been discussed at length here on the forum with the latter being the approach you'll want to go with in your design.
