[silver2]

Hi, new to this forum and I could use some help. I'm building a cnc router with travels of 48"x48" I'm using 8020 for most of the project. Right now I'm confused about linear motion of X and Y, I've seen comments about linear bearings and shafts. Is it realy hard to get these without the problem of them being bent? I'm planning on using 20mm rods, is this adequet for the approximatly 60" length? I want to be able to run aluminum panels without any problems once the machine is complete. I plan to run 2 ball screws on the Y axis and 1 ball screw on the X, any suggestions as to what size to use to prevent whipping? Also is there much of a difference between mounting linear parts on top of rail or on the side? Any suggestions will really help. Thanks

[exitium]

Im new to all this as well and currently dreaming about making my own cnc router or converting my small mill to CNC. Im not sure of the physical characteristics required for linear shafts but if your plan was to use rods from the big box stores and are concerned about them being bent, maybe look at using "drill rod". Its generally made to much higher tolerances.

[harryn]

It would be a shame to spend so much on 8020 extrusions and then loose all of the fram stiffness by using a small round rod for the actual movement support.

If you use a rail which attaches to the frame along its length, then it naturally takes on much of the stiffness of the frame it is attached to. If not, then you have wasted your time and money that you spent on the frame.

For a 60 inch long, unsupported rod to be stiff enough, it will need to be around 2 inches diameter minimum, which is quite expensive. This is why people use smaller rails, but the stiffness comes from bonding the frame along the way.

[TLHarrell]

Take a look at Open Rail | OpenBuilds Store for your linear rails. I'm going to be using them in my small aluminum cutting mill. You certainly do not want to use any form of unsupported shaft. Those are fine for small machines like 3D printers, certainly not for a CNC. Even with a larger rod, when milling aluminum the forces will cause that rod to move vertically or horizontally during the cut, the greatest amount in the center of the axis. You want fully supported linear rail, whether it is THK type rails, ground rods or anything else.

Whipping will be caused by turning too fast. You can use smaller diameter screws with less turns per inch to reduce the amount of RPMs. Larger diameters and larger loads will require larger motors/drivers. You might take a look at using gear track instead.

There is a huge difference to mounting on top of the frame or on the side. Most linear components will have specifications for load based on whether they are top or side mounted. Usually, side mounting load rating is 1/2 to 1/3 of the load rating when mounted on top.

[Lasersolution]

It is easy for us to produce our CNC Router, but if you want make a big cnc router, I think you had better purchase

[MXJ]

Have a look at this website, I am building a 50X27
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