When I worked for DMG MORI I assembled a few machines. On the DMU 50 machine made by DMG MORI the linear rails are facing up and there is only one lead screw offset from center for the X and y axis. But this is on a 5 axis machine that has a rotary/trunnion configuration for the 4th and 5th axis. The linear rails are mounted about 4 or 5 feet above the table and these move the spindle in the X and y axis directions. There is of course a vertical linear rail and ball screw for the z axis. I'm writing this because it seems to me the need for 2 ball screws seems like overkill. The spindle assembly in the DMU 50 is way heavier than a tabletop CNC router/mill. And of course the linear rail handles the weight of the axis assembly not the ball screw. If I remember the pillow blocks for the ball screws have a round roller bearing on one a needle roller bearing on the other. Needle roller bearings are not designed to handle large loads in either direction. They are designed to be self centering. The ball screws on the DMU 50 are maybe 16mm at the most. By memory the linear rails were perhaps 12 to 16mm wide. Earlier today I saw another linear rail/lead screw machine model here in the builds section. How wide are the rails you have?

 

Here's the link to the other build:

https://openbuilds.com/threads/https://openbuilds.com/threads/linear-rail-ox.1269/linear-rail-ox.1269/

 

Of course the bracing is important. Many designs have more than they really need but as long as it's static it doesn't really hurt anything.

Note how the rails and lead screws are above the table. If there is a way to design the gantry so rather than having one wide section to prevent sagging it's designed so there can be more clearance for the z axis to travel more.

Mazak used to design their machines so the spindle is cantilevered to prevent sagging. That way it can extend out from the gantry more. Unfortunately there is a big counterweight behind the the gantry to allow it to have that room.

Another alternative is rather that have the X and Y axis parallel to the floor it's designed so the X axis is parallel to the floor, the Y axis is vertical and the z axis is horizontal. It is referred to as a horizontal mill.

 

The though of going with the linear rails on the topside of the Y axis is interesting. I have been thinking about going along the side, but honestly on the topside will allow for the machine to not be so wide.

 

The place down the road from where I live has linear rail/ball screw kits that look like what you have in the photo.
Here is the link:
High-Torque Stepper Motor, Stepper Motor, Driver, Stepper Motor kit, DC Servo Motor, DC Servo Motor kit, Stepper Motor Power Supply, CNC Router, Spindle, and other Components. Stepper Motor | Stepper Motor Driver | CNC Router | Laser Machine | 3D Printers For Sale.
They also have stepper motor/driver/board kits along with a whole bunch of other stuff. I actually considered buying from him back when I first found the Open Builds web site but when I called him and asked if he could offer me some guidance since I was new to everything. He told me he would not help me at all...which is why I ask a lot of questions on the Open Builds forum.

Mounting the rails on top and elevated above the table gives you the opportunity to get more travel in the Z axis.

It might pay to lean how to use the analysis module of Fusion 360 because you can test out your designs to see how much the gantry and the rest of the machine flexes when under load. I had Finite Elemental Analysis classes in school and training to use a PC based FEA software application a long time ago and may very well re-teach myself how to do this again just to prove to myself that aspect of design engineering.

 

By chance does anyone have 3D models of these linear rail and ball screw/ball nut/pillow block assemblies?

 

Is there a chance I can get those from you? I’ll convert them to STEP files and use SolidWorks to design with. I’d like to get good at Fusion 360 but ...

 

i ended up having to take my mom to the emergency room on saturday and then taking care of things i normally would have done on saturday on sunday...she's in the hospital now going through all kinds of test for a gastrointestinal infection from the antibiotics she was taking after having a TENS unit implanted in her back.

Cutting the rails will have to wait until hopefully next weekend. my friend has a miter saw with a metal cutting blade. He insists that is the better way to go so I am going to try out his setup first. If that doesn't work I will use the miter box I bought.

Not to brag but I have over 60,000 hours of experience with Unigraphics/Siemens NX for modeling, design and CNC programming. Modeling a thread of any kind is a walk in the park. As much as I would love to model the linear rail and ball screw components I would need either dimensioned drawings or the actual part so I can measure it in order to model it.

 

Ok...maybe I was trying to get away with not having to model it myself. I did happen to find some models at GrabCAD.com last night.

 

I will have to check that out...I hadn't even thought about that.
Its funny when I am work I do that all the time and when I walk out the door I try to avoid thinking the way I do when I am work. I used to think about engineering and design related stuff all the time...and now I can turn it off immediately.

 

That’s a decent approach.

Just wondering....I have all the carriage assemblies built and have come to realize that no matter how much time is put into adjusting the eccentrics for how tight against the rails the wheels are the ‘feel’ for every one will be different. I noticed that when I assembled that x-axis carriage that has 18 wheels which will obviously have a different resistance that others. What have you found?