New Machine Build- Bearing and Guide Supports

[geometrix]

All,

I am a mechanical engineer by profession, and I dabble in Microchip microcontrollers and programming. I am in the process of designing my first CNC router and I have 3 HUGE questions:

1. How do I support the guide ends?
2. How do I support the leadscrew ends?
3. How do I prevent endplay of the leadscrew?

I am using Pro|ENGINEER Wildfire 4.0 to design my CNC router. See the attached JPEG's.

I now have a preliminary design based upon many of the other designs that I have seen. I am not sure that I am supporting the guide rods and leadscrews properly. For starters, I am using precision ground rod for the guides and conventional 1/2-10 ACME leadscrew. I am purchasing this hardware from McMaster-Carr. I have also spec'd out P/N 57745K22 for the rod ends and P/N 5967K31 for the end bearings. Furthermore, I am using anti-backlash nuts P/N 6350K61. Once again, all of these off-the-shelf parts are from McMaster-Carr.

I intend to build this router primarily out of HDPE or maybe MDF. I am not sure yet.

Thank you all for any advice that you can provide.

[ger21]

1) It doesn't really matter, but alignment is critical, or you'll get binding.

A bigger concern should be that unsupported shafts are not a good idea. Anything under 1" diameter may result in more flex than you'd like.

2) and 3) both are the same. The bearings that support the screw also need to support it axially, so there is no movement (backlash). THere are multiple ways to do it, from turning the ends of the screws to fit in expensive bearing block mounts, to sliding a flanged bearing over the screw and using clamp on collars to hold the screw in place.

This might help.

http://www.cncrouterparts.com/parts.html

Also, you really should consider a multiple start screw, from 1/2-8 2 start or 1/2-10 2 start up to 1/2-10 5 start. Multiple start screws are nearly twice as efficient (or even more) than 1/2-10 single start, and they'll keep the stepper spinning slower where it has more torque. In most cases you'll get at least double the speed for a few dollars more.