Joe90's BIG RAT Build.

[Andrewg]

Yes, as you say Joe Harris's videos show simple routing of Aluminum is doable if high precision not required. However looks from video that he actually used 15mm+ spacers under his Z bearings and flat plates.

Neale, presumably you have to recess one plate for the ballnut holder, and the other for the BK/BK bearings....or go another way? What am I missing?

[JAZZCNC]

Yes, as you say Joe Harris's videos show simple routing of Aluminum is doable if high precision not required. However looks from video that he actually used 15mm+ spacers under his Z bearings and flat plates.

Neale, presumably you have to recess one plate for the ballnut holder, and the other for the BK/BK bearings....or go another way? What am I missing?

Just because Joe did it that way doesn't mean it's a good way. He did it because it was the easiest way, I'm telling you the other way is better from experience. Those building have to make there own minds up which to route to take based on there own abilty's and equipment just like Joe did.!

This might help with the confusion.

[Neale]

Neale, presumably you have to recess one plate for the ballnut holder, and the other for the BK/BK bearings....or go another way? What am I missing?

As per Jazz's picture, you need a recess in both halves. As I remember (and I can't find a drawing of it to hand) the recess was wider somewhere around the middle of the plate to give space for the ballnut mounting bracket. As ever, make sure that your design allows adjustment to align the ballscrew and nut in two dimensions - well, I needed to as my machining ain't that accurate...

[CNCRY]

Andrewg - I went through this same thinking, and am in the process of building it now. I'm using the spacer method, it's requiring 15mm spacers with the 20mm hiwin rails to get enough clearance with no pocketing. My thinking is that if I can get the CNC up and running I can then pocket out a new piece if needed, as I'm more likely to mess up the plate routing by hand (and no access to mill anytime soon). I'm offsetting the overhang by using 15mm thick tooling plate instead of 20mm. So saving 10mm but spacing 15mm.
Mine is untested so far though! - so I'd go with Jazz's and others advice any day if you are happy to pocket them.