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[Mountaincraft]

Not real sure except that's the way it was designed to be done.. Seems like I tired it your way at first, but ran into a problem...

You'd have to make an 'additional' plate, and you'd loose the ability no mount your router to the 1530 (the tee slots are handy for mounting all sorts of stuff that you'll be wanting to down the line).. but other than that, I'm not sure.. maybe alignment of the motor shaft and acme screw?

I'd run this past Ahren...

[Mountaincraft]

Is your 4" CRS stationary? It looks like your extrusion is bolted to the carriages that move on the Gantry, and that your 4" CRS is is bolted to that in a stationary position... then your Z carriage made of two standard bearing carriages and a high Z plate move up and down on that..

Have I got it right?

If so, you've lost all your Z travel.. You won't be able to get hardly any clearance under that fixed CRS rail...

You need to not only allow for various thickness materials, but vacuum system, and hold down fixtures..

If you really plan on building a machine with only 1" or so of available travel in the Z direction, then I would shorten everything up and move that gantry right down on top of the X rail carriages.. thus reducing the twisting forces on the gantry... If you're not gonna use the extra travel of your Z fixture, why introduce extra force?

[Mountaincraft]

By doing it the way Ahren designed it, you will be able to move the entire Z carriage almost all the way up to the bottom of the gantry... thus using the entire range of your available Z travel...

[Plan_B]

You do have it right - except there is no need for an extra plate. I'll post a photo of the z later.

Actually I have 5.5" of z travel with the present configuration. I can't use it all now the way it is assembled because of the vertical position of the 1530 (It's too low). I could slide it up about 3 1/2 " higher and I would have the 5.5" travel. Right now I have about 2". The Z is kind of just roughed in though. Once the router bracket is here I'll decide on a final configuration.

One other disadvantage I see with my present set up is that vibration and cutting forces will exert higher loads on the 4 bolts holding the extrusion to the extended carriages. Could this result in racking my z by overcoming the clamping forces? My guess is no but I'll be watching for that none-the-less. Your configuration is better in that respect.