Bon, That sounds exactly like what I am doing! I have had an I2 for a while and decided I wanted to design my own and I was also inspired by Carl's bot!
I know that this is pretty early in your design process, but because I'm designing a very similar printer, I'll tell you some things that I learned while designing/partially constructing mine

You currently have the carriage so the horizontal bar end butts up against the face of the carriage. I originally had the same thing, but I found that it had 2 issues.

1: It requires the cut on that horiz. bar to be perfect because if it is too short you won't get a very solid connection, and if it's two long, then it won't fit.
2: There isn't a commercially available (that I could find) way to strongly attach the bar to the carriage. That means that the attachment will have to be printed. It was hard for me to design a printed part that was rigid enough to go there.​

What I would consider instead is putting the bar so one of the faces mounts against the carriage. That does require drilling two holes in the bar into which you can put a bolt that screws into the carriage. If you're willing to drill out the threaded portions in carriage, you could screw the bolts into nuts in the bar instead. There's probably other things you can do as well, those are just the two that occurred to me. As a side benefit, I found that this also allowed me to mount my belt guides with the same bolts.

Another thing is that the Z axis has been really hard to do well. I've pretty much got the X/Y done on my machine, but the Z is giving me lots of trouble. (It's really hard to drill everything perfectly and that leads to some things being a bit out of alignment). Designing for oversize holes and some kind of fitting jig is your friend here.

Good luck with your design and build! (and if you have any suggestions/ideas for my printer, let me know as well!)
~Max Tepermeister

 

Since you are calling this a D-Bot, are you following the design of this D-bot? http://www.thingiverse.com/thing:1001065

 

@Bon Thomassen glad my make inspired you and I am curious what changes and improvements you will make. There are already a D, E, J, & S (Spiff) remixes so there are lots of great ideas to inspire you. Since it is open source and easily hackable/modifieable it is to make it your own version and please do.
The major change from the original C-Bot to D-bot was the offsetting of the Z axis by David Spaulding (hence D-bot) and is a Z axis option in the C-bot Remix/V2.

Check out this photo gallery for inspiration:
Photos from posts

 

How about putting them into a zip file & uploading that?

 

Hey there Carl, I see that you have been into 3D printer buils for awhile now. I took a look at your Cbot build and liked it. Have you learned anything new that leads you to a better more stable 3D printer? Any ideas on what might be a great Design here ?