First time build - Steel Frame CNC Router

[examorph]

Thanks for the advice guys, I ended up changing the arrangement slightly by only making the rear bed support from 3mm box, all other 4 (including front) are 4mm. So there should be enough box section to bolt the bed onto and will leave the back 3mm section as a support.

Spent half the day cutting/grinding more of the box section and the rest of the day, failing at welding Some horror shows for you below:

1st weld on frame:
Attachment 17844

thinking of cutting this off and starting again. It was over two runs, had let it cool down after doing a bit

Few more welds after this:

Attachment 17838Attachment 17839Attachment 17840Attachment 17841Attachment 17843

Ended up grinding it down and squaring it up many times before I got anything close to square. Ended up with the below, plan is to do both sides and then join them with the sections in between.

Attachment 17842

Was jumping from one side of the frame to the other when welding and did not go back to weld the opposite face until I could touch it again, hopefully this is ok.
Settings for the mig were 2 Volts and 3 for the speed.

Before I continue welding/assembling tomorrow, could you guys please help me with a few questions:
- Is it OK to go back over welds to fill in the gaps, if any?
- Any recommendations on getting into the tighter angles for welding?
- I ended up running 100mm constant welds down the side of the 100x50 box section, should I be splitting this into two runs. 50mm at a time and wait for cooling before going again?
- From the images shown, does the amount of "overlap" on each side of the weld look like its enough? I was worrying as I only really concentrated on filling the gap and wasnt sure if I needed to drag the weld over each face enough to properly join the two sections.