Formed steel cnc router

[sbams]

Hi all

i want to start a build log for my first DIY cnc machine.
the construction will be all formed steel welded together.
1/4 plate for the table and 3/16 plate for the gantry. There are still quit a few gussets I will be adding I just wanted the start this log in case I'm way off.
3/8 plate for the main bed and bolted on 3/4 aluminum plate for the cutting area bed.
The reason for the formed steel construction is I can build the whole thing from scrapes at work and not pay for the steel. and I can cnc plasma cut all the parts
the cutting area will be roughly 15" x 15" x 5".
all rails will be 20mm profile
X and Y ball screws will be 1610 with 2.1 pulleys
Z ball screw will be 1605 with 2.1 pulleys
i have Nema 23 motors drawn but not sure if there big enough (one of the questions for you guys).
i want to cut aluminum and stone mostly but I imagine I will cut some hard woods as well.

questions:
How does the design look so far? Will this cut aluminum or am I dreaming!!
Will the Nema 23s be strong enough?
are the pulleys a good idea or should I direct couple them?
what step angle (degrees) is recommended?
i know I will have a lot more questions along the way so thanks I advance for any help.

[AdCNC]

As regards to mounting the bearing rails on the C section you will struggle to get them running level with each other unless you weld the whole lot together and skim the surfaces, but not many people have access to that sort of equipment. but by doing that you are reducing the thickness so welding a pad on first and machining that down and also incorporating a datum edge for one of the rails to but up against would be a good idea.

[sbams]

I do plan on skimming the rail surfaces but not all to getter. My plan is to fome the C section weld in the gussets then machine each rail separately, then weld the whole thing together. I have a 2" thick surface ground welding table I can clamp it to while welding. I'm hoping this will keep it straight enough. I did not think about the pads which I like so I added 3/16 pads under the rails for machining. Thank you :)

[andrewbond]

If the steel is free ... or at least no cost ;) I'd say try and make the c- channels into a box somehow. Also maybe put some forms on the ends of the gantry sides for stiffness, have a look at ShopBotTools CNC Routers (http://www.shopbottools.com/) they use formed steel for the gantry sides. of probably a similar thickness.

[AdCNC]

No matter how you weld it buddy, it will still warp. you may control the amount a bit by clamping to a table but it will still twist. hence you need to perhaps weld on pads where the box or parts mate and machine the surfaces then bolt them together, this way you have a small degree of adjustment and do away with warpage.