Building a plasma table - Utah, USA

[MikeGyver]

Hey guys, first post, I'm hoping I can get some advice on this forum.

I've started building a plasma table from scratch; this is my very first CNC adventure and I'm looking forward to it since I'm into electronics design and welding/fabrication. The table can accomidate a 4ft wide steel plate, and the X-axis travel will be about 3.5 ft (feed the 4x8 ft plate/sheet through to keep cutting out more parts).

http://i1123.photobucket.com/albums/l550/customdesign/CNC/IMG_5331.jpg

My plan so far is to use a direct drive rack and pinion gear setup and the 305oz steppers from hobbycnc.com ( http://www.hobbycnc.com/products/stepper-motors/ ) This might be massive overkill since they should provide somewhere around 30lbs of "push". I'm also planning on using their 4 channel "Pro" controller ( http://www.hobbycnc.com/products/hobbycnc-pro-chopper-driver-board-kits/ ).
There will be 2 X-axis motor's, one on each end of the bridge, one Y axis motor, and exentually a Z-axis.

I'm using these V-groove bearings from ebay ( http://cgi.ebay.com/3-8-V-Groove-Guide-Sealed-Ball-Bearing-RM22RS-inch-/360274593197?pt=LH_DefaultDomain_0&hash=item53e20a05ad ) and my tracks will be lengths of 3/4" 316 stainless angle iron 1/8" thick. 316 stainless is quite hard (Rockwell B91), and springy (60.2kpsi yield), but here is how the bearings sit on the angle. Do you guys think this will cause problems?

http://i1123.photobucket.com/albums/l550/customdesign/CNC/IMG_5336.jpg

For the 2 X-axis motors and the 1 Y-axis motor, I'm going to be using direct drive rack-and-pinion setup. The rack will be on the bottom of the beam that holds the angle iron track, and the motor will pivot and use a spring to maintain backlash and keep the V-groove bearings tightly against the track.
I did a search and it seems everyones going with 20degree 20tooth/inch 1/2"x1/2" racks, is this what I'm goin to want?

Also does anybody have any info for choosing a pinion size. Keep in mind a plasma table wont need as much TQ as a router since there is no contact with the work. I'm making the X-axis bridge mostly out of 2"x3" aluminum tubing to keep inertia minimal.

If anybody has any ideas or recomendations I'm all ears.

[isladelobos]

Hi MikeGyver.

You use the Skate for grind the rails?
I think it is one important part for the accuracy your cuts.
You thinking to use one Hypertherm plasma cutter?

Saludos.

[MikeGyver]

I haven't done anything to the rails, they're just raw angle iron (the ones pictures are mild steel and just for mockup). The sides of the V-groove bearings are contacting the sides of the rails differently, but I'm wondering if this really even matters.

I haven't decided on a plasma cutter yet, but I do like the Hypertherms because they seem to cater to machine control.

[GC3]

I haven't done anything to the rails, they're just raw angle iron (the ones pictures are mild steel and just for mockup). The sides of the V-groove bearings are contacting the sides of the rails differently, but I'm wondering if this really even matters.

I haven't decided on a plasma cutter yet, but I do like the Hypertherms because they seem to cater to machine control.

You better read up more on rails and their use. Then go back and reread then just keep on reading so you do not waste your hard earned dollars.

Congrats on your start

[isladelobos]

Hi MikeGyver.

One good review (http://www.plasma-cutter.org/plasma_cutter_reviews.html) about the most used plasma cutters.

Is possible Esab is the best choice but Hypertherm is most used in cnc.
Esab is the plasma inventor. The prices are very similar.

I'm interest in your plans design.
You can see ones plasma granty kits Here (http://www.precisionplasmallc.com/).
And one maker with this in use Here (http://www.cnczone.com/forums/precision_plasma/104978-precision_plasma_4x4_cnc_table.html).