Help and advice - working with plate steel

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The project description:I'm helping a buddy design a cable railing system using posts made out of 3/8" plate.The posts will be cut with a waterjet and then stitch welded together to prevent warpage.The posts will then be bolted through hard maple stair treads or lagged into a LML beam and then tied to a hard maple handrail.Cable will be threaded through holes drilled at an angle - 34 degrees fromhorizontal - the slope of the stairs and held in tension by the top and bottom posts.The middle posts act as cable guides more than anything.  The cable is from a commercial railing supplier.Now for a set of noob questions - I'd like to find out a several things:1.) Will a waterjet cut holes at an angle? I've only seen them cut perpendicular to the surface being cut.2.) Is there a recommended technique to drilling holes at an angle through plate?3.) To prevent warpage, how should I best specify the welds?  Stitch length and spacing is the information     that I would like to get from the experts.I'm handing off post welding to a seasoned welder - don't feel real comfortable with my skills for anyone else'swork.  Here are some images from SolidWorks.  The right stair stringer is not shown and both the stringers were weldedby a professional company.  Thanks for your help!
Reply:Drilling holes at an angle requires expensive and rigid tooling.  Starting with a small pilot hole helps but small bits tend to flex and walk.  Split points are less likely.  If you have access to any sort of milling machine you can easily make holes at any angle using any two flute end mill.  You could drill the holes oversized and straight and used wedge shaped washers to make the angle.  Angled holes are entirely possible I just have not had good luck with them with hand tooling.
Reply:I would think that water jet would be possible to cut on an off 90 degree if they can rotate the jet. I know our high definition plasma table can rotate the plasma head and cut on angle. We have beveled plate this way. (Thick plate, we use torch)You could center punch the plate and start with a small piolet hole like GMC said but would be time consuming. You would also have to make a jig to hold the plates on angle or rotate the drill press table. Personally I would go the CNC route with either mill, plasma or waterjet if possible. Also laser may work? Haven't felt with laser before.Last edited by oxygen454; 05-15-2014 at 02:27 AM.
Reply:Just WJ the holes straight through, you need some clearance, especially if you have swaged fittings to get through. Think 1/2" holes for 1/4 cable. Also your posts are going to be wobbly without a tee section to help stiffen it up.
Reply:For the welding I would back step, and skip around a lot to combat warpage.Drilling the holes on an angle. I would take an R-8 end mill adapter and a rotabroach. Place the plate in the vice at your desired angle, and drill the holes. Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Thanks for the help gentlemen - see the pictures for the final product
Reply:And some more pictures:
Reply:Stairs look fine.  The air duct looks awful,  it's butted up to door molding and about 4" from a can light.  I wish someone luck to finish that out and make it look good.