First, to bend the tubing, I use a standard tubing bender, or "hickey".  Nothing fancy and this one came from a flea market and cost about $20 I think.  It comes with and indexing arrow and graduations at 30, 45, 60 and 90 degrees.  I made sure I adjusted my design to keep to simple angles that coincided with the markings on the hickey.

     It does a nice job of bending 5/8" OD to 1" OD which is all I need.  It flattens the inside of the bend slightly, but I've never had a strength problem as a result.  The nice thing about EMT is that if you screw up, it is a very inexpensive mistake.

     I cut the tubing into the required lengths and measure off the indexing mark to start the bending at.  For the main seat rails, they are 31½" long, the bend index mark is at 6", and I bend them to 60 degrees.  For the short connecting pieces of tubing that join the two seat rails, I cut them at 13½", the index is at 3 5/8", and I bend them to 45 degrees.  The picture is of the 13½" long pieces, one pre-bending, the other post bending, with the bend indexing mark on it.

     This produces a seat that is about 13½" to 14½2" wide depending on the diameter of tubing used.  In most cases, this is wide enough for all but the most . . . "ample" butts.  For anyone who is too wide for this kind of seat, the steel is quite likely not strong enough to support their weight anyway.

     Prior to welding, I needed to remove the zinc plating on the steel tube for two reasons.  First, in poorly ventilated areas, the zinc oxide fumes from welding can make you sick, and if in high enough concentrations, can kill you.  Secondly, trying to weld while zinc is getting into the bead area produces an ugly bead that doesn't leave you feeling confident about it's strength.

     One way to remove it is to soak it in muriatic acid, and then rinse the area with water after the plating is gone.  You might also need to neutralize the acid with baking soda.  Another method is to use toilet bowl cleaner that is acid based, and again, neutralize with water and/or baking soda.  The problem with these methods is it can be difficult to keep the acid in the desired spot, it can get very messy, and water on bare mild steel, especially if it gets inside the tube, can be problematic for rust.  I prefer mechanical removal because it's fast, you have a very high degree of control, and you can see when the zinc is gone because it changes from a shiney silver colour to a dark grey when the zinc is gone.  I use 60 or 80 grit flap wheels in my drill to remove the zinc plating in the areas I need to weld.  I am careful to use a light touch with the flap wheel so I don't dig too hard into the steel and weaken the tubing by thinning the tube wall.

     Before I put the seat tubing in my handy-dandy seat jig for welding, I take one of the side rails and drill a couple small holes in the one side rail.  I drill the holes where the cross tubes are to meet the side rails so they will be covered and hidden after welding.  I drill the holes so that the air will be able to move in and out of the seat tubes as they heat during welding and cool afterwards.  If you don't drill these little pressure relief holes, the hot, expanding air can pop, and blow a hole in or beside the bead as you're laying it down, and leave a hole that you will need to weld up later.

     The vent holes not only work for welding up the seat frame, but also for later when the tabs need to be added that will secure the seat frame to the trike/bent.

     For the bottom of the seat (where you sit) I measure about 3½" in from the end and mark the side rail.  This is where the lower cross-piece will go.  The top cross piece of tubing for the seat back goes anywhere from 7" to 9" from the top, depending on the bent's frame design and where I want to position the seat back support tube.

     The next step is to put the seat frame pieces in my seat jig.  The jig is nothing more than a few pieces of 1" x .125" box tube.  I picked 1/8" wall for stiffness, and 1/16" wall tubing will not be able to warp and flex a 1/8"wall jig.  Basic physics, I hope :)

     The jig consists of two mirrored side sections that have a piece of box tube welded to them so they can be accurately clamped at 90 degrees to the table edge, and an end stop that makes sure the end of the seat's side rails are both the same distance from table's edge.  Basically the jig holds both side rails parallel to each other, and with their ends lined up.  I use one C-clamp to hold each jig section to the table.

     I clamp on jig section to the table, then mount one of the seat's side rails in/on the jig, and clamp it in place.  I take the other side rail, and hold it against the other jig section with one hand, while I hold the first cross tube with my other hand.  I just slide the other jig section and side rail along the table edge til it is tight against the end of the cross tube, and then clamp the jig and side rail to the table too.  I take the other cross tube(s) and slide them into place on the seat's back.  The pressure of the jig, and the slight variation in length and notching is more than enough to hold the other cross piece(s) on their marks without even clamping them.

     I usually use 3/4" EMT and that only requires a cross tube at the 3½" mark(from the end) for the seat bottom, and the 9" mark(from the top) for the seat back.  In these pictures, I used 5/8" EMT to save a little weight, so I added a third cross tube just above the bend on the seat frame's back.  So far, with a 6'2", 220lb rider, the 5/8" tube seems to be more than strong enough.  I'll have to weigh the 3/4" and 5/8" frames and see how they compare for weight.  A 3/4" EMT tube seat is good for about 230 to 240lbs, and it would likely be smart to add a 3rd cross tube for larger riders.  Don't quote me on the higher weights, as I have not tested this myself . . . yet.

     After the tabs are sufficiently lined up, I clamp the lower cross tube to the tabs, and use a piece of wood or scrap tubing to hold the seat back at the required height to weld up the bottom tabs.  Just prior to this I use the flap wheel to remove the zinc plating on the area that I'll be welding the tabs to.  I pre-marked the center of the lower cross tube to help position it in the center of the tabs.  I confirm the alignment of the center of the seat back in the same way, and make sure that the ends of the seat tubes are the same height from the table top.

     When the alignment is good to go, I tack the tabs, remove the frame, and do a full bead where the tabs meet the cross tubes.  I then re-mount the seat frame now using the lower tabs, and repeat the procedure for to weld the top tabs.

     As pictured to the right, I used to overlap a 2" section of mesh along the edge of the seat, and sew in a length of 2" webbing or seat belt.  Then I'd punch out holes and install grommets.  It worked, but was time consuming, loud (from banging on the grommets) and a pain if a grommet had to be removed from a poor set.  After viewing some of my friend Larry's creations, I decided to wake up and do it the easy way like he does.

     So, the new way is much easier to do and a fair bit faster.  Instead of doubling up the edge of the seat an extra 2", I double it up 2½".  Then, I fold it in half again so the overlapped section is only 1¼" wide now and then I double stitch it along the inside edge.  This double stitching is for extra strength and it leaves a nice little "pocket" at the outside edge that you can see the AL rod sticking out of.  The punch in the picture is used to punch ~¼" holes every 2" and about 5/8" in from the outside edge.  You simply slide the AL rod into the pocket, put the mesh on the seat frame, and bend the AL rod to fit the contours of the seat frame.  Thread the end of the cord through the holes, and around the AL rod, and lace the seat up as normal.  

     The one thing that bothered me with the mesh seats was the string.  I couldn't find many colour options, so I usually went with white cotton or nylon.  Sometimes I'd find some green or yellow cord that felt very "plastic" and was a real pain to keep tight (like the green cover on the red seat frame).  I liked cotton or nylon cord because it would stay tight better but it would get pretty grungy with me handling it while my hands were dirty.  Again, Larry told me that he had dyed some cord, so I did the same and it worked most excellently.

     I got a packet of standard dye from Wal Mart and gathered up the cord I wanted to try.  According to instructions, I boiled about a gallon of water (I had a lot of cord to dye), and dropped my cord into it to pre-soak and pre-heat for a few minutes.  Then, I dumped the whole packet of dye into the water, stirred it for a few minutes to make sure it was fairly evenly dispersed in the water, and then let it sit for 2 or 3 hours.  The cotton and nylon cord dyed very well, but different brands of cord produced slightly different results.  The white and blue cord beside the dye box is made of polyester and it didn't take the dye at all.  Moving to the right were various brands of cotton and nylon cord and they all dyed very well.  A couple of them turned out a deep purple/black colour as opposed to straight black and some had lighter "highlight" areas that show up as specks of white in the camera flash.  The white bundle at the top is what the original cords all looked like.  In the end, I'm very happy with it because it makes it a little more "pro" looking and it certainly hides the dirt better than the white cord.  It was also very cheap and so simple even I couldn't screw it up.  Definitely the way I'll be doing it from here on in.