pdf plans here

There are several things you really must get right with the seat frame. Firstly you must mirror the bends as closely as possible. To do this I ended up welding two 4" nails to the pivot plates on the pipe bender (shown below). I found that if I measured the distance between the tips of these nails once I got the angle right, I could repeat the bends. The final thing that is critical is making sure that the seat is mounded square, centered and level to your frame.

Here is what the finished seat frame look like. I added the loop on the top for a head rest.

9 Feb 2007

Here I am using a small washer to trace the circle that I will use to cut round fillets on the ends of the seat mounts. They will be machined and drilled as a goup.

Here are the finished seat mounts. Item 38 was actually cut as a single piece 96mm long, then I used the 20mm hole saw to cut it in half and fish mouth it all in one go. However, this didn't turn out to be all that helpful, I still had to reshape them by hand to fit them to the seat brace before welding.

16 Feb 2007

To bend the seat rails and braces I used my modified 12ton hydraulic pipe bender. It is overkill for light pipe like this, but its all I have. The nice thing about this bender is all you have to do is place a line where you want the bend, center it in the bender and measure the angle between the plates, once it is reached the bend is complete and centered right on your line.

Here you can see the shoe? pushing against the plates.

Here is a finished bend. It does flatten the bend ever so slightly.

Here is a close-up of the plates I made for it. The pipe bender came with rollers, which were completely useless, these plates work much better.

Here are the finished pieces for the seat.

To fish mouth the ends of the seat braces I used the bench grinder. I have tried using a whole saw in the XY vice of the drill press, but I ended up having to shape it anyway, so it seems like more of a hassle than it is worth.

Once the braces are done, you need to square up your seat rails and clamp them so you can tack weld the braces on. To do this I used two lengths of RHS that I ran down each side of my work bench. At this end you may see the chalk line I used the line up the top of each rail. The braces were positioned and held in place with a large clamp, then tack welded. Once they were all tack welded, I turned the seat over ant tacked the other side, before doing the final welds.

To do this I used 2mm stainless steel rods (electrodes). They are actually very easy to strike an arc and weld, but you must keep them in an air tight container, because any moisture will ruin them. The slag is quite dangerous, it snaps off as the weld cools and goes flying through the air, so keep a pair of clear safety glasses on under your visor, because you don't want any of this hot slag hitting you in the eye.

17 Feb 2007

Once the seat frame is welded together it is time to mount it onto the frame. The critical thing here is that you weld it on centered, square and level. To do this I clamped two lengths of flat steel square agianst the rear of the frame at the same offset on each side. Then I measures the distance from these to the seat rail, making sure it was equal on both sides. I did the same on the front, using a single length of RHS squared with the frame to ensure the seat was level and centered.

Here you can see the rear seat mount being tack welded in three places. I tacked all the mounts, then took the seat off and repositioned it to make the final welds easier to perform. The stainless is pretty easy to weld, you just have to watch the heat. As with all thin tube welding there is a risk of burn through, so you have to keep the weld pool on the tube, and then let it melt into the butted material.

19 Feb 2007

The mesh seat cover is made from a single piece of nylon reinforced mesh 830 x 650mm. It has a gusset of 32mm wide webbing (used to make straps) sewn front and back along each side. Ten eyelets made from 25mm wide webbing, each 100mm long are folded and sewn 90mm apart down the left and right side. These will be laced with shock cord like a shoe lace to attach the mesh cover the the seat frame. Inside each of the side gussets is also a selvage (YELLOW) made from rubber coated, wire core, clothes line cord. This helps to stiffen the sides and support the weight more evenly. I used a heavy upholstery thread to sew this using a 100 needle.

To make the seat I started by cutting everything out. Then I got a candle and using the flame melted the ends of the webbing to stop them from fraying. I marked two of the side strips with chalk lines 90mm apart so I would know where to place the eyelets. Then I just pinned the webbing down the sides of the mesh, not the eyelets, because they would have been too thick. Then as I sewed down the outside, I would pull out the pin, insert the next eyelet at the mark and sew over it and so on. I started with just a regular stitch on the outside. Then with the eyelets and gusset held in place, inserted the clothes line cord selvage and sewed down the other side. Finally I did a zigzag stitch down each side to stiffen the selvage. Finally I added the gusset to the front and back and hand stitched the corners.

Here is the finished seat cover, ready to be laced onto the seat frame.