making a motorbike seat, seat base?

[ajlelectronics]

How is the top constructed, covering sewed to foam?

Three part sandwich. A base material (I use Calico), some sew foam of the required thickness. (I use 6mm) and the vinyl of your choice on top.

This advice varies amongst us, some don't bother tacking, others glue it tight but here is how I do it...
Cut your plate to size remembering the selvage required and give the back just the faintest whiff of spray adhesive just to tack it to the sew foam. Do the same with the base layer and sew around the perimeter as close to the edge as you can. Cut it out and there is your finished piece ready to sew the pattern and then join to the skirt.

Don't you wander at all doing those parallel lines, the seat with loads of lines must be really hard to not wander a bit, I am thinking how easy it is to follow a
straight line with a jigsaw.

Easier on a sewing machine! You can buy pre-quilted vinyls but the selection is smaller than making your own of course. Rule your guide lines with a Chinagraph pencil or Tailors' chalk. The one pictured is highly likely to have been done with a double needle machine, there is no way to get such accuracy with a single needle (in my experience anyway). Use a thicker thread in a contrasting colour for the decoration.

How is the side sewn to the top?

It is sewn inside out. The top piece is known as the "plate" and the surround is the "skirt". To join them, you offer the two edges together, centred according to which end you want the seam and I often staple at this point. Then it is just starting at one end with some overlap and finishing the other end with a similar overlap. The stitching doesn't go right up to the centre line as yet. Pull the two overlaps into position and mark the centre line on both. Staple if you wish and then sew the two ends together along the mark. (I would French seam it here for appearance sake, but that's a guide for another day.) Lay the loose pieces onto the plate and now finish sewing along the seam. Turn inside out and you have joined them. You may want to top stitch (aka felled seam) around the edge, which required the selvage (from seam to material edge) clipped at intervals and around the curves to reduce the bulk.

If you want to do some research, then look for "how to sew a box cushion" which is similar although only one plate of course.

 

[keithski122]

Vinyl is tack glued to 10mm scrim foam then topstitched, I don't use calico as a base anymore as it will stop the panel from stretching into position just thicker foam.13 years of practice keeps the lines straight. All stitch lines are sealed with waterproofer.4 is the underside of 5 after cutting to shape(material will shrink with top stitching so is first cut oversize).Two bands for the sides, one for the base and one for the curved top part all sewn with a piped edge.

 

[keithski122]

Easier on a sewing machine! You can buy pre-quilted vinyls but the selection is smaller than making your own of course. Rule your guide lines with a Chinagraph pencil or Tailors' chalk. The one pictured is highly likely to have been done with a double needle machine, there is no way to get such accuracy with a single needle (in my experience anyway). Use a thicker thread in a contrasting colour for the decoration.

I think the pre quilted vinyls that are not custom made always look a bit dodgy, they just don't have the quality look of hand sewn diamonds.Intersections of stitching sometimes looks a bit wonky.
All my sewing is done by a single needle machine, I do use a guide for the second line of stitching though.Straight or slightly curved lines are easy,try doing squiggles by hand!

 

[ajlelectronics]

I think the pre quilted vinyls that are not custom made always look a bit dodgy, they just don't have the quality look of hand sewn diamonds.Intersections of stitching sometimes looks a bit wonky.

My first one ever, a test panel for the owner to look at to see if he actually liked the quilting and a partly covered in black stitching photo. The construction can be seen in the latter but I can't find a completed one.

 

[ajlelectronics]

Some of my work from years past...

 

[ajlelectronics]

These might help to show construction, photo one shows the French seam with its reinforcement...

 

[Duisky]

…

Keithski&Duisky. Those seat look pretty good, if I was closer to you I would be knocking on your door.
I can see parts of what I want to do in both seats. I was going to try and do the parallel lines,…

For parallel lines, you might be time and effort ahead by buying some quality ‘fluted vinyl’, although you will be limited for colour.

Fluted vinyl already has a slight backing to the material, and the face is already ‘lined’ with a heat embossed seam so already waterproof. Some even have a fake stitch moulded into the design to further enhance it. Marine grade is probably the best (plenty options given it’s really designed for yachts), but relatively expensive, however you’re only going to be needing a meter or so. One benefit is however, is that there will be plenty excess to practice with in the first instance.

 

[ajlelectronics]

but relatively expensive

Nope. One of the lowest cost materials out there.

 

[Duisky]

Nope. One of the lowest cost materials out there.

I was referring to fluted vinyl specifically. You can buy it from as little as £10 per meter from wherever vs. 3/4 times that for bonafide marine grade from a specialist supplier, hence it being relatively more expensive.

 

[keithski122]

For parallel lines, you might be time and effort ahead by buying some quality ‘fluted vinyl’, although you will be limited for colour.

Fluted vinyl already has a slight backing to the material, and the face is already ‘lined’ with a heat embossed seam so already waterproof. Some even have a fake stitch moulded into the design to further enhance it. Marine grade is probably the best (plenty options given it’s really designed for yachts), but relatively expensive, however you’re only going to be needing a meter or so. One benefit is however, is that there will be plenty excess to practice with in the first instance.

Good for boats but just doesn't have the same quality look as a nice stitch line. To be honest it doesn't take long to draw out and sew small panels, the diamond one I did was probably about 10 minutes and the squiggle one 20minutes. I have a lot of designs made out on stencils so the marking out doesn't take long.Plus I can do a lot more colour stitching.

 

[keithski122]

I was referring to fluted vinyl specifically. You can buy it from as little as £10 per meter from wherever vs. 3/4 times that for bonafide marine grade from a specialist supplier, hence it being relatively more expensive.

Try martrim for material, their marine grade vinyl is £16 per metre.