That is actually a more common problem than you might think. Each saddle seems to have its own peculiarities; for example, some saddles will work with just a loop for the billet straps, but others require velcro on that loop because of the way the saddle is made. Saddle pads are actually easy to make if you sew at all, or know someone who does, and can be made with a standard home sewing machine. I figured this out years ago after a friend (one who I did not realize sewed) gave me a gift of a custom made saddle pad she had made to fit one of my saddles. Start with the pad that fits your saddle the best and use that for the basic pattern, then adjust the basic pattern to fix the things where even that saddle pad is not a perfect match for your saddle. Heavy cotton works great for the top layer as do many of the upholstery material, but if you use upholstery material, choose one that does not have a rough service that could rub against the underside of the saddle. Terry cloth toweling is excellent for the layer that will be against the horse, but I have learned that one gets a better quality of terry cloth if one buys big towels on sale instead of buying the terry cloth from the fabric stores. The fabric stores don’t seem to ever get the really good quality of terry cloth, and you want to start with good quality material as these saddle pads will often still be in use 20 years later.
For the padding in between the top cotton layer and terry cloth under layer, you can use either foam, which can be bought at many fabric stores or the stuff that is used for the inner layer of quilts. My preference is for a double layer of the quilt stuff.
Use the same pattern for all 3 layers, then stitch the center back seam. I use what I have named a faux flat feld seam, which has the strength of a flat feld seam, without the nonsense of tucking the one layer under. This seam will be in the middle of the pad, so this works fine. Once you have stitched the center back seam, fold both sides the same way, and run two lines of stitching to hold it in place, one fairly close to the original seam and the second closer to the outside edge. Fold the fiberfill layer and the top layer one way, but the terry cloth layer the other way, to even out the thickness. The top cotton layer will be thin, the fiberfill will flatten out, so the thickest original seam will be the terry cloth, which is why the top layer & fiberfill should go one way the the terry cloth the other.
Then pin the layers together, with the top layer on top right side in (the right side is the side you want to be on the outside when done), the terry cloth next, again with right side in & against the right side of the top layer, then the fiberfill or foam layer. Stitch around the outside using a 5/8″ seam, but leaving an opening wide enough at the back end to pull the layers through to turn the pad right side out. Clip all the curved parts of the layers so they will open up and lay flat.
Pull the layers through the opening so that the right sides of the top layer and the terry cloth (or what ever you choose to use) are on the outside, with the fiberfill or foam hidden in the middle. Pin the edges (pin heads to the outside), rolling the seam between your fingers to make it lay flat, & tucking in the seam allowance of the opening. Top stitch about 1/8″ to 1/4″ from the edge, starting before the opening used to turn the pad right sides out, and stitching all around the pad, and then back across the opening. This way, the pad is double stitched on this critical outside edge – – the original seam + the top stitching for most of the pad, and 2 lines of top stitching across the back end opening. Do the top stitching with the top layer on top, as this produces a more finished appearance.
The pads will work better and last longer if you quilt the layers together. I have a 3/4″ thick x 3-1/2″ wide board that I use to mark my quilting line on the top layer with tailors chalk, but any thickness or width will work. Just keep in mind that the wide of the board will determine the size of the quilting pattern – – wider board = a wider gap between lines of stitching, so fewer lines of stitching, while a narrower board will produce less distance between stitching lines, so more of them. You can use other patterns as well, but if you use this one, draw the lines going in one direction, then stitch them down, then draw & stitch the lines going in the other direction. Tailors chalk is designed to not last very long, and if you draw both sets of lines before you start, you may lose your stitching lines before you get them all stitched. I quilt in both directions, ending up with a diamond pattern.
Using a light weight nylon or polypropelene webbing, make top & bottom straps that will fit your saddle, using 3/4″ or 1″ webbing, depending on what will work best for you saddle. Use the positioning of the saddle pad that works best to pin the 4 straps in place, stitching a loop in the top straps or a velcro closure for that loop. Pin all 4 in place and see if they fit correctly by putting the pad on a saddle stand with the saddle on top and try to put the billet straps through the saddle pad straps. Adjust as needed, and make a note of where these straps need to be for each saddle.
When the 4 straps are correctly positioned, stitch the straps to pad. I have found that a Double-Box-X pattern works the best, one Double-Box-X for the top straps, and a Double-Box-X for each side of the bottom strap.
1) Stitch once around the outside of the square.or “box”
2) Stitch diagonally across the square, corner to corner
3) Stitch down or up one side of the square or “box”
4) Stitch across the 2nd diagonal.
5) Stitch down or up one side of the square again
6) Stitch across the first diagonal a 2nd time
7) Stitch up or down one side of the square or “box”
8) Stitch across the 2nd diagonal
Determine which side will get the most stress and start on that side, using the pattern above. This specific pattern is important so that each side & diagonal will be stitched twice and only twice, and you should end up at the side where you started, so you can add a couple extra lines of stitching here, as this side will get the brunt of the thread breaking stress.