I'm modifying/repairing a backpack, and have once again encountered a problem that's fairly common with outdoor gear. In this case it's exacerbated by sewing a very thick stack of fabric where seams come together.
The waterproof coating (probably polyurethane on nylon this time) leads to a lot of friction for the needle. Friction is worse with thick needles but these tough fabrics break thin needles easily. It's not uncommon for my machine to stall with a thick needle, and even those can break. When hand sewing the difficulty isn't in breaking through the coating, but increases as thicker parts of the needle pass through the hole. Even the thread is subject to quite a bit of friction (more of an issue sewing by hand than with a basic machine stitch).
Is there a good way to lubricate the needle as it passes through the coating? I'm not sure oil is a good idea on such fabrics, but (soapy) water can make the fibres swell and I'd be worried about it dripping inside the machine as the foot compresses the fabric.