What did I do wrong to end up with smooth borders but wavy bindings? TIA

Did you use bias binding? Did you use a walking foot to attach the binding?Perhaps you pulled on the binding as you stitched? How wide did you cut it? Did you starch the fabric before cutting? How wavy is it? It’s all just ( maybeS ) without knowing how wavy it is or how you did the binding. So many things can cause it.

After I've finished quilting and cutting away the excess batting and backing, I machine baste with stitch length set at the maximum, 1/8 in. from the edge of the quilt. Then I gently pull a stitch here and there, maybe 4-5 inches apart, to make a very gentle "gather". I stitch on the binding with my walking foot, taking care not to pull anything. This method works very well for me. No wavy binding. And the "gather" sort of flattens out when stitching, so it's not apparent.

This recent thread may be of help to you: Need help with machine binding please!!!

The reasons I can think of are:
(1) the binding stretched while sewing, more likely with bias than straight-of-grain, but can happen with both
(2) if the binding looked fine before the quilt was washed and then wrinkled, it is likely that the binding fabric shrank
(3) if neither of the above, it is likely that you shifted the binding on the final step. In other words, if you had drawn a line on the binding straight across the binding (from edge of quilt to edge of binding), after folding the binding over, it got sewn so that the line is crooked.

Here is a recent post on this topic:
Need help with machine binding please!!!

I see all these ways to fix it and I think to myself....how is mine staying straight because I seem to be doing every thing that is listed not to do? I do all my bindings as bias. If I have a lot of seams on the edge of the quilt, I will stitch a normal 2.0 stitching line around it to keep the seams from separating. I snug up my bias binding as I sew it on. Not stretching it, but making sure it fits snugly with no extra wave and I use a 1.8 stitch. I have never had any problems with my quilts. However, if I cut the bindings on the wof, I have a mess. It waves and I actually get wrinkles in the binding. That's why I converted over to bias bindings. They have been a success for me. No amount of ironing, fitting or anything will keep the WOF bindings flat and pretty.

i am finding out how wonderful walking feet are . i have one for all my machines now. just love them

Hi Barb, I completely agree with you.

I'm really wondering if a lot of the problems some have is because some machines simply feed better than others. And if you are using a 1/4" foot on a machine, make sure it's lined up with the feed dogs in a way that is not going to cause it to feed unevenly.

I own walking feet for my newer machines, (and have a collection of vintage ones) and have never used one. Only time I've been tempted is matching up plaids.

i just bound two quilts with wof binding, and don't have a wave anywhere, even after washing. I use to do bias more often, but now have no trouble with wof so only use bias if I want the pattern to go a specific way.

One thing I've found, I no longer baste stitch around the edge of my quilt when quilting. I found that caused me a lot more grief when putting on the binding, so I stopped doing it. BTW - I will stitch around the outer edge of the floppy if needed to keep seams from opening and that causes no problems.