I thought it might be useful for me to do a post on clamshell quilting. I do use this overall design quite often on my baby quilts as it is a fun way to quilt and always looks great on those little quilts. Babies and clamshell just go together for some reason.
I recently finished a charity quilt with clamshells and while I was quilting along I thought that some may look at this and think that it is too hard to do over an entire quilt.
I use the Handiquilter Multi Clamshell ruler to do the quilting however there are other rulers you can use, i.e. the Handiquilter Versa tool or a circle. A circle, of course, is a little bit harder as you do not have those nodges that stop your foot from going over the line when you place one clamshell over the other.
For most baby quilts I use the 4in size of the Multi Clamshell ruler. I do not mark lines onto the quilts to keep me straight basically because that would involve a lot of precise work to get that right and I don't think it's necessary.
Starting from the bottom up, I first inspect my edge. It is very important that the edge is straight. If it is not you will need to establish a straight line on the bottom as all your other clamshells (and their straightness) will be based on that. Maybe for the first row of clamshells, also make yourself a mark every 4in so you get the first row down perfectly.
And this is basically where perfection ends (coming from a perfectionist). As you quilt, there will be a slight amount of compaction. The above charity quilt had a puffy wool batting, so the compaction started to happen literally straight away meaning that the center line of your clamshell ruler will not necessarily align with the valley of the clamshell underneath. That is incredibly distracting and can throw you a bit. I have found that I can largely ignore this. Instead I focus in on keeping my clams straight and in line by marking the center of each clamshell as I go along. So I will quilt a row, then stop, mark the center of each clamshell just quilted and continue with the next row placing the clamshells exactly where they should be.
Next issue will be that your clamshells will not necessarily end up exactly on those points because as you are quilting you have put too much pressure on your ruler and things have moved over ever so slightly. Also very normal and happens every time. The good thing with my center marks is that I can see how I am doing, i.e. where I am definitely not on point. This is where the fudging begins. Usually this happens in the middle of a row. So as I am quilting I now have one or two clamshells that are slightly out of alignment. In this instance I might shorten my clamshell a bit by starting to quilt the clam, stopping in the middle and shifting the ruler over a bit to hit the next clamshell at the marked point. Other times I might carry that shift over to the next clamshell a bit to see how the shifting carried on over the row and adjust it then a bit. As I am now on high alert I will check my row, making sure that I end up on the side in the same position. Also when marking the next row in the center I will usually check the alignment underneath to ensure that the clamshell is in the center and straight.
Over the next few rows, particularly as you are nearing the center slight mis-alignments will occur...sometimes in the middle and other times towards the edge and I will keep fudging to get them back into their right position. If it is a pieced quilt I will also check the height of my clamshells as I pass over a horizontal seam which will give me a pretty good idea on whether I am dead straight or not. Again, there are adjustments you can make. If one clamshell is taller than the other you can adjust this in the next row by just shifting your clamshell ruler up a bit when you come to the offending spot.
Once you reach the middle of your quilt, you will likely have to turn the quilt and start quilting your clamshells towards you. Often my clamshells shift a fair bit in that row just because of the change in positioning the ruler. In the little quilt above I was mis-aligned towards the edge quite obviously. In this scenario I will look the other way and have a mis-aligned clamshell but ensure that I mark the next row perfectly using a longer ruler to align to the valleys of the clamshells underneath to get back to the alignment as it should be.
The point I am trying to make is that you cannot see this once it is all done as your eyes only see the very consistent and repeating clamshells. The real test comes in the last row when you hit the edge as this will show how straight and consistent you have kept your clamshells. In my example, I was pretty consistent, maybe out by about 1/16in in terms of the height going towards one side, so it was not dead straight. However, the way the clamshells miraculously lined up with the top edge meant that I just made the clams on one side ever so slightly higher to hit the edge and the issue was solved. As you apply the binding on the edge, no one is going to measure that and definitely no one will see that.
Let me know if you have any questions. Happy to talk more on this
