quilting question
 

I made a table topper sized quilt with 3 1/2" squares. They finished at 3". I stretched the back and taped it down. Followed by cotton batting and a well pressed top. The seams were straight at this point. I pinned in the center of each block. Which meant, pins 3" apart. Seams still straight. During the quilting, on my Pfaff home sewing machine something happened. Several places "pushed". The seams were no longer straight after stitching in the ditch. What caused this ?

Backing should not be stretched; it should just be smoothed out. Spray basting will keep things together better than pins because there is continuous contact between the layers. Did you have to "manipulate" the sandwich as you quilted? I found out the hard way that over-handling, pushing, pulling, stretching, etc. all can contribute to distortions in the quilting. One technique that can help is lifting up the quilt sandwich as you allow it to feed to the machine.

Machine basting with water soluble thread is another way to prevent distortions, especially when quilting on a DSM. I usually do a grid, with lines about 4-5 inches apart.

Are you using your walking foot? That can make a difference too. The loft of the batting can distort, the backing being stretched, and the pins in the center of the blocks, nothing holding the seams straight. I generally thread baste or use fusible batting for small projects, placemats, table toppers. It adheres well to the top and backing , keeps everything smooth & together through quilting.

I can't stand the spray basting but like Prism said too much manipulating can created havoc in your quilting. I always let the fabric rest after pressing or ironing. It needs to calm down. Sounds like your pin basting is ok depending on your batting which often determines the space in your basting. The last quilt I did, I had my ironing board and another table butt up to each other and my sewing surface to help with the weight of the quilt. I also had a flannel back vinyl fabric with the vinyl side up to help maneuver the quilt easily. Worked for me.

No layers should be stretched--I did that when I first started and got lots of shifting/puckers when I pin basted. Then I shifted to spray adhesive basting and get
Much better results! It seems counterintuitive, but making the layers too Tight works against you as the layers are at different tensions and go through the machine at different rates. Just be sure all three layers are smooth and flat not tight.
Also be sure to use a walking foot so that both the top and bottom layers are feeding through your machine at the same rate. If you don't have a walking foot and are just using a regular pressure foot, you will likely need to reduce the pressure foot tension some to prevent a drag on the top layer.

When finished the back was not tight. I guess my back was more taped smooth than "stretched" as I did not tug on it. I am not a new quilter, have not had this happen before. But it is the first project quilted on this particular machine. I was wondering if the pressure on the foot was too much.

I am going to try fusible batting for my next small project. But does it only come in polyester?

Lilrain, I also have a Pfaff dsm and have done a lot of FMQ with it without any problems but recently when trying to do some grid quilting on a table runner, I had the same problem. Since the grid was straight line quilting I did not FMQ and I think I had the integrated walking foot engaged, but had the same problem. I just put it away and later will need to remove the stitches. I'm thinking it must be too much pressure on the presser foot. Very odd, I thought.

I quilt one direction before going the other direction when quilting on a DSM. Just a thought. By all means use a walking foot! they are worth the money!