Dealing with Thread Bunches Under Fabric - Sewing - as part of the expert series by GeoBeats. When your thread bunches up under the fabric, you have got one of two things going on. Either you have not threaded the machine properly, so what you want to do is unthread the machine and completely rethread it based on the instructions in your manual or it could be that your tension is not set high enough. Now your tension is the small disk that is on the face of the machine here. Sometimes it is hidden back inside a small groove and sometimes different manufactures will have it on the top of the machine. If your tension is not high enough, it is not going to be pulling the threads to seat them into the fabric properly. So you want to double check. Either your tension is not high enough or the machine is not threaded properly. So double check those and then try the seam again and see if it works.