problem with thread spools

I'm not sure if this is the right place to post this (sorry, I'm new!)  My machine has an upright pole for the thread spool to sit on.  When I use a smaller spool of thread, every now and then something happens.  It's like the spool "jumps" and then the thread gets tangled up, the tension is messed up, and it just creates problems.  My moms machine (an older Singer) has a place for the spool to sit horizontally, with a cap that holds the spool in place.  Is there anything I can do to keep the spool in place on my machine?  There is not enough space for a "cap" like hers.  Should I just use a bigger spool? 

I don't think the problem is with the spool. Having a verticle or horoztonal spool shouldn't affect the tension.

It sounds like the problem is the tension. Check your needle to be sure it's threaded correctly, take out your bobbin and make sure it's the right size and shape for your type of machine, and lastly re-thread everything. Usually, the problem lies in something little that was an oversight. I still do this my-self from time to time and if I just sit down and go through everything, I can figure it out.

(Oh, I just thought of something! I remember I had problems like this once when I was using an older Coats & Clark spool of thread that had the little plastic lip where a notch is cut into it to hold the thread on the spool. Well, I figured out that as I was sewing, at times the thread would catch in that notch and cause my tension to go wacky and eventually the thread to break. You might want to check that as well. I just filed mine down with a nail file and it was fine.)