Does the thread on your vintage sewing machine get tangled around the spool pins?  If so, the chances are good that you are using a cross wound spool of thread rather than a stack wound spool. 

Vintage sewing machines were made to use stack wound thread.  Back in the day, there was only stack wound thread.

Modern thread is often cross wound.  Modern sewing machines therefore often have a horizontal spool pin to allow the thread to come off the end of the spool without spinning the spool.

If you put cross wound thread on a vertical spool pin (such as is commonly found on vintage sewing machines,) a couple of loops of the thread can "fall" from the spool.  The next pull of the take-up lever then pulls the thread tight, making a knot in the thread around the spool pin.  Thread then breaks on the next stitch.

Some vintage sewing machines had an accessory to use cross wound thread.  This was a horizontal spool pin that could be mounted on a vertical spool pin.  I've seen such accessories on a Pfaff 30.

Most of the thread I use for sewing leather on my Adler 8 comes cross wound.

While working on my on my latest project (a clip to hold my eyeglasses in my shirt pocket), the thread tangled on the spool pin and broke one time too many.

To prevent future problems, I made an adapter to hold cross wound spools horizontally on the vertical spool pins of my Adler.

Here's a look at my home made horizontal spool pin:

It is made of bits and pieces of stuff I had around the house - brass rod, a brass knob bought for some other project but never used, wing nuts, threaded rod, and a piece of 10x10mm iron rod. 

It took a drill press, a set of drill bits, an M4 tap and die, some silver solder (and flux,) a propane torch, a hacksaw, a file, a disc sander, and a couple of hours of time to make. Oh!  I almost forgot the buffing wheel and polishing compound to make the brass nice and shiny.

If you have trouble with your cross wound thread tangling on your vintage sewing machine, see if you can find a horizontal spool pin adapter for your machine - or just make one yourself.

Alternatively, buy (or make) a cone stand and use your cross wound spools on it.