Putting in bobbin case for old Singer machine

Here's a manual for your machine:

Singer Golden Touch Sew 630 Instructions Manual

Singer website has a plethora of manuals to download, http://www.singerco.com/accessories/instruction-manuals is the link, your manual is there for $15. If the bobbin thread is knotting up in the bobbin then I'd say you need to rewind a fresh bobbin and make sure it is smooth with even tension as it goes onto the bobbin. If your bobbin thread looks a bit chunky and uneven, then you won't get good results from it. Also, check that you are putting the bobbin into the bobbin case the right way, the thread needs to come off the bobbin and make a reverse direction into the tension spring (assuming yours is a removeable bobbin case, not top loading)

http://www.tandtrepair.com/Athena2000.html
Here is an excellent place where you can download a free manual and various pdf files that will help you.
Trudi in Va.

Your first step is to go to the Singer site and download your user manual -- it's available free. You need to check to make sure that you are inserting it properly in the first place. Please keep in mind that the bobbin does NOT turn--the thread unwinds from the stationery bobbin.

Next, I would manually sew using the hand wheel and no fabric with the needle plate off and observe what it's doing. You CAN replace the bobbin case if necessary.

You can purchase that slide plate here:
Singer 758 Sewing Machine Slide Plate

To wind a bobbin put the cotton reel on the top pin, take the thread to the left and round the little wheel and back to the bobbin that should be on the winder, wind the thread round a few times to take a grip, release the stop motion in the balance wheel, turn the winder button so the winder moves to the balance wheel and press on the foot control slowly.
When you put the bobbin in the bobbin case make sure it turns anti clockwise.

http://www.tandtrepair.com/700_TanS_Items.html The second link in the 'free items' is Bobbin Winding. I would have typed this all out for you, but since tandtrepair has it all laid out with pictures I figured I'd just link you to it. Hope this gets you back up and sewing.

Take the bobbin case out. Then when you go to put it in, realize there are 2 ways to get it. You have found one way. The other way is first look in the the slot with a flashlight before you insert it. There is a flat piece of metal the bracket needs to be slid under as it is inserted. This acts like a spring making it tight

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check out this  good luck  thanks.

Read your manual, then watch the excellent video. If you can't find your manual go to Singer.com and download one for free.