My husband bought me a used Viking 500 Computer Sewing Machine for Christmas off of ebay. Since I got it my sewing and tension hasn't been that great. I tried all the different suggestions on testing tension. New needles, Better thread, making sure everything is cleaned and no lint. Sometimes it was ok but not great but mostly the stitches weren't what it should be. I can't afford to take it in for maintenance yet as the beginning of the year with all my deductibles on my medical and prescriptions make money tight. I'm sure many others are having the same troubles.
Well I found a good resource for sewing machine problems. look at bottom of post for link and copy of what he said to do:
Following his instructions I took the Dropin Bobbin case out of my machine. To my surprise there was a broken needle tip in there and you can see where the bottom of the machine was scratched up by the broken metal piece being scratched. There was also a big wad of gunk. A mixture of oil and lint stuck directly under the bobbin case. It is no wonder I couldn't get my bobbin tension to work. I clean the machine as I read after every use and I even have a small vacuum to vacuum out any of the lint but with the oil making it stick to the bottom and where it was explains why I couldn't vacuum it out. Now I'm very new to sewing and quilting. The first time I used a sewing machine was 3 months ago. Learning all these tricks is so helpful and the info I learn on here has helped me more than anything else. I just wanted to return the favor with what I learned.
Here is what he wrote that was so helpful to me:
Specific detail on bobbin case adjustment (with picture) near halfway down reply, the remainder will help you achieve a balance of top and bottom tensions.
Ensure that all is clean and free of lint and jams, this is the most likely cause....now for tension troubleshooting .......
This solution is for tension problems...if you cannot form any sort of stitch, the issue is quite different, so please let me know if you need a different problem solved.....
It is quite long, but just work through each section in order.
The "knotting up" can reveal a lot. If you have loose threads on one side or the other, the tension on the opposite side will be the culprit.
QUICK SUMMARY FIRST:
Ensure sharp new needle,
Thread guides and Bobbin are Clean & Clear of lint
Set Top Tesion to 4 ....then....
Balance Bobbin to suit.
TOP THREAD TENSION:
If the looping threads are on the underside as you sew, it is the top tension. Top tension ought to be between 4 & 6 (this variation to allow for the different weights of fabric in your projects).
IS YOUR NEEDLE SHARP ?
If you are using a needle that has seen quite a deal of work, or you suspect it may be blunt, change it for a new one !
TOP TENSION & GUIDES:
Make sure that when you thread the machine the presser foot is up so the thread goes between the discs and not to one side, top tension between 4 and 6, and that you have threaded through all the guides, including the last one, usually on the needle arm, just above the needle clamp.
It may be there is lint trapped between the discs, this will keep them slightly apart and reduce the actual tension, sometimes dramatically.
If tensions appear correct, and the thread is definitely in the channel between the discs, but still too loose and looping, try raising presser foot and remove your thread.
Now, with a 2" (50mm) wide strip piece of fabric 8 - 10" (20 - 25cm) moistened with methylated or denatured spirit, gently insert the fabric strip and clean between the discs with a see saw / to and fro action.
In the worst cases, gentle use of a needle to pick & remove the jam may be necessary, but be very gentle and make sure the tension is set at Zero and the presser foot is raised, (to disengage tension plates).... do not gouge or score the plates, they need a polished surface to work correctly.
Far less common, but if the loose threads are on the top, it is bobbin tension that is loose, it too may have lint in the spring and be giving a "false" tension.
I would not recommend fiddling with bobbin tension without good reason, it may end up with missing small screws and spring pieces, however, you can take the needle plate off to clean
the hook race area (where bobbin case sits)
...this is just good housekeeping, my wife does this every time she replaces the bobbin....
just take it out and clean the bobbin case and the fixed metal hook race with a small brush to remove lint. If there is a significant amount of lint, use a vacuum and small brush to get the worst.
Then wipe all this area with a cloth or cotton bud (Q tip) moistened (not soaked) with methylated spirit, especially if there appears to be fine dirty deposits....oil and lint combine to conspire against you.
If it seems likely that you ......really ....do .....actually .....need .....to adjust the bobbin case, first check there is no lint trapped in the metal spring where the thread is tensioned.
Drop-in Bobbin case will look similar to this image with the tension screw in the middle of the metalwork....
...the other screw at one end is holding it all together, so beware....it is not a tragedy to undo the whole lot and clean it, but very gingerly and lay the bits out in sequence and orientation, or you risk tearing your hair out !
....this is a bobbin case from a front loading machine and works in a very similar fashion to the top loader with drop in bobbin, again, if you dismantle it, take care so you can put it all
GETTING THE BALANCE RIGHT:
When you are certain there's no trapped lint in top tension or bobbin, set the top tension to 4 and the bobbin tension to a point where you just begin to feel resistance.
Try using good quality thread of contrasting colours so you can more easily spot the changes.
Set your zigzag to one width less than maximum (eg. 5 of 6 ...or... 4 of 5 etc) and sew a sample for a few inches and check the result.... adjust the bobbin tension screw very little at
a time, perhaps 1/16 of a turn.
You may find you are playing with this balance for some little while and if you are putting the needleplate on and off each time begin to think it cannot be correct to do this.....BUT....it is,
and eventually, you do get a "feel" for the correct tension and then it happens quite quickly.....as a user you won't be doing it very often unless there is lint built up (or are there small hands at work around the house !?!?!)
If you live near the ocean as we do, salt air can play havoc with metalwork inside and out, so to help minimise this, keep a few small packets of dessicant (silica gel) in your machine
case....no case ? then make some sort of cover !
Same applies in any damp or humid environment, keep your machine dry and dust free.
Budget for a proper full service every couple of years (more often if heavily used) and if you don't use your machine for a few years, be aware that old oil will dry out and combining with
dust and form a "clag" like glue (another reason for some sort of cover, even a teatowel !)
FINALLY, A WORD ON THREAD:
If it is worth spending the time, energy and money on making something that you would like to give lasting enjoyment......use quality thread, .......it may seem to cost a little more at the
time, but the results, ease of use and added longevity will be worth the extra, and as a bonus, your tension troubles may be fewer and further between, because there is a more consistent diameter with good thread, and less compensating to be done by your tension plates and less thread breaks