On the Featherweight model 221 or the Model 301..........and others Singer machines........
Many machines do not put the needle into the needle plate's hole in a way we may feel is perfect. Absolute dead center in the hole is not what Singer was after as they manufactured your machine. There was an "allowable tolerance" that meant that if the machine functioned, that was Singer's bottom line, things just needed to be within a working allowable tolerance. If the needle is not dead center in the needle plate's hole, sorry. You can get a very small diameter "mouse tail" file (at higher end hobby shops)and file the hole wider and away from the needle to center the needle better in a slightly larger hole.
If the needle is touching one of the toes of the presser foot, this can be adjusted away.
But First; check to find if the needle is bent? Using the hand wheel; withdraw the needle from the needle plate's hole and keep turning slowly until the needle is ready to reenter the needle plate. Watch the needle in relation to the needle plate hole as the needle descends into the hole. As the needle travels down, if the needle drifts closer to one side of the hole and then backs off again as you withdraw the needle you've got yourself a bent needle. If so, replace the needle. If this ain't the case, read on.
Remove/open the faceplate and look at the presser bar. The presser bar is made of two parts you can see (there is a spring hiding inside), the bottom half of the bar is about a 1/4 in diameter shiny steel rod that that becomes a 3/16ths (approx) black steel rod above. This assembly of two rods runs from the top of the machine's head (inside), from the adjustable knob at the top of the head to the presser foot down under the head. On this shaft/rod/bar/assembly (let's call this the "bar" from here on) is a metal block (looks like 3/8ths X 3/8ths)that is part of the presser bar assembly and is about half way up the bar assembly. It has a set screw looking straight out at you and the block and bar move up and down with the presser bar if you lift the chrome lever hanging out the back side of the machine's head. Loosen that set-screw a tiny bit. we want the bar to be able to turn with moderate effort and not just drop as it is under moderate spring pressure pressing downward (but not dangerously so). Loosen the set-screw and as you begin loosening it the screw will kind of make a "pop" when it breaks free of having been tightened for 40 years. Stop loosening the set-screw.
Reach down to the presser foot's toes at the bottom of the bar and use it like a small tiller on a small sail boat to straighten the foot out a small amount. To do this the presser foot should be lifted (the up position as in when removing your fabric from under the foot) off of the needle plate so you can get a grip on the toes of the foot/tiller to turn/twist the toes into alignment so the needle does not strike the toes any more. You might have to loosen the set-screw a bit more, but do such in tiny increments. If you have turned the foot and you think its about right, with the machine's needle centered between the toes, let the foot down gently onto the needle plate and the slots for the feed-dogs will act as a guide to confirm the foot is aligned with the the feed dogs and they are no longer angled across them slightly. If things look good, tighten the set-screw again. Or keep fiddling.
As you loosened the set-screw; the presser bar may have dropped down to the needle plate because the set-screw was loosened a bit too much. Not to worry, we'll reset that. Internally, within the two part presser bar, is a spring that will encourage the bar to drop. If the set-screw was loosened a bit too much (which never happens to me) tighten the set-screw ever so little so the bar resits being turned but can be turned with a little effort. Go get a pocket book and and open it to about page 150, which will be about 5/16ths of an inch of pulp including one of the covers. Measure it so we are fairly accurate. 5/16ths of an inch. You don't need to buy a dial indicator, just a ruler will do fine, but try to be accurate, within reason.
With the presser foot lifted; put the pocket book's 150 pages (w/cover) under the presser foot. If you need to force the book to get it under the foot; loosen that set screw centered in the metal block ever so little, and twisting the bar by the presser foot's toes, pull the bar up or down as needed within the block until the book just fits under the foot. Turning the bar by the foot's toes will help the bar move within the block and once it turns it can now move up and down within the block with relative ease. The foot should be resting (not pressing firmly) on the pages of your book and not hovering above the the pages. If you have had to twist the toes of the foot to get the bar to move up/down within the block you may find the foot will be crooked again and you will do the juggling act of aligning the foot and not letting the bar drop down next. The secret is how tight is the set-screw. The bar must be able to be turned within the block but not loose.
If you have something that is 5/16ths of an inch thick and it is easier to work with than a book, use it. I made a "Go-No-Go gauge" (it "fits of it don't") of 5/16ths thick Plexiglas to do this with, but I work with a lot of machines and I don't know if this is a practical thing to make for yourself out of any material if you have but one machine to work with. The foot doesn't go out of alignment very often. I prefer to use a gauge as it is so hard to read a book with the presser foot pressing down on the pages as I work, and turning the pages is just plain problematic.
Source: Dave's Blog