Which way does the flat side of the needle go towards in a 215 model?

Depends on your sewing machine. Most needle flat surfaces face the back of the machine so the eye is threaded from the front, but on some machines the flat surface faces toward the harp of the machine (so the thread is threaded through the eye from the left side).

FWIW, usually, if the bobbin loads from the front of the machine the needle's flat surface faces the back. If the bobbin loads from the left side, the needle's flat surfaces faces the harp.

If you install the bobbin, thread it, and it will not pick up the bobbin thread or create a stitch, then it is likely the needle is installed incorrectly. Also, installing the needle the wrong way could cause it to strike and break, so test it SLOWLY!

The ideal would be to consult the owner's manual. Search for:

Make Model manual
or
Make Model threading

Could it be the needle is not installed correctly or all the way up? Most machine needles install with the flat side facing the back of the machine. If the bobbin is installed on the left side of the machine, then the needle's flat side usually faces the right (toward the harp of the machine).

You can try searching for a manual:

Make Model manual

...

Search the internet for:

Manufacturer + Model + the word "Manual"

Search YouTube for some videos:

**NOTE: Remember the position of the old needle when you remove it. If the needle's eye is facing you, the needle's flat side is installed facing the back of the machine. If the needle's eye is facing to the side, then the flat side of the needle faces inward toward the throat of the machine. The instructions below show only the needles where the eye faces forward and the flat side faces backward.

How To Change Sewing Machine Needle

How To Change or Replace the Needle on Sewing Machine Beginner

All About Needles

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To find a user's manual, search the internet for:
Manufacturer + Model + the word "Manual"

Search YouTube videos for threading tutorials:

Nelco Zigzag Sewing Machine Final Test Demonstration Video

VINTAGE ALL METAL NELCO MODEL 400 2 SEWING MACHINE

NIFTYTHRIFTYGIRL Vintage Nelco model 250 sewing machine

With your Nelco, be sure that you install the needle properly. Frequently, Nelco machines take the needle with the flat side facing toward the throat of the machine--not toward the read like most other machines. The upper thread will thread through the needle's eye from the left toward the right. They also are a left needle position machine--meaning, the standard position of the needle when sewing straight stitch is at the left side of the presser foot, not center like most other machines.

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Here is what I found Hope it helps. I didn't download anything, I just clicked on the pages and scrolled down. Here is the contents page

http://homeappliance.manualsonline.com/manuals/mfg/brother/cs770.html?p=5

Here is the page you need:
http://homeappliance.manualsonline.com/manuals/mfg/brother/cs770.html?p=23

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Checking the needle
Sewing with a bent needle is extremely dangerous since the needle may break while the machine is being operated.
Before using the needle, place the flat side of the needle on a flat surface and check that the distance between the needle and the flat surface is even.
aFlat side
bNeedle type marking
?Correct needle
aFlat surface
?Incorrect needle
If the distance between the needle and the flat surface is not even, the needle is bent. Do not use a bent needle.
aFlat surface
Replacing the needle
Replace the needle as described below. Use the screwdriver and a needle that has been determined to be straight according to the instructions in "Checking the needle" .
a
Raise the needle by turning the handwheel toward you (counterclockwise) so that the mark on the wheel points up. (With models equipped with (needle position button), raise the needle by pressing once or twice.)
b
Turn off the sewing machine.
c
Lower the presser foot lever.
aPresser foot lever

the flat side of the shaft goes toward the back,,insert the needle as high as it will go,,& tighten the needle clamp screw

make sure the sewing machine is turned off first
the flat side of the shaft of the needle goes toward the back of the machine
insert the needle as far up as it will go

Hi. This may sound silly, but check to make sure that the needle is inserted correctly. All needles have a flat side and that side needs to face a particular direction, depending on your machine. In my experience, most modern machines need that the flat side of the needle is facing away from you, toward the rear. Unless the flat side is facing the correct way, the top thread will not pick up the bobbin thread.

Another thing to check is that your needle isn't bent, but in most cases the needle is inserted wrong.

Happy Sewing,

Robbie

As a rule of thumb, the flat side of the needle always goes towards the opposite side of the last thread guide. So on your machine, since the last thread guide is in the front of the needle bar, the flat side of your needle goes toward the rear. The needle threads front to back.and needle clamp is tight position is must

Loosen both screws and wiggle the needles out. change the new needle As a rule of thumb, the flat side of the needle always goes towards the opposite side of the last thread guide. So on your machine, since the last thread guide is in the front of the needle bar, the flat side of your needle goes toward the rear. The needle threads front to back.