This is why I don't like slant shanks
 

I've never bent and/or broken so many needles in my life. Usually when going backwards through thick fabric. I really miss my Necchi. Sob.

Wow! That looks scary. My friend sews on her mother's Necchi purchased new in metro D.C. area and I'm hoping that the machine lasts as long as she needs it to because I can't picture her trying to use anything else.

I have only had one machine with a slanted shank. It was not my favorite machine either. I finally gave it away. I hope you have another machine you can use. Also I know this is something you most likely have already done, but check your needle to be sure it is in correctly. My slanted shank the needle bedded to the side.

Being slant shank probably has little to do with your problem. Many of the later slant shank machines are of poor quality and low power, particularly after the Singer 600 machines. Your machine probably is just too low powered to sew many layers of heavy fabric. Your Necchi probably had a bigger motor.
bkay

Sorry you are having such a bad day. The needle pic would make me cry too!

Frustrating. My Aunt gave me her Slant needle Singer and it never gave either of a problem. She bought it mid 60’s and I sold it 2019. It was well used by both of us.

I sew quite a bit on a Singer 301, the original Slant-O-Matic, and I love it! The visibility of the sewing area is great. My 301 has a potted, gear driven motor, so it doesn't balk at thick fabric.

Sorry for the bent needle!

I'm using a 401a, but I do have a 301 I've never used because I liked this one just fine. Maybe I'll rotate the steeds and try that one. That would sound crazy to other people, but I know you understand, lol.

Call me crazy but on the picture, it looks like the snap-on foot hole might be a tad too small... Do such incidents occur with the original zigzag foot too?

I've actually been wondering and thinking a lot about the theory behind Slant Shanks recently myself. I grew up with my mom's Golden Touch & Sew, bought my first machine and several others that are straight needle machines, and ultimately fell in love with and restored a Rocketeer. My next project is the straight-needled 319.
It seems to me from the reading I've done that the majority, if not all, of the reasoning behind the slant shank is to put the business end of the machine closer to the sewer and make things more visible. When you think about what slanting the needle actually does for *sewing* though, it's definitely true that that slant effectively increases the relative thickness of the material being sewn. Straight through a thickness of leather is the shortest distance from one side to the other; slant the needle and you're lengthening the path, even by a little bit. So I wonder if the potential problems of slant shank ultimately could outweigh the "I can see the work better" factor, particularly for certain things like sewing thick material.
I have to wonder if for thick/tough material, a straight needle machine like the 201 or others (or if zig zag is needed, a 319, 237, etc) wouldn't be a better deal. Also, I bet industry never used slant-shank machines for precisely this reason...

(Along the same lines.. the zig-zag feature of machines like the 401, 500, etc is "swing needle" and the needle literally swings left and right, which also means a bit of an angle through material -- but the 237 sees not only a straight needle bar, but the entire bar is moved left and right for zig zagging, which means at all times and on any stitch, the needle is going straight through the material.)

Just some thoughts!
Matt