Singer 306k – needles

When I picked up my Singer 306k from a man who was as retired as me, he told me that he had used it to make sails (for boats), and when I started working on it I found a size 16 or 18 15×1(130/705, HAx1) needle in it and some very thick thread on the bobbin. A few packs of similar needles were part of the goodie pack included. So I am fairly certain this is what he used, but I am also pretty sure he didn’t use any zigzag stitches either.
I bought some 206×13(Sy2029, Hpx13) needles to use while repairing servicing and adjusting the machine, I always do these things with the correct and best needles and thread I can get.
The machine is now working well, I have some adjustments to do with the bight and needle offset, but that is a whole different level of fun.
On the 306 group I read about using DBx1(287 WH/1738) round shank needles as an alternative to the 206x13s which can only be purchased online where I live. So I thought I would do some careful needle testing.
The main difference with the DBx1 is the round shank. This raises two issues, firstly fitting the needle into the machine can be a bit fiddly, lining up the grooves in the right directions.
There is a tool to help with this, on the other end of my needle threader.

The second issue is the needle positioning with regards the hook. Obviously the flat facing backwards makes the needle move slightly to the back of the needle clamp, and the point of the needle sits a bit further back. The hook is positioned to go very close to the scarf of the needle, and using a needle with a round shank may move the needle too close to the scarf. However, the round shanks are 1.5mm in diameter, and 15×1 needle shanks are 1.91mm in diameter, and the distance from the flat of the shank to the opposite side is 1.43mm. So a maximum of 0.07mm discrepancy. Seeing as I set the hook position on its driveshaft by eye, probably close enough.

The DBx1 shank is also longer than the shanks with flats, and in some cases this can interfere with the fabric if it is many layers or thick. The picture below shows how close the needle shank gets to the work piece.

As I would have expected the needle sewed well, no dropped stitches, no collisions with the bobbin carrier or hook. Zigzag stitches worked perfectly, and a couple of other fashion discs also worked fine.
It’s worth pointing out that these machines are over 60 years old, mine is 71. Tolerances when they were made aren’t the same as tolerances after 71 years.
And on to the 15×1 needle. This is the same dimensions as the 206×13, with exception that the distance between the eye and the point is about 4mm on the 15×1 and 2mm in the 206×13, making the needle slightly longer overall. This causes two issues. Firstly needle strike on the bobbin carrier as the needle is longer. Secondly if the needle does not rise high enough before the feed dogs move, it may still be in the fabric if the fabric is particularly thick or many layers. Both these issues are bad news for the needle, and there are many damaged bobbin carriers out there too.
My machine had been used for sewing sail cloth with a 15×1 needle, and there was no damage to the bobbin carrier or hook when bought it, so how was this working?
Only one way to find out, and that’s to use a 15×1 needle and see how it works.
Straight stitching was absolutely fine, perfect stitches, no needle strike. Watching the needle/feed dog synchronisation, the needle was well out of the fabric before the fabric moved forward. Next some tentative trials with the zig zag disc, starting with a bight of zero and working up. Everything was fine until the bight got to 3, and then the needle started striking the hook when at the left side of the stitch (but only size 11 upwards, 10 is fine). So great for straight stitching but not for any decorative stitching above a bight of 2.5.
As part of my 3D printed fashion disc work, I created a straight stitch disc, so regardless of bight setting or stitch position, it sews a straight stitch down the middle. It’s also a very quiet disc.

My machine has an open bobbin carrier part number105032, and the hook is part number 276251.

What do I take from all this?
For most of my sewing I will probably use 206×13 size 14 needles, which will handle most of what I do.
If I become a sail maker, or have to repair my heavy canvas tents I will be able to use a large size 15×1 needle, size 16 or 18 or more in straight stitch only. I can make this safer by using my straight stitch fashion discs.
Finally, if I need to do more delicate work I can buy DBx1 needles in sizes 11,12 and 14 if needed, and maybe in different point types. I can use these with my fashion discs as necessary.
This machine really does keep on giving.

15×1 needles are 38mm long, DBx1 37.5mm and 206×13 37mm, with eye to point measurements of 4,3 and 2mm respectively.