When he showed me he was using 69 as well and how it was threaded through the additional tensioner, still passed thru the original tensioner. He told me he used it to sew heavy marine vinyl for his boat and showed me how it sews thru 5 layers. Although the needle he was using was a 180 so I suspect you are right about 138. He told me he bought a walking foot machine so was selling this one. My guess is the DB did almost everything but made the mod and it didn't work.
I've threaded it using the additional tensioner rig and thru the original tensioner as he showed me but I can't see adjusting the tension on the additional making any difference to tension result at all. The balance isn't affected. Only thing that affects it is the original tensioner, I suspect this is because of the tension spring at the end of the additional tensioner and before the original tensioner is buffering the thread so there is no constant tension.
It may be there is no difference also because I only been testing on s single layer of vinyl and it doesn't need more tension which I suspect he was looking for the additional tensioner to provide. I think he had the right idea to spread the tension out but needs to bypass additional tension spring.
From what I can see using his setup there is no real fine grained control on the tension and therefore stitch balance.
So what I'm thinking of doing is bypassing the original tension spring and putting an adapter plate that will allow the foot lever to still operate the tension of the additional tension set. It means I can remove it no harm done. Crazy? But if it works I think it'll work really nice and give me a larger tension range. I've got some 138 here and will try it out as well probably on the weekend as I've removed the additional tension set to look at how to make the adapter plate and also I have to reseat the press fitting on it.
