Being relatively new to the machine embroidery discipline, I humbly request the guidance of the more experienced members with regards to what I'm seeing on my Toyota 830.
I bought this Toyota 830 from an individual who had relatively severely neglected it. I have disassembled the entire needle case, reciprocator, thread wiper, and rotary hook assemblies down to the last screw, removing the built-up dirt and hardened grease and replacing worn and broken parts, before re-lubricating and reassembling. I've cleaned, renewed, and recalibrated virtually every inch of this machine, stopping short of disassembling the upper and lower shaft gear linkages.
Top thread: Madeira Polyneon 40wt and Robison-Anton Super Brite 40wt
Needle: Organ DBxK5 75/11
Bobbin thread: Fil-Tec magnetic black polyester
Hoop: Durkee round 180mm diameter
Stabilizer: Two layers of Vilene water-soluble
Base: TwillUSA PSA Sport Twill (pressure-sensitive adhesive polyester)
1. Thread Tensions
Most sources indicate that bobbin tension should be between 18 and 22 grams, with a few saying that 25–30 is normal for polyester. Those same sources suggest top thread tension between 120–150g for polyester. However, the Toyota 830 user manual states that bobbin tensions between 25–30g are nominal, and it declines altogether to specify any absolute needle thread tension, only providing the 1/3 bobbin thread rule for satin stitches as an indicator of proper tension.
Using a bobbin tension gauge, I set my Towa bobbin case to about 30g. When running tests, I've been unable to achieve the ideal 1/3 bobbin ratio on my satin stitches unless I drastically reduce top thread tension, often to as low as 100g, according to the Tajima gauge. If I want to bring top thread tension up to about 120–130g while still producing the 1/3 bobbin ratio, I'm forced to raise my bobbin tension to at least 35g, a condition that seems to produce excess pulling of the thread and material while stitching. Things are further complicated by direct relationship between top thread tension and machine stitching speed
When dialing in tensions, I usually use a short, horizontal 4mm satin stitch and sometimes a series of tests consisting of the letters "TOX" in various sizes.
Question: What is normal behavior? Will low top thread tensions increase the likelihood of top thread loops, or are some loops inevitable? If every source I've read agrees on 120–150g top thread tension, why does my machine seem to prefer lower tension?
2. Intolerance of Higher Speeds
My machine seems to perform far better at 350–400SPM. When I start to edge the stitching speed up to 600SPM, all sorts of inaccuracies and anomalies begin to surface.
I highly doubt it's the pantograph belt tension, as I've already been through extensive troubleshooting down that path, but I'm always expecting to be schooled. Perhaps it could be an aged capacitor on the motherboard sending unstable current to the DC motor? Could it be aged belts that need to be replaced entirely? Something else?
Question: Is the inaccuracy at such a normal speed (600SPM) by today's standards expected for such an old machine, or should I keep trying to track down the problem?
Again, I'm extremely grateful for any help you can offer. Some of the projects I'm trying to complete require a high degree of both accuracy and precision, and I'd very much like to give this machine a second lease on productive service.
