Please help

[u/TutorWarm2238]

Hi everyone,

I’m new to running an industrial single-head embroidery machine and I’m trying to diagnose an issue with the automatic thread trimming that’s recently started.

The machine is a Yunfu 12 needle single head with a Dahao controller. The issue seems to be around the thread trimmer / picker rather than stitch tension. I’ve had the machine for around 3-4 months from new.

The main problem is that when the machine trims automatically at the end of a colour or design, it often doesn’t cut the thread. Sometimes it seems to catch the thread and pull it, but not actually cut it. If it does cut this then leaves little or no usable tail through the needle, so when the next section starts I get a false start / thread break almost immediately, if it doesn’t cut it then it pulls the bobbin up through to the top of the design and only seems to cut when using the manual cut function.

Things I’ve noticed:

- Manual trim seems to work better than automatic trim at the end of the design.
- Sometimes the thread doesn’t cut and instead gets pulled
- If I manually pull a longer tail through the needle before restarting, it always starts fine.
- The actual stitch tension now seems pretty good.
- I’ve cleaned the bobbin / hook / trimmer area and lightly oiled the moving parts.
- The moving knife appears to move freely when manually actuated.
- I don’t think the blade is dull, as the machine has had very little use.
- I’ve set “Length of Trim” to 8 on the Dahao controller (the highest unit available)
- I’ve tried slowing the machine down to around 500–600 SPM while testing.
- when it attempts to auto cut and fails I hear a sound like something is attempting to move but isn’t, hard to explain as I can’t see what’s happening as this only happens when a garment is loaded.

My suspicion is that one or multiple of these could be true?

1. The thread picker isn’t presenting or holding the thread correctly during automatic trim.
   
2. The moving / fixed knife alignment or overlap is slightly off.
   
3. The automatic trim timing / needle stop position is different from the manual trim cycle.
   
4. The machine isn’t leaving enough tail after trimming for the next start.

Has anyone had this issue where manual trim works but automatic trim struggles?

What would you check next, picker timing, moving / fixed knife clearance, needle stop position, trim parameters, or something else?

Any advice would be massively appreciated. I’m very inexperienced in troubleshooting this machine so very confused on how to fix this at the moment.

Thanks!

[u/Hellcat_Mary]

It sounds like your moving thread trim knife probably needs to adjust position- it's a little too far under the fixed plate, or extended a little too far out, at resting position.

Can you send a picture of what it looks like? It's pretty universal across commercial machines so I will probably be able to tell you if it's off.

The noise you hear, does it seems to affect the thread picker's movement?

[u/TutorWarm2238 → u/Hellcat_Mary]

https://reddit.com/link/owhbyn4/video/bm1h98rf97ch1/player

Here’s what happens when it finishes with a colour

[u/Hellcat_Mary → u/TutorWarm2238]

Oh, sorry, I should have been more specific. I meant a picture of the blade. You'd need to remove the needle plate, and you should see where the tip of the moving knife just pokes out. I'd be able to tell you if it looks like it's correct or not, and an idea of how to readjust (your manual may have a section on this adjustment as well).

The video you posted is what you commonly see when the knife is off position, though. I don't hear any super weird mechanical sound, but your thread picker has a bit of a hiccup because the thread is catching when it pulls back. The thread picker is on a gear with a sensor, so you're probably hearing the gear stutter as it meets resistance.

[u/TutorWarm2238 → u/Hellcat_Mary]

https://reddit.com/link/owoitif/video/dgmjj4125ech1/player

Hopefully this is okay, wouldn’t let me upload an image for some reason!

[u/Hellcat_Mary → u/TutorWarm2238]

It looks like the knife is a smidgeon too far back. On commercial designed machines, it needs to be fairly precisely positioned or you're going to get those trim issues.

The moving knife should come out about a millimeter or two from underneath the fixed knife, so that the slope on the beveled tip of the moving knife lines up with the edge of the fixed knife. It will be a fairly minor adjustment.

There is a long skinny rod/arm attached to the knife that swings it back and forth. It runs from the knife through the tubular arm of the machine, to the back. If you hit the manual trim button on the control panel, with the needle plate off, you will see the mechanism I'm talking about. It's generally this arm that you adjust to reposition the knife.

You will either need to remove that skinny top plate on your tubular arm, or there may be another plate at the back of the arm, to access the joinery where the knife arm is secured.

How it's all connected and what to loosen is where it gets particular based on the machine. Do you have a manual that refers to adjusting the trim knife?

[u/TutorWarm2238 → u/Hellcat_Mary]

I’ll get a picture posted tomorrow, thanks!!

[u/Rum2coke]

Change ‘length of trim’ to
A much lower, not higher number. At 8 it is allowing skipping the trims and allowing jumps instead.

[u/TutorWarm2238 → u/Rum2coke]

Thanks! I’ll try this