Skipped Stitches - Brother HE-800A Service Manual

Cause
Rotary hook
Upper thread amount
Bobbin case

5-2. Skipped stitches

Cause
Needle
Thread take-up
spring
Work clamp
Rotary hook
Check
Needle bar height and
needle bar lift amount
Gap between needle and
rotary hook
Rotary hook lubrication
Thread twisted around
rotary hook
Arm thread guide position
Damaged outside of
bobbin case and bent
bobbin holder spring, etc.
Check
Needle facing
Needle installation height
Bent needle
Blunt needle tip or burr
Thin needle
Thread take-up spring
tension and stroke
Work clamp pressure
Relation between work
clamp assembly and
sewing length
Blunt rotary hook point
Needle bar height and
needle bar lift amount
Gap between needle and
rotary hook
Remedy
Adjust the needle and hook timing.
1. Adjust the needle bar height to "1" on the gauge.
2. Adjust the needle bar lift amount to "2" on the
gauge.
Adjust the gap between needle and rotary hook to
0.01 - 0.08 mm. (Adjust to as large as possible
without causing skipped stitches to occur.)
* Check that rotary hook point does not strike needle
in zigzag motion.
⋅ Too small quantity of lubrication oil will cause
thread breakage. Adjust the quantity of lubrication
oil.
⋅ The lubrication holes between rotary hook and
rotary hook joint do not match up.
Remove any twisted thread from the inner and
rotary hook.
Adjust the arm thread guide position
Polish with buff or replace the part.
* Use the HE-800A bobbin case.
Remedy
As viewed from the direction of the face plate, attach
needle so that the notched part of needle faces
frontward.
Insert the end of the needle shank so that it touches
the top edge of the needle hole of the needle bar.
Replace needle
Replace needle
Use a needle with a count that matches the thread
and material.
Loosen the thread take-up spring tension or shorten
the stroke to such a degree that does not cause
double hooking. Adjust it while checking bar tacking
stitches.
Increase work clamp pressure.
* The standard height of the adjustment screw is
approximately 30 mm, so tighten it further than
this.
Replace work clamp assembly that fits for sewing
length.
* When using knits or woven materials, replace the
parts with the –3 specification parts:
Length feed plate (for specification -3), work clamp
assembly (for knits), needle plate 1.2 (for
specification -3)
Polish with buff or replace the part.
Adjust the needle and hook timing.
1. Adjust the needle bar height to "1" on the gauge.
2. Adjust the needle bar lift amount to "2" on the
gauge.
Adjust the gap between needle and rotary hook to
0.01 - 0.08 mm. (Adjust to as large as possible
without causing skipped stitches to occur.)
* Check that rotary hook point does not strike needle
in zigzag motion.
HE-800A
5. TROUBLESHOOTING
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