Welcome to Lesson 5 of the HTVRONT E15 Embroidery Machine tutorial series. In Lesson 4, we covered upper thread threading — the first half of a balanced stitch. Today, we're focusing on the second half: bobbin thread tension.
Before starting any embroidery project, it's essential to check the bobbin tension. Even a perfectly threaded upper thread can produce poor-quality stitches if the bobbin tension is off. The good news is that this check takes less than a minute, and it prevents the most frustrating embroidery problems — bird-nesting, puckering, thread breaks, and uneven stitch density.
In this lesson, we'll use the bobbin case drop test to quickly check the bobbin tension, then adjust it in small increments until the stitch balance is right. Let's get started.
Key Takeaways
The drop test takes seconds — hold the bobbin case by the thread and give it a gentle bounce.
Slow, smooth descent = correct tension. Fast drops mean too loose; no movement means too tight.
Adjust in small increments — turn the tension screw by tiny amounts and retest.
Run the "I" test pattern after adjusting to confirm upper and bobbin threads are working together correctly.
Recheck tension whenever you change thread or bobbin — different materials and weights can shift the balance.
Why Bobbin Tension Matters
The bobbin thread and the upper thread work together to form every single stitch. The needle pulls the upper thread down through the fabric, and the rotary hook passes the bobbin thread through that loop to create a locked stitch. For the stitch to look clean on both sides of the fabric, both threads need to meet in the middle with roughly equal tension.
If the bobbin tension is too loose, the bobbin thread will get pulled up to the top of the fabric — showing up as loops or tangles on the right side. If the bobbin tension is too tight, the upper thread can't pull the bobbin thread up properly, and you'll see the upper thread pulled down to the wrong side of the fabric, causing puckering and distortion of the design.
Signs that your bobbin tension needs attention:
Loops of thread appearing on the top surface of the fabric
Bird-nesting — a tangled cluster of thread forming under the fabric
Puckering around the edges of the design
Bobbin thread visible on the right side of the fabric
Frequent thread breaks or needle breaks
Checking the bobbin tension before every project is a quick, reliable way to avoid all of these problems. And once you've dialed it in, it usually stays consistent until you change to a different bobbin weight or thread type.
Step 1: Prepare the Bobbin Case
First, remove the bobbin case with the bobbin installed. Open the bobbin cover underneath the machine, unlatch the bobbin case, and pull it out carefully — the bobbin should stay seated inside.
Hold the thread so the bobbin case hangs freely from your fingers. The bobbin case should dangle at a natural angle, with the thread supporting its weight.
Pro Tip: Make sure the thread tail is long enough to hold comfortably — around 15–20 cm (6–8 inches). If the tail is too short, you won't be able to perform the drop test accurately. If it's too long, the bobbin case might swing instead of dropping.
Step 2: Perform the Bobbin Case Drop Test
Hold the thread and gently bounce it up and down a few times while observing how the bobbin case moves. You're not dropping the bobbin case from a height — you're letting it slide down the thread under its own weight, controlled by the tension set by the bobbin case's tension spring.
Watch for three specific behaviors:
Slow, smooth descent — the bobbin case slides down a few centimeters with each gentle bounce. This is the ideal result and means the bobbin tension is properly set.
Quick drop or falls easily — the bobbin case slips down very fast or drops without any resistance. The tension is too loose.
No movement or heavy resistance — the bobbin case doesn't slide down, or only moves with noticeable resistance. The tension is too tight.
Note: The bobbin case should not free-fall. If it drops all the way to your hand in a single bounce, the tension is definitely too loose. If it stays completely still, tension is definitely too tight.
Step 3: Check and Adjust the Bobbin Tension
If the tension is correct
If the bobbin case drops slowly and smoothly when gently bounced, the bobbin tension is properly set. You can move on to the tension test pattern (see below) to confirm the full stitch balance.
If the tension is too loose
If the bobbin case slides down quickly or drops too easily, the bobbin thread tension is too loose. Use a small screwdriver to turn the tension screw slightly clockwise to increase the bobbin tension.
⚠️ Small turns only: Turn the screw by no more than 1/8 of a turn at a time, then perform the drop test again. The bobbin tension screw is very sensitive — a full turn is a massive adjustment that will throw off the tension completely.
If the tension is too tight
If the bobbin case does not drop or moves only with noticeable resistance, the bobbin tension is too tight. Turn the tension screw slightly counterclockwise to reduce the bobbin tension.
After each adjustment, repeat the drop test. When the bobbin case drops slowly and smoothly after a gentle bounce, the bobbin tension is properly set.
Pro Tip: If you lose track of how many turns you've made, you can always reset the tension screw to its factory position and start over. Remember the position it was in when the machine arrived — that's usually close to the correct starting point for the included bobbin weight.
Confirm with the "I" Tension Test Pattern
After checking the bobbin tension, run the "I" tension test pattern to confirm that the upper and bobbin threads are working together correctly. This test design stitches a simple "I" shape and includes color changes that reveal whether tension is balanced across all needle positions.
When you examine the finished test stitch-out, check the following:
Upper side: The bobbin thread should not be visible — the stitch should look clean and even, with no loops or tangles.
Bobbin side (underside): The bobbin thread should form roughly two-thirds of the stitch, with the upper thread visible at the edges as small dots. The two threads should meet in the middle of the fabric.
No puckering: The fabric should lie flat around the stitched design — no wrinkles, no pulled-in edges.
No thread breaks: The test should run through all the design's color changes without any thread breaks or needle breaks.
What the "I" pattern reveals: A simple, linear design like the letter "I" makes it easy to spot tension problems. If the bobbin thread is pulling up, you'll see it immediately on the top surface. If the upper thread is pulling down, the underside will look messy or the fabric will pucker. This test catches issues that a more complex design would hide.
Quick Bobbin Tension Checklist
Run through these points before starting any embroidery project:
✅ Bobbin case removed from the machine with the bobbin installed
✅ Thread tail long enough to hold comfortably (15–20 cm / 6–8 inches)
✅ Bobbin case held by the thread and allowed to hang freely
✅ Drop test performed with a gentle bounce
✅ Bobbin case descends slowly and smoothly (not fast, not stuck)
✅ Tension adjusted in small increments if needed (1/8 turn at a time)
✅ "I" tension test pattern stitched and inspected
✅ No loops or bobbin thread visible on the top surface
✅ No puckering around the stitched area
✅ No thread breaks during the test
Tutorial Video
Prefer to watch rather than read? Follow along with this quick bobbin tension check tutorial for the E15 embroidery machine:
Conclusion
You've now mastered the bobbin case drop test — one of the fastest and most reliable ways to check bobbin tension on the E15 embroidery machine. This simple, 30-second check is the difference between a finished design that looks professionally stitched and one that gets pulled apart by loops, puckers, or thread breaks.
Make the drop test part of your regular pre-project routine, especially when:
You've just installed a fresh bobbin
You're switching to a different bobbin thread weight
You're starting a new type of fabric or design
You've noticed any tension problems in recent projects
In the next lesson, we'll move to the other half of the tension equation: the upper thread tension check. You'll learn how to inspect and fine-tune the upper tension dial, how to read the "I" test pattern for specific stitch problems, and how upper and bobbin tension work together to produce perfectly balanced stitches on every fabric. Stay tuned — Lesson 6 is where the full picture comes together.
How often should I check the bobbin tension on the E15 embroidery machine?
Check it whenever you install a fresh bobbin, switch to a different bobbin thread type, or notice any tension problems in your stitching. For everyday use with the same bobbin weight and thread type, once you've set the correct tension, it typically stays consistent for many projects. If you rotate between different bobbin weights — for example, switching from a standard 60-weight bobbin to a 40-weight bobbin for heavier designs — you'll need to recheck and adjust each time.
What does it mean if my bobbin case drops all the way down without any resistance?
It means the bobbin tension is too loose. When the tension is too loose, the bobbin thread can get pulled up to the top of the fabric during stitching, showing up as loops, tangles, or bird-nesting. Turn the tension screw clockwise in small increments (about 1/8 turn at a time) and repeat the drop test until the bobbin case descends slowly and smoothly.
My bobbin case doesn't move at all during the drop test — what should I do?
Your bobbin tension is too tight. A bobbin case that doesn't move with a gentle bounce indicates excessive tension on the bobbin thread. This can cause the upper thread to be pulled down to the underside of the fabric, leading to puckering, distortion, and needle breaks. Turn the tension screw counterclockwise in small increments (about 1/8 turn at a time) and retest until the bobbin case descends slowly and smoothly.
What is the "I" tension test pattern and why should I use it?
The "I" tension test pattern is a simple, built-in design that stitches the letter "I" along with color changes to help you verify that both upper and bobbin tension are balanced. Because the design is linear and simple, any tension problems become immediately visible — loops on the top surface, puckering, or messy stitching on the underside. Running this pattern takes less than a minute and confirms that your tension settings are correct before you start a real project on expensive fabric.
Can I damage the bobbin tension screw by adjusting it too much?
The tension screw itself is durable, but over-adjusting it can throw the tension far out of range and make it hard to find the correct setting again. This is why we recommend turning the screw by no more than 1/8 of a turn at a time and retesting after each adjustment. If you lose track of the original position, refer to your machine's user manual or contact HTVRONT support — they can help you reset the screw to its factory default position.
Does bobbin tension need to change for different embroidery designs?
Bobbin tension itself usually stays the same across designs, but the upper thread tension may need adjustment. The bobbin tension is set based on the bobbin thread weight and type — it's a mechanical setting that doesn't change with each new design. However, upper tension often needs fine-tuning based on the design density, stitch type, and fabric weight. If you notice stitching problems, adjust the upper tension knob first, then recheck bobbin tension only if the problem persists.
Keep Learning
Want to master more E15 embroidery techniques and grow your business? These guides will help:
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