Sewing Machine Friction Clutch vs. Posi-Pin® Safety Shear

Simply put, a clutch slips when the balance wheel rotates but the needle can’t pierce the fabric. Our Posi-Pin Safety Shear prevents any slippage whatsoever and eliminates residual loss of power, allowing the needle to power through any material type and thickness every time — guaranteed.

What Is a Sewing Machine Clutch?

A clutch is a mechanism used to disengage the operation of the sewing machine for bobbin winding. Doing so is important on lockstitch machines to refill the bobbin thread without having to remove your work from under the needle of the machine. Otherwise, if the machine were allowed to operate, the needle would repetitively punch holes in the fabric, weakening it. The most common type of clutch is called a friction clutch. Sailrite offers something far better: the Posi-Pin Safety Shear.

What Is a Friction Clutch?

Before we explain what the Posi-Pin does, you first need to understand how a standard friction clutch operates. A friction clutch system consists of a long drive shaft that runs the length of the machine and ends with a special bushing to which the balance wheel is attached. When the balance wheel rotates, it either turns or doesn’t turn the drive shaft, depending on how the clutch is set. Setting the clutch in the “locked” position causes the sewing machine to function and, ultimately, produce stitches.

This locking is done via friction. At the end of the bushing, a threaded bushing knob presses a special washer with pronounced tabs (leaf springs) against the balance wheel, which sandwiches it firmly against the bushing flange and creates the surface friction that “locks” the parts together. These two surfaces are smooth, however, and as you might expect, this form of surface friction is often not strong enough to keep the parts from slipping against one another, especially when sewing heavy fabric assemblies. This design is inadequate for sewing canvas, sails and heavy upholstery fabric.

The common way to address a slipping clutch is to overtighten the bushing knob — some people even do so with vice-grips. This does create a little more friction, but in the end it only exacerbates the problem since the knob will now be difficult to loosen for bobbin winding. And over time the leaf springs on the washer will flatten, and this component will become defective. In a nutshell, friction clutches are ineffective for anything other than sewing light home fabrics. They are not capable of handling big needles, heavy-weight thread and thick fabric assemblies.

The Posi-Pin Difference

Here’s how the Posi-Pin works: A specially designed pin is positioned through a hole in the balance wheel and into a matching hole in the shaft bushing’s flange to engage and disengage the drive. This creates a constant positive connection between the balance wheel, bushing and drive shaft. It locks the components together — no washer, no friction needed — so you get no loss of power at any time, resulting in zero chance of clutch slippage and 100% transfer of power from the balance wheel to the needle. This strong connection means that you get the most power delivered right to your needle, enabling you to penetrate heavy fabric assemblies, even at incredibly slow speeds.

The Posi-Pin is a revolutionary advancement in sewing machine technology. With the Posi-Pin installed on your Ultrafeed, handling thick, heavy fabric assemblies is easy. A Posi-Pin equipped machine can power through virtually anything you can fit under the presser foot. And because Sailrite owns the patent on this invention, the Posi-Pin can only be found on Sailrite sewing machines.

Posi-Pin Safety Shear: Designed to Protect Your Machine

One of the most important features of the Posi-Pin is that it is designed to protect your Ultrafeed’s internal components from damage when a crash occurs. When you hit an internal metal component while sewing, or if you sew through a metal snap, grommet or zipper, your machine will crash and stop working correctly. This safety feature helps to protect your machine and save your valuable investment from potential damage. In fact, this patented sacrificial pin (Patent #7438009) is only found on Sailrite sewing machines. If you sew over something you shouldn’t, the pin will break and the Ultrafeed will stop operating in order to protect the machine. If the Posi-Pin breaks when sewing, all you have to do is replace the broken pin with a new one, check the cap spring for damage and change the needle. You can continue sewing without issue — no tuning or retiming required. Pulling the pin out makes the machine immediately inoperable, another excellent safety feature if children are around.

Watch the video below to learn more about the Posi-Pin Safety Shear. In the video, we intentionally cause a machine crash so you can see for yourself how easy it is to replace the Posi-Pin with a new one and get right back to sewing.

How Does Bobbin Winding Work?

Bobbin winders on portable cast-iron sewing machines are all generally very similar to one another. The idea is that the bobbin spindle can be slid over next to the side or edge of the balance wheel. The connection is via a rubber wheel that looks like a donut on a hub. This wheel then tracks along the side of the balance wheel as it turns and a bobbin placed on the spindle is filled with thread as it spins.

To wind bobbins with a friction clutch system, you have to loosen the friction clutch knob in order to sever the connection from the balance wheel to the drive shaft. Severing the connection allows for bobbin winding without having to operate the needle and machine. Then once the bobbin is filled and you’re ready to sew again, you have to retighten the friction clutch knob. As explained above, over time the washer on a friction clutch will flatten, making it more and more difficult to tighten the knob hard enough to create enough friction to prevent the clutch from slipping.

With the Posi-Pin, the process is much simpler. In fact, the biggest convenience and an excellent bonus factor of the Posi-Pin Safety Shear is the fast and easy bobbin winding. All you have to do is pull out the Posi-Pin to disengage the drive shaft — it couldn’t be easier!

Superior Power for Superior Sewing

The Posi-Pin Safety Shear comes standard on all post-2007 Sailrite sewing machines. It works in conjunction with the Power Plus®, WorkerB®, Stitch PRO and Monster® II Balance Wheels to provide unequaled slow speed power and control. Whether you need slow, controlled sewing or you need to power through multiple layers of canvas and webbing, vinyl window material, and even leather assemblies, Sailrite sewing machines can handle all your sewing needs.

As always, we’re here to answer any questions you might have. Give us a call or email us anytime and we’ll be happy to help!