As part of Sew Mama Sew's Sewing Machine Month, they're doing a special blog post on how to do buttonholes (if you haven't checked out Sew Mama Sew, you should!). They're linking to a few different blogs that show how to use the buttonhole attachments for different brands of sewing machines. Here's how to use the buttonhole attachment for my Husqvarna/Viking machine.
I have a Husqvarna/Viking Scandivania 100 with a 5-step buttonhole feature.
Presser foot "C" is the buttonhole attachment.
In order to get a buttonhole that is the right size, you need to take the button that you want to go through this buttonhole and place it between the two guides on the attachment.
You can either do this before you attach the buttonhole attachment to the machine or after it's already attached to the machine. Either way, be careful not to bump it after you've removed the button.
Here's what my machine looks like when it's set up for the first step of the button hole. The orange dot on top tells me it's on the first step for the buttonhole and I have the stitch length set for a buttonhole.
When you put your fabric in to make the buttonhole, remember that the buttonhole will end up behind where you're starting. This is the opposite from normal, so I often forget this.
When you use the buttonhole feature on your machine, you should do the first step of the buttonhole (creating the left side) until it touches the red notch on the buttonhole attachment that was set by your button earlier. This is what that looks like on my machine.
When you get to the step on your machine for creating the other side of the buttonhole (for me, this is step 4), you are supposed to keep the left side in the opening of the buttonhole attachment. I find it easier to open the buttonhole if I keep the left side of the buttonhole a little off center of that opening.
If you measured your button correctly, when you get done, your button should slide easily through the buttonhole!