CNC Sewing machine question

I think that the way to do this is to use adaptive-feed to halt the fabric when the needle is down.

How do you know the needle position? The stepgen outputs a position. If you add homing for the spindle then you can use a custom HAL component to output the adaptive-feed ratio.

But how to home a spindle? Currently that's not built-in behaviour. But it could be part of your custom hal component

Have you seen the commercial sewing machine servos? They are surprisingly cheap, and have a rudimentary encoder:
www.ebay.co.uk/itm/392335513626
as an example, Cheaper ones exist, and more expensive more powerful ones too.

I think I would be looking to use one of those, and then try to work out the adaptive feed from the needle-up signal and some cleverness in a HAL component.

The stepper should work, but the dedicated motors are a lot more powerful.

Tell us which way you want to go, and I think we can come up with something.

You could trigger a program-pause.

halui.program-pause

linuxcnc.org/docs/2.7/html/man/man1/halui.1.html

How are you controlling the machine? Is the needle slaved to XY?

By "hook" do you mean "foot"?

If the needle is a rotary axis then you can just make sure you only stop at specific positions?