If you are using the machine's spring you screw it into the spindle.

If you are using the featherweight you remove it and use just the bit in the featherweight that then screws into the spindle.

Philadelphia, PA (Really Bensalem)

When you finally understand it completely... it changes.

Thanks to all who replied to my post. I was very confused about this, because the page in the manual instructing how to put the cutter into the spindle shows the cutter inserted into the cutter button. However, it also says that you should have as many cutter knobs as you have cutters, so you can leave them together and keep the settings for possible jobs to be carried out in the same conditions in the future. I couldn't figure out how (or if) the cutter knob was supposed to go on the spindle, or how to use the burnishing adapter. I finally spoke to a tech at Gravograph, who told me that you don't use the cutter knob, and you don't use a burnishing adapter with the M40. He said that the reference to cutter knobs in the manual applies to a different engraver.
I would like to thank everyone who tried to help...I appreciate it so much!

From the picture I just viewed it looks like a bottom loading collate with the top of the spindle covered, unless it is some sort of a hinged cover that does not show well in the picture.

They also have a blurb that it is auto Z sensing.

Those two things make me ask how to burnish with that machine unless you can set the spindle to a very low pressure. If it senses on every cutter-down that is possible.

Right now it is still a very valid question to me.

Philadelphia, PA (Really Bensalem)

When you finally understand it completely... it changes.