How does the LGX Lite groove mount actually attach to a Dragon Burner?

The groove mount adapter does not replace the main hotend mounting points on the front of the toolhead; it works in conjunction with them. The holes you see on the front are for a support piece that slides over the hotend, and then the hotend itself bolts into that support piece. With the LGX Lite, the official groove mount is designed to sit between the existing toolhead mounting points and the hotend itself. Essentially, you're using the driver's setup, which utilizes two specific pieces of hardware to sandwich the groove mount into place. One piece attaches to the toolhead front and the other piece, which is often a printed part, attaches to the hotend body. The assembly dictates that the driver inserts the hotend into the designed receiver that the groove mount sits in. It's a specific layered design. The whole point of the groove mount is to provide a specific offset and clearance relative to the extruder body.

Since the LGX Lite is designed for the Dragon Burner, the overall height should be exactly what is required, assuming you are using the correct supporting piece, which is sized to ensure the nozzle height is correct for the print chamber. If you are worried about height, you should check the documentation for the specific toolhead support component you are using to make sure it is the right height offset for the groove mount combo. I don't know exactly which printed parts you have on your desk, but if you are using the official setup, you are following the required procedure. The key is that the groove mount itself is the interface, not the entire clamping mechanism.

I run this combo and the thing that tripped me up was printing the wrong front piece at first. There are a few variants in the repo and only one lines up with the groove mount setup, so double check the filename before you hit print. Mine sits at the same height as a normal dragon mount, no wierd offset issues. Only other tip I'd give is don't overtighten the extruder screws onto the adapter, the plastic can flex a bit and you'll chase a crooked nozzle for an hour like I did. Took me two tries to get it all seated clean.

Ran into the same confusion when I built mine, and what actually saved me was a cheap pair of digital calipers. I measured the groove on the adapter against the hotend barrel before printing anything else, and it was obvious which printed piece matched. Also dry fit the whole stack without the extruder screws first, holding it togehter by hand, just to see how the layers sit. Mine ended up at normal height too. If your adapter came with a little diagram sheet, that little drawing cleared up more for me than any of the online docs did.

Been running groove mount setups since the V6 days when we just printed a split clamp and hoped for the best, so this stack doesn't scare me much. One thing I'd add is to spin the extruder gears by hand before you button it all up, make sure the filament path lines up dead center with the hotend inlet. I once had a slightly crooked feed on a similar build and it chewed filament at the top of the heatbreak for weeks before I figured it out. Takes two minutes to check and saves you a mystery underextrusion later.

Update: took the calipers advice and measured the groove against the barrel, which finally made it clear which printed piece I needed. Dry fit the whole stack without the extruder too, sits normal height like you said. Still fuzzy on one thing though: does the support piece bolt to the front holes first, or does the hotend go in before that slides on?