What should be the last step of a spray finish?

I would caution spraying outside, there could be some interaction with the sunlight causing bubbles depending on the heat and conditions. If you haven’t had any problems so far then I wouldn’t worry about it but would keep an eye out for anything happening.
One last (dry) sanding with 220 or 240 before your last coat should be enough, then nothing should be needed after your final coat.
Last coat doesn’t need to be light, should be a good wet coat, as all coats should be.
I’m a heavy sprayer myself (not always good as most people prefer more lighter coats) I spray as heavy as I can without the product running.

-- Because I'm gone, that's why!

I usually spray a 2-4 mil coat and lightly sand with 400G if needed between coats. I don’t do anything after the last coat on larger projects. However, it depends on the look/feel you are after. The finish can be rubbed out to increase the gloss or dulled if you want to decrease the sheen. Many people will apply a coat of wax to give a very smooth feeling finish especially on small projects like decorative boxes.

I work all the way through my intended finishing schedule on scrap to ensure I will get the results I want before attacking my completed project. HTH

-- Art

Since the cabinets take up so much space, outdoors was my only workable option. The sunlight didn’t seem to impact the lacquer. However, when I was putting on the second coat of pure tung oil, the sun didnt do it any favors. I ended up having to re-sand a few of the pieces that were facing the light. It was a PITA.

Probably would have been a good idea to get a few projects under my belt with the HVLP set up before diving in, but where would the fun be in that?

Thanks for the insight.

I like to wet sand the final (second) coat of lacquer with water and 1500 grit soft sponges. It leaves a glass smooth surface, without the mess of wax and steel wool.

If you thin your lacquer 15-20% it will lay down really nice.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

Don’t know about the last step but the first I’d do is get a #4 ford cup and match your finishes vorticity to you nozzle size.

Here’s a chart that will help with that.

http://homesteadfinishingproducts.com/wp-content/uploads/2014/05/paintspraying_ver3.pdf

-- Alaskan's for Global warming!

I’m confused – you said you were spraying deft lacquer, then later make a reference to 2nd coat of “tung oil”. Slow drying “tung oil” varnishes kind of defeat the purpose of spraying. If you want lacquer, I would recommend a pre-cat lacquer – I’ve had very good luck with Sherwin-Williams. One of the nice things about lacquer (and shellac) is each coat “burns in”, melting some of the previous material, creating a contiguous coat – easy to fix screw ups. For the last coat, sand any rough areas or dust nibs with 400 or 600, and shoot a wet coat. Any rough areas or dust nibs in the final surface lightly sand with 600 or 800 and rub out the scratches.

Nothing should be necessary after the final coat. I don’t wax cabinetry but I do wax furniture.

-- Sam Hamory - The project is never finished until its "Finished"!

BEER

It was a pure tung oil, not one of the varnish types. I put two coats on the walnut. Waited a couple of weeks and then sprayed the Deft Lacquer. I think I have them at an acceptable place now. So it will be the extra fun steps now…demo and electrical, plumbing. Just the fun stuff.